Ice Age gives clues to global warming: study

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.