New York Mayor Bill de Blasio called it "an extraordinarily effective act" -- the Vatican's move to draw together 60 mayors from around the world to sign a statement today that "human-induced climate change is a scientific reality and its effective control is a moral imperative for humanity." 

Of course, it's easy to be skeptical of the value of high-minded but non-binding statements like this one. But on a number of counts, it seems to be a very smart form of political engagement.

First of all, it's meant that Pope Francis's encyclical Laudato Si' is playing on the evening news once again in 60 cities, and then some. Second is that the national leaders who've been slow to respond to global warming are being circumvented with a pitch to big-city mayors , who have to deal up close with poverty and the extremes of weather that may be caused by climate change. And, depending on the country and region, the mayors do have local authority in such areas as transportation, local real estate development, taxes and so forth. The mayors can push their national governments to do more--and they gain some political cover by being able to portray themselves as carrying out the mission of  a popular pope. De Blasio, who is not affiliated with any religion, described Francis in his speech at the conference as "the highest moral authority." 

It's worth noting, as the Guardian did, that all of the U.S. mayors who participated--they included Betsy Hodges of Minneapolis; Ed Murray of Seattle; Edwin Lee from San Francisco; Mitch Landrieu from New Orleans and Boston's  Martin Walsh--were Democrats. "While some Republican mayors were invited to attend the function, a person familiar with the organisation of the conference said that none accepted," the Guardian reported.

Whether Francis's visit to the U.S. in September can help to encourage a consensus remains to be seen.