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)
Table 12.1
The long-term carbon cycle
What happens when spreading rates at mid-ocean ridges increase?
Late Paleocene torrid age (65 – 55 million years ago)
Continental position
1.
Ice age formation needs a continent over one of the
poles.
2.
North America must be at a high latitude
location for ice to form on it.
Deflection of Equatorial currents poleward. Example:
Closing of the Isthmus of Panama ~3 million years ago.
Intermediate-Term Changes in Climate
1.
2.
Operates on time scales of 10,000’s to 100,000’s of
years.
During the Pleistocene Epoch, coming and going of ice
ages and interglacial periods.
The last ice age
was called the
Wisconsin in
North
America.
Wisconsin lasted
from ~80,000
– 10,000
years before
present.
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
axis.
Effect of Milankovitch Cycles
When insolation levels result in cooler summers in the high
latitudes of the Northern Hemisphere, glaciers advance.
When predictions based on the cycles are compared actual
timing of glacial advances and retreats, the correlation is
very strong.
Short-term climate change
Cycles that last a few hundred to a few thousand years.
Examples: The “little climatic optimum” (~900 – 1200 A.D.)
and the “little ice age” (16th to mid-19th century).
Causes of Short-TermClimate Change
Volcanic eruptions
Causes short-term climate cooling
2.
Sunspot cycles and solar output
3.
Disruption of the Ocean Conveyor Belt
Heinrich Events- armadas of icebergs
adding cold, fresh water to the ocean
surface.