CO2 Emissions May Prevent Projected Ice Age

Nov. 12, 2008 -- Scheduled shifts in Earth's orbit should plunge the planet into an enduring Ice Age thousands of years from now but the event will probably be averted because of man-made greenhouse gases, scientists said Wednesday.

They cautioned, though, that this news is not an argument in favor of global warming, which is driving imminent and potentially far-reaching damage to the climate system.

Earth has experienced long periods of extreme cold over the billions of years of its history.

The big freezes are interspersed with "interglacial" periods of relative warmth, of the kind we have experienced since the end of the last Ice Age, around 11,000 years ago.

These climate swings have natural causes, believed to be rooted particularly in changes in Earth's orbit and axis that, while minute, have a powerful effect on how much solar heat falls on the planet.

Two researchers built a high-powered computer model to take a closer look at these intriguing phases of cooling and warmth.

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In addition to the planetary shifts, they also factored in levels of carbon dioxide (CO2), found in tiny bubbles in ice cores, that provide an indicator of temperature spanning hundreds of thousands of years.

They found dramatic swings in climate, including changes when Earth flipped from one state to the other in a relatively short time, said one of the authors, geoscientist Thomas Crowley of the University of Edinburgh, Scotland.

These shifts, called "bifurcations," appear to happen in abrupt series, which is counter-intuitive to the idea that the planet cools or warms gradually.

"You had a big change about a million years ago, then a second change around 650,000 years ago, when you had bigger glaciations, then 450,000 years ago, when you started to get more repeated glaciations," Thomas said.