A recent press release from "The U.S. Senate Committee on Environment and Public Works" detailed how many former "pro global warming" scientists have changed their minds, and are now skeptics.
Dr. David Evans, a mathematician and engineer who formerly did carbon counting for the Australian government, gave a credible, logical reason for his conversion:
“I devoted six years to carbon accounting, building models for the Australian government to estimate carbon emissions from land use change and forestry. When I started that job in 1999 the evidence that carbon emissions caused global warming seemed pretty conclusive, but since then new evidence has weakened the case that carbon emissions are the main cause. I am now skeptical,” Evans wrote in an April 30, 2007 blog.
“But after 2000 the evidence for carbon emissions gradually got weaker -- better temperature data for the last century, more detailed ice core data, then laboratory evidence that cosmic rays precipitate low clouds,” Evans wrote.
“As Lord Keynes famously said, ‘When the facts change, I change my mind. What do you do, sir?’”
Other experts quoted in the article include Dr. Claude Allegre, a top French geophysicist; geologist Bruno Wiskel of the University of Alberta; Dr. Nir Shaviv, a top Israeli scientist; Dr. Tad Murty, former Science Research Scientist for Fisheries and Oceans in Canada; Dr. David Bellamy, UK botanist; Dr. Chris de Freitas, climate scientist at the University of Auckland, NZ; meteorologist Dr. Reid Bryson; Hans H.J. Labohm, global warming author and economist; paleoclimatologist Tim Patterson of Carlton University in Ottawa; physicist Dr. Zbigniew Jaworowski, chairman of the Central Laboratory for the United Nations Scientific Committee on the Effects of Radiological Protection in Warsaw; paleoclimatologist Dr. Ian D. Clark, professor of the Department of Earth Sciences at University of Ottawa; environmental geochemist Dr. Jan Veizer, professor emeritus of University of Ottawa...
You get the idea. There's a lot of 'em, and they have very impressive credentials.