Indicators of Climate Change1 2 Indicators of Climate Change for British Columbia, 2002 3 About the Trends 6 Average Temperature 8 Maximum and Minimum Temperature 11 Precipitation

Climate ChangeIndicators of

Change in AverageTemperature

1895-1995(°C per century)

for British Columbia 2002

BOREALPLAINS

TAIGAPLAINS

NORTHERNBOREAL

MOUNTAINS

SUB-BOREAL

INTERIOR

COAST ANDMOUNTAINS

CENTRALINTERIOR

SOUTHERNINTERIOR

MOUNTAINS

SOUTHERNINTERIOR

GEORGIADEPRESSION

NORTHEASTPACIFIC

+0.6

+0.5

+1.7

notrend

notrend

+1.1

+1.1+1.1

+1.1

A B O U T T H E C O V E R

Air temperature is an important property of climate and the most easily measured, directly observable, and geographically consistent indicator of climate change. Historical data show that the average annual temperature increased in most parts of British Columbia between 1895 and 1995. Temperatures increased by 0.5°C to 0.6°C on the coast, 1.1°C in the interior, and 1.7°C in the north. Atmospheric warming of this magnitude affects other parts of the climate system, including precipitation, air, wind and ocean currents, and the hydrological cycle. Climate change affects ecosystems and species, and has both positive and negative impacts on human communities.

National Library of Canada Cataloguing in Publication DataMain entry under title:Indicators of climate change for British Columbia, 2002

Cover title.Also available on the Internet.Includes bibliographical references: p.ISBN 0-7726-4732-1

1. Climatic changes - British Columbia. 2. Greenhouse effect, Atmospheric. 3. Global warming. I. British Columbia. Ministry of Water, Land and Air Protection.

QC981.8.C5I52 2002 551.69711 C2002-960055-3

P R O D U C T I O N T E A M

Research coordination: Dr. Risa Smith, Ministry of Water, Land and Air ProtectionWriting and research: Jenny Fraser, Ministry of Water, Land and Air ProtectionDesign, production and editing: Beacon Hill Communications Group Inc.

Copies of this report may be: downloaded from the Internet at http://www.gov.bc.ca/wlap.

picked up from the Water, Air and Climate Change Branch, Ministry of Water, Land and Air Protection2975 Jutland Road, Victoria, BC, or

ordered from Water, Air and Climate Change Branch, Ministry of Water, Land and Air ProtectionPO Box 9341, Stn. Prov. Govt., Victoria, B.C. V8W 9M1

Technical papers that document methodologies and present the data behind the indicators are available on the Internet at http://www.gov.bc.ca/wlap.

Please email comments to: [email protected]

1

2

Indicators of Climate Change forBritish Columbia, 2002 3

About the Trends 6

Average Temperature 8Maximum and Minimum Temperature 11Precipitation 14Snow 17

Glaciers 20Freezing and Thawing 22Timing and Volume of River Flow 24River Temperature 26Salmon in the River 28

Sea Level 30Sea Surface Temperature 32Salmon at Sea 34Seabird Survival 36

Growing Degree Days 38Mountain Pine Beetle Range 40

Heating and Cooling Requirements 42Human Health 44

Climate Change: Past Trends and Future Projections 46

ACKNOWLEDGEMENTS

INTRODUCTION

CLIMATE CHANGE DRIVERS

CLIMATE CHANGE ANDFRESHWATER ECOSYSTEMS

CLIMATE CHANGE ANDMARINE ECOSYSTEMS

CLIMATE CHANGE ANDTERRESTRIAL ECOSYSTEMS

CLIMATE CHANGE ANDHUMAN COMMUNITIES

APPENDIX

CONTENTS

2

ACKNOWLEDGEMENTS

The Ministry of Water, Land and Air Protection thanks the followingindividuals, who have provided technical papers, reviewed papers and drafts,provided images, or otherwise contributed their time, ideas, and support tothe development of this document.

Peter Ashmore, University of Western Ontario; Diane Beattie, Ministry ofWater, Land and Air Protection; Elisabeth Beaubien, University of Alberta;Doug Bertram, Simon Fraser University; Allan Carroll, Natural ResourcesCanada; Stewart Cohen, Environment Canada; Bill Crawford, Institute ofOcean Sciences; Mike Foreman, Institute of Ocean Sciences; Howard Freeland,Institute of Ocean Sciences; Richard Gallacher, Vancouver Cancer Centre;John Garrett, 2WE Associates Consulting Ltd.; Jeff Grout, Fisheries andOceans Canada; Brian Hanlon, energy consultant; Rick Lee, Canadian Institutefor Climate Studies; Steve Macdonald, Fisheries & Oceans, Canada; RobinMcNeil, Ministry of Sustainable Resource Management; Eva Mekis,Environment Canada; John Morrison, Institute of Ocean Sciences; PhilipMote, Joint Institute for the Study of the Atmosphere and Ocean; TrevorMurdock, Canadian Institute for Climate Studies; Michael Quick,Universityof British Columbia; Dr. Schwartz, University of Wisconsin; Walter Skinner,Environment Canada; Heather Smart, Ministry of Water, Land and AirProtection; Dan Smith, University of Victoria; Daithi Stone, University ofVictoria; Bill Taylor, Environment Canada; Rick Thomson, Institute of OceanSciences; Andrew Weaver, University of Victoria; David Welch, Fisheries andOceans, Canada; Paul Whitfield, Environment Canada; Rick Williams,Ministry of Water, Land and Air Protection; Bob Wilson, 2WE AssociatesConsulting Ltd.

3

Both the UN Intergovernmental Panel on Climate Change and the US NationalAcademy of Science have concluded that the global atmosphere is warming.They agree, moreover, that most of the warming observed over the last 50

years can be attributed to human activities that release greenhouse gases into theatmosphere. British Columbia, for example, produced almost 16 tonnes of green-house gases per person in 1999, most through the burning of fossil fuels for trans-portation and industrial activity.

Atmospheric warming affects other parts of the climate system, includingprecipitation, air, wind and ocean currents, cloud cover, and the hydrological cycle.Climate change in turn affects other closely related physical systems, as well asbiological systems, and the human communities that depend on these systems.

This report documents how the climate in British Columbia changed during the20th century and the rates at which these changes occurred. It outlines the potentialimpacts of these changes on freshwater, marine, and terrestrial ecosystems and onhuman communities. It describes how climate change is likely to affect the provinceduring the 21st century.

CLIMATE CHANGE TRENDS

The trends described in this report are based on a set of environmental indicators thatrepresent key properties of the climate system, or important ecological, social, oreconomic values that are considered sensitive to climate change. The report describeschanges in these indicators over time. Past trends are based on analysis of historical data.Future impacts are based on the most up-to-date projections of climate researchers.

Indicators of Climate Changefor British Columbia, 2002

I N T R O D U C T I O N

4

Past impacts

Analysis of historical data indicates that many properties of climate have changed

during the 20th century, affecting marine, freshwater, and terrestrial ecosystems in

British Columbia.

• Average annual temperature warmed by 0.6ºC on the coast, 1.1ºC in theinterior, and 1.7ºC in northern BC.

• Night-time temperatures increased across most of BC in spring and summer.

• Precipitation increased in southern BC by 2 to 4 percent per decade.

• Lakes and rivers become free of ice earlier in the spring.

• Sea surface temperatures increased by 0.9ºC to 1.8ºC along the BC coast.

• Sea level rose by 4 to 12 centimetres along most of the BC coast.

• Two large BC glaciers retreated by more than a kilometre each.

• The Fraser River discharges more of its total annual flow earlier in the year.

• Water in the Fraser River is warmer in summer.

• More heat energy is available for plant and insect growth.

Future impacts

Climate models and scenarios suggest that the climate in British Columbia willcontinue to change during the 21st century. This will have ongoing impacts onecosystems and communities.

• Average annual temperature in BC may increase by 1ºC to 4ºC.

• Average annual precipitation may increase by 10 to 20 percent.

• Sea level may rise by up to 88 centimetres along parts of the BC coast.

• Many small glaciers in southern BC may disappear.

• Some interior rivers may dry up during the summer and early fall.

• Salmon migration patterns and success in spawning are likely to change.

• The mountain pine beetle — an important pest — may expand its range.

The indicators presented in this report document some of the changes that haveoccurred during the past century. Many more potential indicators remain to beexplored. For example, climate change may influence the frequency of extremeweather events, the extent of permafrost, ecosystem structures and processes, andspecies distribution and survival. It may affect provincial infrastructure, forestry,energy and other industries, insurance and other financial services, and human


5

settlements. In addition, the impacts may vary from one region, ecosystem, species,industry, or community to the next. Research into the regional impacts of climatechange is ongoing, and this report is therefore designed to be updated and expandedas new information becomes available.

RESPONDING TO CLIMATE CHANGEThe impacts of climate change on British Columbians will depend on the time, theplace, and the individual. For example, homeowners may see a warmer climate as abenefit if it means lower home heating bills. Resort operators may see it as a cost ifit means a shorter ski season. Farmers may see it as a benefit if it allows them tointroduce new crops, and as a cost if it increases the need for irrigation. Overall,however, the risk of negative impacts increases with the magnitude of climate change.

Much attention has been paid over the last decades to slowing down the rate ofclimate change by reducing greenhouse gas emissions. Success in this area has beenmixed. In BC, for example, total emissions actually increased by more than 20percent between 1990 to 1999 as the population of the province grew. Even ifmitigation efforts are successful in reducing greenhouse gas emissions, they cannotprevent climate change. The greenhouse gases humans have already added to theatmosphere will likely continue to drive global climate change for centuries to come.British Columbia and other jurisdictions will therefore have to adapt.

The Kyoto Protocol commits its signatory parties to the development of nationalaction programmes that include measures both to mitigate climate change and tofacilitate adaptation to climate change. In Canada, the federal, provincial, andterritorial governments are developing a national impacts and adaptation framework.Some municipal governments, including Vancouver, are starting to incorporatepotential climate change impacts into long-term plans for drinking water supply,drainage, and storm-water infrastructure.

Through adaptation, we may be able to reduce some of the adverse impacts ofclimate change and enhance some of its potential benefits. Adaptation, however,will incur costs. It will probably be easier for human systems than for physical andbiological systems to adapt to change. And countries and communities with access totechnology, education, information, skills, and resources will be more able to adaptthan those without such access.

A greater understanding of climate change trends and impacts is expected to helpBritish Columbians prepare for and adapt to climate change at the same time as theprovince works to reduce the scale of future impacts through renewable energy,energy efficiency, sustainable transportation, new technology, water conservation,and other sustainable practices.


6

Ecoprovinces ofBritish Columbia

BOREALPLAINS

TAIGAPLAINS

NORTHERNBOREAL

MOUNTAINS

SUB-BOREALINTERIOR

COAST ANDMOUNTAINS

CENTRALINTERIOR SOUTHERN

INTERIORMOUNTAINS

SOUTHERNINTERIORGEORGIA

DEPRESSION

NORTHEASTPACIFIC

Fort St John

Fort Nelson

Cassiar

Prince George

Quesnel

Kamloops

Nelson

Victoria

Vancouver

Prince Rupert

Queen Charlotte City

About the trendsThe report documents changes during the 20th century in some of the key properties ofthe climate system and in some ecological, social, or economic values that are consideredsensitive to climate change. Such changes are referred to as “trends.”

Where possible, the report identifies trends for each region of the province. Thegeographical unit used is the ecoprovince — an area delineated by similar climate,topography, and geological history. There are tenecoprovinces in British Columbia —nine terrestrial and one marine.

Much of the information onpast trends is based on aseries of technical paperscommissioned by theMinistry of Water, Landand Air and available onthe Ministry website athttp://www.gov.bc.ca/wlap/.

The information onfuture trends is basedon the 2001 reports ofthe IntergovernmentalPanel on Climate Change,available in summary formon the Internet at http://www.ipcc.ch/

During the past 1,000 years,the climate of BC has varied fromyear to year and decade to decade as aresult of natural cycles in air and oceancurrents (see Appendix). In particular the BCclimate is strongly influenced by cyclical changes inthe surface temperature of the Pacific Ocean. The Pacific Decadal Oscillation (PDO) has awarm and a cool phase. It tends to remain in each phase for 20 to 30 years, and a completecycle from warm to cool and back again takes about 50 to 60 years. The PDO affects airtemperature and other properties of climate across BC.

One of the challenges in identifying climate trends for BC is to distinguish theinfluence of the PDO from the influence of atmospheric warming caused by the build-up


7

of greenhouse gases in the atmosphere. In general, trends based on long historical records— about 100 years or longer — are most likely the result of climate change. Trends basedon relatively short records — less than about 60 years — are most likely influenced by thePDO. As historical records for northern BC tend to be shorter, there are often not enoughdata to reveal trends associated with climate change for this part of the province.

Some of the trends presented in this document can be attributed to climate change, butothers cannot. The ideal would have been to report only on those trends that can beattributed to climate change. This would mean trends that are both statistically significantand based on long historical records. The collection of climate data in British Columbia,however, dates back only to the late 19th century, and the collection of biological data iseven more recent. For this reason, this document describes trends in values consideredsensitive to temperature and other properties of climate, whether or not the record is longenough to link the trends definitively to climate change. Values that are sensitive tochanges in temperature or precipitation, for example, are likely to be sensitive to climatechange. As long as British Columbians continue to collect data about these values, in a fewdecades stronger climate change trends may emerge.

Even when the data are adequate, sorting out the influence of climate change fromthat of natural climate variability is a complex task. Analytical methods are still evolving.Smaller trends are more difficult to detect. For these and other reasons, some of the trendsdocumented in this report may need to be adjusted in future. They are neverthelessinstructive in providing information about some of the ways that climate change hasaffected BC.

INTERPRETING THE TREND INFORMATION• The report presents only those results there were found to be significant at

the 95 percent level through standard statistical tests. This means that thechance the trend arose randomly is less than 5 percent.

• Some of the trends are based on long records and almost certainly reflect climatechange. Other trends are based on shorter records and likely reflect climatevariability. These differences are documented in the text.

• Where the data record is relatively long — more than about 60 years — but failsto reveal a trend that is statistically significant at the 95 percent level, the reportpresents this as “no trend.”

• Where the data record is relatively short — less than about 60 years — and failsto reveal a trend that is statistically significant at the 95 percent level, the reportpresents no result.


8

Although the records are relatively long forthe Taiga Plains (59 years) and the Boreal Plains(65 years), the the data fail to reveal trends in averageannual temperature for northeastern BC.

Average global temperature increased by 0.6ºCduring the 20th century. Most of this warmingoccurred from 1910 to 1945 and from 1976 to 2000.The 1990s were the warmest decade in the last 1,000years. Globally, the greatest warming occurred in thehigher latitudes of the Northern Hemisphere. Thetrend towards greater warming in northern BC isconsistent with this global trend.

SEASONAL TEMPERATURE TRENDSSpring across most of British Columbia is nowwarmer, on average, than it was a century ago.

On the coast, spring temperatures have increasedby 0.8ºC. In southeastern BC they have increased by1.2ºC to 1.4ºC. In the interior they have increased by1.7ºC to 1.9ºC. All of these trends are based on longrecords (101 years) and almost certainly reflectclimate change.

In the Northern Boreal Mountains ecoprovince,spring has warmed by 3.8ºC. This trend is based ona relatively short data record (52 years) and likelyreflects natural climate variability. The records are

Changein AnnualTemperature,1895-1995(ºC per century)

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SOURCE: Data from Archive of Monthly Climate Data and 1961-90 Normals, Environment

Canada, and Canadian Historical and Homogenized Temperature Datasets. Analysis by

Canadian Institute for Climate Studies, 1999 for BC Ministry of Water, Land and AirProtection. NOTES: A positive sign indicates a warming trend.

ABOUT THE INDICATORSThe indicators measure changes in average annualtemperature and average temperature in each of thefour seasons. Trends are based on available data from1895 to 1995 for weather stations in each of the nineterrestrial ecoprovinces. Records for the BorealPlains, Northern Boreal Mountains, and Taiga Plainsare shorter. Seasonal trends are based on averages forspring (March-May), summer (June-August), fall(September-November), and winter (December-February).

