Climate scientists hit back at sceptics with new research
Climate scientists hit back at the sceptics yesterday 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.
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."
Publication of the research in the journal Wiley Interdisciplinary Reviews: Climate Change comes at the height of controversy over the reliability of climate science.
Scientists have found themselves on the ropes after the University of East Anglia emails scandal, and criticism of the Intergovernmental Panel on Climate Change.
Two inquiries are now being held into accusations based on leaked emails that UEA scientists manipulated and suppressed climate change data.
In a separate set-back for the scientists, the IPCC - whose researchers influence global government policy - admitted it had issued flawed information about the rate at which Himalayan glaciers were melting.
The new research involved drawing together evidence from more than 100 climate change studies, many of which were conducted since the last major IPCC report in 2007.
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 0.5˚C. Currently, the Earth is getting warmer at the rate of around 0.16˚C per decade.
These trends are reflected in recent measurements from deep below the surface of the oceans. In all the large ocean basins - the Atlantic, Pacific and Indian - the same warming pattern is seen.
"Over 80 per cent of the heat trapped in the climate system, as related to greenhouse gases, is being exported into the oceans, and we can see that happening," said Dr Stott.
Warmer temperatures had led to more evaporation from the surface of the oceans, most noticeably in the sub-tropical Atlantic, he said. As a result, the sea was getting saltier.
Evaporation in turn affected humidity and rainfall. The atmosphere was getting more humid, as climate models had predicted, and amplifying the water cycle.
What this meant was that more rain was falling in high and low latitudes and less in topical and sub-tropical regions around the equator.
"The whole of the water cycle is changing," said Dr Stott, speaking at the Science Media Centre in London. "Wetter regions are getting wetter and dry regions are getting drier."
The study 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. For example, solar heating would have warmed both upper and lower layers of the atmosphere, the stratosphere and troposphere. But what was seen was that the stratosphere had cooled while the troposphere had warmed.
Warming due to Sun would also have caused temperatures to increase more rapidly early than late in the 20th century - the reverse of what actually occurred.
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."
He added: "The science reveals a consistent picture of global change that clearly bears the fingerprint of man-made greenhouse gas emissions.
"This shows the evidence of climate change has gone beyond temperature increases - it is now visible across our climate system and all regions of the planet. Our climate is changing now and it's very likely human activity is to blame."
Summer minimum levels of Arctic sea-ice were declining at a rate of 600,000 square kilometres per decade, an area about the size of Madagascar, studies showed.
In the Antarctic there had been a small increase in sea ice extent since satellite records began in 1978. This was consistent with the combined effects of greenhouse gas increases and reductions in the ozone layer.
Over the past 100 years, global temperatures had increased by about 0.75˚C, said the scientists. The last 10 years had been the warmest on record, with human influence detected on every continent.