When President Bush plucked him from civil service obscurity in 2005 to run the Environmental Protection Agency, Stephen Johnson probably never imagined that he would someday find himself at the center of the policy struggle over global warming. But that is where he is now, courtesy of the Supreme Court’s ruling in March that greenhouse gases could be regulated under the Clean Air Act, a law administered by the E.P.A. Unfortunately, Mr. Johnson and the agency have not done anything meaningful since.

Mr. Johnson is now being challenged again. Last week, five states, New York City and four environmental groups petitioned the E.P.A. to force the nation’s airlines to reduce their emissions of carbon dioxide and other greenhouse gases. In early October, the same groups petitioned the agency to regulate emissions from large, ocean-going ships.

Aircraft account for 3 percent of total United States emissions of carbon dioxide and 12 percent of emissions from transportation sources, but they are growing rapidly. According to a recent report from a British royal commission, airplanes also generate ozone-forming pollutants and water vapor that together could triple the effect of aircraft-emitted carbon dioxide. The report’s authors suggested various ways to curb emissions, including the use of lighter and more efficient aircraft and operational measures to cut distances and flying times.

This is Mr. Johnson’s responsibility. The Supreme Court’s ruling that the E.P.A. could regulate carbon dioxide and other greenhouse gases  a position that had been opposed by the White House  applied specifically to automobile emissions. But it clearly inferred that the agency had the power to regulate greenhouse gases from other sources, including power plants, ships and jets.