Why are there ‘Ice Ages’

Question

Why are there ‘Ice Ages’

In: 2

Answer 1

A truthful answer is, we don’t fully understand why. It’s not entirely clear why there was an ice age for the last 2.5 million years, but not the previous 60.

There are known mechanisms that contribute to them. Lower levels of greenhouse gasses, like CO2 and methane are a major one. You basically cannot have an iceage with higher levels of those, even if everything else lines up perfectly.

Another factor is the distribution of land on earth. More landmass at the poles helps ice start growing. Ice doesn’t like growing on water.

Anything that reflects sunlight helps ice grow. Clouds help lower temperatures. Ice is very reflective too. So some ice can help more ice grow.

Then there’s cycles in earth’s orbit and rotation. They’re called Milankovitch cycles. The earth itself wobbles on it’s axis, which means that it can be more tilted from upright. At that point, the poles get less sunlight in winter, and get colder.

The earth’s orbit isn’t perfectly circular either, it’s an elipse. It’s called eccentricity. So the earth is closer to the sun at one end of the elipse than the other. But this also changes in cycles, with in growing more or less eccentric, putting the earth further away from the sun at it’s furthest.

The earth’s axis also rotates, and because of the tilt, it can mean that which pole faces the sun and which faces away at the point furthest from the sun also changes.

So ice is more likely to grow if CO2 levels are low, there’s a lot of landmass around a pole, and the Milankovitch cycles line up so that average yearly temperatures around the pole are low. But ultimately, when an ice age happens or not doesn’t line up perfectly with predictions based on all of these factors, so we’re missing something.

I’m also not entirely sure which combination of milankovitch actually results in lower temperatures. You’d think “pole as far away from the sun as possible in the winter makes it coldest”, but that also means it’s closest during summer, meaning the warmest summers possible. I don’t know if there even is one correct answer, or does it purely depend on the circumstances.