The 2,500 or so scientists, economists and other experts of the U.N. Intergovernmental Panel on Climate Change (IPCC) call global warming "unequivocal" and think it "very likely" that humans have contributed to the problem. The world's governments agree with the panel, which also shared last year's Nobel Peace Prize.

Then there's the Non-Governmental International Panel on Climate Change (NIPCC). These 23 individuals from 15 countries, including a handful of scientists, disagree. Led by physicist S. Fred Singer—best known for his denial of the dangers of secondhand smoke—they argue the reverse: "Natural causes are very likely to be the dominant cause" of climate change.

The NIPCC goes on to contend: "We do not say anthropogenic greenhouse gases cannot produce some warming. Our conclusion is that the evidence shows they are not playing a significant role."

In other words, even skeptics, deniers, contrarians—pick your favorite term—agree that global warming is real, or so it appears from the recent three-day conference in New York City put together by the Heartland Institute, a bastion of free-market thinking on the perils of junk science and government economic regulation. They just disagree—even amongst themselves—whether it is man-made.

On the one side sits Patrick Michaels, the recently resigned state climatologist of Virginia who ascribes global warming to fluctuations in the sun's energy output aided and abetted by human activity. In his conference dinner address, Michaels said: "Global warming is real and people have something to do with it."

On the other side is astrophysicist Willie Soon of the Harvard–Smithsonian Center for Astrophysics in Cambridge, Mass. He lays the blame on the sun for all the agreed-on warming. And meteorologist William Gray of Colorado State University in Fort Collins believes the sun will soon reverse its effect. "We should begin to see cooling coming on," he predicts. "I'm ready to make a big financial bet."

If you are interested in seeing a contrarian in action, here is your chance:

See the president and co-founder of the Heartland Institute, Joseph Bast, explain how the science of climate change is shifting, how a little global warming would be a good thing, and the reason not to vote. (download the original)