Global warming "lull" only temporary, German researchers caution

3rd June 2008, Comments 0 comments

Reduced effects of global warming over the next decades does not mean the end of environmental problems, according to German scientists

Hamburg -- A "lull" in global warming over the next decade should not be misinterpreted as meaning that the greenhouse effect has stopped, German researchers warn.

North Atlantic sea surface temperatures may actually decrease slightly in the next decade, according to the researchers with Germany's Leibniz Institute of Marine Sciences in Kiel.

Their paper also suggests global surface temperatures may not actually increase either. But they caution that their findings should not be interpreted to mean that global warming has stopped.

On the contrary, the "lull" is only a temporary phenomenon associated with ocean currents, writes Dr. Noel Keenlyside in the report published in Nature.

The effect of rising fossil fuel emissions will mean that warming will accelerate again after 2015 when natural trends in the oceans veer back towards warming, according to the German researchers' computer model.

"Our prediction is that there will be no warming until 2015 but it will pick up after that," Keenlyside says.

The new computer model attempts to predict what might happen to the climate of the North Atlantic over a period of decades. It suggests the temperature of the sea and Europe and North America may cool slightly.

The Kiel researchers say the North Atlantic has variability on a 70 to 80-year cycle and the meridional overturning circulation (MOC), a giant "conveyor belt" which brings warm water northwards into the area, had an important role to play in driving those fluctuations.

When the circulation is strong, it creates warmer temperatures.

The scientists' study created a model which used sea surface temperatures and attempted to simulate the variability of the MOC in a bid to predict climate over coming decades.

The model, which was tested by comparing retrospective "predictions" against what has actually happened, suggests the MOC may weaken towards a long term average, leading to slightly cooler temperatures in the North Atlantic.

However, sea surface temperatures in the tropical Pacific will remain unchanged, the scientists in Kiel warn.

Writing in Nature, they say: "Our results suggest that global surface temperature may not increase over the next decade, as natural climate variations in the North Atlantic and tropical Pacific temporarily offset the projected anthropogenic warming."

In a commentary on the piece in the same issue of Nature, Dr. Richard Wood of Britain's Hadley Centre explains that this cooling effect is only a "lull": "Such a cooling could temporarily offset the longer term warming trend from increasing levels of greenhouse gases in the atmosphere.

"That emphasises once again the need to consider climate variability and climate change together when making predictions over timescales of decades."

The Kiel report spawned media reports that global warming had "stopped" and that oil corporations were rethinking their environmental expenditures. Keenlyside responded to those reports.

"We thought a lot about the way to present this because we don't want it to be turned around in the wrong way," a Bloomberg report quotes Keenlyside as saying.

"I hope it doesn't become a message of Exxon Mobil and other sceptics."

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