ANNUAL TEMPERATURE TRENDSCoastal BC has warmed at a rate equivalent to 0.5ºCto 0.6ºC per century, or at roughly the same rate asthe global average. The interior of BC warmed at arate equivalent to 1.1ºC per century, or at twice theglobal average. The records for these ecoprovincesare long (101 years) and the trends almost certainlyreflect climate change.

Northwestern BC warmed at a rate equivalent to1.7ºC per century, or about three times the globalaverage. The record for this region — the NorthernBoreal Mountains ecoprovince — is relatively short(52 years) and the trend is likely influenced byclimate variability as well as by climate change.

BOREALPLAINS

TAIGAPLAINS

NORTHERNBOREAL

MOUNTAINS

SUB-BOREAL

INTERIOR

COAST ANDMOUNTAINS CENTRAL

INTERIOR

SOUTHERNINTERIOR

MOUNTAINSSOUTHERNINTERIOR

GEORGIADEPRESSION

NORTHEASTPACIFIC

+0.6

+0.5

+1.7

notrend

notrend

+1.1

+1.1+1.1

+1.1

C L I M A T E C H A N G E D R I V E R S

A V E R A G ET E M P E R A T U R E

Average temperature increased overmost of BC during the 20th century.Spring is warmer on average than it was 100 years ago. Higher temperatures drive other changes in climate systemsand affect physical and biological systems in BC. They can have both positive and negative impacts on human activities.

9

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relatively long for the Taiga Plains (59 years) and theBoreal Plains (65 years), but the data fail to revealseasonal trends.

Trends are less consistent across other seasons.Most of the interior of BC warmed during thesummer at rates of 0.8ºC to 1.2ºC per century. TheCoast and Mountains ecoprovince warmed duringthe winter by 1.4ºC. The Georgia Depressionwarmed during the fall by 0.5ºC. The SouthernInterior warmed during all four seasons. All of thesetrends are based on long data records and almostcertainly reflect climate change.

On the ground, the date that each season arrivesvaries from one part of BC to the next, depending onclimate, latitude, and elevation. Spring comes earlierto the coast, to southern BC, and to valley bottoms,for example, than it does to the north and to alpineareas. The seasonal trends described in thisdocument are based on calendar dates, and as suchmay not reflect reality on the ground for some partsof BC.


WHY IS IT IMPORTANT?Air temperature is one of the main properties ofclimate and the most easily measured, directlyobservable, and geographically consistent indicatorof climate change. Atmospheric warming affectsother parts of the climate system, and in BC is linkedto sea surface warming and increased precipitation insome regions.

Changes in climate can affect other physicalprocesses, including the duration of ice on rivers andlakes, the proportion of snow to total precipitation,and temperature in freshwater ecosystems. Suchchanges can in turn affect biological systems. Watertemperature, for example, affects the date of emer-gence of the young of many aquatic species. Warmingmay drive broad scale shifts in the distribution ofecosystems and species. Trees may be able to grow inareas once too cold for them. Some alpine meadowsmay disappear as high-elevation areas becomewarmer. Beneficial and pest species may appearfurther north, or higher in elevation, than theirhistoric range.

The impacts of warmer temperatures will varyfrom one part of BC to another and from one seasonto another. They will have both positive and negativeimpacts on human activities.

Warmer springs may promote earlier break upof lake and river ice, and resulting changes in riverhydrology. They may mean a longer season forwarm-weather outdoor recreation activities.

Warmer summers may increase rates ofevaporation and plant transpiration. Reducedmoisture may contribute to dust storms and soilerosion, increased demand for irrigation, loss ofwetlands, slower vegetation growth, forest fires, andthe conversion of forest to grasslands. It may contri-bute to declines in ground-water supplies and inwater quality in some areas. Higher temperaturesmay increase temperatures in freshwater ecosystems,creating stressful conditions for some fish species.

Warmer winters may mean that less energy isrequired to heat buildings. They may mean a shorterseason for skiing and other winter sports and lossesin the winter recreation sector.

SOURCE: Data from Archive of Monthly Climate Data and 1961-90 Normals,

Environment Canada, and Canadian Historical and Homogenized TemperatureDatasets. Analysis by Canadian Institute for Climate Studies, 2001 for BC Ministry of

Water, Land and Air Protection. NOTES: All trends are positive and indicate warming.

BOREALPLAINS

TAIGAPLAINS

NORTHERNBOREAL

MOUNTAINS

SUB-BOREAL

INTERIOR

COAST ANDMOUNTAINS

CENTRALINTERIOR

SOUTHERNINTERIOR

MOUNTAINS

SOUTHERNINTERIOR

GEORGIADEPRESSION

NORTHEASTPACIFIC

+1.9 +.8no

trendno

trend+1.4 +1.2

notrend

notrend

spring

winter fall

summer

+3.8no

trend

notrend

notrend

+1.7 notrend

notrend+1

notrend

+.8 notrend

+1.4

+1.2 +.9+.8+1.8

+.5

+.8 notrend

notrend

L E G E N D

Change inSeasonalTemperature,1895-1995(ºC per century)

10

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Global Temperatures,1856-1999 andProjected Change to 2100

Glo

bal

Ave

rag

e Te

mp

erat

ure

(°C

)

IPCC estimateHigh

Most likely

Low

14

20001850 1870 1890 1910 1930 1950 1970 1990

15

16

17

18

132010 2030 2050 2070 2090

21001900

1999

19

SOURCE: Temperatures 1856-1999: Climatic Research Unit,

University at East Anglia, Norwich UK. Projections: IPCC, 1995.

WHY IS TEMPERATURE INCREASING?Air temperature in BC is strongly affected by twonatural cycles in air and ocean currents (seeAppendix), which cause year-to-year and decade-to-decade variability in climate across the province. Thewarming trends observed during the 20th century areabove and beyond such natural variability, and almostcertainly reflect long-term climate change. The rate ofwarming is accelerated in more northerly regions,likely through a positive feedback mechanism. As airtemperature increases, snow and ice melt, exposingmore of the ground and sea surface. While snow andice tend to reflect solar energy back into space, newly-exposed rocks, soil, and water tend to absorb andretain it as heat.

The Intergovernmental Panel on Climate Change(IPCC) has concluded that most of the observedglobal atmospheric warming of the last 50 years isprobably due to increases in greenhouse gasconcentrations. Greenhouse gas emissions resultfrom a variety of human activities, including theburning of fossil fuels and the clearing of land foragriculture and urban development.

The IPCC suggests that greater warming in someseasons may be the result of large-scale changes inatmospheric circulation, or of feedback mechanismsinvolving the melting of snow and ice.

WHAT CAN WE EXPECT IN FUTURE?Average annual temperature across BC will continueto vary from year to year in response to natural cyclesin air and ocean currents. Relatively warm years,however, will almost certainly increase in frequency.

Climate models project further warming in BC atthe rate of 1ºC to 4ºC per century. The interior of theprovince will warm faster than other areas and willexperience higher rates of warming than in the past.The north will continue to warm at rates consider-ably greater than the global average. Ocean tempera-tures have a moderating effect on the climate of thecoast, which will warm more slowly than the rest of BC.

Although temperature increases of a few degreesmay seem small, they are associated with importantphysical and biological changes. A rise in averagetemperature of 5ºC about 10,000 years ago wasenough to melt the vast ice sheets that once coveredmuch of North America.

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BOREALPLAINS

TAIGAPLAINS

NORTHERNBOREAL

MOUNTAINS

SUB-BOREAL

INTERIOR

COAST ANDMOUNTAINS

CENTRALINTERIOR

SOUTHERNINTERIOR

MOUNTAINS

SOUTHERNINTERIOR

GEORGIADEPRESSION

NORTHEASTPACIFIC

+2.1

+1.7

+.9

+.9

+1.3+.9

+1.7

+1.4+.9

maximum

minimum

no trend

no trend

no trend

no trend

no trend

no trend

no trend

no trend

no trend

L E G E N D

M A X I M U MA N D M I N I M U MT E M P E R A T U R E

Night-time minimum temperatures in most regions of BC are warmer on average than they were a century ago, particularly in spring and summer. Higher minimum temperatures in spring may increase the length of the frost-free season. In summerthey may prevent buildings from coolingdown during the night.

ABOUT THE INDICATORSThe indicators measure change in the average annualday-time maximum temperature and the averageannual night-time minimum temperature. They alsomeasure changes in maximum and minimumtemperature in each of the four seasons. Trends arebased on available data from 1895 to 1995. Recordsfor the Boreal Plains, Northern Boreal Mountains,and Taiga Plains are shorter. Seasonal trends arebased on averages for spring (March-May), summer(June- August), fall (September-November), andwinter (December-February).

TRENDS IN MAXIMUM TEMPERATUREAnnual day-time maximum temperatures increasedby 0.9ºC in the Southern Interior and the SouthernInterior Mountains ecoprovinces. These trends arebased on 101 years of data and almost certainlyreflect climate change. In four other ecoprovinces(Georgia Depression, Coast and Mountains, CentralInterior, Sub-Boreal Interior) the records are long(101 years), but the data fail to reveal trends inannual maximum temperature. In the three northernecoprovinces the records are relatively short and thedata fail to reveal trends.

Change inMaximumand MinimumTemperature,1895-1995(ºC per century)

SOURCE: Data from the Canadian Historical HomogenizedTemperature Datasets. Analysis by Canadian Institute for Climate

Studies, 2001, for Ministry of Water, Land and Air Protection.

NOTES: All trends are positive and indicate warming.

Seasonal data indicate that maximum springtemperatures increased across much of BC. They failto reveal trends in maximum temperature in the fallanywhere in BC.

In the interior of British Columbia, daytimemaximum spring temperatures increased by 1.2ºCto 1.7ºC. The records for these ecoprovinces arerelatively long (101 years) and the trends almostcertainly reflect climate change.

In coastal British Columbia, daytime maximumsummer temperatures decreased. Daytime maximumwinter temperatures in the Coast and Mountainsecoprovince increased by 1.9ºC. The records forthese ecoprovinces are relatively long (101 years) andthe trends almost certainly reflect climate change.

Daytime maximum spring temperatures increasedby 3.6ºC in the Northern Boreal Mountains and by2.8ºC in the Taiga Plains. The records for theseecoprovinces are relatively short (55 and 47 years)and these trends are likely influenced by climatevariability.

Daytime maximum summer temperatures in theBoreal Plains decreased by 1.9ºC. The record for thisecoprovince is relatively long (65) years and thetrend likely reflects climate change.

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12

TRENDS IN MINIMUMTEMPERATUREAnnual night-time minimum temperaturesincreased by 0.9ºC per century on the coast andby 1.3ºC to 1.7ºC per century in parts of theinterior. These trends are based on 101 years ofdata and almost certainly reflect climate change.The greatest increase in minimum temperaturehas been in the Northern Boreal Mountainsecoprovince, where minimum temperaturesincreased at a rate equivalent to 2.1ºC percentury. In this ecoprovince, the record isrelatively short (52 years) and likely reflectsclimate variability. In the two other northernecoprovinces the records are relatively shortand the data fail to reveal trends.

Seasonal data indicate that night-timeminimum spring and summer temperaturesincreased across much of BC. They increasedacross all seasons in southern BC and in theGeorgia Depression ecoprovince.

In the interior, minimum temperaturesincreased in spring by up to 2.2ºC, in summerby up to 1.7ºC, in fall by 0.8ºC, and in winterby up to 2.6ºC. On the coast, minimumtemperatures increased in spring by 1.2ºC, insummer by 0.7ºC, and in fall by up to 0.8ºC.They increased in winter by 0.9ºC in theGeorgia Depression. The records for the coastand interior are long (101 years) and the trendsalmost certainly reflect climate change.

Minimum temperatures increased insummer in the Taiga Plains, and in spring andsummer in the Northern Boreal Mountains.The records for these ecoprovinces are short(47 and 55 years), and the trends likely reflectclimate variability. In the Boreal Plains,minimum temperatures increased in springby 2.4ºC and in summer by 1.1ºC. The recordfor this ecoprovince is relatively long (65 years)and the trends likely reflect climate change.

Change inMaximumTemperature,by season,1895-1995(ºC percentury)

SOURCE: Data from the Canadian Homogenized Temperature Datasets.

Analysis by Canadian Institute for Climate Studies, 2002, for Ministry of Water,

Land and Air Protection. NOTES: A positive trend indicates warming, and anegative trend indicates cooling.

Change inMinimumTemperatureby season,1895-1995(ºC percentury)

SOURCE: Data from the Canadian Homogenized Temperature Datasets.

Analysis by Canadian Institute for Climate Studies, 2002, for Ministry of

Water, Land and Air Protection. NOTES: A positive trend indicateswarming, and a negative trend indicates cooling.


BOREALPLAINS

TAIGAPLAINS

NORTHERNBOREAL

MOUNTAINS

SUB-BOREAL

INTERIOR

COAST ANDMOUNTAINS

CENTRALINTERIOR

SOUTHERNINTERIOR

MOUNTAINS

SOUTHERNINTERIOR

GEORGIADEPRESSION

NORTHEASTPACIFIC

+1.7no

trendno

trend

notrend

+1.4no

trendno

trend

notrend

+2.8no

trendno

trend

notrend

+1.2no

trendno

trend

notrend

spring

winter fall

summer

+3.6no

trend

notrend

notrend -1.9no

trendno

trendno

trend+1.3 notrend

notrend

notrend

notrend

-1.4notrend

+1.9

-.8no

trend

notrend

notrend

L E G E N D

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TAIGAPLAINS

NORTHERNBOREAL

MOUNTAINS

SUB-BOREAL

INTERIOR

COAST ANDMOUNTAINS

CENTRALINTERIOR

SOUTHERNINTERIOR

MOUNTAINS

SOUTHERNINTERIOR

GEORGIADEPRESSION

NORTHEASTPACIFIC

+2.2

+2.6

+1.5no

trend

spring

winter fall

summer

+3.9+1.3no

trendno

trend

notrend

notrend

notrend

+2.4+1.1no

trendno

trend+2.1+1.7no

trend+2.2

+1.2no

trend +0.7+0.7

+1.2 +1.3+.8+2.4

+1.4+1.6+.8+1.6

+.8

+.7

+.9

+1.2

L E G E N D

+1.3

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13

WHY IS IT IMPORTANT?The overall pattern suggests that most regions ofBC are warming because night-time minimumtemperatures are increasing, not because day-timemaximum temperatures are increasing. One couldsay that BC has actually become “less cold” ratherthan “hotter.” The strong, increasing trends inminimum temperature, especially during the springand summer, have likely made the greatest contri-bution to the general warming trends across theprovince.

In regions and in seasons where trends in bothminimum and maximum temperatures wereobserved, minimum temperatures increased fasterthan maximum temperatures over the record period.National trends indicate minimum temperatures rosetwice as fast as maximum temperatures from 1895 to1991. Global trends indicate minimum temperaturesincreased twice as fast as maximum temperaturesbetween 1950 and 1993. As a result, the temperaturerange during the average day has decreased.

The Intergovernmental Panel on Climate Change(IPCC) has concluded that the increase in minimumtemperatures has lengthened the freeze-free season inmany mid-and high-latitude regions. Higher night-time minimum temperatures in fall, winter, andspring may enhance the growing conditions forboth valuable and pest plant and insect species.In summer, they may increase heat-related stress inhumans and other species because buildings andhabitats may not be able to cool down adequatelyat night.

WHY HAVE MAXIMUM AND MINIMUMTEMPERATURES CHANGED ATDIFFERENT RATES?The reason for greater warming at night than in thedaytime is not yet fully understood. During the earlypart of the 20th century, however, cloud coverincreased over the mid-latitudes of Canada. Climatechange may increase atmospheric moisture andcloud cover, both of which can act as a blanket tokeep more of the heat that builds up on the groundduring the daytime from radiating back into the

atmosphere during the night. Increased cloud coverin summer over coastal BC may contribute to thecooling trend in summer.

WHAT CAN WE EXPECT IN FUTURE?Climate models project that in the 21st century,night-time lows in many areas will continue toincrease more than day-time highs. A number ofmodels suggest that in the Northern Hemispherethe gap between the daily maximum and the dailyminimum will decrease in winter and increase insummer.

