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What is an Ice Age?

Michael Anissimov
Updated May 21, 2024
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An Ice Age is a period of time, typically about 30 million but occasionally as long as 300 million years, during which ice sheets cover at least the Earth's polar areas. Individual Ice Ages have sub-Ice Ages, called glacials (when cold) or interglacials (when warmer) that operate in cycles of 40,000 and 100,000 years. When the term "Ice Age" is used colloquially, it often refers to these shorter glacials, periods when the ice caps extend significantly beyond the poles and into the hearts of continents such as North America and Eurasia. In this sense, "the last Ice Age" refers to what is formally called "the last glacial period", which began about 70,000 BP and ended between 15,000 and 10,000 BP. This is the Ice Age that was experienced by early man.

Scientists cannot say exactly what causes Ice Ages, although there are a number of inter-implicated variables at play. These include atmospheric composition (greenhouse gases), slight changes in the Earth's orbit known as Milankovitch cycles, the Earth's albedo (reflectivity), changes in the location and amount of crust at different points on the Earth's surface, variations in solar output, large meteor impact, the release of methane clathrates, and supervolcanism. The short-term (40,000/100,000 year) cycles are known to be caused by variations in the Earth's orbit.

Because there is ice covering Antarctica and Greenland, we are in the middle of an Ice Age, one that began 40 million years ago. Ice Ages are fairly atypical circumstances for the Earth; aside from six Ice Ages, the Earth's poles have been largely ice-free. Fossils of trees have been found at land which was just a few hundred miles from the poles at the time they lived. Ice Ages are about as rare as mass extinctions, occurring once every 100 million years or so.

The typical average global temperature when the Earth is not in an Ice Age is about 22° C (71.6° F). During an Ice Age, it dips about 10° C to an average of 12° C (53.6° F). At the poles, the temperature is far below freezing practically all the time.

During Ice Ages, large quantities of water get locked up in ice sheets, lowering the global sea level. During the most recent Ice Age, the global sea level was about 100 ft less than it is now, opening up large sections of land such as the North Sea, and connecting Papua New Guinea to the Southeast Asian mainland and Russia to Alaska via the Bering land bridge. Because of the Ice Age, our ancestors could cross over into the Americas. It would be over 10,000 years before humans who traveled to the Americas would be reunited with their distant cousins from Europe, Asia, and Africa.

All The Science is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Michael Anissimov
By Michael Anissimov
Michael Anissimov is a dedicated All The Science contributor and brings his expertise in paleontology, physics, biology, astronomy, chemistry, and futurism to his articles. An avid blogger, Michael is deeply passionate about stem cell research, regenerative medicine, and life extension therapies. His professional experience includes work with the Methuselah Foundation, Singularity Institute for Artificial Intelligence, and Lifeboat Foundation, further showcasing his commitment to scientific advancement.
Discussion Comments
By anon990777 — On May 09, 2015

Cooling will take place gradually in selected areas. Based on posted videos, the new north pole will be situated in between North America and Europe.

By anon157869 — On Mar 04, 2011

sorry i am not a scientist but i wonder if it's all true then where do religions stand. if there are living human beings in other planets then what kind of religion they have adopted well i think i have no right to talk about such sensitive issues. saeed k.

By Proxy414 — On Feb 10, 2011


Scientific study would dictate otherwise. Though subjective and "personal" experience may make you loathe the cold and wish for global warming, the earth is still warming. Our pollutants do have a very real and negative effect on the environment, so please, at least for your own sake, be careful with them.

By SilentBlue — On Feb 09, 2011

Global warming? It seems to me that the earth is getting colder. I see littler personal evidence for global warming. I think that we're going through a freeze of the earth. Pollutants have little to no effect on the ozone.

By GigaGold — On Feb 06, 2011


It might seem cold and harsh during a severe winter, but what we experience in the temperate zones is nowhere near the harsh conditions of the ice age. The Antarctic and Arctic regions would be a good example of what it was like, with bitterly frigid conditions and ice and snow which is a mile deep. The only animal life which can even survive in some of these regions is either subaquatic animal life or blubbered penguins.

By Armas1313 — On Feb 03, 2011

It seems to me as thought there is currently an Ice Age descending upon New England, and even much of the United States. Snowpiles have become too high to increase. Shoveling to the ground is ridiculously hard. Sleeping at night requires a lot of blankets and turning the heat up extra high. I fear that the world is becoming very cold.

Michael Anissimov
Michael Anissimov
Michael Anissimov is a dedicated All The Science contributor and brings his expertise in paleontology, physics, biology...
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