An international team of scientists led by Britain's Met Office -- the country's national weather service -- has spent the past year reviewing 110 studies published since 2007 that tracked changes in the earth's climate. Their paper, published in the journal Wiley Interdisciplinary Reviews: Climate Change, concluded that the possibility the world is warming because of natural variations in climate (such as increased volcanic or solar activity) is "increasingly remote." Instead, they firmly pin the blame on man's burning of fossil fuels.
"The science reveals a consistent picture of global change that clearly bears the fingerprint of man-made greenhouse gas emissions," said Peter Stott, head of climate monitoring at the Met Office Hadley Centre for climate research. "Our climate is changing now, and it's very likely human activity is to blame."
Stott says the new Met Office report isn't an attempt to counter this growing wave of skepticism, as the team started work a year ago, long before those so-called Climategate scandals broke. But it is an unashamed attempt to refocus the public debate on the actual science of climate change, rather than claims made about individual scientists in the media. "I hope people will look at that evidence and make up their minds informed by the scientific evidence," he told the Guardian.
His team put together the new set of evidence by comparing computer models of possible causes of climate change, both human and natural, to actual measured changes in air and sea temperature, Arctic sea ice cover, global rainfall patterns and other factors. This forensic technique, known as "optimal detection," reveals how much an observation can be explained by natural changes, such as volcanoes or El Niño, and how much it's attributable to atmospheric increases in carbon dioxide and other greenhouse gases.
The study found that the climate system had changed in ways that closely followed the pattern of man-made climate change predicted by computer models. Human activity, it states, is almost certainly the only explanation for climatic variations recorded across the world -- such as the increase of rain in the northern countries and the decrease in the south, or the retreat of Arctic sea ice.
Stott dismissed a popular idea put forward by many skeptics that changes in the solar radiation (or "global brightening") could be behind the shifts. "There hasn't been an increase in solar output for the last 50 years," he said, "and solar output would not have caused cooling of the higher atmosphere and the warming of the lower atmosphere that we have seen."