Met Office analysis reveals 'clear fingerprints' of man-made climate change

It is an "increasingly remote possibility" that human activity is not the main cause of climate change, according to a major Met Office review of more than 100 scientific studies that track the observed changes in the Earth's climate system.

The research will strengthen the case for human-induced climate change against sceptics who argue that the observed changes in the Earth's climate can largely be explained by natural variability.

Climate scientists and the UN's climate body, the Intergovernmental Panel on Climate Change (IPCC), have come under intense pressure in recent months after the IPCC was forced to admit it had made two errors in its fourth assessment report published in 2007. Emails hacked from climate scientists at the University of East Anglia in November have also sparked a series of inquiries into allegations of a lack of transparency by researchers and manipulation of the peer review process.

Asked whether his study was specifically scheduled as a fightback, Peter Stott, who led the review, said that the paper was originally drafted a year ago. But he added: "I hope people will look at that evidence and make up their minds informed by the scientific evidence."

Scientists matched computer models of different possible causes of climate change - both human and natural - to measured changes in factors such as air and sea temperature, Arctic sea ice cover and global rainfall patterns. This technique, called "optimal detection", showed clear fingerprints of human-induced global warming, according to Stott. "This wealth of evidence shows that there is an increasingly remote possibility that climate change is being dominated by natural factors rather than human factors." The paper reviewed numerous studies that were published since the last IPCC report.

Optimal detection considers to what extent an observation can be explained by natural variability, such as changing output from the sun, volcanic eruptions or El Niño, and how much can be explained by the well-established increases in carbon dioxide and other greenhouse gases in the atmosphere.

According to Nasa, the last decade was the warmest on record and 2009 the second warmest year. Temperatures have risen by 0.2C per decade, over the past 30 years and average global temperatures have increased by 0.8C since 1880.

The evidence that the climate system is changing goes beyond measured air temperatures, with much of the newest evidence coming from the oceans. "Over 80% of the heat that's trapped in the climate system as a result of the greenhouse gases is exported into the ocean and we can see that happening," said Stott. "Another feature is that salinity is changing - as the atmosphere is warming up, there is more evaporation from the surface of the ocean [so making it more salty], which is most noticeable in the sub-tropical Atlantic."

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