What do scientists that say global warming is not man-made believe?

Answer 1

It is in the nature of scientists that they rarely agree on anything. Scientific reputations and careers are not made by agreeing with the general consensus but by disagreeing and by finding credible reasons for disagreeing. Nevertheless, relatively few research scientists say that global warming is not at least substantially caused by human activities, although only around 47 per cent of economic geologists (typically employed by oil companies and the like) say they believe that global warming is man-made.

One scientist who doubted the consensus of climate scientists was a Physics Professor, Richard Muller. As a long-time critic of government-funded climate studies, he believed that the reality of global warming was exaggerated as a result of errors such as insufficient adjustment for the 'urban island effect'. With the Berkeley Earth Surface Temperature project at the University of California, he set out to address what he called "the legitimate concerns" of sceptics. But Professor Muller unexpectedly told a congressional hearing the work of the three principal groups that have analysed the temperature trends underlying climate science is "excellent ... We see a global warming trend that is very similar to that previously reported by the other groups." Professor Muller acknowledged that previous studies accounted for the urban effect. "Did such poor station quality exaggerate the estimates of global warming?" he asked in his written testimony. "We've studied this issue, and our preliminary answer is no."

Those scientists who have expressed views that still query the conclusions of climate scientists do so not so much because they believe there is evidence against those conclusions, but because they believe they should wait for further evidence before committing to those conclusions.