Glaciations and Past Climates
Learner Objectives: At the end of this lecture you
will be able to describe:
1. Suspected causes of natural climate change
and how they are not plausible theories for
all long term climate change
2. How the Milankovitch cycle is consider
the theory which explains long term
natural climate change
Terms
Insolation is a measure of solar radiation
energy received on a given surface area in a
given time.
Albedo is reflectivity of surface
What is a Glaciation?
• Ice Age-large continental ice sheet (millions
of years)
• Glaciations-glaciers at max
• Pleistocene 20 kya
Evidence of Glaciations: Sea Level
• Glaciation –low sea level
Evidence of Warming
W. W. Norton. Adapted from
McKenzie, 1998.
Shoreline of North
America During Ice
Age
Sea Level
Possible Cause of Glaciations
• Volcanic Emissions-usually short term
impact
• Location of continents-explains only a few
glaciations
• Sun spot variation-only 10 year impact
• Milankovitch Cycle (yes!)
Tracking the Path of
Sulfuric-Acid Mist
Source: Image by G.J. Orme, Department of the Army, Ft. Bragg, NC.
Pinatubo Effects on Near-Surface Temperatures
1991
Source: Data from National Geophysical Data Center.
Location of the Continents
• Surface waters move from equator to poles
• Affects air currents and climate
• Move by temperature and density
differences
Location of Continents affects
currents
(doesn’t explain all glaciations
Sunspot: Variation over 10 yrs
• Need 1000 yrs to initiate major ice age
Milankovitch Cycle
Fig. 22.41 a
W. W. Norton
Fig. 22.41 b
W. W. Norton
Fig. 22.41 c
W. W. Norton
Fig. 22.41 d
W. W. Norton
Milankovitch Cycles: Combining
eccentricity, tilt, precession
Milankovitch Cycle
• 100,000 year cycle can decrease average
temperatures 4 °C (5.4 °F)…cold but not
cold enough
• Need other factors that are positive
feedback to decrease temperature by 5-7°
C (7-13 °F) on coasts and 10-13°C (1822°F) on land
Positive Feedback
– Changing albedo (increased snow decreases the
amount of radiation absorbed)
– Short/cold summers (more so than long cold
winters)
– Shut down of global heat conveyor
– Biological processes change-ocean plankton
increase and absorb more CO2
The Milankovitch cycle
A.
B.
C.
D.
Explained the Medieval Warm Period
Explains major glaciations
Explains the greenhouse effect
Is a major factor in ozone production