Texas Gov. Rick Perry has made it clear he doesn't believe that human beings are contributing to global warming, and he expounded on the issue in detail at a campaign stop in Bedford, N.H.



"I do believe that the issue of global warming has been politicized," Perry said. "I think there are a substantial number of scientists who have manipulated data so that they will have dollars rolling into their projects. I think we're seeing it almost weekly or even daily, scientists who are coming forward and questioning the original idea that man-made global warming is what is causing the climate to change."



He added that plans to address climate change by limiting carbon emissions would cost "billions, if not trillions" and that America should not spend that much money on "scientific theory that has not been proven and from my perspective is more and more being put into question."



Perry is the latest candidate to enter the race for the Republican nomination for president, announcing on Aug. 13, 2011, that he is running. Perry has served as the Texas governor since 2000.



So is Perry correct? Is there significant disagreement on the causes of global warming?



We looked at this question in some detail in a previous fact-check on candidate Tim Pawlenty, who has since dropped out of the race. Pawlenty said, "The weight of the evidence is that most of it, maybe all of it, is because of natural causes ... it's fair to say the science is in dispute." We rated that statement False. This report reviews much of the same evidence.



We'll start with the basics.



One of the most oft-cited reports is from the U.N. Intergovernmental Panel on Climate Change (IPCC), a scientific body considered the leading international organization on climate science. It includes the scientific consensus of thousands of researchers from 194 countries.



"Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations," the most recent report states. "The observed widespread warming of the atmosphere and ocean, together with ice mass loss, support the conclusion that it is extremely unlikely that global climate change of the past 50 years can be explained without external forcing, and very likely that it is not due to known natural causes alone." (External forcing refers to anything outside of the normal climate system that changes the climate, including the results of human activity, sunspots or volcanic eruptions.)



In the United States, the U.S. Global Change Research Program coordinates and integrates federal research on climate. Its 2009 report mirrored the IPCC's conclusions: "Observations show that warming of the climate is unequivocal. The global warming observed over the past 50 years is due primarily to human-induced emissions of heat-trapping gases. These emissions come mainly from the burning of fossil fuels (coal, oil, and gas), with important contributions from the clearing of forests, agricultural practices, and other activities."



Earlier this year, a committee organized by the National Research Council and the National Academy of Sciences again reviewed the current research on climate change. The committee concluded that climate change is occurring, that it is caused primarily by the emission of greenhouse gases from human activities, and that it poses significant risks for a range of human and natural systems. It specifically rejected the view that that those findings are in some way questionable.



"Although the scientific process is always open to new ideas and results, the fundamental causes and consequences of climate change have been established by many years of scientific research, are supported by many different lines of evidence, and have stood firm in the face of careful examination, repeated testing, and the rigorous evaluation of alternative theories and explanations," the committee said.



We asked the Perry campaign for comment on this, but we didn't hear back. In response to similar questions from the Washington Post, the Perry campaign pointed to various writings questioning climate change. But the Post's report noted these writings were anecdotal and "not evidence of the groundswell of opposition suggested by Perry." We concur.



To be clear, we're not saying that no scientists -- as in zero -- dispute climate change is caused by human activity. We looked into the work of the most prominent and best credentialed people who have questioned the IPCC's conclusions on global warming. Generally speaking, even these scientists do not claim that humans are making no contribution at all to rising temperatures. Rather, they tend to make more nuanced points. They question whether carbon emissions alone are driving up temperatures, or whether other human activities contribute as well. They question whether extreme weather events such as storms or floods can be conclusively linked to rising temperatures. And, they question whether significant changes to public policy are necessary as a means of coping with rising temperatures.



Climate change skeptics also have their own petition, commonly called the Oregon petition, that has been endorsed by 31,000 signers opposing restrictions on carbon emissions. But that petition has been criticized for not checking the credentials of its signatories or even proving that all the signatories exist.



Several scientific studies have attempted to quantify just how much agreement there is among scientists when it comes to climate change.



A 2010 study published in the Proceedings of the National Academy of Sciences -- the official publication of the United States National Academy of Sciences -- found that out of 1,372 climate researchers under review, approximately 97 to 98 percent of those actively publishing in the field said they believe human beings are causing climate change, which they term anthropogenic (i.e., man-made) climate change. It also concluded that "the relative climate expertise and scientiﬁc prominence" of the researchers unconvinced of man-made climate change are "substantially below that of the convinced researchers."



An earlier survey published in the 2009 issue of Eos -- a publication of the American Geophysical Union -- asked scientists from a wide range of disciplines (approximately 3,146): "Do you think human activity is a significant contributing factor in changing mean global temperatures?" Approximately 82 percent of the surveyed scientists answered yes to this question. Of those climate change specialists surveyed, 97.4 percent answered yes.



Perry also charged that scientists have been manipulating data. He could be referring to a 2009 incident when stolen e-mails from the Climatic Research United at the University of East Anglia were released on the Internet. Global warming skeptics said the e-mails showed climate researchers were manipulating data.



But several inquiries debunked those allegations, including investigations by the British Parliament, the U.S. Department of Commerce, Pennsylvania State University and the InterAcademy Council. The inquiries found that, while the scientists had made rude remarks about people who questioned climate change, they were not falsifying data. Some of the investigations recommended greater transparency and sharing of climatic data, but the independent investigations exonerated the researchers of falsifying data.



Perry's remarks give the impression that the science of global warming is in dispute, that some scientists feel one way, and some scientists feel another way. He says that skepticism is growing. In fact, our research shows that's not the case. We found that there is solid consensus among the major scientific organizations and that the skeptics seems to be small minority. We rate his statement False.