for National Geographic News
Deep ice sheets would cover much of the Northern Hemisphere thousands of years from now—if it weren't for us pesky humans, a new study says.
Emissions of greenhouse gases—such as the carbon dioxide, or CO2, that comes from power plants and cars—are heating the atmosphere to such an extent that the next ice age, predicted to be the deepest in millions of years, may be postponed indefinitely (quick guide to the greenhouse effect).
"Climate skeptics could look at this and say, CO2 is good for us," said study leader Thomas Crowley of the University of Edinburgh in Scotland.
But the idea that global warming may be staving off an ice age is "not cause for relaxing, because we're actually moving into a highly unusual climate state," Crowley added.
"I think the present [carbon dioxide] levels are probably sufficient to prevent that from ever happening," said Crowley, whose study will appear tomorrow in the journal Nature.
Permanent Ice Sheets?
For the past three million years, Earth's climate has wobbled through dozens of ice ages, with thick ice sheets growing from the poles and then shrinking back again.
These ice ages used to last roughly 41,000 years. But in the past half a million years, these big freezes each stretched to about a hundred thousand years long.
Meanwhile, the temperature swings during and between these ice ages became more extreme, soaring to new highs and lows.
These extreme climate swings don't appear to be easing anytime soon, according to evidence recorded in Earth's rocks, Crowley said. "The latest two glaciations were two of the biggest we've seen."
The increasing variability is a sign that Earth's climate will soon move into a new state, according to a computer model used by Crowley and a colleague, William Hyde of the University of Toronto in Canada. They had previously used the model to simulate past ice ages.
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