But it makes me wonder: if all of these facts are acknowledged right there in their own articles, why are the agreement’s supporters bursting with triumphalism?

To begin with, it serves an immediate practical purpose. Consider Obama’s pronouncement that the agreement is “a testament to American leadership.” “We came together around a strong agreement the world needed. We met the moment.” For a president whose administration is known for the absence of American leadership and who is palpably not “meeting the moment,” you can see the incentive to pretend that he is by signing some phony-baloney agreement to solve a phony-baloney problem…

But there’s more to it than that, because the feverish excitement, the boosterism, the triumphalism are real and extend beyond those with an immediate financial incentive to jump on the bandwagon. They actually seem to feel they are doing something big, historic, important, and transformative. Yes, to some extent it’s all a con, but they’re also conning themselves.

I suspect the reason for the excitement is that these people really take their favorite idea of “consensus” seriously. It’s not just a talking point; it’s something with personal psychological meaning to them. So it matters less to them whether they actually got a practical result in the latest talks. What matters, and what has them so giddy, is that they got a lot of people to sit down and agree with one another — including, most notably, big developing nations like China and India — even if they committed to nothing specific.