A U.S. blog site called stopgreensuicide posted the 14-chapter draft report, which then showed up on another site critical of climate science, the Australian Broadcasting Corp. reported Friday.
One section of the draft was highlighted by the leaker and other climate skeptics to suggest cosmic rays from the sun may have a greater influence on warming than had been claimed, ABC said.
Steve Sherwood, lead author of the highlighted chapter and the director of the Climate Change Research Centre at the University of New South Wales, said the idea the chapter confirms a greater role for solar and other cosmic rays in global warming is "ridiculous."
"I'm sure you could go and read those paragraphs yourself and the summary of it and see that we conclude exactly the opposite -- that this cosmic ray effect that the paragraph is discussing appears to be negligible," he said.
"What it shows is that we looked at this. We look at everything."
Research has disproved the idea sunspots are more responsible for global warming than human activity, he said.