New Ice Age Predicted -- But Averted by Global Warming?
for National Geographic News
|November 12, 2008|
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.
In about 10,000 to 100,000 years, the study suggests, Antarctic-like "permanent" ice sheets would shroud much of Canada, Europe, and Asia.
"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.
The researchers found that between 10,000 and 100,000 years from now, Earth would enter into a period of permanent ice sheets—more severe than any seen in millions of years.
In some ways the ice age would be like those in the past few hundred thousand years, with a thick ice sheet covering North America, the study predicted.
But in the model, Europe and Asia also succumbed to ice sheets up to 2 miles (3.5 kilometers) thick, stretching from England to Siberia—something never before seen in models of past ice ages.
"We were surprised," Crowley said. "There's no evidence for this in Asia" during ice ages in the past few million years.
Hard to Know
Though this extreme ice age would be unusual, so is the climate that people are creating by emitting huge amounts of greenhouse gases, Crowley said (global warming fast facts).
"It's hard to say what's going to happen," Crowley said. "The very fact that you have this nonglacial [warming] atmosphere with polar ice caps [still present], presents a bizarre scenario.
"I don't know that we have a comparable analogy for it in the geologic record."
Prehistoric-climate expert Lorraine Lisiecki said, "This is the only study of which I am aware that suggests the next ice age could be much more extreme than those of the previous one million years."
Many more tests are needed to see if the study's prediction seems correct, said Lisiecki, of the University of California, Santa Barbara.
But she agreed that we might never find out what would have happened naturally, due to human-caused global warming.
"Current greenhouse gas concentrations are probably similar to those that occurred three million years ago and are high enough to prevent an ice age for hundreds of thousands of years," she said.
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