For instance, Yeager said that countries that make up the Arctic Council, including the United States, pledged in 2009 to reduce black carbon. But since then, the Obama administration has cut back on domestic efforts to phase out dirtier diesel engines because of budget constraints. Until 2009, Congress had appropriated between $75 million and $150 million for the Diesel Emissions Reduction Act, which gave grants to retire or retrofit polluting diesel vehicles. The program got a boost to $300 million under the American Recovery and Reinvestment Act, but it has not received any more money since.

State Department spokeswoman Emily Cain said the United States has spent $60 million to support methane reduction projects overseas and has pledged to spend an additional $50 million over the next five years. The administration has also committed $5 million to an Arctic Council initiative to reduce black carbon emissions in Russia.

Yeager and Shindell said that reducing methane and soot, while laudable as a short-term strategy for dampening global warming, would not solve the long-term problem.