The cries of protest have been fierce, warning that President Obama’s plan to cut greenhouse gases from power plants will bring soaring electricity bills and even plunge the nation into blackouts. By the time the administration is finished, one prominent critic said, “millions of Americans will be freezing in the dark.”

Yet cuts on the scale Mr. Obama is calling for — a 30 percent reduction in emissions from the nation’s electricity industry by 2030 — have already been accomplished in parts of the country.

At least 10 states cut their emissions by that amount or more between 2005 and 2012, and several other states were well on their way, almost two decades before Mr. Obama’s clock for the nation runs out.

That does not mean these states are off the hook under the Obama plan unveiled this week — they will probably be expected to cut more to help achieve the overall national goal — but their strides so far have not brought economic ruin. In New England, a region that has made some of the biggest cuts in emissions, residential electricity bills fell 7 percent from 2005 to 2012, adjusted for inflation. And economic growth in the region ran slightly ahead of the national average.