© AMS 1 Chapter 15 Climate and Climate Change AMS Weather Studies Introduction to Atmospheric Science, 4th Edition

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Chapter 15Chapter 15

Climate and Climate Climate and Climate ChangeChange

AMS Weather StudiesAMS Weather Studies Introduction to Atmospheric Science, 4th EditionIntroduction to Atmospheric Science, 4th Edition

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Case-in-PointCase-in-Point

The consensus of scientific opinion is that the present global warming trend is largely anthropogenic in origin– Human activity, principally the combustion of fossil fuels,

is responsible for the build-up of carbon dioxide and other infrared-absorbing gases in the atmosphere

– The amount of anthropogenic CO2 already emitted into the atmosphere ensures a magnitude of warming that will cause an unacceptable rise in sea level in some localities

– The 2007 IPCC Fourth Assessment Report estimates that msl will be 0.2 to 0.6 m higher than now by the year 2100 An example of an island nation that is particularly vulnerable to

rising sea level is the Maldives– Migration may be their only alternative

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Driving QuestionDriving Question How and why does climate change?How and why does climate change?

– Climate changes over a broad range of time Climate changes over a broad range of time scalesscales Years, decades, centuries, millenniaYears, decades, centuries, millennia

– Many forces working together are responsible for Many forces working together are responsible for climate changeclimate change Variability in available solar energyVariability in available solar energy Volcanic eruptionsVolcanic eruptions Changes in the Earth’s surface propertiesChanges in the Earth’s surface properties Human activitiesHuman activities

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Earth’s Climate SystemEarth’s Climate System Climate: The weather of some locality Climate: The weather of some locality

averaged over some time period plus averaged over some time period plus extremes in weatherextremes in weather– Varies spatially and temporallyVaries spatially and temporallyDescribed quantitatively in terms of:Described quantitatively in terms of:

NormalsNormals MeansMeans ExtremesExtremes Weather elements including wind, temperature and Weather elements including wind, temperature and

precipitationprecipitation

NOAA’s National Climatic Data Center (NCDC)NOAA’s National Climatic Data Center (NCDC) Collects (from NWS), processes and archives dataCollects (from NWS), processes and archives data Makes available to usersMakes available to users

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The Climatic NormThe Climatic NormAverage value of some climatic elementAverage value of some climatic element– Encompasses the total variation in the climate Encompasses the total variation in the climate

record, including both averages plus extremesrecord, including both averages plus extremes– Computed averages of weather elements over a Computed averages of weather elements over a

30-year time period30-year time period Adjusted every 10 years to add the latest decade and Adjusted every 10 years to add the latest decade and

drop the oldestdrop the oldest In the U.S. 30-year averages only done for In the U.S. 30-year averages only done for

temperature, precipitation and air pressuretemperature, precipitation and air pressure

Earth’s Climate SystemEarth’s Climate System

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Climatic AnomaliesClimatic Anomalies– Departures from long-term climatic averagesDepartures from long-term climatic averages

Positive anomalies: above long-term averages Positive anomalies: above long-term averages Negative anomalies: below long-term averagesNegative anomalies: below long-term averages

Precipitation anomalies usually form more complex Precipitation anomalies usually form more complex patterns than temperature anomaliespatterns than temperature anomalies Due to greater spatial differences in precipitation arising from:Due to greater spatial differences in precipitation arising from:

– Variability of storm tracksVariability of storm tracks– Almost random distribution of convective showersAlmost random distribution of convective showers

Middle and high latitudes have a geographic non-Middle and high latitudes have a geographic non-uniformity of climatic anomaliesuniformity of climatic anomalies Due to prevailing westerly wave patternDue to prevailing westerly wave pattern

Geographic non-uniformity also applies to trends in Geographic non-uniformity also applies to trends in climateclimate

Earth’s Climate SystemEarth’s Climate System

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Climate Boundary ConditionsClimate Boundary Conditions

Boundary conditions are imposed on Boundary conditions are imposed on climate due to:climate due to:

LatitudeLatitude ElevationElevation TopographyTopography Proximity to large bodies of waterProximity to large bodies of water Earth’s surface characteristicsEarth’s surface characteristics Long-term average atmospheric circulationLong-term average atmospheric circulation Prevailing ocean circulationPrevailing ocean circulation

