In June, President Obama broke several years of near silence on how the United States would address climate change. That he did so is notable, but the new plan is mostly the same as the old plan, centered on promoting efficiency and cleaner technologies. Practically nobody is talking about the most important test for Obama’s climate strategy: how it will affect the strategies of other nations.

In 1990, when global warming first rose to prominence as an international issue, the United States could unilaterally set the tone for the world. America was undisputed leader of the global economy and the world’s biggest polluter. Since then, the U.S. share of all gas emissions that cause global warming has dropped from 16 percent to 13 percent. U.S. emissions are now falling, while those from most of the rest of the world, notably China, grow rapidly. Today the global problem is much harder for the U.S. to manage just by changing its policies at home.

The key question for President Obama is whether his new policy can have any impact on other countries. So far, the answer is probably no. U.S. credibility has suffered from the perception that this country is good at criticizing schemes to cut global emissions, such as the Kyoto Protocol, but not very talented at creating alternatives that actually work.

Other countries now understand that political gridlock in Washington makes it hard for American diplomats to promise them anything like backing for a global treaty to cut emissions. It is telling that the new climate plan outlined by President Obama relied mainly on regulatory and funding actions he can take alone, rather than new legislation that would require help from Congress.

There are signs that this strategy might have an effect. In recent months the Obama administration has created new programs with China to study and test low-emission energy technologies. In June the leaders of the two countries agreed to help phase out hydrofluorocarbons, potent global-warming gases used in refrigeration and cooling systems.

The United States is now likely to find it more effective to work with countries individually or in small groups than to focus on large global forums. Smaller forums make it easier to achieve action, and to help other countries find practical ways to coöperate.

Closer to home, the debate over the Keystone XL pipeline that would move crude from Canadian oil sands through the United States may provide the first definite success for that strategy. The pipeline’s fate is in U.S. hands, and although without it, the oil could still travel by alternate routes that bypass the U.S., stalling approval could force the Canadians to promise their own more credible program to cut emissions.

Because emissions anywhere affect the whole planet, every plan, whether conceived by the smallest city or the biggest nation, should be judged by whether it advances the global agenda. On that score, Obama’s new climate plan could signal a fresh start—if it gives the U.S. more practical leverage over the actions of other countries as well as our own.

David G. Victor is a professor at the School of International Relations and Pacific Studies at the University of California, ­​San Diego.