Peter Doran, University of Illinois at Chicago associate professor of earth and environmental sciences, along with former graduate student Maggie Kendall Zimmerman, conducted the survey late last year.

They found that a group of 3,146 earth scientists around the world overwhelmingly agreed that in the past 200-plus years, mean global temperatures had been rising, and that human activity was a significant contributing factor in changing mean global temperatures.

With a view to avoid criticism of earlier attempts to gauge the view of earth scientists on global warming and the human impact factor, the researchers sought the opinion of the most complete list of earth scientists they could find.

The team contacted over 10,200 experts around the world, listed in the 2007 edition of the American Geological Institute’s Directory of Geoscience Departments.

Describing their study in Eos, Transactions, American Geophysical Union, the researchers said that they even e-mailed to experts in academia and government research centres invitations to participate in the on-line poll conducted by the website questionpro.com.

They revealed that only those invited could participate and computer IP addresses of participants were recorded and used to prevent repeat voting.

They further revealed that a polling expert reviewed the questions, and checked for bias in phrasing, such as suggesting an answer by the way a question was worded.

Two questions were key: have mean global temperatures risen compared to pre-1800s levels, and has human activity been a significant factor in changing mean global temperatures.

The researchers found that about 90 per cent of the scientists agreed with the first question and 82 per cent the second.

Doran said that climatologists active in research showed the strongest consensus on the causes of global warming, with 97 per cent agreeing humans play a role, and that petroleum geologists and meteorologists were among the biggest doubters, with only 47 and 64 per cent respectively believing in human involvement.

He compared their responses to a recent poll showing only 58 per cent of the public thinks human activity contributes to global warming.

"The petroleum geologist response is not too surprising, but the meteorologists'' is very interesting. Most members of the public think meteorologists know climate, but most of them actually study very short-term phenomenon," he said.

Doran said that he was not surprised by the near-unanimous agreement by climatologists.

"They’re the ones who study and publish on climate science. So I guess the take-home message is, the more you know about the field of climate science, the more you’re likely to believe in global warming and humankind’s contribution to it," he said.

The researchers concluded: "The debate on the authenticity of global warming and the role played by human activity is largely nonexistent among those who understand the nuances and scientific basis of long-term climate processes."