Global warming slowdown 'does not invalidate climate change'

National science academies of the US and the UK say longer-term warming trend is still evident

The slowdown in rising global surface temperatures is not a sign that climate change is no longer happening, the national science academies of the US and the UK have said.

Publishing a guide on the state of climate change science, the National Academy of Sciences and the Royal Society said the short-term slowdown this century did not "invalidate" the long-term trend of rising temperatures caused by man-made climate change.

"Despite the decadal slowdown in the rise of average surface temperature, a longer-term warming trend is still evident. Each of the last three decades was warmer than any other decade since widespread thermometer measurements were introduced in the 1850s," the publication, Climate Change Evidence and Causes, said.

Scientists have been investigating reasons for the slowdown in temperature rises. Peer-reviewed papers over the last year have suggested 17 sun-dimming volcanic eruptions since 2000, "unusual" trade winds in the Pacific Ocean burying surface heat deep underwater and the world's oceans absorbing greater amounts of heat in recent years may have contributed.

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Thomas Stocker, the co-chair of working group one of the UN's climate science panel, said at the launch of the Intergovernmental Panel on Climate Change's landmark report last September that the recent slowdown in surface temperature rises was not significant because it was over too short a period of time. "Climate relevant trends should not be calculated for periods of less than 30 years," he said.

The new document by the two science academies addresses the issue head on and says: "A short-term slowdown in the warming of Earth's surface does not invalidate our understanding of long-term changes in global temperature arising from human-induced changes in greenhouse gases."

The publication also addresses areas of uncertainty in climate science, saying more work needs to be done to predict the role of clouds in future climate change, as well as the likely impact on the frequency of future hurricanes occurring.

But the academies state unequivocally that the world is warming and will warm by a further 2.6-4.8C by the end of the century.

A claim by the UK environment secretary, Owen Paterson, that a future temperature rise of 1-2.5C would only be "modest", is squarely contradicted, with the scientists noting that the global average temperature in the last ice age was only 4-5C colder than today. "Global warming of just a few degrees will be associated with widespread changes in regional and local temperature and precipitation as well as with increases in some types of extreme weather events," they write.

Sir Paul Nurse, president of the Royal Society, said: "We have enough evidence to warrant action being taken on climate change; it is now time for the public debate to move forward to discuss what we can do to limit the impact on our lives and those of future generations."

Climate scientists who worked on the new guide include Eric Wolff of the University of Cambridge, Inez Fung of the University of California, Berkeley, Brian Hoskins of Imperial College London and the University of Reading, and Kevin Trenberth, of the US-based National Center for Atmospheric Research.


Adam Vaughan

The GuardianTramp

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