Question

What causes ice ages and will we have them again and if so when, roughly?

Answer

Dave: There's various things we call ice ages. Strictly speaking we're actually in an ice age now. Over the last few tens of millions of years we've had periods when the north and south poles have been frozen but there've been other periods in the Earth's history when they haven't been frozen at all. Over the long period we are in an ice age at the moment. People aren't quite sure why that's been happening. It's been suggested it might be something to do with the Himalayas growing and altering he climate patterns in the world. I'm not entirely sure of the reasons for that. On the shorter scale there's various other things that will affect the climate: one of them is we get cycles of exactly where the Earth's pole is pointing. Sometimes it's almost vertical at which point the seasons are very weak. Some times it's keeled over more. Chris: It's the Earth's tilt, isn't it? It's about 23.5? and it wobbles a bit, doesn't it? The planet sort of wobbles backwards and forwards a little bit on its orbit. I think it's over 30,000 years or something like that.Dave: Yeah, there's various different cycles on different forms of vibration. Chris: Why should that make an ice age?Dave: If you suddenly have stronger seasons that will affect it, the way water and air flows around the world. Subtle changes like that can affect the temperature of the whole world. That could be creating ice ages.Chris: It's a sort of positive feedback loop too, isn't it? There's this thing called a Milankovic cycle because where the Earth doesn't go round the sun in a perfect circle it's an ellipse over time you get more of an ellipse than other times. This means that more energy reaches the Earth sometimes from the sun than other times and this means the planet goes into phases of cooling and warming but once you're into cooling it makes it easier for ice to form. Once you have ice forming it means you can have more ice. More ice reflects more light back, because it's very white, back into space so the Earth cools a bit more and it goes into a positive feedback loop: making it very cold. When something breaks that cycle we warm up again. Dave: That's right and that's why we should be so worried about human-led climate change because if we make a small effect you never know, there might be a load of other positive feedback. You might find that there's less snow on the ground so the world heats up even more than it would do just with carbon dioxide. Chris: It's not just as simple as carbon dioxide in the air?Dave: Yeah, basically it's all just horribly complicated.

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