Every year, the United States Department of Energy’s far-flung operations generate millions of tons of climate-warming greenhouse gases. By tightening valves, replacing worn gaskets and such, Josh Silverman and the department’s engineers have managed to cut the annual leaks of one gas by about 35,000 pounds.

Which would seem a pittance. Except that this gas is sulfur hexafluoride, the most potent greenhouse gas in existence — in fact, 23,900 times more potent than carbon dioxide. In three years, they have stanched leaks equivalent to 1.1 million tons of carbon dioxide.

It is as if 200,000 cars were taken off the road for a year. And that is but the beginning. “We’ve cut emissions in half,” Mr. Silverman, who heads the antileak effort as director of the department’s office of sustainability support, said this week in an interview. “The gains are real and sustained, so we’ll continue to see savings.”

It has elevated Mr. Silverman to a finalist for the Service to America Medal, one of the highest honors awarded a federal civil servant. And the accomplishment is all the more remarkable for the fact that a few years ago, nobody suspected that such a leak problem even existed.