Report: 97 percent of scientists say man-made climate change is real - Science Fair: Science and Space News - USATODAY.com Forget the four out of five dentists who recommend Trident . Try the 97 out of 100 scientists that believe in man-made climate change. This data comes from a new survey out this week in the Proceedings of the National Academy of Sciences. The study 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.