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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
Long-Term changes in climate
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
2. The long-term carbon cycle
Over long periods of time, the carbon cycle alters the amount of
carbon dioxide in the atmosphere.
Volcanic activity causes CO2 outgassing
 Outgassing increases when spreading rates at midocean ridges increases
3. Continental position and the role of plate tectonics.
a. Ice ages have only occurred when a continent has
been positioned over one of the poles.
North America must be at a high latitude
location for ice to form on it.
Continental position can also affect ocean currents
and force currents to either flow primarily north/south
or east/west.
Intermediate-Term Changes in Climate
Operates on time scales of 10,000’s to 100,000’s of
The coming and going of ice ages during the last 1.8
million years are operating on this time scale.
During this Pleistocene Epoch, ice ages and
intervening interglacial periods have come and gone
possibly as many as 15 times.
The last ice age
was called the
Wisconsin in
Wisconsin lasted
from ~80,000
– 10,000
years before
Causes of intermediate-term climate change
Changes in earth/sun relationships.
1. The Milankovitch cycles
A. Eccentricity – changes in the shape of the earth’s
orbit around the sun.
B. Axial tilt – changes in the inclination of the earth’s
axis. Range of inclination from 21.5 to 24.5 degrees
from perpendicular.
C. Precession – the wobbling of the earth on it’s
Effect of Milankovitch Cycles
1. When seasonal variations in radiation received in the
Northern Hemisphere are the least; the result is a glacial
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.
Short-term climate change
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
3. Examples would include the “little climatic optimum”
(~900 – 1200 A.D.) and the “little ice age” (16th to mid19th century).
Possible Causes of Short-Term
Climate Change
1. Volcanic eruptions: example Tambora 1815
Causes short-term climate cooling
Sunspot cycles and solar output
Disruption of the Ocean Conveyor Belt
Heinrich Events- armadas of icebergs
adding cold, fresh water to the ocean