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14

SOURCE: Data from Climate Research Branch, MeteorologicalService of Canada. Analysis by the Canadian Institute for Climate

Studies, 2001 for the Ministry of Water, Land and Air Protection.

NOTES: A positive sign indicates increasing precipitation.

ABOUT THE INDICATORSThe indicators measure changes in average annualprecipitation at weather stations in five ecoprovincesin southern BC. They also measure changes inaverage precipitation in each of the four seasons.Trends are based on available data from 1929 to1998. Seasonal trends are based on averages forspring (March-May), summer (June-August), fall(September-November), and winter (December-February). Records for the four northern eco-provinces are not sufficient to generate meaningfulprecipitation trends.

ANNUAL PRECIPITATION TRENDSAverage annual precipitation increased by 3 percentper decade in the Southern Interior and by 4 percentper decade in the Southern Interior Mountainsecoprovinces. The rates of increase in southeasternBC have been relatively steady during the recordperiod, and it is very likely that precipitation willcontinue to increase in this region.

Precipitation in the Central Interior increased by

2 percent per decade. Precipitation increased in theCoast and Mountains ecoprovince by 2 percent perdecade. The data fail to indicate a trend for theGeorgia Depression.

The precipitation trends are based on 70 years ofdata and likely reflect the influence of climate change.All trends represent simple, rather than compound,averages.

Not enough data are available for northern BC todetermine whether or not precipitation in this regionhas changed. The Intergovernmental Panel on ClimateChange (IPCC), however, has concluded that regionsof northwestern Canada experienced a gradualincrease in annual precipitation of more than 20percent from 1901 to 1995, or an increase of almost2 percent per decade.

The IPCC has concluded that precipitation is verylikely to have increased by 0.5 percent to 1.0 percentper decade over most mid-latitudes (30ºN to 60ºN) ofthe continental Northern Hemisphere during the 20thcentury. Precipitation trends in BC surpass thisaverage.

P R E C I P I T A T I O N

Average precipitation increased over most of southern BC during the 20thcentury. More water may be availableto recharge groundwater aquifers,maintain river flows, and replenish soilmoisture. Hydroelectric powergeneration, irrigation, and domesticwater use may benefit. In some seasons, increased runoff may increase the chanceof landslides and debris torrents, or exceed the capacity of municipal drainage and sewage systems.

BOREALPLAINS

TAIGAPLAINS

NORTHERNBOREAL

MOUNTAINS

SUB-BOREALINTERIOR

COAST ANDMOUNTAINS

CENTRALINTERIOR

SOUTHERNINTERIOR

MOUNTAINS

SOUTHERNINTERIOR

GEORGIADEPRESSION

NORTHEASTPACIFIC

+2+2

+3 +4

notrend


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Changein AveragePrecipitation,1929-1998(% per decade)

15

SEASONAL PRECIPITATION TRENDSTrends in seasonal precipitation are inconsistent.In southwestern BC, precipitation has increased inboth spring and summer, by 5 percent to 6 percentper decade. Precipitation has also increased in fall,by 4 percent per decade, in the Southern InteriorMountains.

Precipitation has increased in spring in theSub-Boreal Interior ecoprovince, and in fall in theCoast and Mountains ecoprovince. The data failto indicate trends in winter precipitation, or anyseasonal trends in the Georgia Depression.

The date that each season arrives varies fromone part of BC to the next, depending on climate,latitude, and elevation. The seasonal trendsdescribed here are based on calendar dates, andmay therefore fail to reflect reality on the groundfor some parts of BC.

Change in Seasonal Precipitation,1929-1998 (% per decade)

WHY IS IT IMPORTANT?Precipitation is a fundamental aspect of climate anda key indicator of climate change. It is highly variableacross BC as a consequence of topography andnatural climate variability. Mountain slopes that facethe prevailing westerly winds receive considerablymore rain than leeward slopes or adjacent valleys.El Niño years bring warmer, drier winters, while LaNiña years bring cooler, wetter weather.

Natural and human systems are adapted to suchvariability. Climate change, however, may mean ashift to warmer, wetter years, more frequent wetyears, greater year-to-year variability, or more extremeprecipitation events. Such long-term changes in theamount, form, and timing of precipitation will almostcertainly have significant impacts on freshwater andterrestrial ecosystems. They will have both positiveand negative impacts on human activities. Theimpacts will vary depending on season, and someimpacts may carry over from one season to the next.

In general, an increase in precipitation suggeststhat more water will be available for natural systems,to recharge groundwater aquifers, maintain riverflows, replenish soil moisture, maintain wetlands andmarshes, and support plant growth. Human activitiesthat depend on water supply — including hydro-electric power generation, irrigation, domestic wateruse, and some industrial processes — may benefit.Increased precipitation may also be responsible insome areas and in some seasons for increasedflooding and damage to ecosystems and infra-structure. Increased year-to-year variability inprecipitation may have adverse impacts on wetlandsand other ecosystems and make water planningmore complex.• Where winter precipitation falls as snow — in

the interior of BC, for example — an increase inprecipitation may help local economies based onskiing and other winter recreation activities, butincrease the cost of road maintenance and acci-dents. Snow build-up during the winter mayincrease the amount of water released intostreams and rivers in spring and summer whenthe snow melts.

BOREALPLAINS

TAIGAPLAINS

NORTHERNBOREAL

MOUNTAINS

SUB-BOREALINTERIOR

COAST ANDMOUNTAINS

CENTRALINTERIOR

SOUTHERNINTERIOR

MOUNTAINS

SOUTHERNINTERIOR

GEORGIADEPRESSION

NORTHEASTPACIFIC

+2

no trend

no trend

no trend

+3 no trend

no trend

no trend

spring

winter fall

summer

L E G E N D

+6 +6no

trend +4

+5 +6no

trendno

trend

notrend

notrend

notrend

notrend


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SOURCE: Data from Climate Research Branch, Meteorological

Service of Canada. Analysis by the Canadian Institute for Climate

Studies, 2001 for the Ministry of Water, Land and Air Protection.NOTES: A positive sign indicates increasing precipitation.

16

• Where winter precipitation falls as rain — on thecoast, for example — an increase in precipitationmay increase winter runoff, exceeding the capacityof municipal drainage and sewage systems andreducing water quality.

• More precipitation in spring — already a seasonof high stream flow in many parts of BC — maycreate faster, fuller rivers. In some areas, soilsmay become saturated with water, increasing thechance of landslides and debris torrents. Low-lying areas may flood more often. Flooding mayhave adverse impacts on some freshwater andriparian ecosystems.

• Precipitation increases in summer may help offsetthe potential loss of water in soil and river systemsas a result of higher temperatures and higher ratesof evaporation and plant transpiration.

• More precipitation in fall — typically a seasonof lower stream flow in many parts of BC — maymean higher water levels and better conditionsfor salmon spawning and egg-to-fry survival.

WHY IS PRECIPITATION INCREASING?Atmospheric warming is a component of climatechange. Warmer air can hold more water vapour,pick up water faster from the earth, lakes, andoceans, and carry more moisture to the land, whereit falls as rain or snow. Thus atmospheric warmingis associated with a global increase in precipitationover land.

In BC, prevailing winds carry moisture inlandfrom the Pacific Ocean. As the air rises over coastalmountains, it cools, releasing moisture. Averagesurface temperatures of the ocean and the landincreased during the 20th century. As a result, windscarry more moisture from the ocean to the coast andthe interior of the province.

Particularly in southern BC, summer may becharacterized by increasing precipitation onlybecause the same water is cycling more frequentlyfrom surface to air and back again. Under suchcircumstances, moisture availability and runoff maynot be increasing at all, and may actually bedecreasing.


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WHAT CAN WE EXPECT IN FUTURE?Average annual precipitation across BC will continueto vary from year to year in response to natural cyclesin air and ocean currents. Relatively wet years,however, will almost certainly increase in frequency.

Climate models project that average annualprecipitation in the mid-latitudes of the NorthernHemisphere will continue to increase. Precipitationwill remain within 10 percent of present levels until2050 and will increase by 10 to 20 percent by 2090.In addition, the majority of climate models projectthat there will be an increase of 5 to 20 percent inwinter precipitation in western North Americaduring the 21st century. As temperatures increase,more winter precipitation will fall as rain ratherthan snow.

17

Change inSnow WaterEquivalent,1935-2000(% per decade)

SOURCE: Data from BC Environment Historical Snow Survey.

Analysis by Canadian Institute for Climate Studies, 2001 for

Ministry of Water, Land and Air Protection. NOTES: A positivenumber indicates a trend towards increasing SWE.

ABOUT THE INDICATORSThese indicators measure changes in snow waterequivalent (SWE), the weight of water in a columnof snow, and snow depth. Together, the measuresprovide information about snow density. Trends arebased on data collected at provincial snow surveystations in winter (February) and spring (March andApril). Most stations are located between 1,000 and2,000 metres above sea level. The periods of recordrange from 36 to 64 years, depending on dataavailability.

SNOW TRENDS IN BRITISH COLUMBIAOverall, the BC trends in SWE and snow depth areconsidered weak because they are not consistentacross all months sampled and between adjacentregions.

In the Southern Interior Mountains, SWEincreased in February at a rate of 4 percent perdecade. The record is relatively long (63 years) andthe trend may reflect climate change. The data fail toindicate SWE trends for March and April or trends insnow depth.

In the Sub-Boreal Interior, SWE increased inMarch and April at a rate of 6 percent per decade.

The record is relatively short (41 years) and the trendlikely reflects climate variability. The data fail to showa SWE trend for February or trends in snow depth.

In the Southern Interior, Coast and Mountains,and Georgia Depression ecoprovinces, the record isrelatively long (51 to 66 years) but the data fail toshow trends in SWE. Snow decreased in theCoast and Mountains ecoprovince in February by6 percent per decade and in the Southern Interior inMarch by 3 percent per decade.

In the Boreal Plains, Central Interior, NorthernBoreal Mountains, and Taiga Plains ecoprovinces,the data fail to show SWE trends. Snow depth in theCentral Interior decreased by 9 percent per decade inMarch. The records for these ecoprovinces are short(36 to 44 years) and these trends likely reflectclimate variability.

Together, SWE and snow depth provide infor-mation about snow density. In general, as SWEincreases for the same volume of snow, or as depthdecreases while SWE remains constant, densityincreases. Snow density may have increased in fiveecoprovinces, the two where SWE increased anddepth remained the same and the three where SWEremained the same and depth decreased.

S N O W

The water content and the density of snow may be increasing, or the depthdecreasing, in some parts of BC. Changes in snowpack may affect the amount ofwater that is stored over the winter and released to groundwater aquifers, streams, and rivers in the spring and summer. They may affect the timing of snowmelt and local heat exchange processes.

BOREALPLAINS

TAIGAPLAINS

NORTHERNBOREAL

MOUNTAINS

SUB-BOREAL

INTERIOR

COAST ANDMOUNTAINS

CENTRALINTERIOR

SOUTHERNINTERIOR

MOUNTAINS

SOUTHERNINTERIOR

GEORGIADEPRESSION

NORTHEASTPACIFIC

+4

+6

notrend

notrend

notrend


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WHY IS IT IMPORTANT?Snow acts as a temporary storage system for winterprecipitation, and SWE is a measure of how muchwater is stored as snow. When snow melts in springand early summer, this water becomes available torecharge groundwater aquifers, fill reservoirs, andreplenish soil moisture.

Many rivers in BC are snowmelt dominated,meaning they are characterized by a surge of waterwhen snow melts in the spring and early summer.This freshet helps keep temperatures at a comfortablelevel for fish and other aquatic organisms. In manyparts of BC, it also ensures that enough water isavailable in summer for irrigation, hydro-electricpower generation, industry, fisheries, and domesticwater use.

Snow depth affects the capacity of snow to act asan insulator. In general, the deeper the snow, thegreater its insulating value. Changes in snow depthmay therefore affect the local rate of heat exchangebetween the land and water and the atmosphere, andthe rate and time at which ice melts.

Snow density can affect the timing and rate ofmelting. Denser snow is closer to its melting point.Increasing density may signal earlier or more rapid

Change inSnow Depth,1935-2000 (% per decade)

spring melting. Particularly on the coast, when heavyrain falls on top of dense, wet snow, it can triggerrapid melting and flooding and damage to eco-systems and infrastructure. Denser snow is lesssuitable for skiing, but more suitable for some otherforms of backcountry recreation.

The geographical extent of snow cover is asimportant as its physical characteristics. Satellitedata show that in the Northern Hemisphere, theextent of snow cover has probably decreased byabout 10 percent since the late 1960s. This hasadverse implications for water supplies. It may alsocontribute to local warming as exposed groundabsorbs and retains heat.

WHY IS THE SNOWPACK CHANGING?Snow accumulation and its characteristics arethe result of air temperature, precipitation, stormfrequency, wind, and the amount of moisture in theatmosphere. Changes in these and other climateproperties can therefore affect snowpack.

BOREALPLAINS

TAIGAPLAINS

NORTHERNBOREAL

MOUNTAINS

SUB-BOREALINTERIOR

COAST ANDMOUNTAINS

CENTRALINTERIOR

SOUTHERNINTERIOR

MOUNTAINS

SOUTHERNINTERIOR

GEORGIADEPRESSION

NORTHEASTPACIFIC -3

-9-6 no

trend

notrend


SOURCE: Data from BC Environment Historical Snow Survey. Analysis by Canadian

Institute for Climate Studies, 2001 for Ministry of Water, Land and Air Protection.

NOTES: A negative number indicates a trend towards decreasing snow depth.

SOURCE: Tourism BC

19

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Winter warming is the most likely cause ofincreasing snow density. As winter temperatureswarm, more winter precipitation is likely to fall asheavy “wet” snow. Rain or sleet may compact snowalready on the ground. Warmer air temperatures cancause snow already on the ground to melt onto itself.

Temperature also affects the altitude of thesnowline in mountainous areas and hence the totalsize of the area above the snowline. As temperatureincreases, the area above the snowline shrinks. Thisin turn affects the proportion of total precipitationthat falls and is stored as snow and the amount ofrunoff in spring and summer. The IntergovernmentalPanel on Climate Change (IPCC) has concluded thatthere is a highly significant correlation betweenincreases in surface temperatures and decreases inthe extent of snow and ice in the NorthernHemisphere.

WHAT CAN WE EXPECT IN FUTURE?The amount of precipitation that falls as snow willcontinue to vary from year to year in response tonatural climate cycles. Climate models project,however, that as the Earth continues to warm, theextent of snow cover in the Northern Hemispherewill continue to decrease during the 21st century.The IPCC has concluded that in mountainousregions of North America, particularly at mid-elevations, higher temperatures could lead to a long-term reduction in peak snow-water equivalent, withthe snowpack building later in the year and meltingsooner.


Projected Change in Extent ofSnow Cover in the ColumbiaRiver Basin, 2000 – 2100

SOURCE: Adapted from snow cover map produced by

Joint Institute for the Study of the Atmosphere andOcean, University of Washington. NOTES: In areas still

snow covered in 2095, models predict lower SWE.

2000

~2025

~2095

BC

Washington

BC

Washington

BC

Washington

MARCH

20

SOURCE: Data from National Hydrological Research

Institute. Analysis by A. Berger, 1999 for the Ministryof Water, Land and Air Protection.

Change in Glacier TerminusPosition, 1895-1995

ABOUT THIS INDICATORGlaciers advance and retreat in response to changesin local climate. This indicator measures changesin the length and position of the front edge, or“terminus,” of two southern British Columbiaglaciers between 1895 and 1995. Helm Glacier(49º58'N, 123º00'W) is in Garibaldi Provincial Park,and Illecillewaet Glacier (51º15'N, 117º30'W) is thenorth-extending tongue of the Illecillewaet Icefieldin Glacier National Park.

TRENDS IN GLACIER TERMINUSPOSITIONThe terminus positions of Helm Glacier in south-western BC and Illecillewaet Glacier in southeasternBC both receded by more than 1,100 metres from1895 to 1995. Most of the other glaciers and icefieldsthat have been studied in Alberta and BC also lostsignificant ice volume in the 20th century. Somesmall glaciers in the Rocky Mountains may have lostas much as 75 percent of the ice volume they had100 years ago. Wedgemont Glacier near Whistler,BC has retreated hundreds of metres in the past twodecades alone.

