Last Ice Age: The Earth has been in an Ice House Climate for the last 30 million years

last ice age

When the Earth is in its "Ice House" climate mode, there is ice at the poles. The polar ice sheet expands and contacts because of variations in the Earth's orbit (Milankovitch cycles). The last expansion of the polar ice sheets took place about 18,000 years ago.

During times of low sea level the continents are emergent, land faunas flourish, migration routes between continents open up, the climate becomes more seasonal, and probably most importantly, the global climate tends to cool off. This is largely because land tends to reflect the Sun's energy back to space, while the oceans absorb the Sun's energy.

Also, landmasses at the poles permit the growth of permanent ice sheets, which because they are white, reflect even more energy back to space. The formation of ice on the continents, also, lowers sea level, which exposes more land, which cools the Earth, forming more ice, and so on, and so on. The lesson here is: once the Earth begins to cool (or warm-up) positive feed-back mechanisms push the Earth's climate system to greater and greater cooling (or warming).

During the last half of the Cenozoic the Earth began to cool off. Ice sheets formed first on Antarctica and then spread to the northern hemisphere. For the last 5 million years the Earth has been in a major Ice Age. There have been only a few times in Earth's history when it has been as cold as it has been during the last 5 million years.

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