Throughout the 20th century, the global economy was fueled by burning coal to run factories and power plants, and burning oil to move planes, trains and automobiles. The more coal and oil countries burned — and the more planet-warming carbon dioxide they emitted — the higher the economic growth.

And so it seemed logical that any policy to reduce emissions would also push countries into economic decline.

Now there are signs that G.D.P. growth and carbon emissions need not rise in tandem, and that the era of decoupling could be starting. Last year, for the first time in the 40 years since both metrics have been recorded, global G.D.P. grew but global carbon emissions leveled off. Economists got excited, but they also acknowledged that it could have been an anomalous blip.