Treaty supporters say that just about all the scientists engaged in global warming research now accept that the problem is real and must be addressed. Well, yes and no. Most (but by no means all) scientists engaged in the field agree that industrial emissions are probably affecting the climate. But the evidence is circumstantial. As the United Nations’ International Panel on Climate Change (IPCC) noted in its most recent (1995) report, the evidence thus far “cannot be considered as compelling evidence of cause‐and‐effect link between anthropogenic forcing and changes in the Earth’s surface temperature.”
The “balance of evidence suggests” (in the words of the IPCC) that industrial emissions are the culprit, but that’s hardly conclusive. And the consensus about the matter is not as nearly universal as suggested. Seventeen thousand scientists (half of whom are trained in physics, geophysics, climate science, meteorology, oceanography, chemistry, biology or biochemistry) recently signed a petition written by Frederick Seitz, a past president of the National Academy of Sciences, declaring that there is no compelling evidence to justify reducing greenhouse gas emissions at all.
Nor do scientists agree on how hot it would get if we did nothing. The IPCC’s “best guess” back in 1990 was that industrial greenhouse gas emissions would increase average global temperatures by 5.8 degrees (all temperature figures are Fahrenheit) by the end of the next century. In 1995 the IPCC adjusted its “best guess” down to 3.6 degrees. Three studies published this year (by Hansen, Dlogokencky and Myhre) suggest that the present “best guess” stands at about 2.25 degrees of warming by the end of the next century. Most experts doubt that that amount of warming would be particularly worrisome (indeed, we’re already about half way there temperature‐wise, and the effect of this “global warming” has thus far proven underwhelming, to say the least).