August 25, 2006

Ice Age Gives Clues to Global Warming

By Alister Doyle, Environment Correspondent

OSLO (Reuters) - Ice Age evidence confirms that a doubling of greenhouse gases could drive up world temperatures by about 3 Celsius (5.4 Fahrenheit), causing havoc with the climate, a study showed on Friday.

The researchers made a novel check of computer climate forecasts about the modern impact of heat-trapping gases, widely blamed on use of fossil fuels, against ice cores and marine sediments from the last Ice Age which ended 10,000 years ago.

"A doubling of carbon dioxide concentrations would cause a global temperature increase of around 3 Celsius," said Thomas Schneider of the Potsdam Institute for Climate Impact Research who led the report.

The findings broadly back up other Potsdam forecasts about the effects of a build-up of carbon dioxide emitted by power plants, cars and factories. Some skeptics dismiss such models as exaggerations.

Temperatures have already risen by 0.6 Celsius since before the Industrial Revolution in the 18th century. Many scientists project that higher temperatures will cause more heatwaves, droughts, floods and rising sea levels.

Greenhouse gas concentrations are likely to double from pre-Industrial levels this century unless the world drastically cuts energy use and shifts to clean wind or solar power.

The Potsdam scientists worked out 1,000 climate model versions, each with different assumptions of the behavior of clouds, ocean currents and other factors.

They then checked the likelihood of the scenarios against climate shifts at the end of the Ice Age -- carbon dioxide trapped in air bubbles in ice and the chemical makeup of marine sediments which gives clues to temperatures.

Schneider said the study, published in the journal Climate Dynamics, indicated that the outer ranges of likely temperature rises were 1.2-4.3 Celsius if carbon dioxide levels doubled.

Still, he said the study meant temperatures were unlikely to rise by six or seven degrees, as some studies had suggested.

The European Union wants to limit any rise in temperatures linked to global warming to 2 Celsius -- a threshold it sees as triggering "dangerous" climate change.

Carbon dioxide levels were far lower at the end of the last Ice Age than in the 18th century. Today, concentrations are at their highest level for at least 650,000 years.

The scientific panel that advises the United Nations has forecast that world temperatures could rise by 1.4-5.8 Celsius by 2100. The Potsdam survey merely projects the impact of a doubling of carbon dioxide, without giving any dates.