D: Well, it is winter.
Y: Actually, it's an ice age.
D: Oh, c'mon. It's not that cold.
Y: No, I'm serious, we're in the middle of an ice age.
D: The last ice age ended 20,000 years ago.
Y: That's what most people think, but actually we're just in a relatively warm period during the current ice age.
D: I don't know. It gets pretty warm here during the summer. It's hard to believe we're experiencing an ice age when it's 95 degrees outside.
Y: But it's true. See, ice ages have occurred for roughly two-hundred of the past six- hundred million years, with each ice age lasting up to ten million years at a stretch. During an ice age the polar regions of the earth are cold, there's a big temperature difference between the equator and the poles, and at times ice sheets cover huge chunks of the earth's land mass.
D: Ok, we've got the first two, but I don't see ice covering most of the world.
Y: That's because, like I said, there can be large fluctuations in temperature during an ice age. During the current ice age glaciers have advanced and retreated over twenty times. We're living during one of the warmer periods when the glaciers have retreated.
D: So at some point the glaciers will advance again and we'll be covered in ice.
Y: Right.
D: I'd better invest in some good boots.
Y: I wouldn't worry about it quite yet, Don. But there's one thing we can do right now.
D: What?
Y: Get inside!
