Global warming 'caused by humans'

Climate scientists hit back at the sceptics with new research they say has uncovered the "fingerprint" of man-made global warming.

Researchers working like detectives investigating a crime compared real observational evidence with data from computer simulations to see how they matched up.

They concluded there was an "increasingly remote possibility" of human influence not being the chief driver of climate change. The clues were unravelled using a forensic technique called "optimal detection" that gives different factors - natural and human - an equal chance to explain the changes seen.

They covered a wide range of trends affecting land and sea temperature, the saltiness of the oceans, humidity, rainfall, and Arctic sea ice. Also included was warming in the Antarctic, which has only recently been attributed to human influence.

Dr Peter Stott, from the Met Office Hadley Centre in Exeter, who co-led the study, said: "What we've shown in this paper is that the fingerprint of human influence has been detected in many different aspects of climate change.

"We've seen it in temperature, and increases in atmospheric humidity, we've seen it in salinity changes... we've seen it in reductions in Arctic sea ice and changing rainfall patterns. What we see here are observations consistent with a warming world.

"This wealth of evidence we have now shows there is an increasingly remote possibility of climate change being dominated by natural factors rather than human factors." The research is published in the journal Wiley Interdisciplinary Reviews: Climate Change.

The new research involved drawing together evidence from more than 100 climate change studies. It showed that, on a global scale, predictions made about the effects of greenhouse gas emissions match actual trends seen over the past 50 years.

Since 1980, average global temperature has increased by about 0.5C. Currently, the Earth is getting warmer at the rate of around 0.16C per decade. The study also found that natural forces such as volcanic eruptions and cyclical changes in the brightness of the Sun could not explain what was happening to the world's climate, he said.

Asked if the new research would help to silence the doubters who question man-made climate change, Dr Stott said: "I just hope people will make up their minds informed by the scientific evidence."