Glacier melting in BC is consistent with thefindings of the United Nations Intergovernmental

Panel on Climate Change (IPCC), which identified amassive retreat of mountain glaciers in tropical andtemperate zones during the 20th century. Accordingto the World Resources Institute, the world’s totalglacier mass decreased by about 12 percent overthe century.

WedgemontGlacier,1979-1998

G L A C I E R S

Glaciers in southern BC retreated during the 20th century. In the short term, retreating glaciers may add water to mountain-fed streams and rivers. In the long term, glacier retreat will probably mean less runoff, particularly in the summer months.

C L I M A T E C H A N G E A N D F R E S H W A T E R E C O S Y S T E M S

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1979

1998

WedgemontGlacierterminus

WedgemontGlacierterminus

Stev

e Ir

win

Stev

e Ir

win

Met

res Helm Glacier

Illecillewaet Glacier

-1400

-1200

-1000

-800

-600

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0

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199519751955193519151895

21

There is some evidence that glaciers near coastalareas in northwestern BC — such as the Taku Glacier— and glaciers at high elevations have remainedstable or advanced over the past century.

WHY IS IT IMPORTANT?Glacial meltwater feeds many mountain streamsand rivers in BC, including the Cheakamus River,Pemberton Creek, Slesse Creek, Homathko River,Lillooet River, and Squamish River. In glacier-fedrivers, the highest flows tend to occur in early ormid-summer, depending on latitude, and glacierrunoff can account for a significant portion of theavailable water supply.

Glacier retreat is therefore likely to cause changesin the flow patterns, and possibly the temperature, ofsome streams and rivers. These changes — alongwith other climate-driven changes to hydrologicalsystems (see “Freezing and Thawing”) — will likelyhave significant impacts on freshwater and estuarineecosystems and on aquatic species. They will affectother biological systems and human activities thatdepend on water.

In the short term, melting glaciers will likelydischarge more water into some BC streams andrivers. This may provide short-term benefits tohydroelectric power generation, water-basedrecreation, irrigation, fisheries, and other water users.Higher flows may also, however, increase streamturbidity and damage fish habitat and riparian areas.

In the longer term, glacier retreat will likely meanreduced water volume in glacier-fed streams andrivers, especially during the summer months. Inwater-short regions, this could generate increasedcompetition between various water users.

WHY ARE GLACIERS MELTING?Changes in the position of a glacier’s terminus areindirect and delayed signals of changes in localclimate. The advance or retreat of a glacier representsthe integration of many climate-related events thatmay occur over a period as short as one year or aslong as centuries.

Climate models suggest that in most glaciers,changes in temperature, rather than changes inprecipitation, control the evolution of mass.Although winter precipitation fuels the growth of aglacier, a warm summer can melt large gains frommore than one previous year. The IPCC believes thatwarmer temperatures associated with climate changeare the cause of world-wide glacial melting.

While the dominant global trend is towardsglacier retreat, some glaciers have advanced over thelast few decades, particularly in mountainous coastalregions and at high elevations. Higher than averagelevels of winter precipitation that may also beassociated with climate change probably account forthis advance.

WHAT CAN WE EXPECT IN FUTURE?The IPCC believes that glaciers and ice caps willcontinue their widespread retreat during the 21stcentury. Globally, the actual rate of retreat willdepend on the rate at which the temperatureincreases. The retreat of most glaciers will accelerate,and many small glaciers may disappear. Areas thatare currently marginally glaciated are likely tobecome ice-free in future.

In BC, whether glaciers advance, remain stable, orretreat will depend on their geographic location andelevation. Most glaciers in southern BC are likely tocontinue to retreat. Glaciers with a high proportionof their surface area at high elevations are likely toremain stable. In northwestern BC, increases inprecipitation associated with climate change mayoffset higher temperatures and contribute to theongoing advance of glaciers.


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ABOUT THE INDICATORSThe indicators measure changes in the dates onwhich key freezing and thawing events occur onlakes and rivers in British Columbia. They are:• date of first melt• ice-free date (when rivers and lakes are

completely free of ice)• first date of permanent ice• date of complete freezing

Trends are based on data from six (and for oneindicator, seven) stations. The records span 27 to 51years, and most cover approximately three decades.

MELTING AND FREEZING TRENDSLakes and rivers now start to melt earlier in spring, onaverage, than they did several decades ago. First melthas become earlier by 9 days per decade in DeaseLake, 5 days per decade in Fort Nelson, 7 days perdecade in Omineca River, and 8 days per decade inthe Thompson River region.

Lakes and rivers also become free of ice earlier, onaverage, than they did several decades ago. The icefree date has become earlier by 6 days per decade inthe Thompson River region, 3 days per decade inOmineca River, 4 days per decade at Charlie Lake,

north of Fort St. John, 3 days per decade at DeaseLake, and 2 days per decade at Fort Nelson.

Lakes and rivers in northern BC may freeze later inthe fall, on average, than they did several decades ago.At Charlie Lake, the first permanent ice appears 5 daysper decade later. At Fort Nelson, lakes freeze overcompletely 4 days per decade later. These trends are notreplicated in adjacent stations and are considered weak.

The Intergovernmental Panel on Climate Change(IPCC) has concluded that the annual duration of lakeand river ice in the mid-latitudes of the NorthernHemisphere probably decreased by about two weeksduring the 20th century, or at a rate of 1 to 2 days perdecade. It is difficult to compare the BC trends withthis global average because the BC trends are based ondata collected during a shorter, relatively warm period.The BC trends likely reflect climate variability ratherthan climate change.

WHY IS IT IMPORTANT?The duration of ice on lakes and rivers is importantfor transportation. Vehicles involved in winter loggingand oil and gas exploration can move about moreeasily when water bodies are frozen. Skiers andsnowmobilers can use frozen lakes and rivers asbackcountry roads.

F R E E Z I N GA N D T H A W I N G

Ice on lakes and rivers in BC melts earliernow than it did several decades ago. When ice melts earlier in the spring, it can affect lake productivity, aquaticecosystems, and winter activities.


Change inDate ofFirst Melt,1945-1993(days perdecade)

SOURCE: Data from Meteorological Service of Canada, EnvironmentCanada. Analysis by Canadian Institute for Climate Studies, 2001, for

Ministry of Water, Land and Air Protection. NOTES: A negative trend

means that water bodies start to melt earlier in the year.

NORTHERNBOREAL

MOUNTAINS

COAST ANDMOUNTAINS

CENTRALINTERIOR

SOUTHERNINTERIOR

MOUNTAINS

SOUTHERNINTERIOR

GEORGIADEPRESSION

NORTHEASTPACIFIC

-8North and SouthThompson Rivers

-5Fort Nelson andMuskawa River

-9Dease Lake

-7Omineca River

23

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The duration of ice can also affect theproductivity of freshwater ecosystems. Thetemperature of most lakes varies depending ondepth. When lakes are cold — at high latitudes, athigh elevations, or in winter — water at the bottomof the lake is warmer than water at the top. Whenlakes are warm — in low- to mid-elevations andlatitudes, and in summer — water at the bottom ofthe lake is colder than water at the top. In spring andfall, many lakes go through a period in whichtemperature differences and thermal stratificationdisappear. This allows the water, and the nutrients,oxygen, and micro-organisms it contains, to mixthroughout the lake, increasing productivity.

In lakes that currently undergo thermalstratification in summer, a longer ice-free periodmeans that stratification develops earlier in the yearand lasts longer. Periods of mixing during springand fall may be reduced in length. Increasingtemperatures mean that some lakes that currentlyfreeze over in winter may no longer do so. Theymay move from a regime that includes winterstratification to one that includes winter mixing.

The IPCC has concluded that changes in thermalregimes and lake-mixing properties may have asignificant effect on the concentration of dissolvedoxygen in the deeper layers of many lakes, andconsequently on available fish habitat. They may also

affect primary productivity — the growth ofphytoplankton — in the upper layers of these lakes,with impacts on fish production. The direction andmagnitude of these effects will vary depending on theunique characteristics of the lake.

Many aquatic systems are sensitive to temperature,and thawing and freezing events may mark milestonesin their life cycles. A longer ice-free season may meana longer growing season for these organisms. It mayallow some species to move into new areas that werepreviously not habitable to them.

WHY IS THE ICE MELTING EARLIER?Climate affects the formation, thickening, and meltingof ice — processes that reflect the beginning and endof the cold season and its severity. Air temperature isthe main influence on the rate of heat loss and gainfrom water bodies and the timing of freeze-up andmelt. Other contributing factors include cloudiness,solar radiation, wind speed, humidity, precipitation,the depth and composition of snow on top of the ice,and water temperature. All of these factors reflect localclimate conditions.

During the past century, almost all regions of BChave experienced warmer spring temperatures (see“Average Temperature”). Earlier dates of first melt andice breakup are consistent with these trends.

The IPCC attributes the reduction in the durationof ice during the 20th century to climate change. TheBC trends, however, are based on short data records.Most begin during a slightly cooler period — the1940s and 50s — and end during a warmer period —the 1990s. They are therefore very likely to have beeninfluenced by natural climate variability. If longerrecords were available, they would probably showslower rates of change in BC.

WHAT CAN WE EXPECT IN FUTURE?Climate models project that globally, atmosphericwarming associated with climate change will continueto be more pronounced in winter and spring than insummer and fall. This warming will likely continueto cause earlier thawing of ice on provincial lakesand rivers.


Change inIce Free Date,1945-1993(days perdecade)

SOURCE: Data from Meteorological Service of Canada, Environment Canada. Analysis byCanadian Institute for Climate Studies, 2001, for Ministry of Water, Land and Air Protection.

NOTES: A negative trend means that water bodies are ice-free earlier in the year.

NORTHERNBOREAL

MOUNTAINS

COAST ANDMOUNTAINS

CENTRALINTERIOR

SOUTHERNINTERIOR

MOUNTAINS

SOUTHERNINTERIOR

GEORGIADEPRESSION

NORTHEASTPACIFIC

-6North and SouthThompson Rivers

-2Fort Nelson andMuskawa River

-4Charlie Lake

-3Dease Lake

-3Omineca River

24

SOURCE: Data from the Water Survey of Canada, Environment

Canada. Analysis by John Morrison, Institute of Ocean Sciences,

2001, for Ministry of Water, Land and Air Protection. NOTES: Allvalues are statistically significant. (R2 = 0.1216, p = 0.001).

Change in Timing of One-third ofFraser River Annual Flow, 1912-1998

ABOUT THE INDICATORSThe indicators measure changes in the dates bywhich one-third and then one-half of the total annualvolume of the Fraser River pass the town of Hope.They are based on flow data collected at Hopefor the years 1912 to 1998.

TRENDS IN CUMULATIVE FLOWMilestones in the annual cumulative volume of theFraser River’s flow are occurring earlier in the year.• The date by which one-third of the annual

cumulative flow occurs has advanced at a rateequivalent to 11 days per century.

• The date by which one-half of the annualcumulative flow occurs has advanced at a rateequivalent to nine days per century.

• There was no significant trend in the date orthe height of peak flow from 1912 to 1998.The Fraser River’s flow is subject to regular

season-to-season fluctuations. Average daily dis-charge at Hope ranges from a peak of about7,000 cubic metres of water per second in late June(after the annual spring snow melt) to a low of about1,000 cubic metres per second in the winter.

Flow is also subject to year-to-year changes thatare linked to natural climate variability. The highest

peak flow ever recorded, for example, was15,000 cubic metres per second. In general, riverflow is greater after a La Niña winter, typicallyassociated with higher-than-average precipitationand heavier snowfall. Peak flow arrives earlier in theyear after an El Niño event, which is associated withwarmer spring conditions and earlier melting of thesnowpack. Flow is lower than average the summerfollowing the drier winter conditions associated withan El Niño event. These are all examples of shorter-term natural variations in climate. The trends incumulative flow stand out from such natural cyclesand are probably the result of longer-term climatechange. They are consistent with other trendsobserved in British Columbia, including warmersprings, earlier spring thaws, and melting glaciers.

WHY IS IT IMPORTANT?The Fraser River drains approximately 230,000square kilometres — more than one-quarter of theland area of BC. Outside of the lower mainland, theriver and its tributaries are in a relatively naturalstate, with few dams or control structures. Changesin the timing of its flow can affect both naturalecosystems and human communities.

When a greater proportion of the total flow


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T I M I N G A N DV O L U M E O FR I V E R F L O W

Seasonal changes in the timing andvolume of the Fraser River flow areoccurring earlier in the year on average. This is likely to cause water shortages and negative impacts on salmon and other aquatic organisms.

200019801960194019201900

1/3

Flo

w D

ay

Trend Line

June 28June 23June 18June 13June 8June 3

May 29May 24May 19

25

moves through the river system earlier in the season,higher-than-usual water volume and velocity mayincrease river turbulence and scouring, withpotential negative impacts on aquatic ecosystems,habitats, and organisms. Extreme flows, specificallychanges in the height of peak flow, can affect watersupplies, fisheries, and power generation and posea flood risk to communities, roads, and railways.

Corresponding lower flows in summer andlater in the season may reduce the amount of wateravailable for agriculture, hydroelectric power gener-ation, industry, and communities in some parts of theBC interior. This is a potentially significant problemin drier areas such as the Okanagan Basin, wheremost streams are already fully allocated to waterusers and water shortages already exist. Low, late-season flows are especially a concern in years whenbelow-average summer rainfall coincides with below-average summer flows.

Lower flows are also associated with warmerwater temperatures (see “River Temperature”) anddeclining water quality, both of which threaten thehealth of aquatic ecosystems and of salmon andother aquatic species (see “Salmon in the River”).

WHY IS RIVER FLOW CHANGING?Most of the streams and rivers that contribute tothe Fraser system are snowmelt dominated. In suchwatersheds, very little runoff occurs during thewinter. Instead, the winter snowpack melts and feedsthe river system during the following spring andearly summer.

In snowmelt-dominated river systems, thecharacteristics of the snowpack and spring climateconditions determine the timing of the spring flowor “freshet,” which can vary significantly from year toyear. The trends toward warmer spring temperaturesacross BC, an increase in the water content of snowin parts of the interior, and earlier dates of springthaw are all compatible with an earlier spring freshet.

When spring temperatures are higher, snow andice melt and feed into streams and rivers earlier inthe year. Lower summer flows occur because snowand ice sources have already been depleted by that

time, and because higher summer temperaturesincrease evapotranspiration.

Not all river systems respond in the same way to awarming climate. Warming may cause rivers that aremixed snow-and-rain dominated to release a greaterportion of their flow, and occasionally flood, in winter.Rainfall-dominated rivers may have greater flows inseasons with increased precipitation. And rivers thatare highly managed (for example, the ColumbiaRiver) may show different or no significant trends.

WHAT CAN WE EXPECT IN FUTURE?The timing and volume of river flow will always varyfrom one year to the next.

The United Nations Intergovernmental Panel onClimate Change (IPCC) has concluded that in regionswhere seasonal snowmelt is an important aspect of theannual hydrologic regime — such as the basins of theFraser, Columbia, and Peace rivers — warmertemperatures are likely to result in a seasonal shift inrunoff, with a larger proportion of total runoffoccurring in winter, together with possible reductionsin summer flows. Some snowmelt-dominated riverbasins could shift towards a mixed snow-and-rainregime, with increased runoff during the wintermonths.

According to the IPCC, late summer streamdischarge could decrease suddenly within only a fewyears in some regions.


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SOURCE: Leith R. and P.

Whitfield. 1998. Evidenceof climate change effects on

the hydrology of streams in

south-central BC. Cdn. WaterResources J. 23:219-230.

Flow andTimingVariabilityin a SouthernSnowmelt-DominatedRiver

Upper Similkameen River

Earliersnowmelt

Greaterautumn

rain

Lowersummer

flow

Extendedlow-flow

period

Jan. 1 April 1 June 1 Sept. 1 Dec. 31

Met

res

1

10

100

Averaged flows1971-831984-95

Sou

rce: Leith an

d W

hitfield

, 1998

26

SOURCE: Historical temperature data from the Pacific Salmon Commission,1941-1998. Historical weather data from Meteorological Service of Canada,

Environment Canada 1953-1998. Analysis by John Morrison, Institute of

Ocean Sciences, 2001 for the Ministry of Water, Land and Air Protection.NOTES: Results are statistically significant. (R2 = 0.1151, p = .0226).