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LatitudeLatitude Incoming solar radiation and length of daylight varyIncoming solar radiation and length of daylight vary Earth’s surface temperature responds to these variationsEarth’s surface temperature responds to these variations

Elevation Elevation Temperature drops with increasing elevationTemperature drops with increasing elevation

TopographyTopography Affects the distribution of clouds and precipitationAffects the distribution of clouds and precipitation

Proximity to large bodies of waterProximity to large bodies of water Important in storage and exchange of heat, water, and greenhouse Important in storage and exchange of heat, water, and greenhouse

gasesgases Earth’s surface characteristicsEarth’s surface characteristics

Ocean vs. Land, vegetative cover, semi-permanent snow and iceOcean vs. Land, vegetative cover, semi-permanent snow and ice Influence the amount of incident solar radiation that is converted to Influence the amount of incident solar radiation that is converted to

heatheat

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Atmospheric CirculationAtmospheric Circulation– Encompasses influence of all Encompasses influence of all

weather systemsweather systems– Less regular and less predictable Less regular and less predictable

than other factsthan other facts Prevailing Ocean CirculationPrevailing Ocean Circulation

– Influences radiational heating and Influences radiational heating and cooling of the planetcooling of the planet

– Primary control of the amount of solar Primary control of the amount of solar radiation absorbed at the Earth’s radiation absorbed at the Earth’s surfacesurface

– Ocean is the main source of the most Ocean is the main source of the most important greenhouse gas (water important greenhouse gas (water vapor), major regulator of COvapor), major regulator of CO22

– Transfers heat from lower to higher Transfers heat from lower to higher latitudeslatitudes

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Global Climate PatternsGlobal Climate Patterns TemperatureTemperature

Latitude of highest mean annual surface temperature Latitude of highest mean annual surface temperature (heat equator) located about 10(heat equator) located about 10° north of the ° north of the geographical equatorgeographical equator

Heat equator is located in the Northern HemisphereHeat equator is located in the Northern Hemisphere Polar regions have different radiational characteristicsPolar regions have different radiational characteristics

Arctic is warmer than Antarctic: Arctic is mostly ocean, Arctic is warmer than Antarctic: Arctic is mostly ocean, Antarctic is ice sheets with a higher albedoAntarctic is ice sheets with a higher albedo

Northern Hemisphere has more land then the Northern Hemisphere has more land then the Southern HemisphereSouthern Hemisphere

Land warms much faster than waterLand warms much faster than water Ocean circulation transports more warm water to the Ocean circulation transports more warm water to the

Northern Hemisphere then the Southern HemisphereNorthern Hemisphere then the Southern Hemisphere

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Global Climate PatternsGlobal Climate Patterns

Temperature, continuedTemperature, continued– Systematic patterns appear in January/July Systematic patterns appear in January/July

temperaturestemperatures Isotherms tend to parallel latitude circlesIsotherms tend to parallel latitude circles

– Isotherms shift north and south from January to Isotherms shift north and south from January to July following the SunJuly following the Sun Greater shift over land Greater shift over land

– Steeper isothermal gradients mean more Steeper isothermal gradients mean more vigorous circulation and stormier weather in the vigorous circulation and stormier weather in the winter hemispherewinter hemisphere

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Mean sea-level air temperature for January in Mean sea-level air temperature for January in °C°C

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Mean sea-level air temperature for July in Mean sea-level air temperature for July in °C°C

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Global Climate PatternsGlobal Climate Patterns PrecipitationPrecipitation

Variability in patterns due to:Variability in patterns due to: TopographyTopography Distribution of land and seaDistribution of land and sea Planetary-scale circulationPlanetary-scale circulation

Intertropical Convergence Zone (ITCZ)Intertropical Convergence Zone (ITCZ) Rainfall in the adjacent belt poleward to about 20Rainfall in the adjacent belt poleward to about 20° latitude ° latitude

depends on seasonal shifts of the ITCZdepends on seasonal shifts of the ITCZ

Subtropical anticyclonesSubtropical anticyclones Dominate climate all year between 20Dominate climate all year between 20°° to 35 to 35° N and S° N and S

Prevailing wind patternsPrevailing wind patterns Between about 35Between about 35° and 40° latitude, the prevailing westerlies ° and 40° latitude, the prevailing westerlies

and subtropical anticyclones govern precipitationand subtropical anticyclones govern precipitation

