🔄FROM THE ARCHIVE At least five major ice ages have been documented in Earth's history. And guess what? You're living in an ice age right now. But don’t expect the planet to chill over from pole to pole.
Periodically, global temperatures drop, ice sheets form at the poles, then the ice creeps down to cover the continents. We call these ice ages. There have been five major ice ages in Earth’s 4.5-billion-year history. The last one began about 2.5 to 3 million years ago. And get this:That’s hard to believe in these days of dangerously increasing global temperatures, but ice ages aren’t uniformly hard-frozen.
During the colder winters, snow falls on the land. If the summers are cool enough, the snow lasts until the next winter. Eventually there will be more and more snow building up, and that will pack down into a glacier. The glacier will continue to grow until it’s a continent-sized ice sheet. Meanwhile, the Earth’s orbit changes enough from time to time to cause the ice sheets to retreat, a little or a lot, creating interglacial periods.
And as we’ve all learned, CO2 is a very efficient greenhouse gas. The increase in CO2 heats up the atmosphere so the ice sheets start getting melted from above, as well. As the ice melts, big chunks of ice sheets start to break off — a process called calving — which makes them melt even faster. “They can disappear in, geologically speaking, the blink of an eye,” says Thomas. “It takes very little time to completely destroy an ice sheet.
On the other hand, if we hadn’t been in an ice age when humans started cranking up the heat, things would already be much, much worse. So we do have an ice age to thank for that.
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