Climate and Climate Change Records

Definitions• Weather:

– State of the atmosphere at a particular point in time.– Look outside.

• Climate:– The accumulation of “weather” (atmospheric state)

over a longer time period.– Look outside for a really long time and do statistics. – A combination of temperature and precipitation.

“Climate is what you expect … Weather is what you get.”

Climate VS Weather• Longer-Term (Years

and longer)• Broad composite of

average condition of a region (e.g., temp, rainfall, etc)snowfall, ice cover, winds)

• Mean state of a specific region

• An envelope of values

• Shorter-term (minutes to days).

• State of atmosphere (temp, press, winds, sky cover, rainfall, etc).

• Specific location for specific time.

• A single number

HOW DO WE CLASSIFY CURRENT CLIMATE?

Climate Classification:• A consistent climate

classification scheme to understand numerous climate regions.

• Earliest known scheme was used by the ancient Greeks about 2200 years ago.

• Morphed into the broad scheme to the right.

• 3 Major regions: Frigid, Temperate, Torrid.

Köppen climate classification system• Based on a database of annual and monthly

average temperature and precipitation• Four of five major groups classified by temperature• Fifth group classified by precipitation• Subdivided the five groups further based on

temperature and precipitation relationships• Köppen letter code system

– Three letters; first describes group, second describes precipitation, third describes temperature

• Used as a springboard for modified Köppen System

Modified Köppen Classification System

• Designated by a descriptive name and a series of letters

• First letter = major climate group• Second letter = precipitation patterns• Third letter (if there) = temperature

patterns

HOW DO WE DETERMINE PAST CLIMATE?

Proxy Records

Sources• Tree Rings• Ice cores• Documentary data• Thermometers

Historical Record• Instrumental record ( ~150 years)• Written accounts• Art• Pictures

Grinnell Glacier at Glacier National Park

1910 1997

Rate of Glacial melt in last 20 years = 4x historical rate

Portage Glacier: Alaska

15

Snow Cover Reduced

• Number of days per year with snow cover has reduced since early 1970’s

• Water storage in snow pack is reduced

• More precipitation is rain

Frozen River Thames

Paleoclimatology• Definition: The study of past climates. • Why? To help understand current

climates and future climates. • What about thermometers? They only

go back a few hundred years.• So we use proxies, or substitutes, to

reconstruct past conditions.

Dendrochronology• Tree rings!• Most trees increase trunk diameter by adding

one concentric tree ring for each year of growth.• Count the rings to determine how old the tree is. • During more favorable years (mild temps. and/or

more precip.) tree rings are usually wider. • Compare/correlating dead trees to living trees

helps determine catastrophic events.• Period of record: 10-100s of years. In rare cases

1000s of years.

Cross dating

0

20

40

60

80

100

% D

RO

UG

HT

AR

EA

1150 1253936 1034

1321 1829

YEAR

1915

LONG-TERM CHANGES IN DROUGHT AREA IN THE 'WEST'

THE CENTRAL DATES OF THESIGNIFICANT (p<0.05) EPOCHSARE INDICATED WITH ARROWS

DRIER

WETTER

1613

800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000

Southwestern US

Water is most precious, least abundant resource…

Drought and the AnasaziPopulations expanded dramatically during wet years.

Sustainability of population = water

Population collapses related to megadroughts

Num

ber o

f hab

itatio

n sit

es

Pros and ConsDendrochronology

Pros• Well understood. • Direct correlation

between growth and moisture.

• Indirect correlations between growth and cloud cover, temperature.

• Location of tree is usually known.

• Local climate

Cons• Only record the growing

season.• Tropical trees may not

have obvious annual growth rings

• No clear indication of when tree died, therefor harder to determine when it lived.

• Other influences of growth other than climate.

• Local Climate

Ocean/lake sediments• Lake and ocean sediment cores. • Sedimentation rate.

– Varves: couplets of light (more energy) and dark bands (less energy) produced in some lakes. Thicker = more erosion.

• Trapped organic matter (radio carbon dating)– Seeds, leaves, charcoal.

• Little critters (Foraminifera or forams and diatoms) that die and sink to the bottom of the ocean and we measure their 18O to 16O ratio.

• Period of Record: 10s – 10,000s of years

Oxygen Isotopes– Oxygen Isotopes (atoms of the same element

with different atomic weights because they have different numbers of neutrons) Oxygen 16 and Oxygen 18.

– Both 16O and 18O are found in common molecules such as water (H2O) and calcium carbonate (CaCO3).

– The ratio of 18O to 16O in the water changes based on the climate.

– 16O is lighter so it evaporates more easily, leaving the heavier 18O in the ocean.

Oxygen Isotope Cycle

More 18O In ice because more heat energy

More 16O In ice because less heat energy

Ocean Cores

Lake cores

Varves

Pros and ConsOcean/Lake Sediments

Pros• Relatively

undisturbed by humans

• Fairly consistent rates, especially in the ocean

• Long record. • Local climate

Cons• Influences other

than climate (biology and weather.)

• Bioturbation (worms borrowing!)

• Can be expensive• Local climate

Ice Cores• Drilling ice cores in glaciers and ice sheets all over the

world.• Dating from worldwide events like atom bombs.• The more 18O in the ice the warmer it was because more

heat energy was available to evaporate the heavier oxygen isotope.

• Wind blown dust can hint towards global air circulation patterns

• Trapped air bubbles enable scientists to measure concentrations of CO2 and other gasses that were present in the environment.– Historically, the more greenhouse gasses there were

the atmosphere the less ice on earth. • Period of record: 10s to almost 1,000,000 years

Ice Cores• Age of ice (layers)• Isotope ratio (for temps)• Air bubbles (atm gas content)• Dust content (wind)• Salt content (wind)• Sulphuric acid content (volcanism)

Ice Cores

0˚C : Tipping Point for Climate• Surface energy balance

– Feedback processes rest on crossing the 0˚C threshold

– Above 0˚C , melt ensues, albedo change positive feedback

• Water storage– Below 0˚C , H2O can be stored, not utilized by

plants, evaporate away etc.– Above 0˚C , H2O runs off, leads to plant growth,

evaporation, etc.

Pros and ConsIce Cores

Pros• Actual bubble of past

atmosphere• More global than other

proxy records. • Chemistry is pretty well

understood• Temperature proxy and

atmosphere bubble in same location.

• Easy to compare across different locations.

Cons• Can be hard to date.• Expensive and difficult

to obtain and store.• Glaciers are melting

all over the world. • Hard to find ideal

locations• Cold and hard to get

to locations.

Other• Coral reefs• Relic soils• Pollen• Cave deposits• Shell fish

Sources• Dr. Crystal Kolden• Dr. John Abatzoglou

(http://webpages.uidaho.edu/jabatzoglou/)

More information:• www.westernclimateinitiative.org/• Icenetmatrix.com• http://www.atmos.washington.edu/mm5rt/• http://www.wrcc.dri.edu/research/jtwrcc/idaho-mon/• http://www.wrcc.dri.edu/monitor/WWDT/• http://www.cefa.dri.edu/Westmap/• http://www.cpc.ncep.noaa.gov/products/predictions/90day/