There is no question the earth has been warming. It is coming out of the "Little Ice Age," he said in an interview this week.
"However, there is no credible evidence that it is due to mankind and carbon dioxide. We've been coming out of a Little Ice Age for 300 years. We have not been making very much carbon dioxide for 300 years. It's been warming up for a long time," Bryson said.
The Little Ice Age was driven by volcanic activity. That settled down so it is getting warmer, he said.
Humans are polluting the air and adding carbon dioxide to the atmosphere, but the effect is tiny, Bryson said.
"It's like there is an elephant charging in and you worry about the fact that there is a fly sitting on its head. It's just a total misplacement of emphasis," he said. "It really isn't science because there's no really good scientific evidence."