Why are there ‘Ice Ages’
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Modern Ice Ages (within the past million years) are believed to be primarily caused by natural cycles in the Earth’s orbit called Milankovitch cycles.
Our general climate is at a tipping point where relatively mild orbital changes can trigger an ice age. But with the increasing amount of man made CO2 in the atmosphere may end the cycle of Ice Ages. But at this point we don’t know for sure.
Over thousands of years the Earth orbit changes slightly causing shorter summers. This has a long term knock on effect that causes more and more ice to build up at the poles until it causes a run away effect triggering an ice age.
*On a side note it’s common to refer to only the periods of Glaciation as an Ice Age, but scientists often refer to the period of re-occurring glaciations over Millions of years as one long Ice Age and we just happen to be currently living in a short warm period in a longer ice age.*
Eventually so much ice and glaciers build up in the Northern Hemisphere that entire continents are covered and reflect light back into space making things worse.
The Sea level drops, ocean currents are effected, and the amount of and types of plants that can survive on land are reduced.
Eventually the orbit changes enough that the planet starts to warm up, and again it triggers a runaway effect where all the glaciers start to melt very rapidly ending the ice age.
Ancient Ice Ages (billions of years ago) were caused by different reasons. The Sun had a lower output back then, and the Earths atmosphere had a very different composition than it does now. The continents were also in a different position which affected ocean currents and the weather.
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