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WASHINGTON — The sign is ubiquitous on city buses around the country: “This bus runs on clean burning natural gas.”

But a surprising new report, to be published Friday in the journal Science, concludes that switching buses and trucks from traditional diesel fuel to natural gas could actually harm the planet’s climate.

Although burning natural gas as a transportation fuel produces 30 percent less planet-warming carbon dioxide emissions than burning diesel, the drilling and production of natural gas can lead to leaks of methane, a greenhouse gas 30 times more potent than carbon dioxide. Those methane leaks negate the climate change benefits of using natural gas as a transportation fuel, according to the study, which was conducted by scientists at Stanford University, the Massachusetts Institute of Technology and the Department of Energy’s National Renewable Energy Laboratory.

The study concludes that there is already about 50 percent more methane in the atmosphere than previously estimated by the Environmental Protection Agency, a signal that more methane is leaking from the natural gas production chain than previously thought.

“Switching from diesel to natural gas, that’s not a good policy from a climate perspective,” said the study’s lead author, Adam R. Brandt, an assistant professor in the department of energy resources at Stanford.

But the study does conclude that switching from coal-fired power plants — the nation’s largest source of carbon pollution — to natural gas-fired power plants will still lower planet-warming emissions overall. Natural gas emits just half the carbon pollution of coal, and even factoring in the increased pollution from methane leaks, natural gas-fired plants lead to less emissions than coal over 100 years, the study found.

The report adds weight to efforts by New York and other Northeastern states to push the federal government to regulate methane emissions. Currently, there are no federal regulations on methane emissions from oil and gas production, although some states are considering such rules.

The finding on trucks and buses is a blow to years of public policy efforts to switch the vehicles from diesel to natural gas, an effort aimed at decreasing pollution as well as America’s dependence on foreign oil. President Barack Obama praised natural gas production in his past two State of the Union addresses, and he has noted that natural gas production creates jobs.