Precipitation generally declines poleward of about 40° latitude Precipitation generally declines poleward of about 40° latitude as lower temperatures reduce the amount of precipitable wateras lower temperatures reduce the amount of precipitable water

Tendency in continental interiors for more precipitation in the Tendency in continental interiors for more precipitation in the summersummer

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Mean annual precipitation (rain plus melted snow) in millimeters (mm)Mean annual precipitation (rain plus melted snow) in millimeters (mm)

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Global Climate PatternsGlobal Climate Patterns Climate classificationClimate classification

– Classification schemes group climates Classification schemes group climates according to:according to: Meteorological basis of climateMeteorological basis of climate

Asks why climate types occur where they doAsks why climate types occur where they do

Environmental effects of climateEnvironmental effects of climate Infers the type of climate from environmental indicators Infers the type of climate from environmental indicators

such as the distribution of indigenous vegetationsuch as the distribution of indigenous vegetation

Numerical climate classification schemes also Numerical climate classification schemes also employed that utilize statistical techniquesemployed that utilize statistical techniques

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The Climate RecordThe Climate Record Climate varies from place to place and with timeClimate varies from place to place and with time Reconstructions of past climate based on Reconstructions of past climate based on

historical documents, and longer-term geological historical documents, and longer-term geological and biological evidenceand biological evidence

Geological TimeGeological Time General conclusions made regarding climate over General conclusions made regarding climate over

geological timegeological time Geological past subdivided using geologic time scaleGeological past subdivided using geologic time scale Plate tectonics complicates climate reconstruction by Plate tectonics complicates climate reconstruction by

moving continents and opening and closing ocean moving continents and opening and closing ocean basinsbasins Continental driftContinental drift Alters the course of heat-transporting surface ocean currents Alters the course of heat-transporting surface ocean currents

and the ocean conveyor-belt systemand the ocean conveyor-belt system

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Geologic time Geologic time scalescale

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About 225 million years About 225 million years ago, the super-continent ago, the super-continent Pangaea began to split Pangaea began to split apart into separate apart into separate continents that slowly continents that slowly drifted apart. Ocean drifted apart. Ocean basins opened, and basins opened, and eventually continents eventually continents reached their present reached their present positions. Continental drift positions. Continental drift is responsible for climate is responsible for climate changes operating over changes operating over hundreds of millions of hundreds of millions of yearsyears

The Climate RecordThe Climate Record

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Geologic time, continuedGeologic time, continued 570 million years ago, between Proterozoic and 570 million years ago, between Proterozoic and

Phanerozoic Eons: abrupt climatic changes between Phanerozoic Eons: abrupt climatic changes between extreme cold and tropical heat. Global warming. extreme cold and tropical heat. Global warming.

Mesozoic Era, from about 245 to 70 million years ago, Mesozoic Era, from about 245 to 70 million years ago, remained relatively warmremained relatively warm

Global mean temperature rose 3 - 4Global mean temperature rose 3 - 4°C between Triassic °C between Triassic and Jurassic Periodsand Jurassic Periods

Creaceous Period saw temperatures 6 - 8°C higher then Creaceous Period saw temperatures 6 - 8°C higher then nownow

Cenozoic Era, 55 million years ago, methane released by Cenozoic Era, 55 million years ago, methane released by deep sea sediments enhanced the greenhouse effectdeep sea sediments enhanced the greenhouse effect 40 million years ago saw shift toward colder, drier and 40 million years ago saw shift toward colder, drier and

more variable climatemore variable climate

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The Climate RecordThe Climate Record Past Two Million YearsPast Two Million Years

– Plate tectonics not a major factorPlate tectonics not a major factor– Climate has favored the development of glacial ice sheetsClimate has favored the development of glacial ice sheets

Glacial theoryGlacial theory– Pleistocene Ice age began 1.7 million years ago, and Pleistocene Ice age began 1.7 million years ago, and

culminated about 10,500 years agoculminated about 10,500 years ago The Pleistocene included glacial and non-glacial eventsThe Pleistocene included glacial and non-glacial events Ice sheets caused sea level to drop by 113 to 135 m (370 to Ice sheets caused sea level to drop by 113 to 135 m (370 to

