There have been at least five major ice ages in the earth’s history, and scientists haven’t discovered the exact cause or causes of any of them. Experts think ice ages are most likely brought about by complex interactions between solar output, the earth’s distance from the sun, the position and height of the continents, the composition of the atmosphere, and ocean circulation.
Maximum Extent of Glacial Ice in the Northern
Hemisphere During the Most Recent Ice Age
Actually, the driver of Ice Ages is well known and proven to be driven by changes in the Earth’s orbit around the sun. This theory was first proposed by Mutin Milankovitch in the 1920s, and was proven in the 70’s with the SpecMap project where multiple sea floor cores were taken and analyzed from around the world.The variations in the orbit of the Earth around the sun are caused by the gravitational pull of the other planets in the solar system on our Earth. Because this gravitational influence is a function of the orbits of the planets – it is very regular (occuring most recently at approximately 100kyr intervals : here is a good record: http://lorraine-lisiecki.com/stack.html – you can replace the vertical axis with temperature) and can be calculated. Peter Huybers at Harvard has written equations describing the amount of sunlight at any point on the earth on any day given these orbital variations. Here is a good article talking about what causes Ice Ages in the journal Science: http://www.sciencemag.org/cgi/content/full/sci;313/5786/455
The orbital changes really aren’t that hard to understand – an Ice sheet is more likely to grow quickly if the winters are warm (more snow falls in New York ~50 inches per year than in Antarctica ~2 inches per year for example), and if summers are cool (less snow melts). Earth’s orbit is not circular – it is kinda shaped like an egg – with the Earth being closer to the sun at some times than others. Summer comes when the Northern Hemisphere is tilted towards the sun, and winter when the northern hemisphere is tilted away. If the northern hemisphere is tilted towards the sun when the earth is further away from the sun – this makes for a cooler summer; likewise if the earth is tilted away from the sun while it is closer in its orbit to the sun, then the winter is warmer than usual.
When the world warms carbon dioxide in the atmosphere increases amplifying the warming, and when the world cools carbon dioxide in the atmosphere tends to decrease amplifying the cooling.
Solar output, while variable does not cause Ice Ages.
Ocean Circulation does not drive Ice Ages, but merely redistributes heat from on place to another. (This is what I am studying for my PhD at Columbia University – Ice Age Ocean Circulation) Certianly earth’s oceans circulated differently during glacial times.
I could go on all day – but if you have any related questions I would be glad to try to answer them.
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