for National Geographic News
Violent swings in weather patterns occurred after Earth's climate crossed "tipping points" thousands of years ago, a new study argues.
In as little as three years, patterns in the atmosphere have suddenly shifted and flipped into a new state, apparently contributing to rapid warming of the Northern Hemisphere, according to the new analysis of an ice core from northern Greenland.
The study focused on two quick warming periods14,700 and 11,700 years agothat together pushed our planet out of the last ice age.
During such ice ages, Earth's climate was more variable overall than it has been relatively recently; spanning the past 11,700 years, our planet's current climatic periodknown as the Holocenehas been marked by an unusually warm and stable climate.
But it's possible this could change quickly, the new study suggests.
"We are changing the climate," with greenhouse gas emissions, said study co-author Dorthe Dahl-Jensen, an ice and climate scientist at the University of Copenhagen, Denmark. "We are moving out of that stable state now."
Dahl-Jensen adds that scientists can't say that similar rapid changes will result from human-caused global warming.
But the new study, appearing tomorrow in the online edition of the journal Science, does "tell us about a capacity in our weather systems to change so fast," she said. "I think that's worth drawing attention to."
Snow falling on central Greenland lays down a distinct layer each year, trapping bubbles of atmospheric gas, dust, and other impurities and gradually compacting into ice that captures an ancient climate record stretching back tens of thousands of years.
(Related story: New Ice Core Reveals 800,000 Years of Climate History [July 5, 2007])
In their study, researchers focused on an ice core drilled by the North Greenland Ice Core Project
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