Change in Average Fraser RiverTemperature, 1953-1998

ABOUT THE INDICATORThis indicator measures changes in the averagesummer temperature of the Fraser River at Hell’sGate. It is based on daily measurements of watertemperature taken from July 1 to September 15 forthe years 1953 to 1998.

TRENDS IN RIVER TEMPERATUREThe temperature of the Fraser River at Hell’s Gate insummer warmed during the period 1953 to 1998 ata rate equivalent to 2.2ºC per century .

The Fraser River is subject to seasonal and year-to-year variations in temperature that are related toshort-term natural climate variability. In general,summer river temperatures are warmer after an ElNiño event and cooler after a La Niña event. Becausethe period of record is only 45 years, these short-term climate variations may have as much influenceon the observed trend towards river warming asclimate change.

The average temperature of the Columbia Riverat or near the international boundary during thesummers of 1959 to 1997 also appears to havewarmed, but the data are not sufficient to establish atrend. In addition, because the Columbia is a highly

regulated river system, any apparent trend mightbe due to human-induced changes in the timingand volume of river flow, or to the temperatureand volume of water reservoirs, rather than toclimate change.

WHY IS IT IMPORTANT?The Fraser River flows 1,370 kilometres from itsheadwaters in the Rocky Mountains to the PacificOcean. It supports ecologically important salmonruns, including the majority of Canadian sockeyestocks. Almost all runs must pass through Hell’s Gatein their migration upriver to spawn. Warmer rivertemperatures are expected to affect salmon and otheraquatic organisms.

In general, warm water temperatures reducesalmon fitness, survival, and reproductive successand promote potential long-term population declines(see “Salmon in the River”). Declines in Fraser Riversalmon stocks have negative impacts on provincialfishing and tourism industries and aboriginal andother communities that rely on fish. They affectpredators such as bald eagles and bears and coastalecosystem processes that depend on the nutrientsprovided by salmon carcasses.

R I V E RT E M P E R A T U R E

The average summer temperature of the Fraser River has warmed over the past five decades. River warming can have negative impacts on the health, distribution, and survival of salmon but positive impacts on aquatic species that can tolerate warmer water.


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Tem

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re (

°C)

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Trend Line

27

In addition, many provincial salmon stocks areclassified as at moderate to high risk of extinction.The United National Intergovernmental Panel onClimate Change (IPCC) believes that, withoutappropriate management, climate change will lead tochanges in freshwater ecosystems that will causesome species currently classified as “criticallyendangered” to become extinct and the majority ofspecies classified as “endangered” or “vulnerable” toapproach extinction in the 21st century.

Over the long term, higher temperatures areexpected to result in a shift in the distribution ofsalmon and other cold-water species to higherlatitudes and elevations, together with increasedpopulation fragmentation in more southerly parts oftheir ranges. If other factors were to limit these rangeshifts, an overall reduction in the distribution ofcertain species would be the result.

River warming may have positive impacts onaquatic species that can tolerate warmer watertemperatures. Native warm-water species may beable to expand their range into higher-altitude lakesand more northerly regions. For example, a 4ºCincrease in average air temperature is projected toexpand the ranges of smallmouth bass and yellowperch northward across Canada by about 500kilometres. There is also an increased likelihood ofsuccessful invasion by non-native species that requirewarmer water temperatures.

WHY IS RIVER TEMPERATUREINCREASING?River temperature is the result of complexinteractions between the characteristics of the riveritself, climate, and adjacent land-use practices.

Many streams and rivers in the Fraser system aresnowmelt dominated. In these river systems, climatechange is associated with earlier melting of ice inspring, an earlier spring freshet, and lower summerflow volume (see “Timing and Volume of RiverFlow”). The average summer temperature of theFraser River is increasing because the average annualtemperature is getting warmer and because there isless water in the river to heat. In addition, when

snow melts earlier in the season, it reduces thebuffering effect of the cold spring freshet on streamtemperature in early summer.

Examination of weather records suggests thatlong-term changes in climate are responsible for55 percent of the Fraser River warming. During theperiod studied (1953-1998), summer climate asmeasured upriver of Hell’s Gate at Prince Georgeand Kamloops changed in the following ways: airtemperature increased; cloud cover decreased; solarradiation (the amount of sunlight reaching theground) increased; wind speed decreased; and dewpoint temperature increased. Each of these changesfavours river warming.

Changes in adjacent land use over the recordperiod may also have affected river temperatures.Forestry, agriculture, industrialization, and hydro-electric generation tend to decrease the amount ofvegetation cover along rivers and streams, exposingmore of the river surface to the sun’s heat. Theimpacts of these events are small, however, incomparison to the impact of climate.

WHAT CAN WE EXPECT IN FUTURE?River temperatures will continue to vary from oneyear to the next in response to short-term naturalclimate variability. If the climate is warming,however, years with warmer river temperatures areexpected to occur more frequently. In addition, rivertemperatures may more often exceed those that areoptimal for fish.

Atmospheric temperature and other aspects ofclimate affect river temperature. Climate modelsproject that air temperatures in British Columbiawill increase at rates of 1ºC to 4ºC per century. Thehigher rate of warming is projected to occur over theinterior — the region of the province that containsmost of the rivers and streams that feed the FraserRiver system.


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28

SALMON IN THE RIVER

Natural year-to-year variations in river flow andtemperature affect the survival of sockeye

salmon stocks. Long-term changes in river flow andtemperature associated with climate change aretherefore likely to have an impact on Fraser Riversockeye populations over time.

Fish are sensitive to temperature, which regulatesmany of their physiological processes. When theirenvironment is warmer, their metabolic rateincreases, speeding up internal processes such asoxygen consumption, digestion, and mobility.

Salmon tolerate temperatures of up to about24.5ºC but prefer temperatures from 12ºC to 15ºC.Because sockeye prefer coldertemperatures than other salmonspecies, sockeye may be thespecies that is most sensitive toclimate change. Temperaturesabove 15ºC can cause stress insockeye, depleting their energyreserves, making them moresusceptible to disease andreducing their capacity toproduce viable eggs and sperm. Temperatures above18ºC can impair their swimming ability. They candie from several days’ exposure to temperaturesbetween 22ºC and 24ºC or from brief exposure totemperatures above 24ºC.

Fraser River Watershed

SOURCE: Ocean Science and

Productivity, Fisheries and OceansCanada.

Each summer and fall, adultsockeye return from the ocean tospawn in more than 150 natalstream, river, and lake spawningareas in the Fraser River water-shed. Different stocks start theirlong swim upriver at different times.The summer run group, includingstocks that originate in the Quesnel

and Chilko rivers, starts its migration upriver in lateJuly and August. The late run group, includingShuswap stocks, arrives at the mouth of the FraserRiver in August, but typically waits four to six weeksbefore entering the river to start migration.


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Warmer river temperatures areassociated with increased mortalityin migrating salmon stocks. Changesin river flow and temperaturelinked to climate change areexpected to have profound negativeimpacts on some salmon stocks.

Stuart L.C hi l c o L.

Lytton

Kamloops

Kamloops L .

F R

A S

E R

F R

R A

E S

R I V E R

WilliamsLake

R I V E R

PrinceGeorge

Stua tr R.

KenneyDam

Lillooet

Shuswap

L.

Chilcotin R.

Quesnel R. Quesne

l L.

Adam

s R.

Nec

hako

River

Bonaparte R.

NechakoReservoir

Horsefly R.

Nicola R.

Fraser RiverWatershed

Strait

of

Georgia

Va n c o u v e r

I s l a n d

HELL‘S GATE

Blue R.

R.

Jasper

HOPE

N. Thompson

Quesnel

Thom

p son

Th omps

on R.River

N.Th

omps

on River

S.

VANCOUVER

British Columbia

K E Y M A P

Tom Hall

29

HOW DOES RIVER TEMPERATUREAFFECT SOCKEYE SALMON?Most Fraser River sockeye stocks must pass throughHell’s Gate, above Hope, in their migration upriver.Measurements taken at Hell’s Gate show considerableyear-to-year variability in river flow and temperature.

Research has established a link between waterflow and temperature and mortality in Fraser Riverspawning stocks. Fish may die while in transit up theriver (“en route mortality”) or they may not spawnwhen they arrive at their spawning grounds (“pre-spawning mortality”).

In several years during the past decade, enroute mortality in several runs has been greater than50 percent. Records from 1978 to 1998 indicatethat en route losses have been greatest in yearswith warm river temperatures. The connection isparticularly strong in the summer run group, whichmigrates when river temperatures are at their highest.In recent years the late run group has been startingmigration early and is therefore also at risk.

Pre-spawning mortality across all Fraser Riversockeye stocks over a five-decade period rangedfrom 0 to 85 percent. Studies suggest a weak linkbetween higher rates of pre-spawning mortality andwarmer-than-average river temperatures.

Long-term trends in river flow and temperatureassociated with climate change are therefore reasonsto be concerned about the prospects for many FraserRiver salmon stocks. Records show that the FraserRiver is now discharging more of its annual volumeearlier in the year (see “River Flow and Timing’).Earlier spring runoff is associated with lowersummer flows and higher water temperatures (see“River Temperature”).

WHAT CAN WE EXPECT IN FUTURE?While river flow and temperature will still vary fromone year to the next, summers with lower flow andwarmer temperatures will likely occur more often inthe future. This is expected to have profoundnegative impacts on Fraser River sockeye stocks overthe long term. More research is needed to determinewhether stocks in more northerly rivers — theSkeena, Nass, and Somass — and the Rivers Inletand Smith Inlet areas will experience the sametemperature extremes and will face the same threatsas a result of climate change.

SOURCE: Data and analysis by S. Macdonald and J. Grout, Fisheries and OceansCanada, 2001. NOTES: En route mortality is the difference between estimates

of the number of fish entering the Fraser River, and the number reaching the

spawning grounds. A negative number represents fish lost en route. A positivenumber represents uncertainties in estimation, and/or en route fishing activities.

Results are statistically significant at the 95% level.


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Migration Success ofSummer Run Sockeyeand Temperature atHell’s Gate, 1978-1998.

En-r

ou

te m

ort

alit

y

1,500,000

1,000,000

500,000

0

-500,000

-1,000,000

-1,500,000

93

96

92

97

81

94

98

15 16 17 18 19

Temperature at Hell's Gate (°C)

SOURCE: Burghner, R.L. 1991. Life History of Sockeye Salmon. In Pacific Salmon Life

Histories. University of British Columbia, p.3-117. Graphic from Temperature Rising:

Climate Change in Southwestern British Columbia, 1999.

R i v e r

O c e a n

Hig

h s

tres

s

Salm

on

str

ess-

o-m

eter22°C

21°C20°C19°C18°C17°C16°C15°C14°C

warmer watersincrease bacterial/fungal infections

of salmon

warmer winterreduced snowpack,

and snowmeltlonger

summerdrought

warmerriver

temperature

lowersummer

flow

warmer waterscause salmon to

burn energy faster

salmon dieen route dueto exhaustionand infection

stressed salmonreach spawning

grounds, butfail to spawn

30

Changein AverageSea Level,1909-1999(cm per century)

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SOURCE: Data from Marine Environmental Data Service and Canadian

Hydrographic Service. Analysis by J. F. Garrett, 2WE Associates

Consulting Ltd. for Ministry of Water, Land and Air Protection, 2001.NOTES: A positive trend indicates rising sea level.

ABOUT THE INDICATORThis indicator measures changes in the average levelof the sea relative to the adjacent land and trends inthe height of unusually high and low water. It is basedon records from 1909-1999 (with some gaps) fromfour monitoring stations along the British Columbiacoast.

The trends identified for coastal BC reflect thecombined impacts of climate change and the verticalmovements of coastal land masses as a result ofgeological processes. The coast of BC is stillrebounding upwards at rates of 0 to 40 centimetresper century from the melting of the massive ice sheetthat once covered much of the province. As a result ofother geophysical processes, Vancouver Island istilting. The southwest coast of the island is rising at arate of up to 40 centimetres per century in addition tothe rate of rebound. The rest of the island is sinking.

SEA LEVEL TRENDSDuring the 20th century, average relative sea levelrose 12 centimetres at Prince Rupert, 8 centimetres atVictoria, and 4 centimetres at Vancouver. These trendsreflect the combined impacts of vertical movementsof the shoreline and a rise in average global sea level.Relative sea level fell at Tofino at an average rate of

13 centimetres per century. This is because thesouthwest coast of Vancouver Island is rising fasterthan the sea.

Tide gauge data — which show relative sea level— suggest that global average sea level rose between10 and 20 centimetres during the 20th century. Thisrate is about 10 times faster than the rate over theprevious 3,000 years.

The height of extreme high water events hasincreased at a faster rate than the mean sea level hasincreased. It increased by 22 centimetres per centuryat Prince Rupert, 16 centimetres per century atVancouver, and 34 centimetres per century at PointAtkinson, near Vancouver. The lack of a clear trendat Victoria may be the result of the relatively shortrecord length (37 years) for this indicator. At Tofino,where average sea level has fallen, the height ofextreme high water events showed little change.

WHY IS IT IMPORTANT?Rising sea level will likely contribute to increasedflooding of low-lying coastal areas. This may threatenwetlands, beaches, dunes, and other sensitive coastalecosystems, and some Aboriginal heritage sites. Itmay also strain drainage and sewage systems in somecoastal communities. Salt water may intrude into

+12

-13

+8+4

Tofino

Prince Rupert

VictoriaVancouver

C L I M A T E C H A N G E A N D M A R I N E E C O S Y S T E M S

S E A L E V E L

Average sea level has risen along most of the BC coast over the past 95 years. Higher sea levels increase the risk of flooding of low-lying coastal areas and may damage coastal ecosystems and infrastructure.

31

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groundwater aquifers, making the water they containunfit for household or agricultural use. Even beforethey are actually inundated, low-lying agriculturallands may become too saline for cultivation.

Higher mean sea level and more frequent extremehigh water events will increase the likelihood thatstorms will damage waterfront homes, wharves, roads,and port facilities and contribute to coastal erosion.

Areas particularly at risk are the Fraser River delta,where 100 square kilometres of land are currentlywithin 1 metre of sea level, and Prince Rupert, whereextreme high water events are occurring three timesmore frequently than in other areas of the coast.

Changes in the height and direction of prevailingocean waves, storm waves, and surges as a result ofclimate change may also have serious impacts on somecoastal areas.

Coastal Regionsat Risk

WHY IS SEA LEVEL RISING?The rise in average global sea level observed duringthe 20th century is very likely due to climate change.As the atmosphere warms, sea water warms andexpands in volume. Thermal expansion is believed tohave been a major influence on past changes in sealevel. It is expected to make the greatest contributionto a rising sea level over the next century.

Sea level also changes when the overall mass ofwater in the ocean increases or decreases. As ice capsand glaciers melt, water previously stored on land asice and snow is added to the ocean. Such processesare expected to contribute substantially to a rise insea level over the next century.

Processes not related to climate change alsoinfluence sea level. These include vertical movementsof the land and short-term natural changes in oceantemperature and circulation patterns. Long-termchanges in climate patterns — for example, strongeronshore winds or more severe low pressure systems— may influence the frequency of extreme changesin sea level.

WHAT CAN WE EXPECT IN FUTURE?Climate models project a further rise in global meansea level of 9 to 88 centimetres by 2100. The rateand magnitude of this rise in sea level will not beuniform over the globe. It will vary from one basin toanother, reflecting variations in the amount of oceanwarming and the way in which ocean currentsredistribute heat and mass.

In most areas, climate change is expected toproduce mean and extreme water levels higher thanany yet recorded. Extreme high water levels areexpected to occur with increasing frequency.

Sea level is expected to continue to rise, even ifgreenhouse gas concentrations in the atmospherestabilize. The deep ocean responds slowly to climatechange, and thermal expansion of the ocean is likelyto continue for hundreds of years. Ice caps are likelyto continue to melt for thousands of years.