443 ft)443 ft) Land bridge was exposed linking Siberia and AlaskaLand bridge was exposed linking Siberia and Alaska During interglacial episodes, ice sheets thinned and retreated, During interglacial episodes, ice sheets thinned and retreated,

sometimes disappeared entirelysometimes disappeared entirely During glacial episodes temperatures were cooler than today, During glacial episodes temperatures were cooler than today,

but cooling was not geographically uniformbut cooling was not geographically uniform– Polar amplification: an increase in the magnitude of a Polar amplification: an increase in the magnitude of a

climatic change with increasing latitudeclimatic change with increasing latitude

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A.A. Variation in global Variation in global glacial ice volume glacial ice volume from the present from the present back to about 600 back to about 600 million years agomillion years ago

B.B. Temperature Temperature variation over the variation over the past 160,000 yearspast 160,000 years

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Extent of glacial Extent of glacial ice cover over ice cover over North America North America about 20,000 to about 20,000 to 18,000 years 18,000 years ago, the time of ago, the time of the last glacial the last glacial maximummaximum

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The Climate RecordThe Climate Record Past Two Million Years, continuedPast Two Million Years, continued

Fluctuations between major glacial and interglacial climatic Fluctuations between major glacial and interglacial climatic episodes over the past 600,000 yearsepisodes over the past 600,000 years

Last major glacial climatic episode began about 27,000 years Last major glacial climatic episode began about 27,000 years ago, reaching its peak about 18,000 to 20,000 years agoago, reaching its peak about 18,000 to 20,000 years ago

Present interglacial known as the HolocenePresent interglacial known as the Holocene

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Past Two Million Years, continuedPast Two Million Years, continued Over the past 1000 years, there has been a Medieval Over the past 1000 years, there has been a Medieval

Warm Period (about 950 to 1250 CE) followed by a Warm Period (about 950 to 1250 CE) followed by a cooling known as the Little Ice Age (about 1400 to 1850 cooling known as the Little Ice Age (about 1400 to 1850 CE)CE)

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Instrument-Based Temperature TrendsInstrument-Based Temperature Trends Invention of weather instruments and establishment of weather Invention of weather instruments and establishment of weather

observing networks made climate record much more detailed observing networks made climate record much more detailed and dependableand dependable

– Highest confidence is in temperature records dating from the late 1800s with the birth of national weather services along with the founding of the International Meteorological Organization (WMO today)

– Examination of temperature trends over the past 140 years or so is instructive as to climate variability and climate change

General consensus in the scientific community holds that an overall global-scale warming trend has prevailed since the end of the Little Ice Age

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Lessons of the Climate PastLessons of the Climate Past Climate is inherently variable over a broad spectrum of Climate is inherently variable over a broad spectrum of

time scales ranging from years to decades, to time scales ranging from years to decades, to centuries, to millenniacenturies, to millennia

Variations in climate are geographically non-uniform in Variations in climate are geographically non-uniform in both sign (direction) and magnitudeboth sign (direction) and magnitude Some areas may experience warming while others coolingSome areas may experience warming while others cooling

Climate change may consist of a long-term trend in Climate change may consist of a long-term trend in various climate elements and/or a change in the various climate elements and/or a change in the frequency of extreme weather eventsfrequency of extreme weather events

Climate change tends to be abrupt rather than gradualClimate change tends to be abrupt rather than gradual Abrupt means change is shorter than duration of episodesAbrupt means change is shorter than duration of episodes

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Lessons of the Climate PastLessons of the Climate Past Only a few cyclical variations Only a few cyclical variations

can be discerned from the can be discerned from the long-term climate recordlong-term climate record Regular cycles: diurnal and Regular cycles: diurnal and

seasonal variations, incoming seasonal variations, incoming solar radiationsolar radiation

Quasi-regular variations: El NiQuasi-regular variations: El Niñño, o, Holocene millennial-scale Holocene millennial-scale fluctuations, major glacial-fluctuations, major glacial-interglacial shiftsinterglacial shifts

Climate change impacts Climate change impacts societysociety

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Causes of Climate ChangeCauses of Climate Change Match a possible cause (or forcing) with a specific climatic Match a possible cause (or forcing) with a specific climatic

oscillation (or response) based on similar periods of oscillation (or response) based on similar periods of oscillation oscillation Example: El NiExample: El Niñño may account for climate shifts lasting several o may account for climate shifts lasting several

monthsmonths

Global energy budgetGlobal energy budget Changes in energy input/output will change the planet’s climateChanges in energy input/output will change the planet’s climate

