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Terms in this set (27)
Boundary condition examples:
-composition of atmosphere
-distribution of veg
-Earth's position relative to sun
Science works best when...
There is a certain degree of skepticism
study of past climates. Relies on proxies, such as tree rings and ice cores.
Why are proxy records important?
-most observations are under 100 years
-allow comparisons between regions and time periods
-instrumental records are limited
-natural history and biogeographies
...but all proxies are limited
Methods used in paleoclimatology (7)
2) Ice cores
6) Past vegetation
7) Animal middens
Insect as a proxy
Since the insect's life cycle is temp dependent, it can make a decent temp proxy. Species often show clear patterns with climate.
Ice cores as proxy
Scientists can determine isotope ratios in ice cores. The isotopes can tell them what temperature and what the composition of the atmosphere was like.
Landforms as a proxy
Ex: isostatic rebound. Occurs after deglaciation periods.
Vegetation as a proxy
When veg occupies a region, pollen and plant microfossils can be preserved in lakes or bogs. Past climates can also be inferred by tree rings. The width related to growing conditions.
The arctic tree line is...
Associated with the 10℃ isotherm
Geological time scale (biggest to smallest):
Divisions are based on:
Eras, periods, epochs
Geological and fossil evidence of past conditions
The most recent epoch of the Late Cenozoic Ice Age, beginning about 1.8 million years ago and marked by as many as 20 glaciations and interglaciations of which the current warm phase, the Holocene epoch, has witnessed the rise of human civilization.
last Glacial Maximum
20,000 years ago. Earth was under a glacier. Sea level was lower. Different gas composition. Ice volume greatest over NH.
Was LGM uniform?
Nooooo. Abrupt climate fluctuations were common.
What also happened 20,000 years ago?
Human migration across the Bering straight.
The current interglaciation period, extending from 11,500 years ago to the present on the geologic time scale.
Factors involved in climatic change over geological timescales: (4)
1) Variations in solar output (disputed)
2) Changes in orbital parameters (glacial/interglacial)
3) Land configuration and surface characteristics
4) Shifts in atmospheric gases (some uncertainty)
affects intensity of the seasons. amount of radiation
increases summer radiation at the high lats. affects seasonal insolation
alters timing of the solstice and equinox. affects seasonality
Long-term: plate tectonics
Short-term: deforestation, surface temps, albedo
effect of suspended particles in atmosphere (aerosols). Affects insolation. Either absorbed or reflected
Major volcanic eruptions inject aerosols into the atmosphere....
Leads to temporary cooling
90% of historic emissions come from...
Ex: black soot on ice as a negative feedback. VERY LARGE UNKNOWNS.
Which latitudes show higher warming rates?
The higher ones! Think: ice
Cold periods in thermohaline circulation=