ShorelineInundation


SOURCE: Clague J.J. and

B.D. Bornhold. 1980.

Morphology and littoralprocesses of the Pacific

Coast of Canada. In The

Coastline of Canada:Littoral Processes and Shore

Morphology; Geol. Survey

of Canada Paper 80-10,p.339-380. Graphic from

Temperature Rising, 1999.

Clag

ue an

d B

orn

ho

ld, 1980

Shoreline vulnerable to erosion

Fraser River delta

Other low-lyingareas

FR

AS

ER

R.

S T R AI T O

F GE O

R GI A

Nanaimo

Vancouver

Victoria

FRASERRIVER

CANADA

USA

VancouverIsland

L E G E N D

SOURCE: Clague and Bornhold.

1980. Graphic from Temperature

Rising, 1999.

1999 sea level

highersea level

Future Inundation

Today

eroded marsh

Richmond

dyke

1999 sea level

marsh

Richmond

dyke

Delta sediment

32

+1.6

+1.8+0.9

West Coast Vancouver Island

Georgia Basin

Queen Charlotte

Sound

SOURCE: Data from the Institute of Ocean Sciences (IOS), Fisheries andOceans Canada. Analysis and discussion by H. Freeland, IOS, and R. Lee and T.

Murdock, Canadian Institute of Climate Science, 2001 for Ministry of Water,

Land and Air Protection. NOTES: A positive trend indicates a rise in SST.

ABOUT THE INDICATORSThere are two important sea surface indicators. Thefirst measures temperature changes in the top 10metres of the sea surface at lighthouses along the BCcoastline. Trends are based on data from 1914 to2001 in the Georgia Basin, from 1934 to 2001 on thewest coast of Vancouver Island, and from 1937 to2001 in Queen Charlotte Sound. The secondindicator measures changes in salinity. Together,temperature and salinity provide information aboutthe density of sea water.

SEA SURFACE TRENDS IN BRITISHCOLUMBIADuring the 20th century, sea surface temperature(SST) increased at a rate equivalent to 0.9ºC percentury along the west coast of Vancouver Island,1.6ºC per century in Queen Charlotte Sound, and1.8ºC per century in the Georgia Basin. The trendsare based on relatively long records and likely reflectclimate change.

Sea salinity decreased along the west coast ofVancouver Island during the record period. Seadensity in this area also decreased. Density reflects acomplex relationship between temperature andsalinity; in general, as temperature increases and

salinity decreases, density decreases. Although therecords for the Georgia Basin and Queen CharlotteSound are relatively long (87 and 67 years), the datafail to reveal trends in sea salinity and density inthese areas.

The Intergovernmental Panel on Climate Change(IPCC) suggests that average global sea surfacetemperature has increased by 0.4ºC to 0.8ºC sincethe late 19th century. The rate of warming along thewest coast of Vancouver Island — the coastal areamost exposed to trends in the Pacific Ocean — issimilar to the global average.

WHY IS IT IMPORTANT?Temperature, salinity, and density are importantmeasures of marine ecosystem health and produc-tivity. Long-term changes in one or more of thesemeasures are likely to affect marine species andecosystems and the human communities andresource industries that depend on the sea.

Higher sea surface temperatures are linked tochanges in salmon distribution and migrationpatterns and subsequent potential declines inreproductive success (see “Salmon at Sea”). They arealso associated with reduced availability of food anddeclines in seabird populations (see “Seabird

Change inSea SurfaceTemperature,1914-2001,(ºC per century)

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S E A S U R F A C ET E M P E R A T U R E

Sea surface temperature in BC's coastal waters increased during the 20th century. Higher temperatures are associated withreduced ocean productivity and potentialadverse impacts on marine resources and the human communities that depend on them.


33

Survival”). In addition, sea temperature is importantbecause it affects the stability of the water column,which in turn affects ocean productivity.

The upper 100 metres or so is the most biologi-cally productive part of the ocean. In this zone,sunlight drives photosynthesis, supporting growth ofmicroscopic plants. These phytoplankton becomefood for microscopic animals — or zooplankton —that in turn support fish and other marine animals.

In spring and summer, as phytoplanktonpopulations grow, they use up nutrients in the upperlayer of the ocean. These nutrients are typicallyreplaced in the fall through mixing processes thatbring mineral-rich water from the ocean depths to thesurface. Such mixing is the result of waves, storms,tides, and prevailing winds. The deeper the mixing,the more nutrients rise to the surface, and the greaterthe productivity of the ocean the following year.

Temperature affects the stability of the watercolumn and therefore the depth to which mixing canoccur. Temperature and salinity in the deep ocean arestable. The sea surface is typically warmer, less saline,and less dense than the deeper water and thereforetends to “float” on top of it. When the sea surface iswarmer than usual, the difference in density betweenthe surface and deeper water is greater, the surface sitsmore securely on top of the deeper water, and mixingbecomes more difficult.

Natural cycles are associated with cycles in oceanproductivity. In an El Niño year, the sea surface insummer is warmer than usual, and the upper watercolumn is more stable. Mixing may therefore occur toa depth of only 100 metres. In a La Niña year, the seasurface in summer is cooler than usual, and the watercolumn is less stable. Mixing may occur down to 140metres, which results in greater ocean productivity.

Scientists have a high degree of confidence that ifwarm, El Niño-like events increase in frequency, thebiomass of plankton and fish larvae will decline,and this will have a negative impact on fish, marinemammals, seabirds, and ocean biodiversity. Thetrends towards warmer temperatures, reduced salinity,and reduced density observed in surface waters off theBC coast are therefore of great concern.

WHY IS THE SEA SURFACE CHANGING?The ocean is an integral and responsive componentof the climate system. At its surface, it exchangesheat, water (through evaporation and precipitation),and carbon dioxide and other gases with the atmos-phere. The 20th century trend towards higher seasurface temperatures is related to increasing atmos-pheric temperatures. The trend towards decreasingsalinity may be the result of higher sea surfacetemperatures because warmer water is typically lesssaline than cold water. It may also be influenced byincreased precipitation over the ocean or increasedfreshwater runoff from the adjacent land.

Of BC’s three regions of coastal waters, the westcoast of Vancouver Island is the most exposed to thePacific Ocean and the most likely to reflect oceanictrends. In the other two regions (Georgia Basin andQueen Charlotte Sound), local evaporation andprecipitation rates and freshwater runoff from riversand streams may affect temperature and salinity.

WHAT CAN WE EXPECT IN FUTURE?Sea surface temperature will likely continue to varyfrom year to year and from decade to decade inresponse to natural cycles. Climate models project,however, that the Earth will continue to warm andthat average global sea surface temperature willincrease by 1ºC to 6ºC by the end of the 21stcentury.The ocean will warm more slowly than theland. Current models do not yet allow scientists toproject with confidence the future frequency,amplitude, and spatial pattern of El Niño events.

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34

Natural variations in sea surface temperature areassociated with changes in the distribution and

survival of sockeye salmon. As a result, the effect ofclimate change on long-term increases in averageocean temperature is likely to have an impact onsockeye populations over time.

Salmon and other fish are cold-blooded, andthe temperature of their environment regulates manyof their physiologicalprocesses. Warmer watertemperatures raise theirmetabolic rate and speed upmovement and internalprocesses such as growth,oxygen consumption, anddigestion.

Studies suggest that salmon prefer a temperaturevery close to the temperature that promotes optimalgrowth. When food is abundant, they can afford —from a biological perspective — to stay in warmerwaters. The abundance of food makes up for thehigher requirements needed to fuel a more activemetabolism. When food is limited, however, fishmove into cooler waters, where they need less food togrow and survive.

The temperature range that fish prefer is species-specific. In general, salmon like cold water, andsockeye prefer colder water than other salmonspecies. For this reason, sockeye may be the salmon

species most sensitive to climate change. Fraser Riversockeye stocks are of particular concern because theyare already close to the southern boundary of therange for sockeye and are thus more likely than othersockeye stocks to be exposed to water temperaturesoutside their preferred range.

Most Fraser River sockeye stocks enter the oceanas smolts in the spring and spend a few weeks in theStrait of Georgia before migrating northwards alongthe coast of British Columbia to Alaska in earlysummer. During this migration, they stay on thecontinental shelf — a relatively shallow zoneextending 20 to 30 kilometres offshore. In lateautumn and winter, after reaching the AleutianIslands, they move southwards into the open ocean.They spend one to three years at sea before theyreturn as adults to the Fraser River in late summerand swim upstream to spawn and die.

HOW DOES SEA TEMPERATURE AFFECTSOCKEYE SALMON?The sea surface is subject to natural cycles ofwarming and cooling and corresponding periods of

lower and higher oceanproductivity (see “Sea SurfaceTemperature”). These cycles areassociated with year-to-yearvariability in sockeye production.Warmer sea surface temperaturesare associated with increasedjuvenile sockeye mortality,

changes in ocean distribution, changes in the timingof migrations, and smaller returning adult fish.

During warm years, ocean productivity is rela-tively low and may result in slower growth in juv-enile salmon, making them vulnerable to predationfor a longer period of time. In addition, subtropicalfish such as mackerel migrate northwards duringwarm years and can compete for food with, or preyupon, young salmon in coastal waters.

Some researchers have associated increasing seasurface temperatures with a decrease in the habitablearea for sockeye in the North Pacific. During theiryears in the open ocean, sockeye undertake extensive

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SALMON AT SEA

For sockeye salmon, warm years are associated with increased juvenile mortality, reduced distribution, increased competition, and reduced spawning success.


S. Kirkvold

35

migrations within a region bounded by the BeringSea in the north and 40ºN latitude in the south.Within this region, the area used by sockeye variesby season and is closely associated with watertemperature. The southern limit of their distributionvaries from between the 6ºC and 7ºC isotherms inwinter, to the 9ºC isotherm in spring and earlysummer, and the 13.5ºC isotherm in summer. Inyears when sea surface temperature is higher, thehabitable area for sockeye is smaller.

Ocean temperature appears to affect the timing ofsockeye migrations from the ocean back to the FraserRiver. Evidence suggests that in warm years, sockeyearrive later at the mouth of the river. Salmon thatarrive later than normal at the mouth of the rivermay also arrive late at their spawning grounds. Latespawning can have a negative effect on the timewhen young salmon emerge the following spring andtheir subsequent survival.

Ocean temperature also appears to affect the sizeof the returning fish. In warmer years, if fishcongregate within a smaller habitable area andcompete for the same amount of food, individual

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growth may be slower, and returning fish may besmaller than normal. In addition, warmer years areassociated with reduced ocean productivity and thepotential for increased competition for food. In 1997— a particularly warm year in the northeast PacificOcean — returning sockeye were much smaller thannormal. Smaller fish may not be able to migrateupstream through the Fraser River system to theirspawning grounds as effectively as larger fish.

WHAT CAN WE EXPECT IN FUTURE?Coastal waters in BC have warmed during the pastcentury, and climate models suggest that oceanwarming associated with climate change willcontinue. While sea surface temperature will stillvary from one year to the next, it will be “warm”during proportionally more years. For sockeye, warmyears are associated with increased juvenile mortality,restricted distribution, increased competition forfood, and reduced spawning success. An increase inthe proportion of warm years can thereforereasonably be expected to have a profound long-termnegative impact on Fraser River sockeye stocks.

Winter and SummerDistribution ofSockeye Salmon in thePacific Ocean, UnderCurrent (1XCO2) andFuture (2XCO2)Concentrations ofAtmospheric CO2


December

2XCO2

1XCO2

July

1XCO2

2XCO2

SOURCE: Welch, D.W., Y. Ishida, and

K. Nagasawa. 1998. Thermal Limits and

Ocean Migrations of Sockeye Salmon(Oncorhynchus nerka): Long-Term

Consequences of Global Warming.

Can. J. Fish. Aquat. Sci. 55:937-948.NOTES: 1XCO

2 refers to the current

atmospheric concentration of CO2.

2XCO2refers to the doubling ofatmospheric CO

2 concentration from

this baseline. Climate models predict

that 2XCO2 will occur during the 21stcentury. As CO

2 concentration increases,

atmospheric and ocean temperature

increase, and fish move northwards intocooler water.

36

The reproductive success of the Cassin’s auklet(Ptychoramphus aleuticus) is sensitive to ocean

temperature. Increases in sea surface temperatureassociated with climate change may thereforethreaten the long-term survival of this seabird.

The auklet breeds in a few large colonies alongthe western coast of North America. Triangle Island,an ecological reserve off thenorthern tip of VancouverIsland, is home to the world’slargest colony, consisting of1.1 million breeding birds.

Some populations ofCassin’s auklet have declinedin recent years. A colonyon the Farallon Islands inCalifornia experienced a 65percent decline between 1972 and 1997. TheTriangle Island population declined between 1989and 1999, and in several years, breeding success waspoor. However, a third population that breeds onFrederick Island off the coast of northern BritishColumbia showed no signs of population declineduring the 1990s and has had consistently goodbreeding success.

WHY ARE POPULATIONS DECLINING?The evidence suggests that population declinesare linked to a long-term reduction in the availabilityof zooplankton — a major food source for Cassin’sauklet chicks — in the marine ecosystem thatextends from California northwards as far as north-ern Vancouver Island. Research has documented arelationship between warmer spring ocean tempera-tures, reduced availability of zooplankton, anddecreased growth rates and survival of seabirdchicks.

Cassin’s auklets attempt to raise a single chickper year, and the survival of each chick is thereforeimportant to the long-term survival of the entirepopulation. Cassin’s auklet parents care for theirchick for 40 to 60 days after it hatches, feeding itzooplankton — primarily small shrimp-like organ-isms called copepods. Both parents use their wingsto “fly” underwater in search of food for their chick,transporting the food within a throat pouch andregurgitating it for the chick when they get back tothe burrow. The growth and survival of Cassin’sauklet chicks depend on the availability of copepods

in the top 30 metres of theocean — the depth to whichthe auklet parents are ableto dive.

Copepods inhabit the seasurface for only a brief periodduring the spring. Theirmetabolic rate, growth, anddevelopment are synchronizedwith temperature. As surface

temperatures warm up, copepod larvae migrate fromdeep ocean waters to the surface, where they feedon phytoplankton and grow to adult size beforereturning to the deeper waters of the ocean. Whenspring surface waters warm earlier in the season,the copepods develop more quickly, become adultsfaster, and migrate back to deeper waters sooner thanthey do in years when spring surface waters are cool.

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SEABIRD SURVIVAL

Higher ocean temperatures will affect the long-term survival of Cassin's auklet populations in BC because warmer surface water decreases the food supply for developing chicks.


SOURCE: BC Parks

37

In warm years, the times when seabirds breedand when food is most available are poorly matched.By the time the Cassin’s auklet chicks hatch, thecopepods are already returning to deeper water, andthere is a diminishing food supply for the chicks. Asa result, the chicks grow slowly and often starve todeath later in the season.

In contrast, when spring surface-water tempera-tures are cool, the copepods persist longer in thesurface waters, so that food is available for chicksthroughout the development period, from hatching tothe time when they are ready to leave the burrow. Thelocation of Frederick Island explains the health of itsCassin’s auklet population. Because the island is so farnorth, the sea surface temperature during the periodwhen chicks are growing and developing remains cool

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enough — even in warmer years — to ensure thatthey have enough food.

Climate change is linked to an increase in averagesea surface temperature in waters off the coast of BC.In the 1990s, these temperatures were some of thehighest ever observed in the 20th century. In yearssuch as 1996 and 1998, when spring was early andsea surface temperatures were warmer than usual,the growth rates of Cassin’s auklet chicks on TriangleIsland were much lower than in cooler years suchas 1999.

WHAT CAN WE EXPECT IN FUTURE?Average global sea surface temperature has increasedby 0.4ºC to 0.8ºC since the late 19th century and isexpected to continue to rise during the next century.Populations of Cassin’s auklet on Triangle Island aretherefore likely to continue to grow slowly, and chickmortality is likely to continue to increase. If the adultbirds cannot replace themselves, the population willcontinue to decline.

The story of the Cassin’s auklet is one example ofhow climate change may affect the distribution andsurvival of individual species in BC. Many otherspecies — marine, freshwater, and terrestrial — maybe similarly affected during the decades to come.

