The survey of 3,146 earth scientists from around the world found overwhelming agreement that in the past 200 years, mean global temperatures have been rising, and that human activity is a "significant contributing factor" in changing mean global temperatures.
Peter Doran, an associate professor of earth and environmental sciences at the University of Illinois at Chicago, along with former graduate student Maggie Kendall Zimmerman, conducted the survey late last year.
The findings appeared Monday in the journal "Eos, Transactions," a publication of the American Geophysical Union.
"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," the researchers conclude.
There are many human activities and natural processes that contribute to climate change. Burning coal, oil and gas to generate electricity or to power cars, trucks, trains, planes and ships releases greenhouse gases that blanket the planet, keeping the Sun's heat from radiating back into space.
Cutting forests prevents the trees from absorbing the main greenhouse gas, carbon dioxide. Methane, an even more potent greenhouse gas, is given off by landfills, coal mines, oil and natural gas operations, agriculture, and melting permafrost.
Natural causes also exist. For instance, volcanoes can affect the climate because they can emit aerosols and carbon dioxide into the atmosphere.
Greenhouse gases rise from a petrochemical refinery in Edmonton, Alberta, Canada. (Photo by Wolfgang Schlegl)
To overcome criticism of earlier attempts to gauge the view of earth scientists on global warming and the human impact factor, Doran and his team sought the opinion of the most complete list of earth scientists they could find, contacting more than 10,200 experts listed in the 2007 edition of the American Geological Institute's "Directory of Geoscience Departments."
Experts in academia and government research centers were e-mailed invitations to participate in the on-line poll conducted by the website www.questionpro.com.
Only those invited could participate and computer IP addresses of participants were recorded and used to prevent repeat voting. Questions used were reviewed by a polling expert who checked for bias in phrasing, such as suggesting an answer by the way a question was worded. The nine-question survey was short, taking just a few minutes to complete.
The 3,146 participating scientists were asked two key questions - "Have mean global temperatures risen compared to pre-1800s levels?" and, "Has human activity been a significant factor in changing mean global temperatures?"
About 90 percent of the respondents agreed with the first question and 82 percent the second.
Doran determined that climatologists who are active in research showed the strongest consensus on the causes of global warming, with 97 percent agreeing humans play a role.
Petroleum geologists and meteorologists were among the biggest doubters, with only 47 and 64 percent, respectively, believing in human involvement.
Doran compared their responses to a recent poll showing only 58 percent of the public thinks human activity contributes to global warming.
"The petroleum geologist response is not too surprising, but the meteorologists' is very interesting," he said. "Most members of the public think meteorologists know climate, but most of them actually study very short-term phenomena."
Doran was not surprised by the near-unanimous agreement by climatologists.
"They're the ones who study and publish on climate science," he said. "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."
The challenge now, the researchers say, is how to effectively communicate this to policy makers and to a public that continues to mistakenly perceive debate among scientists.
They can draw support from a statistical study published earlier this month by scientists in Germany and Switzerland who determined that the global increase of warmer years after 1990 is no accident.
The likelihood that the 13 warmest years since 1880 could have occurred after 1990 by accident is no more than one in 10,000, they conclude. Or, in other words, the likelihood is the same as tossing 14 heads in a row in a coin toss.
"Our study is of a purely statistical nature and cannot attribute the increase of warm years to individual factors," said Dr. Eduardo Zorita at the GKSS Research Center in Geesthacht, Germany.
"But it is in full agreement with the results of the Intergovernmental Panel on Climate Change that the increased emission of greenhouse gases is mainly responsible for the most recent global warming," he said.
The results of the statistical study will be published in the journal "Geophysical Research Letters."
However, some scientists are still climate skeptics. More than 650 dissenting scientists are listed in a report released January 14 by the U.S. Senate Environment and Public Works Committee's office of the Ranking Member Republican James Inhofe of Oklahoma.
A typical comment is that of physicist Dr. Will Happer, a professor at the Department of Physics at Princeton University and former director of energy research at the U.S. Department of Energy, who is quoted in the Inhofe report as saying, "I am convinced that the current alarm over carbon dioxide is mistaken. ... Fears about man-made global warming are unwarranted and are not based on good science."
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