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Causes of Climate ChangeCauses of Climate Change Climate and Solar VariabilityClimate and Solar Variability

Earth’s climate system can be altered by Earth’s climate system can be altered by fluctuations in the Sun’s energy output, fluctuations in the Sun’s energy output, sunspots, or regular variations in Earth’s sunspots, or regular variations in Earth’s orbital parametersorbital parameters A sunspot is a dark blotch on the face A sunspot is a dark blotch on the face

of the Sun that develops where an of the Sun that develops where an intense magnetic field suppresses the intense magnetic field suppresses the flow of gases transporting heat from the flow of gases transporting heat from the Sun’s interiorSun’s interior

Typically last for a few days, total Typically last for a few days, total number varies systematicallynumber varies systematically

Satellite monitoring reveals that Sun’s Satellite monitoring reveals that Sun’s energy output varies directly with energy output varies directly with sunspot numbersunspot number

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Causes of Climate ChangeCauses of Climate Change

Variation in mean annual sunspot numberVariation in mean annual sunspot number

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Causes of Climate Causes of Climate ChangeChange Earth’s Orbit and Climate Earth’s Orbit and Climate

ChangeChange– Milankovitch CyclesMilankovitch Cycles

Regular variations in the Regular variations in the precession and tilt of Earth’s precession and tilt of Earth’s rotational axis and the rotational axis and the eccentricity of its orbit around eccentricity of its orbit around the Sunthe Sun

Caused by gravitational Caused by gravitational influences exerted on the Earth influences exerted on the Earth by other large planets, the by other large planets, the moon and sunmoon and sun

Tilt of Earth changes from 22.1° Tilt of Earth changes from 22.1° to 24.5° over about 41,000 to 24.5° over about 41,000 yearsyears

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Milankovitch CyclesMilankovitch Cycles

Past and future Past and future variations in the variations in the

Milankovitch Milankovitch cyclescycles

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Causes of Climate ChangeCauses of Climate Change Volcanoes and Climate ChangeVolcanoes and Climate Change

– Only explosive eruptions rich in sulfur Only explosive eruptions rich in sulfur dioxide (SOdioxide (SO22) are likely to impact global or ) are likely to impact global or

hemispheric climate for a few years at the hemispheric climate for a few years at the mostmost

– When combining with water vapor, droplets When combining with water vapor, droplets of sulfuric acid (Hof sulfuric acid (H22SOSO44) and sulfate ) and sulfate

particles form; together called particles form; together called sulfurous sulfurous aerosolsaerosols Can remain in stratosphere for many Can remain in stratosphere for many

monthsmonths Collectively thicken the stratospheric Collectively thicken the stratospheric

aerosol veilaerosol veil Absorb both incoming solar and outgoing Absorb both incoming solar and outgoing

infrared radiation, warming the lower infrared radiation, warming the lower stratospherestratosphere

In the presence of chlorine destroy ozoneIn the presence of chlorine destroy ozone

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Volcanoes and Climate ChangeVolcanoes and Climate Change

Temperature anomalies in Fahrenheit degrees in the Midwest during June, July, and August 1992

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Causes of Climate ChangeCauses of Climate Change Volcanoes and Climate Volcanoes and Climate

ChangeChange– The combination of stratospheric The combination of stratospheric

warming and ozone depletion warming and ozone depletion strengthens the circumpolar strengthens the circumpolar vortexvortex This is associated with a non-This is associated with a non-

uniform change in surface uniform change in surface temperaturestemperatures

A violent sulfur-rich eruption is A violent sulfur-rich eruption is unlikely to lower the mean unlikely to lower the mean hemispheric or global hemispheric or global temperature by more then 1 temperature by more then 1 °C°C Local and regional Local and regional

temperature change may be temperature change may be greatergreater

Large scale cooling followed Large scale cooling followed massive volcanic eruptions that massive volcanic eruptions that

emitted SOemitted SO22 into the stratosphere into the stratosphere

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Causes of Climate ChangeCauses of Climate Change Earth’s Surface Properties and Climate ChangeEarth’s Surface Properties and Climate Change

