A top NASA climatologist huddled under a tent Tuesday to talk about coal and global warming.

With UNC-Chapel Hill's massive coal-burning cogeneration plant as a backdrop, outspoken NASA scientist James Hansen pushed the university - and others - to take the lead in weaning off of coal as an energy source.

Hansen, who gave a speech and spoke in some classes as well this week, gamely donned a gaudy, yellow "Beyond Coal" T-shirt - the same as those worn by about 15 sign-toting activists - to speak Tuesday as a guest of the local Sierra Club.

That's the organization whose lobbying helped prompt UNC Chancellor Holden Thorp to recently form a new energy task force to examine the university's use of coal and other issues.

Hansen, an internationally recognized expert on global climate change, spoke as rain dropped and slushy ice crunched underfoot. The crux of his argument: The United States needs to wean itself entirely off of coal use, and sooner rather than later. Universities, he said, must take the lead in this venture.