History of Climate Change. During earth’s history, climate has generally been warmer than it is today, but is periodically interrupted by short cooler periods. Our climate today exists in one of those cooler periods. (last 2 million years). Long-Term changes in climate
During earth’s history, climate has generally been warmer than it is today, but is periodically interrupted by short cooler periods.
Our climate today exists in one of those cooler periods. (last 2 million years)
Long time scales refer to periods of many millions of years or more.
1. Changes in solar luminosity - Our young sun shone 25 – 30% less brightly than it does today.
But, climate during early earth’s history was generally warmer than today.
2. The long-term carbon cycle
Over long periods of time, the carbon cycle alters the amount of carbon dioxide in the atmosphere.
a. Ice ages have only occurred when a continent has been positioned over one of the poles.
b.North America must be at a high latitude location for ice to form on it.
c. Continental position can also affect ocean currents and force currents to either flow primarily north/south or east/west.
Wisconsin lasted from ~80,000 – 10,000 years before present.
The one primary cause during the Pleistocene had to do with changes in earth/sun relationships.
A. Eccentricity – changes in the shape of the earth’s orbit around the sun.
Range of inclination from 21.5 to 24.5 degrees from perpendicular.
2. When seasonal variations in radiation received in the Northern Hemisphere are the greatest; glaciers retreat and we enter into an interglacial period.
When predictions based on the cycles are compared actual timing of glacial advances and retreats, the correlation is very strong.
1. Within ice ages or interglacial periods, there are much shorter term cycles of climate warming and cooling.
2. These cycles may last a few hundred to a few thousand years.
3. Examples would include the “little climatic optimum” (~900 – 1200 A.D.) and the “little ice age” (16th to mid-19th century).
Causes short-term climate cooling
2. Sunspot cycles and solar output