| Climate results from the uneven
distribution of heating over the surface of the earth caused by the
earth's tilt. This tilt is the angle between the earth's rotational axis
and its orbital plane around the sun. Currently this angle is 23.5
degrees.
Long term climate is also affected by the
heat balance of the earth which is driven mostly by the concentration of
CO2 in the atmosphere.
Climate change can result if the pattern or
solar radiation is changed and/or if the amount of CO2 changes.
There is abundant evidence that the earth does undergo climatic change.
Climatic change can be a limiting factor for the evolution of many
species.
Climate Change:
- Periodic Ice Ages
---> Glacial-Interglacial Periods
- Major Period:
---> 100,000 years; 9 degree F decrease
- Minor Period:
---> 12,000 years; 5 degree F decrease
- Smaller Periods??:
---> 1,000 years; 3 degree F decrease
We currently are nearing
the end of a small, minor interglacial period
- Major Ice Ages: Most of
the Planet is Covered
- Minor Ice Ages: 40o
Latitude and Above. The most recent one of these occurred about 15,000
years ago and the coverage of the ice sheet is shown
here
- Little Ice Age:
(1000-1850 AD; Irish Potato Famine; Nisqually Glacier)
Effects of Ice Ages
- Changes sea level by 100 meters exposes
continental shelfs
- changes continental shelf composition
due to increased deposition during melt
- changes hydrological cycle through less
evaporation
- changes landscape Great Lakes; Seattle;
Stoss and Lee
- Changes drainage patterns
- changes topsoil characteristics
- massive flooding episodes
--> Eastern Washington
Causes of Ice Ages --> needs to be
PERIODIC!
- Solar Cycle --> no evidence
- Volcanic Dust in Atmosphere --> why
periodic?
- CO2 Cycle --> why
periodic? --> factor 2 reduction causes 7 F drop --> Record
of CO2 and temperature variations
- Increased precipitation at poles due to
changing orientation of continental land masses
- Changes in mean temperatures of ocean
currents --> what mechanism?
The most Probable Cause:
- Orbital Variations of the Earth!
- Eccentricity variation 90,000 years 5
variation around mean value. This is due to Jupiter.
- Change of tilt of axis 24,000 years
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