Other things equal, more G.D.P. tends to mean more pollution. What transformed China into the world’s largest emitter of greenhouse gases? Explosive economic growth. But other things don’t have to be equal. There’s no necessary one-to-one relationship between growth and pollution.

People on both the left and the right often fail to understand this point. (I hate it when pundits try to make every issue into a case of “both sides are wrong,” but, in this case, it happens to be true.) On the left, you sometimes find environmentalists asserting that to save the planet we must give up on the idea of an ever-growing economy; on the right, you often find assertions that any attempt to limit pollution will have devastating impacts on growth. But there’s no reason we can’t become richer while reducing our impact on the environment.

Let me add that free-market advocates seem to experience a peculiar loss of faith whenever the subject of the environment comes up. They normally trumpet their belief that the magic of the market can surmount all obstacles — that the private sector’s flexibility and talent for innovation can easily cope with limiting factors like scarcity of land or minerals. But suggest the possibility of market-friendly environmental measures, like a carbon tax or a cap-and-trade system for carbon emissions, and they suddenly assert that the private sector would be unable to cope, that the costs would be immense. Funny how that works.

The sensible position on the economics of climate change has always been that it’s like the economics of everything else — that if we give corporations and individuals an incentive to reduce greenhouse gas emissions, they will respond. What form would that response take? Until a few years ago, the best guess was that it would proceed on many fronts, involving everything from better insulation and more fuel-efficient cars to increased use of nuclear power.

One front many people didn’t take too seriously, however, was renewable energy. Sure, cap-and-trade might make more room for wind and the sun, but how important could such sources really end up being? And I have to admit that I shared that skepticism. If truth be told, I thought of the idea that wind and sun could be major players as hippie-dippy wishful thinking.