Logic Error--the Whole and the Parts

From Ezra Klein's blog, Brad Plumer has a piece on why cities can't tackle global warming by themselves--an excerpt:

Nate Berg points to an intriguing new paper in the Journal of Urban Economics by McGill’s Adam Millard-Ball that finds two things. First, from analyzing a large sample of localities in California, Millard-Ball found cities that sign climate pledges really do take more steps to reduce their emissions. They have more green buildings. They spend more on biking and walking infrastructure. They capture more methane from landfills. But here’s the hitch: Those cities also tend to have eco-conscious residents and would’ve adopted these measures anyway, even without the plans.

I want to quibble with the last sentence.  Plumer doesn't quote any evidence for it so I'm free to argue the importance of the whole: yes, there's cases where a group action, like a city adopting an environmental plan, is mostly meaningless.  But even in those cases, there's a signaling function, an affirmation of what's important.  It's the same sort of thing as warning labels on cigarette packs and smoking bans; they say that the community disapproved of smoking which has its affect over the long haul.