Has Global Warming Been Proven?

There are still global warming skeptics:

Jonathan Chait of the New Republic magazine points out that a recent National Journal poll found that 84 percent of House and Senate Republicans surveyed didn't believe that it has been ``proven beyond a reasonable doubt that the Earth is warming because of man-made problems.''

That rather stunning poll result causes one to ask whether these skeptics have even made themselves aware of the Fourth Assessment of the Nobel Prize-winning Intergovernmental Panel on Climate Change. In that report, the panel's 2,000-plus scientists concluded that there was more than a 90 percent chance that human activity was the main cause of global warming over the last half- century.

What do you think?