Climate scientists have estimated that, in order to avoid runaway global warming, the world would need to cut its carbon emissions roughly in half by 2050. Since emissions in developing countries like China and India are still rising fast, meeting this target would require developed nations to aim for a figure more like 80 percent. When you consider that the United States, the largest polluter in the developed world, has no real strategy in place to achieve that -- and that no binding international agreements appear to be on the horizon -- the goal can start to sound nigh impossible.

The task is so intimidating that even serious people are starting to entertain extreme-sounding geoengineering ideas like flying business jets into the stratosphere and spraying sulfuric acid all over the place to try to deflect sunlight before it reaches the Earth. Others reckon it’s already too late to prevent catastrophic warming -- we’ll have to build sea walls and hope for the best. President Obama alluded to a possible cap-and-trade system in Tuesday’s State of the Union address, but few believe such a sweeping policy would pass Congress.

Yet in a report released on Thursday, the nonprofit Urban Green Council makes the case that the country’s largest population centers needn’t rely on a federal breakthrough. Specifically, the 51-page report, titled “90 by 50,” finds that New York City could slash its emissions by a whopping 90 percent by 2050 without any radical new technologies, without cutting back on creature comforts, and maybe even without breaking its budget.

That’s a far more aggressive target than even the city’s own relatively ambitious goal of reducing emissions by 30 percent by 2030. How is it possible? The strategy has plenty of familiar components -- electrifying the transit system, converting to renewable power sources. But it all hinges on one seemingly mundane yet surprisingly potent move: retrofitting almost every building in the city to keep the heat in during the winter and out during the summer. In a nod to Rudy Giuliani, Bill Bratton, and James Q. Wilson, I’ll call it the “triple-pane-windows theory” of greenhouse-gas reduction.