A new survey out this week in the Proceedings of the National Academy of Sciences ... found that 97 percent of scientific experts agree that climate change is very likely" caused mainly by human activity. The report is based on questions posed to 1,372 scientists. Nearly all the experts agreed that it is "very likely that anthropogenic greenhouse gases have been responsible for most of the unequivocal warming of the Earth's average global temperature in the second half of the twentieth century." As for the 3 percent of scientists who remain unconvinced, the study found their average expertise is far below that of their colleagues, as measured by publication and citation rates. In the study, the authors wrote: "This extensive analysis of the mainstream versus skeptical/contrarian researchers suggests a strong role for considering expert credibility in the relative weight of and attention to these groups of researchers in future discussions in media, policy, and public forums regarding anthropogenic climate change." The report comes as the Earth continues to sizzle in 2010. So far, through May, 2010 is the warmest year ever recorded, according to the National Climatic Data Center.