Average Growth Rate (grams/day)of Cassin’s Auklet Chicks andSea Surface Temperature nearTriangle Island

SOURCE: Original data and analysis from Doug Bertram, Simon

Fraser University, Centre for Wildlife Ecology and CanadianWildlife Service, 2001 for Ministry of Water, Land and Air

Protection. NOTES: Average growth rate (grams/day) of Cassin’s

Auklet chicks is based on weight change between 5 and 25 daysfrom date of hatching. Cassin’s Auklet chick growth rates and

survival decline as ocean temperature increases (April SST >

7.5ºC). The slope of the line is statistically significant (F1, 7=12.5;P=0.009). Editor's Note: "1891," above, should read "1981."


April Sea Surface Temperature

Gro

wth

Rat

e G

ram

s/D

ay

7.0 7.5 8.0 8.5 9.0 9.5

6

5

4

3

Trend Line

19992000

19781891

1995

1997

1994

1998

1996

38

ABOUT THE INDICATORThis indicator measures changes in the amount ofheat energy available for plant growth, expressed inunits called Growing Degree Days (GDD).

Assessment of annual GDD is based on availabletemperature records from 1888 to 1992 from low-elevation weather observation stations in each of thenine terrestrial ecoprovinces.

GDD TRENDS IN BRITISH COLUMBIAAnnual GDD increased during the 20th century atrates of 16 percent per century in the Boreal Plainsecoprovince, 13 percent per century in the Coast andMountains, 5 percent per century in the SouthernInterior, and 13 percent per century in the SouthernInterior Mountains. These trends are consistent withtrends over the past century toward higher averageannual temperatures across British Columbia.

The trends for three ecoprovinces (Coast andMountains, Southern Interior, and Southern InteriorMountains) are based on long records (94 to 102years) and probably reflect the effects of climatechange. The record for the Boreal Plains is relativelyshort (58 years) and is therefore more likely to havebeen influenced by natural climate variability.

Annual GDD(%change/century)

G R O W I N GD E G R E E D A Y S

The average heat energy available for plant growth and development has increased over the past century, particularly in southern BC.

Change inAverageAnnual GDD(% per century)

The records for the Georgia Depression, theCentral Interior, and the Sub-Boreal Interiorecoprovinces are relatively long (93 to 105 years) butthe data fail to reveal trends in GDD. The records forthe Northern Boreal Mountains and Taiga Plainsecoprovinces are relatively short (55 and 47 years)and are insufficient to determine whether or nottrends exist.

WHY IS IT IMPORTANT?Plants and invertebrates require a certain amount ofheat to develop from one stage in their life cycle toanother. The measure of accumulated heat is knownas “physiological time” and is measured in unitscalled “degree days.” All individuals of the samespecies require the same number of degree days todevelop from one life stage to another. Whentemperatures are warmer, they develop faster.

Each plant species — and each insect species —has its own minimum temperature requirementfor growth. For example, spinach can grow whenaverage daily temperatures are as low as 2.2ºC,while corn requires temperatures of at least 10ºC.

Because of these differences, agrologists some-times refer to an average minimum temperature of

SOURCE: Data from Environment Canada, Archive of Canadian

Monthly Climate Data. Analysis by Canadian Institute for Climate

Studies, 2001 for Ministry of Water, Land and Air Protection.

NOTES: A positive trend indicates an increase in GDD.

C L I M A T E C H A N G E A N D T E R R E S T R I A L E C O S Y S T E M S

BOREALPLAINS

TAIGAPLAINS

NORTHERNBOREAL

MOUNTAINS

SUB-BOREALINTERIOR

COAST ANDMOUNTAINS

CENTRALINTERIOR

SOUTHERNINTERIOR

MOUNTAINS

SOUTHERNINTERIOR

GEORGIADEPRESSION

NORTHEASTPACIFIC

+13

+13

+16

+5

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39

5ºC when they talk about the heat requirementsof agricultural plants as a group. For the typicalagricultural plant, GDD for one day is calculated asthe difference between average daily temperature and5ºC. So on a day when the average temperature is12ºC, the GDD is 7. GDD is calculated for only thosedays when the average temperature is higher than5ºC. Annual GDD is calculated as the sum of GDDfor the year.

A significant increase in available heat energycould allow farmers to succeed in introducing newvarieties of crops that were previously marginal ornot viable in their region. If adequate soil moisture,soil fertility and light are also available, this couldallow agriculture to expand to new regions and siteswithin the province.

Some of the other impacts of climate changecould have negative impacts on agriculture. Changesin hydrological systems combined with warmertemperatures and greater evapotranspiration, forexample, may mean less available soil moisture insome regions. And warmer temperatures may alsomean that new insect pest species are able to moveinto a region.

WHY IS GDD INCREASING?During the 20th century, average annual tempera-tures warmed in much of BC at rates of 0.6ºC to 1ºCper century. Because GDD is related to average dailytemperature, it is not surprising that the amount ofenergy available for plant growth and developmenthas also increased.

WHAT CAN WE EXPECT IN FUTURE?Climate models indicate that temperatures willcontinue to rise in BC by 1ºC to 4ºC during the next100 years. The higher rate of warming is projected tooccur over the interior of the province. Annual GDDshould continue to increase as the climate continuesto warm.

The United Nations Intergovernmental Panel onClimate Change (IPCC) suggests, however, thatincreases in average annual temperature of more thana few degrees centigrade will result in a generalreduction, with some variation, in potential cropyields in mid-latitudes.


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Species Minimum Degree Day Threshold Requirements (over threshold temperature)

Sweet corn 10°C 855

Thompson grape 10°C 1600-1800

Codling moth 11°C 590

Pea aphid 5.5°C 118

Heat requirementsof Agricultural Cropand Pest Species

40

The mountain pine beetle is a native insect withan important role in maintaining many pine

ecosystems. It is also the most important forest pestin western Canada and has killed an estimated300 million trees in British Columbia over the last20 years and damaged timber worth an estimatedsix billion dollars.

While mountain pinebeetle will attack mostwestern pines, its primaryhost throughout most of itsrange is lodgepole pine.Mountain pine beetlesburrow into the bark of thehost tree and lay their eggsthere in summer. The eggshatch inside the tree and larvae remain there over thewinter. During the following spring, larvae completetheir development. Burrowing and feeding activitiesof the larvae create networks of channels known asgalleries beneath the bark, causing the death ofthe tree.

Adult beetles emerge from their host tree in mid-to late summer and disperse in search of new trees tocolonize. Dispersal may be within the same stand orover distances of 100 kilometres or more. Once the

MOUNTAIN PINE BEETLERANGE

SOURCE: Canadian Forest Service

beetles find a new host tree, mated females borethrough the bark to lay their eggs, starting anew cycle.

Endemic populations of mountain pine beetleare common throughout lodgepole pine forests. Theytend to inhabit individual trees dispersed throughouta stand that are weaker and less resistant to invasion.In these endemic populations, births and deaths arein balance. Predators, disease, and competition forfood and space control population size. The capacityof most healthy trees to resist a normal beetle attackalso helps control the beetle population.

Mountain pine beetle populations increase fromtime to time within a stand when conditions allow —for example, when trees are stressed by crowding,flooding, or root disease. Such stand-level infestationscan quickly become a full-scale outbreak under idealconditions, with beetles invading — and ultimatelykilling — many trees across the forest landscape.Periodic mountain pine beetle outbreaks like thiscreated ideal conditions for fire, which has historicallyplayed a vital role in maintaining native pine eco-systems by eliminating competing vegetation,preparing the seedbed, and releasing seeds fromcones, which require heat to open.

HOW DOESTEMPERATURE AFFECTMOUNTAIN PINEBEETLES?Temperature is one of the primarysources of mortality for mountainpine beetles.

When temperatures in thesummer and fall are warm enough, larvae hatch andgrow adequately before the onsetof winter. When they are at the late larval stage,mountain pine beetles are resistant to cold and canwithstand temperatures close to -40ºC for longperiods of time.

When temperatures in the summer and fall arerelatively cool, however, the larvae grow more slowlyand may not reach the ideal life stage before winter.As a result, many will die. For this reason, the


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Temperature limits the range and size of mountain pine beetle populations. Warmer temperatures may allow the beetles to move northwards into new regions and upwards into new ecosystems.

41

mountain pine beetle cannot establish populations athigh elevations or at northern latitudes. Its distribu-tion is bounded by the -40ºC isotherm, which joinssites where the average of the lowest temperaturerecorded each year (1921-1950) is -40ºC.

Lodgepole pine ecosystems — the preferred forestof the mountain pine beetle — extend north into theYukon and the Northwest Territories and east intoAlberta. Climate limitations currently prevent themountain pine beetle from establishing itself in theseregions. Warmer temperatures, in particular warmerwinter temperatures associated with climate change,may allow the mountain pine beetle to extend itsrange northwards and eastwards into these eco-systems. With warming, regions that are currentlytoo cold for the mountain pine beetle will becomemore suitable.

A 2.5ºC increase in temperature would likely shiftthe northern boundary of the region suitable for themountain pine beetle a further 7 degrees of latitudenorth. A range expansion of this size would allowbeetles potential access to formerly unoccupiedlodgepole pine habitat. It would also give them thepotential to invade jack pine forests, a major compo-nent of the boreal forest that is currently free of beetles.

Warmer winter temperatures may also allow themountain pine beetle to extend its range upwardsinto high-elevation pine forests — for example,whitebark and limber pine forests in southeasternBC — that are not adapted to the beetle’s impacts.

An additional concern is the possibility thatclimate change may allow mountain pine beetleinfestations and outbreaks to occur more regularlyand with greater severity within the beetle’s currentrange. At present, mountain pine beetle outbreaks inBC are limited to the southern portion of theprovince. Outbreaks occur almost exclusively inregions where it is warm enough for mountain pinebeetles to complete their development within a year.In such regions, when weather conditions are warmerthan usual, a large number of larvae can survive thewinter. Larger populations of adult beetles can moreeasily overcome the resistance of healthy trees, allowingthe development of stand-level infestations and ofoutbreaks. Consequently, it is highly possible that an

increase in winter temperatures associated with climatechange could increase the potential for outbreaks.

WHAT CAN WE EXPECT IN FUTURE?Monitoring indicates that average temperatures overmost of British Columbia warmed during the pastcentury, with the greatest increases occurring in thenorth. Climate models project that this warmingtrend will continue. Most importantly, the data showthat minimum temperatures have warmed during thistime period.

Because minimum temperatures delineate thenorthern range of the mountain pine beetle, thisincrease in minimum temperatures provides forestmanagers with reason for concern.

Distribution of Mountain Pine BeetleInfestations, 1910-1970

SOURCE: A. Carroll, Pacific Forestry Centre, 2001. Adapted from Safranyik, L. 1990.

Temperature and insect interactions in western North America. Proceedings of the Society of

American Foresters National Convention. Washington DC. SAF Publication 90-02. pp. 166-170.Isotherms from Department of Mines and Technical Surveys. 1957. Atlas of Canada.


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A L B E R T A

B R I T I S H

C O L U M B I A-30

-40

L E G E N D

Areas where there is not enough accumulated heat for beetles to complete development on a one-year cycle. (i.e. average degree-day accumulation <833 above 5.6°C)

Range of lodgepole pine

Recorded MPB infestations 1910-1970

-30°C isotherm-40°C isotherm

42

ABOUT THE INDICATORSThese indicators measure changes in the annualenergy requirements for heating and cooling. Thetrends are based on available temperature recordsfrom 1888 to 1993 from weather observationstations in populated valleys.

Heating requirements are measured in unitscalled Heating Degree Days (HDD). HDD for one dayis calculated as the difference between 18ºC and theaverage outdoor temperature. For example, a daywith an average temperature of 8ºC has an HDD of10. The HDD calculation looks only at days whenthe average outdoor temperature is less than 18ºC.Annual HDD represents the sum of daily HDD forthe year.

Energy requirements for cooling are measured inunits called Cooling Degree Days (CDD). CDD forone day is calculated as the difference between theaverage outdoor temperature and 18ºC. For example,a day with an average temperature of 21ºC has aCDD of 3. The CDD calculation looks only at dayswhen the average temperature is more than 18ºC andcooling is required. Annual CDD represents the sumof daily CDD for the year.

Change inAverage HeatingRequirements,1888-1993,(% per century)

SOURCE: Data from Environment Canada. Analysis by Canadian Institute for ClimateStudies, 2001 for Ministry of Water, Land and Air Protection. NOTES: A negative sign

indicates a decrease in heating requirements.

HEATING AND COOLING TRENDSFour ecoprovinces show trends towards lower annualheating requirements. The trends for three eco-provinces (Coast and Mountains, Southern Interior,and Southern Interior Mountains) are based onrelatively long records (94 to 102 years) and almostcertainly reflect climate change. The trend for theBoreal Plains is based on a shorter record period(58 years) and may be influenced by climate variabilityas well as by climate change.

The records for the Georgia Depression, the CentralInterior, and the Sub-Boreal Interior ecoprovinces arerelatively long (93 to 105 years) but the data fail toreveal trends in HDD. The records for the NorthernBoreal Mountains and Taiga Plains ecoprovinces arerelatively short (55 and 47 years) and are insufficientto determine whether or not trends exist.

Cooling requirements have increased by24 percent in the Southern Interior ecoprovince andby 39 percent in the Southern Interior Mountains overthe last century. Both trends are based on relativelylong record periods (102 and 94 years) and almostcertainly reflect climate change. In the seven otherecoprovinces, days with significant cooling require-ments are infrequent. Thus the data are insufficient toassess whether or not there are trends.

H E A T I N G A N D C O O L I N G R E Q U I R E M E N T S

In coastal and southeastern BC, the amount of energy required for heatingsimilarly constructed and insulated buildings decreased during the past century. In southern BC, the amount of energy required for cooling increased.

C L I M A T E C H A N G E A N D H U M A N C O M M U N I T I E S

BOREALPLAINS

TAIGAPLAINS

NORTHERNBOREAL

MOUNTAINS

SUB-BOREALINTERIOR

COAST ANDMOUNTAINS

CENTRALINTERIOR

SOUTHERNINTERIOR

MOUNTAINS

SOUTHERNINTERIOR

GEORGIADEPRESSION

NORTHEASTPACIFIC

-8

-5 -8

-18

notrend

notrend

notrend

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43

WHY IS IT IMPORTANT?Building managers, owners, and residents typicallytry to maintain buildings at a comfortable interiortemperature of 18ºC. They tend to begin interiorheating when the outdoor temperature is below 18ºC(although this threshold may be lower for homesconstructed more recently). As outdoor temperaturegoes down, the amount of energy required forheating goes up.

The energy supply industry uses annual HDDfigures extensively to measure and project heatingrequirements. Annual HDD figures help the energyindustry estimate demand for residential and otherheating and maximum demand on energy supplysystems during extremely cold periods. All else beingequal, when annual HDD decreases, there is lessdemand for energy for heating.

With respect to cooling, residents of warmerclimates tend to turn on their air conditioners whenthe average daily outdoor air temperature exceeds acomfortable 18ºC and when there are several hoursof uncomfortable heat during the day.

CDD affects energy demand because most airconditioning and refrigeration systems use electricityto operate fans and pumps. In most of BC, however,cooling places minor demands on the energy system,

and CDD is not an important factor in energymanagement and planning decisions.

WHY ARE HEATING AND COOLINGREQUIREMENTS CHANGING?During the 20th century, average annual tempera-tures increased across most of BC. Because heatingand cooling requirements are directly linked totemperature, it is not surprising that they, too.should have changed during the same period.

This rise in average annual temperature is onlypart of the story, however. Surface warming trendsand trends in daily maximum and minimum temp-erature vary by season and from one region of BC toanother (see “Average Temperature” and “Maximumand Minimum Temperature”), affecting heating andcooling requirements.

In winter, less energy is required to keep build-ings warm when average daily temperatures increase,as they have in the Coast and Mountains andSouthern Interior ecoprovinces. The trends alsosuggest that in the Southern Interior and SouthernInterior Mountains, heating requirements have gonedown mainly because winter nights are not as chillyas they were in the past (see “Maximum andMinimum Temperature”).

