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 ID: 260625
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Slide1
Climate and Climate Change RecordsSlide2
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.”Slide3
Climate VS Weather
Longer-Term (Years and longer)
B
road
composite of
average condition of a region (e.g., temp, rainfall, etc) snowfall, ice cover, winds)Mean state of a specific regionAn 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 Slide4
How do we classify current climate?Slide5
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.Slide6
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 relationshipsKöppen letter code systemThree letters; first describes group, second describes precipitation, third describes temperature
Used as a springboard for modified
Köppen
SystemSlide7
Modified
Köppen
Classification System
Designated by a descriptive name and a series of letters
First letter = major climate group
Second letter = precipitation patternsThird letter (if there) = temperature patternsSlide8Slide9
How do we determine past climate?Slide10
Proxy Records
Sources
Tree Rings
Ice cores
Documentary data
ThermometersSlide11
Historical Record
Instrumental record ( ~150 years)
Written accounts
Art
PicturesSlide12Slide13
Grinnell Glacier at Glacier National Park
1910
1997
Rate of Glacial melt in last 20 years = 4x historical rateSlide14
Portage Glacier: AlaskaSlide15
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 rainSlide16
Frozen River ThamesSlide17
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. Slide18
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. Slide19
Cross datingSlide20Slide21
Southwestern US
Water is most precious, least abundant resource…Slide22Slide23
Drought and the Anasazi
Populations expanded dramatically during wet years.
Sustainability of population = water
Population collapses related to
megadroughts
Number of habitation sitesSlide24
Pros and Cons
Dendrochronology
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 ClimateSlide25
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
18
O to
16
O
ratio.
Period of Record: 10s – 10,000s of yearsSlide26
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
16
O and
18O are found in common molecules such as water (H2O) and calcium carbonate (CaCO3
).
The ratio of
18
O to
16
O in the water changes based on the climate.
16
O
is lighter so it evaporates more easily, leaving the heavier
18
O in the ocean.Slide27Slide28
Oxygen Isotope Cycle
More
18
O In ice because more heat energy
More
16
O In ice because less heat energySlide29
Ocean CoresSlide30
Lake coresSlide31
VarvesSlide32
Pros and Cons
Ocean/Lake Sediments
Pros
Relatively undisturbed by humans
F
airly consistent rates, especially in the oceanLong record. Local climate
Cons
Influences other than climate (biology and weather.)
Bioturbation
(worms borrowing!)
Can be expensive
Local climateSlide33
Ice Cores
Drilling ice cores in glaciers and ice sheets all over the world.
Dating from worldwide events like atom bombs.
The more
18
O 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 patternsTrapped 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 yearsSlide34
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)Slide35
Ice CoresSlide36Slide37
0˚
C : Tipping Point for Climate
Surface energy balance
Feedback processes rest on crossing the 0
˚
C thresholdAbove 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.Slide38
Pros and Cons
Ice Cores
Pros
Actual bubbl
e
of past atmosphereMore global than other proxy records. Chemistry is pretty well understoodTemperature 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.Slide39
Other
Coral reefs
Relic soils
Pollen
Cave deposits
Shell fishSlide40
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
/