Earth’s surface, comprised of approximately 71% ocean Earth’s surface, comprised of approximately 71% ocean water, is the prime absorber of solar radiationwater, is the prime absorber of solar radiation

Changes in the physical properties of water or land Changes in the physical properties of water or land surfaces, or relative distribution of ocean, land or ice surfaces, or relative distribution of ocean, land or ice may affect Earth’s radiation budget and climatemay affect Earth’s radiation budget and climate

Variations in snow coverVariations in snow cover Snow has refrigerating Snow has refrigerating

effect on atmosphereeffect on atmosphere Reflects 80% of solar radiationReflects 80% of solar radiation

reducing solar heatingreducing solar heating Emits infrared radiation, Emits infrared radiation,

radiating heat to spaceradiating heat to space

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Causes of Climate ChangeCauses of Climate Change Earth’s Surface Properties and Climate Change, Earth’s Surface Properties and Climate Change,

continuedcontinued Changes in sea ice or glacial ice coverage have longer-Changes in sea ice or glacial ice coverage have longer-

lasting impacts on climatelasting impacts on climate Ice is much more reflective of incident solar radiation than Ice is much more reflective of incident solar radiation than

ocean or snow-free landocean or snow-free land

Changes in sea surface temperature and ocean Changes in sea surface temperature and ocean circulationcirculation SST patterns can exert a strong influence on the location of SST patterns can exert a strong influence on the location of

major features of the atmosphere’s planetary scale circulationmajor features of the atmosphere’s planetary scale circulation Ocean circulation transports heat throughout the world; Ocean circulation transports heat throughout the world;

changes in circulation patterns can cause changes in climatechanges in circulation patterns can cause changes in climate

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Causes of Climate ChangeCauses of Climate Change Human Activity and Climate ChangeHuman Activity and Climate Change

– Modification of the landscapeModification of the landscape Clearing forests, urbanizationClearing forests, urbanization Alters radiative properties of the Earth’s surfaceAlters radiative properties of the Earth’s surface

– Combustion of fossil fuelsCombustion of fossil fuels Alters concentrations of gases and aerosolsAlters concentrations of gases and aerosols Rising concentrations of CORising concentrations of CO2 2 and other infrared-absorbing gases and other infrared-absorbing gases

enhance greenhouse effect, contributing to global warmingenhance greenhouse effect, contributing to global warming Rapid rise in CORapid rise in CO22 with start of Industrial Revolution with start of Industrial Revolution

– Rise of other infrared-absorbing gases (e.g., methane and Rise of other infrared-absorbing gases (e.g., methane and nitrous oxide) could also enhance greenhouse effectnitrous oxide) could also enhance greenhouse effect Methane is a product of organic decay in the absence of oxygenMethane is a product of organic decay in the absence of oxygen Nitrous oxide increase likely due to industrial air pollutionNitrous oxide increase likely due to industrial air pollution

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Anthropogenic vs. Natural Forcing of ClimateAnthropogenic vs. Natural Forcing of Climate

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The Climate FutureThe Climate Future Global Climate Models (GCMs)Global Climate Models (GCMs)

– Simulate Earth’s climate systemsSimulate Earth’s climate systems– Use mathematical equations that describe physical Use mathematical equations that describe physical

interactions among the various components of the climate interactions among the various components of the climate systemsystem

– Differ from numerical models in that GCMs predict broad Differ from numerical models in that GCMs predict broad regions of expected positive and negative temperature and regions of expected positive and negative temperature and precipitation anomalies and mean locations of circulation precipitation anomalies and mean locations of circulation featuresfeatures

– For example, used to predict potential climatic impacts of For example, used to predict potential climatic impacts of rising levels of greenhouse gases using boundary rising levels of greenhouse gases using boundary conditionsconditions

– GCMs are in need of considerable refinementGCMs are in need of considerable refinement May miss important feedback processesMay miss important feedback processes Need a greater resolutionNeed a greater resolution

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The Climate FutureThe Climate Future

Search for Cycles and AnalogsSearch for Cycles and Analogs– Climate records an alternative approach to predicting Climate records an alternative approach to predicting

climate futureclimate future– Instrument-based and reconstructed climate record

probed in search of regular cycles that might be extended into the future, and analogs that show how the climate in specific regions responds to global-scale climate change Identification of any statistically significant periodicities or trends

in the climate record would be a powerful tool in climate forecasting

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The Climate FutureThe Climate Future