The summer temperature trends suggest that,in the Southern Interior and Southern InteriorMountains, more energy is required to keepbuildings cool during the hot part of the day becausesummer nights are warmer now than in the past.Buildings therefore do not cool down as muchduring the night (see “Maximum and MinimumTemperature”).

WHAT CAN WE EXPECT IN FUTURE?Climate models indicate that temperatures willcontinue to rise over BC during the 21st century andthat atmospheric warming will be more pronouncedin winter and spring than in summer and fall.Consequently, winter heating requirements will likelycontinue to decrease, and summer coolingrequirements to increase.


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BOREALPLAINS

TAIGAPLAINS

NORTHERNBOREAL

MOUNTAINS

SUB-BOREALINTERIOR

COAST ANDMOUNTAINS

CENTRALINTERIOR

SOUTHERNINTERIOR

MOUNTAINS

SOUTHERNINTERIOR

GEORGIADEPRESSION

NORTHEASTPACIFIC +24 +39

Change inAverageCoolingRequirements,1888-1993,(% percentury)

SOURCE: Data from Environment Canada. Analysis by Canadian Institute forClimate Studies, 2001 for Ministry of Water, Land and Air Protection. NOTES: A

positive sign indicates an increase in cooling requirements.

44


HUMAN HEALTH

Warmer temperatures, and changes in precipitation and other aspects of the climatesystem have the potential to adversely affect humanhealth. Although at this time there are no data thatdirectly link climate change and health in BritishColumbia, studies from other regions suggest thatsuch links may exist.

HOW CAN CLIMATECHANGE AFFECTHUMAN HEALTH?Heat-related Illness:Climate models predictthat over the next centurysummer heat waves willoccur more frequently, particularly in urban areas,where buildings and pavement absorb and retainheat. Between 1951 and 1980 in Victoria, an averageof three days per year were warmer than 30ºC. Inthe 21st century, hot days are expected to more thanquadruple, to 13 days per year. Hot days will beeven more frequent in the Lower Mainland andthe interior of BC. As a result, heat-related healthimpacts — including heat stroke, dehydration, andcardiovascular and respiratory illness — are expectedto increase.

Respiratory Illness: Heavy emissions from motorvehicles and industrial activities can contribute to thedevelopment of smog. This is particularly a problemin Vancouver and the Fraser Valley. A component ofsmog — ground level ozone — is linked to respiratoryirritation, affecting individuals with asthma andchronic lung disease. Even healthy individuals canexperience chest pain, coughing, nausea, and lungcongestion when exposed to low amounts of thisozone.

On hot days, the reactions that produce smog andground level ozone occur more quickly. The rise inaverage temperature associated with climate changewill likely increase the incidence of smog. TheIntergovernmental Panel on Climate Change (IPCC)has therefore concluded that ongoing climate changecould exacerbate respiratory disorders associated withreduced air quality in urban and rural areas.

Water Contamination: Water quality deterioratedbetween 1985 and 1995 at 11 percent of provincialwater sampling stations. Past discharges from miningoperations, non-point source pollution, and high

waterfowl concentrationshave made water in somecommunities unfit forrecreation or drinking.Climate change posesadditional threats. Sea levelrise may inundate watersystems in some low-lyingcoastal areas with saltwater,chemicals, and disease

organisms. Extreme precipitation events may strainmunicipal drainage and sewage systems and increasethe risk of contamination. Summer water shortagesmay exacerbate water quality problems in some areasby increasing the concentration of contaminants.

Water-borne Disease: Increased precipitation,runoff, and flooding associated with climate changemay increase the transmission of parasites from otheranimals to humans through the water system. In 1995Victoria experienced an outbreak of toxoplasmosis, adisease that causes symptoms ranging from swollen

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Climate change may increase thefrequency of heat-related and respiratory illness, water contamination and water-borne diseases, vector-borne diseases, and some weather-related accidents.

45


lymph glands to lung complications, lesions onmajor organs, and disorders of the central nervoussystem. The outbreak was linked to extreme preci-pitation, causing high levels of runoff that picked upthe parasite from animal feces and carried it intodrinking water reservoirs. In recent years BC has alsoexperienced outbreaks of cryptosporidiosis, anotherserious water-borne disease transmitted throughanimal feces.

Increases in marine and freshwater temperatureassociated with climate change may also contributeto the survival of pathogens. Red tide, a disease ofshellfish, is caused by a toxic algae that grows inwarm coastal waters during the summer. Shellfishconcentrate the red tide toxins in their flesh, andhumans who eat contaminated shellfish can becomeseriously ill. Ocean warming associated with climatechange may increase the incidence of red tide alongthe BC coast. In fresh water, warmer temperaturesmay create ideal conditions for the pathogen res-ponsible for giardiasis, which is transmitted fromanimals to humans through water.

Vector-borne Disease: Animals, birds, andinsects that carry human diseases are known asdisease “vectors.” Warmer temperatures associatedwith climate change may enable vectors — and thediseases they carry — to extend their ranges. Thechance of humans contacting the disease maytherefore increase. Vectors of concern in BCinclude rodents, ticks, and mosquitoes.

The deer mouse is the primary vector in Canadafor hantavirus, and it transmits the virus to humansthrough its feces. When the feces dry, the virus isreleased into the air and can be inhaled by humanswho are in the vicinity. Six cases of hantavirus inhumans are known to have occurred in BC, two ofthem resulting in death.

Various species of ticks can carry Lyme diseaseand transmit it to humans. The most importantvector in BC is the western black-legged tick, whichis extremely common on the coast during the earlyspring and summer. The microorganism that causesLyme disease has also been detected in adult ticks inthe Fraser Valley.

Mosquitoes are the primary vector in NorthAmerica for encephalitis. Viral transmission ratesfrom mosquitoes can increase sharply as tempera-tures rise. Studies elsewhere show a correlationbetween temperature and the incidence of tick-borneencephalitis in humans. Swedish studies suggest thatthe relatively mild climate in the 1990s in Swedencontributed to increases in the density and geo-graphic range of ticks. At high latitudes, warmer-than-usual winter temperatures were related to anorthward shift in tick distribution. Further south,mild and extended autumn seasons were related toincreases in tick density.

Weather-related Accidents: In general, climatechange is associated with increased precipitation,flooding, landslides and extreme weather-relatedevents. Such events may increase the incidence ofaccident-related injuries and deaths in BC. Otherimpacts of climate change — for example, reducedwinter snowfall — may decrease the potential foraccidents. The IPCC has concluded that in sometemperate countries reduced winter deaths wouldoutnumber increased summer deaths from climate-related factors.

WHAT CAN WE EXPECT IN FUTURE?No cause-and-effect relationships have beenestablished between climate change and provincialhealth impacts. More research is needed before wewill be able to assess the degree of risk that climatechange poses to the health of British Columbians.Little information is available about possible healthbenefits. The IPCC has also noted that potentialadverse health impacts of climate change could bereduced through appropriate public health measures.

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46

Climate reflects weather conditions for a specifiedarea over a relatively long time period, usuallydecades or centuries, but sometimes even millennia.It is typically described in terms of averages andextremes in such properties as air temperature,precipitation, humidity, sunshine, and stormfrequency.

Climate is characterised by:• temperatures of the surface air, water, land, and

ice• wind and ocean currents, humidity, cloudiness

and cloud water content, groundwater, lakes, andwater content of snow and sea ice

• pressure and density of the atmosphere andocean, salinity and density of the ocean,composition of dry air, and boundaries andphysical constantsThese properties are interconnected through

physical processes such as precipitation, evaporation,infrared radiation emitted by the earth and theatmosphere, vertical and horizontal movementsof the atmosphere and ocean, and turbulence.

Historically, the climate of the earth has variedfrom year to year, decade to decade, century tocentury, and millennium to millennium. Suchchanges may be the result of climate variability,climate change, or both.

CLIMATE VARIABILITYClimate variability involves relatively short-termchanges and can occur as a result of natural altera-tions in some aspect of the climate system. Forexample, increases in the concentration of aerosols inthe atmosphere as a result of volcanic eruptions caninfluence climate for a few years. Climate variabilitycan also result from complex interactions betweendifferent components of the climate system: forexample the ocean and the atmosphere.

The climate of British Columbia is stronglyinfluenced by two natural cycles in the Pacific

Ocean: the El Niño Southern Oscillation (ENSO)and the Pacific Decadal Oscillation (PDO). Bothocean patterns have an influence on patterns ofatmospheric circulation and both affect westernNorth America.

ENSO is a tropical Pacific phenomenon thatinfluences weather around the world. El Niño, theso-called “warm phase” of ENSO, brings warmerwinter temperatures and less winter precipitation toBC. La Niña, the “cool phase” of ENSO, is associatedwith cooler and wetter winters. During neutral years,ENSO is in neither a warm nor a cool phase and haslittle influence on global climate. ENSO tends to varyfrom the two extremes and the neutral state withintwo to seven years, usually staying in the same statefor no longer than a year or two. There is evidencethat ENSO is a permanent feature of the climatesystem and that El Niños have occurred for millennia.

The PDO is a widespread oscillation of seasurface temperature in the northern Pacific Ocean.Like ENSO, it has a warm and a cool phase. ThePDO tends to remain in one phase for 20 to 30 years.It was in a cool phase from about 1900 to 1925 andfrom 1945 to 1977. It was in a warm phase from

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British Columbia Coastal SeaSurface Temperature 1900-1995

1900 1920 1940 1960 1980

Tem

per

atu

re A

no

mal

y (º

C)

2000

SOURCE: University of Washington, Department of Atmospheric Sciences.NOTES: SST along the BC coast reflects the influence of the PDO. Dotted

vertical lines indicate the years in which the PDO has switched from

warm to cool or vice versa.The graph shows values above (in blue) andbelow (in grey) average sea surface temperatures.

Climate ChangePast Trends and Future Projections

A P P E N D I X

47

1925 to 1945 and from 1977 onwards. A change fromwarm to cool may have occurred in the mid-1990s.

The PDO is associated with cyclical changes in thesea surface temperature of the northern Pacific Ocean.Because prevailing winds blow from the North Pacifictowards the BC coast and air temperature is affectedby sea temperature, average air temperatures over BChave also fluctuated over a 50- to 60-year cycle.

CLIMATE CHANGEClimate change represents longer-term trends thatoccur over many decades or centuries.

There is strong evidence that change is an ongoingfeature of the global climate system. At present,however, it is occurring at an unprecedented rate.Global temperature, for example, has increased by0.4ºC to 0.8ºC since the 19th century. The rate ofwarming is probably faster than at any other timeduring the past 1,000 years. Weather observationsalso reveal significant changes in average globalprecipitation and atmospheric moisture, as well aschanges in patterns of atmospheric and oceaniccirculation and the frequency of extreme weather.

Climate change occurs simultaneously with,and also influences, natural climate variability. Forexample, El Niño events have become more frequentin recent years, and four of the ten strongest El Niñoevents of the 20th century have occurred since 1980.

Some of the causes of climate change — includinglong-term changes in the amount of energy radiatingfrom the sun and variations in the orbit of the eartharound the sun — are entirely natural. Others areanthropogenic — of human origin. Some humanactivities — in particular the burning of fossil fuelsand land-use changes — are associated with anincrease in the proportion of carbon dioxide andother greenhouse gases in the atmosphere over thelast century and a half. There is a strong connectionbetween the proportion of these gases in theatmosphere and atmospheric temperature.

Anthropogenic climate change appears to beresponsible for much of the atmospheric warmingobserved during the past century, and especially thelast 50 years. The earth is currently exposed to the

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Atmospheric CO2 Concentrations,1000–2000 AD

SOURCE: IPCC, 2001

Atm

osp

her

ic C

on

cen

trat

ion

of

CO

2 (p

pm

)

1000 1200 1400 1600 1800 2000

360

340

320

300

280

260

1.5

1.0

0.5

0.0

highest levels of CO2 in the atmosphere — and the

warmest surface air temperatures — in at least 1,000years. And some greenhouse gases are persistent —they remain in the atmosphere for centuries. Climatemodels project that even if we stop burning fossilfuels tomorrow, the atmosphere will continue towarm for a few centuries.

A P P E N D I X

Northern Hemisphere Temperatures,1000-2000 AD

SOURCE: Mann et al. 1999. Northern Hemisphere temperatures during the past

millennium: inferences, uncertainties, and limitations. Geophysical Research

Letters, 26:759-762. NOTES: The average temperature for the calibration period(1902-1980) is roughly 15ºC. For most of the period from 1000 to 1850 AD, average

temperatures in the Northern Hemisphere were decreasing. Since the late 1800s,

average temperatures have been increasing. Temperatures from 1000 to 1850 ADare based on tree ring, ice core, geological, coral and other proxy data.

1000 1200 1400 1600 1800 2000Year

1.0

0.5

0.0

0.5

1.0

Tem

per

atu

re A

no

mal

y (°

C)

reconstruction (AD 1000-1980)

instrumental data (AD 1902-1998)

calibration period (AD 1902-1980) mean

reconstruction (40 year smoothed)

linear trend (AD 1000-1850)

1998

48

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Relationship between ClimateVariability and Climate Change

DISTINGUISHING PAST TRENDSEven during a period of general global atmosphericwarming, climate variability can result in cooler-than-average regional temperatures. To obtain long-term climate change trends from historical datarecords it is therefore necessary to identify the“signal” of climate change against the “backgroundnoise” of climate variability.

Climate variability in BC is characterized by the50-to 60-year cycle of the PDO. Data records thatspan 40 to 60 years or less may be too stronglyinfluenced by this natural cycle to producemeaningful climate-change trends. Only data recordsthat span one or more full cycles of the PDO, or thatbegin and end at roughly the same point in the cycle,can be used to distinguish the effects of climatevariability from the effects of climate change.

The majority of the climate-change and relatedtrends described in this report were obtainedthrough the analysis of historical data collected atweather and other monitoring stations across BC.Particularly in northern BC, the available data issometimes insufficient. It may come from too fewmonitoring stations within an ecoprovince, or thedata records may be too short. As a result, it is notalways possible to identify a long-term climate-change trend for every indicator and for everyecoprovince.

MODELLING THE FUTUREThis report describes how the climate in BC maycontinue to change during the 21st century and theongoing impacts climate change may have on marine,freshwater, and terrestrial ecosystems, and on humancommunities.

Most information about future trends is based onreports published in 2001 by the IntergovernmentalPanel on Climate Change (IPCC). The findings of theIPCC about future climate change are largely based onclimate models — simplified representations of theclimate system that take into account relevantphysical, geophysical, chemical, and biologicalprocesses. While the models have been tested toensure that they can reasonably simulate past andcurrent climates, they present a range of possiblefuture climates rather than specific predictions.

Climate models incorporate scenarios of possiblefuture states of the global climate. The most commonscenarios are based on a range of socioeconomicassumptions (for example, future global population,gross domestic product) which drive the models. Themodels project global temperature increases rangingfrom 1.4ºC to 5.8ºC by 2100, accompanied bychanges in precipitation and other aspects of theclimate system.

In general, the ability of climate models to provideinformation about future changes in temperature,precipitation, and other climate variables at theregional level is limited, but improving. Mountainousregions such as BC — where valleys may have quite adifferent climate from adjacent mountainous terrain—- present particular problems. Models do not yetinclude the level of detail required to makeprojections at the local level. In general, projectionsabout temperature are more reliable than projectionsabout precipitation or other weather elements.

Finally, information about how natural and humansystems respond to shorter-term climate variabilityprovides insights into how the same systems mightrespond to climate change.

Reference PeriodClimate Variability

Climate Change

Long term:multidecadal to century trends

Short term: (years)rises and falls aboutthe trend line

Tem

per

atu

re

SOURCE: Canadian Institute for Climate Studies. NOTES: The ReferencePeriod corresponds to one cycle of the PDO. The graph shows a long

term climate change trend above and beyond natural climate variability,

and for a period of time longer than one PDO cycle.

A P P E N D I X

Documents

Indicators of Climate Change1 2 Indicators of Climate Change for British Columbia, 2002 3 About the Trends 6 Average Temperature 8 Maximum and Minimum Temperature 11 Precipitation