2. What is an Ice Age ?
Ice ages are times when large areas of the earths surface are covered with ice sheets
The term is used to describe time periods when
a) the earth is at a cooler temperature than usual( million years), or
b)shorter time periods when glaciers are at their maximum extent(10s of thousands of years) = Glaciation Cycle

3. Causes of Ice Ages
There are many factors thought to influence the start and end of ice ages
Milankovich Cycles
Plate Tectonics
Ocean and Atmospheric Circulation
Volcanic eruptions
Sunspots

4. Milankovich Cycles
Milankovich Cycles deal with the way the earth travels around the sun
There are three main ways in which the earth changes its motion around the sun; Orbital Eccentricity, Obliquity, and Precession
These factors affect the amount of radiation the earth receives from the sun

5. Orbital Eccentricity
The earths orbit around the sun is slightly elliptical with the elongation of the ellipse changing about every 100,000 years
The more elliptical the orbit of the earth, the greater the contrast in temperature between summers and winters in both hemispheres

6. Orbital Eccentricity

7. Obliquity The axis of the earth is tilted 23.5 degrees at this time
The tilt of the earth varies from 22.1 degrees to 24.5 degrees
The tilt of the earth varies on a 41,000 year cycle
The smaller the tilt angle, the less radiation the poles receive

8. Obliquity
Tilt: smaller larger

9. Precession Precession is the wobble of the earth axis
The means that the seasons are not always at the same spot on the earths orbit
A Precession cycle takes about 23,000 years

10. Precession
Change of time of year when Earth is nearest to the Sun (now January)

11. Milankovich Cycles
The conditions most conducive to an ice age would be
Orbital eccentricity at its maximum
Obliquity at its minimum
Precession so that summer is farthest from the sun and winter is closest to the sun

12. (red line is my rough average) Toba eruption Note SHARP changes
in climate found in
data (Greenland cores)
Toba eruption

13. Plate Tectonics
Plate tectonics is an important factor in the development of ice ages
There needs to be landmasses in and near the polar regions for large ice sheets to start to form
Plate Tectonics also can affect atmospheric and ocean currents

14. Atmospheric and Oceanic Circulation
Changes in Atmospheric and Oceanic Circulation can promote the beginning of an ice age
Any change in these currents that brings warmer water near the polar regions can start ice ages because of increased precipitation

15. Atmospheric and Oceanic Circulation
For example, 3.5 million years ago, the Isthmus of Panama formed. The cut off east-west ocean current circulation, which strengthened the gulf stream. The gulf stream then brought warmer water to the northern hemisphere which increased precipitation over the north pole, initiating the formation of ice sheets.
That is, warmer conditions apparently yielded a glaciation cycle!

16. Volcanic eruptions
Violent volcanic eruptions can effect the radiation from the sun that reaches the surface of the earth by releasing great quantities of ash into the air
It takes an extremely large eruption to effect global climate, e.g. Mt. Tambora, 1815, Toba, 70,000 BC
The Mt Pinatubo eruption in 1991 only affected the climate of Europe by about 1 degree for 1 year

17. Volcanic Eruptions

18. Sunspots
Sunspots are solar magnetic regions that are cooler than the rest of the sun
The radiation coming from the sun is raised when there are more sunspots, even though they are cold spots
This is because of great magnetic activity causes increased radiation
Thus, fewer sunspots means less radiation coming from the sun and a lower temperature for the Earth and its climate

19. Factors Lengthening Ice Ages
Once large continental ice sheets form, they create a positive feedback loop making the temperature colder
This is due to the high albedo of ice, which means that it reflects light well
Thus, less of the sun’s radiation is absorbed by the earth and the temperature drops.

20. More factors
Further; glaciation causes erosion of rocks by the overlying ice
This takes minerals and rock debris to the sea where they react with CO2 in the air
This causes a reduction of CO2 which results in an “Ice House” Effect

21. Physical Effects of Ice ages
Rise and fall of sea level as water is confined by/released from glaciers
Great amounts of erosion and sediment deposition
E.G.: The carving of mountain valleys by glaciers, and formation of flat topography and the rich soils in the northern Midwest resulted from the glaciation cycles.
Isostatic depression and rebound from effects of continental glaciers

22. Predictions for the next ice age
Most predicts are that the next ice will occur sometime between the next 5,000 and 50,000 years
This is mostly based on Milankovich cycles
The greenhouse effect could make it more difficult for ice ages to happen, or can cause one
On the other hand, catastrophic volcanic eruption of epic proportions can occur at any time (Huckleberry Ridge model of Yellowstone)
There would drastic effects on human populations, if any of these occur while populations are high.