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Scientists Tout Climate Skepticism at Heartland Conference Kickoff
...Michaels was joined on the platform by other skeptical scientists, including blogger Anthony Watts, who said he believed man-made climate change was occurring until he saw data that indicated temperatures were rising in California's cities but staying largely the same in its rural areas. He said this convinced him that other factors than human emissions were causing the warming.

Tim Ball, a retired climatologist and former professor at the University of Winnipeg, said that the U.N. Intergovernmental Panel on Climate Change and others had not calculated how much the climate is changing naturally, so he said it was impossible to decide how much observed warming might be linked to human emissions.

"You have to know what is happening naturally, and we simply don't," he said. ...