The answer is, the usual suspects: greed and cowardice.

If you want to understand opposition to climate action, follow the money. The economy as a whole wouldn’t be significantly hurt if we put a price on carbon, but certain industries  above all, the coal and oil industries  would. And those industries have mounted a huge disinformation campaign to protect their bottom lines.

Look at the scientists who question the consensus on climate change; look at the organizations pushing fake scandals; look at the think tanks claiming that any effort to limit emissions would cripple the economy. Again and again, you’ll find that they’re on the receiving end of a pipeline of funding that starts with big energy companies, like Exxon Mobil, which has spent tens of millions of dollars promoting climate-change denial, or Koch Industries, which has been sponsoring anti-environmental organizations for two decades.

Or look at the politicians who have been most vociferously opposed to climate action. Where do they get much of their campaign money? You already know the answer.

By itself, however, greed wouldn’t have triumphed. It needed the aid of cowardice  above all, the cowardice of politicians who know how big a threat global warming poses, who supported action in the past, but who deserted their posts at the crucial moment.

There are a number of such climate cowards, but let me single out one in particular: Senator John McCain.

There was a time when Mr. McCain was considered a friend of the environment. Back in 2003 he burnished his maverick image by co-sponsoring legislation that would have created a cap-and-trade system for greenhouse gas emissions. He reaffirmed support for such a system during his presidential campaign, and things might look very different now if he had continued to back climate action once his opponent was in the White House. But he didn’t  and it’s hard to see his switch as anything other than the act of a man willing to sacrifice his principles, and humanity’s future, for the sake of a few years added to his political career.

Alas, Mr. McCain wasn’t alone; and there will be no climate bill. Greed, aided by cowardice, has triumphed. And the whole world will pay the price.