consensus vs. doubt

I was profoundly surprised when I learned that an old friend is still in denial. He concedes the reality of climate change, admits that it has anthropogenic causes, but maintains that "science is still undecided over whether this poses a threat". This may have accurately described the status of climate science in 1975, but forty years later it's just false. Surprising about this declaration of doubt is that this friend is holds a Ph.D. from an excellent university in Scotland and is a senior faculty (full professor) in the humanities. Despite his sterling credentials, he indulges in a skepticism that is nothing but scientific illiteracy.

What can one do with this prejudice? Any rational discussion would have to center on the exact location of doubt. The friend maintains that "according to some scientists, climate change may be good for us." There are two aspects to this. The one is the question of benefits of climate change, and the other is the question of some scientists saying so. Now, it is true that climate change will have positive impacts on some regions, as in the northern latitudes, and in some ways, as over the length of the growing season. But such positive impacts are only of a regional kind and are outweighed by negative impacts not only everywhere else but also in the very regions that partly benefit from the warming climate. Negative impacts in the far north range from direct harms to nonhuman life (disruptions of indigenous ecosystems and extinctions of indigenous species) to indirect harms to local human populations (whose territories will become targets of mass migrations and military annexation when climatic conditions worsen in the south.) If one takes the contention of benefits as an argument, its flaw lies in confusing limited local impacts, which can be positive, with the overall, global, or net impact, which is decidedly negative.

The other aspect is the identification of climate science with "some scientists" who tout the benefits of climate change.  The flaw here is the confusion of individual viewpoints (the notorious three percent of deniers across the sciences) with the collective sum of viewpoints, the scientific consensus. Both confusions are identically flawed; they commit the pars pro toto fallacy, the error of reasoning to mistake a part as the whole.

The US National Aeronautics and Space Administration maintains a wonderfully lucid climate site. The drop-down menu under the heading "facts" in the upper right hand corner leads to NASA's page on the consensus. It cites statements on climate change from 18 national scientific associations. The statements by the largest organization, the American Association for the Advancement of Science (AAAS) and by specialized professional societies, as the American Chemical Society (ACS), the American Geophysical Union (AGU), the American Medical Association (AMA), and the American Physical Society (APS), all express the consensus that climate change is "a growing threat to society" (AAAS); that it is "potentially a very serious problem" (ACS); that it is "negative" (AGU) or "adverse" (AMA); and that it threatens "significant disruptions" (APS).

For philosophers and other colleagues in the humanities, it would be prudent to take these unanimous joint statements at face value. Don't deny the consensus.