Enhanced Greenhouse Effect and Global WarmingEnhanced Greenhouse Effect and Global Warming Over the next 10,000 - 20,000 years, Milankovitch Over the next 10,000 - 20,000 years, Milankovitch

cycles favor return of Ice Age conditionscycles favor return of Ice Age conditions Rising concentrations of greenhouse gases are likely to Rising concentrations of greenhouse gases are likely to

cause global warming to continue throughout this cause global warming to continue throughout this centurycentury

– Climate models predict that over the subsequent 20 years, the global mean annual temperature will increase at an average rate of about 0.2 Celsius degrees per decade Even if greenhouse gas emissions were to stabilize at present

levels, global warming would likely continue well beyond the 21st century

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Potential Impacts of Global Climate Potential Impacts of Global Climate ChangeChange

Shrinking Glaciers and Rising Shrinking Glaciers and Rising Sea LevelSea Level– Persistence of the current global

warming trend appears likely to cause sea level to rise in response to melting of land-based polar ice sheets and mountain glaciers, coupled with thermal expansion of seawater

– Amplification of the warming trend at higher latitudes would threaten the ice sheets of Antarctica and Greenland

Melting could cause a considerable rise in sea level

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Potential Impacts of Global Climate ChangePotential Impacts of Global Climate Change

Shrinking Glaciers and Rising Shrinking Glaciers and Rising Sea Level, continuedSea Level, continued– The shrinkage of mountain The shrinkage of mountain

glaciers and ice fields whose glaciers and ice fields whose seasonal would be a major seasonal would be a major concern, as people, livestock, and concern, as people, livestock, and crops rely on the season runoff for crops rely on the season runoff for fresh waterfresh water

– Thermal expansion of warming Thermal expansion of warming seawater will be a greater seawater will be a greater contributor to mean sea level rise contributor to mean sea level rise than melting of land-based than melting of land-based glaciers during the 21glaciers during the 21stst century century

– Higher mean sea level would Higher mean sea level would accelerate coastal erosion, accelerate coastal erosion, inundate wetlands, estuaries, and inundate wetlands, estuaries, and islands, and make coastal zones islands, and make coastal zones more vulnerable to storm surgesmore vulnerable to storm surges

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Grinnell GlacierGrinnell Glacier

19381938 19811981 19981998 20062006

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Arctic EnvironmentArctic Environment– Shrinkage of Arctic sea ice is likely to

trigger an ice-albedo feedback mechanism that would accelerate melting of sea ice and amplify warming

– As sea ice cover shrinks, the greater area of ice-free ocean waters absorbs more solar radiation, sea-surface temperatures rise, and more ice melts

– Less sea ice cover on the Arctic Ocean is likely to increase the humidity of the overlying air leading to more cloudiness

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Sea Ice in the Northern Hemisphere Sea Ice in the Northern Hemisphere Polar RegionPolar Region

September 2008September 2008 March 2009March 2009

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Other ImpactsOther Impacts– Higher temperatures and more frequent drought may Higher temperatures and more frequent drought may

affect food productionaffect food production– Possible concern for an increase in hurricane intensityPossible concern for an increase in hurricane intensity

High SST only one factor contributing to tropical cyclone High SST only one factor contributing to tropical cyclone formationformation

Improved models of the climate system are needed to better Improved models of the climate system are needed to better

assess the effect of warming on hurricane activityassess the effect of warming on hurricane activity

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Ocean AcidificationOcean Acidification– CO2 that is absorbed by the ocean participates in

chemical reactions that increase the acidity (lowers the pH) of ocean waters Potentially harmful to marine organisms that use carbonate ions

(CO3-2) to build calcium carbonate (CaCO3) shells or skeletons

– Marine organisms that are particularly vulnerable to ocean acidification are coccolithophorids, foraminifera (phytoplanktonic organisms), and pteropods (small marine snails) All important food source in marine food webs Corals which filter plankton from ocean water and secrete

calcium carbonate are also vulnerable

Documents

© AMS 1 Chapter 15 Climate and Climate Change AMS Weather Studies Introduction to Atmospheric Science, 4th Edition