DURING HIS confirmation hearing Thursday, Sen. John Kerry (D-Mass.), President Obama’s pick to be the next secretary of state, said that he intends to press China on climate change. The rapidly developing behemoth, he noted, “is soon going to have double the emissions of the United States.” His words are a welcome dose of reality.

In 2007 China blew past the United States as the largest emitter of greenhouse gases. Large, developing countries, particularly China and India, are projected to be responsible for a significant amount of the growth in global emissions over coming decades. These nations’ rapid economic expansion, which is pulling millions out of poverty, requires cheap energy. It’s little surprise, then, that China gets roughly 70 percent of its energy from abundant, dirty coal and has continued to build coal-fired power plants.

These facts have led some to argue not only that climate change is an issue for the secretary of state as much as it is for the head of the Environmental Protection Agency but also that the United States should not act until it has ironclad assurances that other big emitters will move with comparable ambition. Following Mr. Obama’s promise, in his second inaugural address, to deal with climate change, Sen. Charles E. Grassley (R-Iowa) told NPR that “individual legislation for the United States” was inappropriate absent a worldwide “treaty.” While it would be heartening if Mr. Grassley favors an international climate-change pact, his conclusion is wrong.

The record suggests that the world is more likely to approach the climate issue with a bundle of national policies, rather than a comprehensive, top-down climate pact. Decades of effort have resulted in a stagnant debate but a surprising amount of movement within many countries absent a mutually binding accord. Even China has advanced modest medium-term emissions targets, has negotiated directly with the United States on climate commitments and appears willing to tie promotion within Communist Party ranks to meeting stated environmental goals.

The problem is that this collection of policies is still small compared with the scale of emissions cuts scientists recommend. Much harder choices lie ahead for national leaders balancing short-term growth against long-term ecological concerns. One major reason for that is that the United States has not led. The nation is finally on a downward emissions trajectory, but the political debate gives little hope that the national commitment to long-term emissions cuts is durable. If we have reason to mistrust the Chinese on this, the Chinese have reason to mistrust us.

Passing national climate legislation would remove one of the most potent excuses the Chinese have not to do more. American diplomats such as Mr. Kerry would be able to apply pressure without remaining open to charges of American hypocrisy. Sticks as well as carrots would be available. If Congress enacted a carbon tax, lawmakers could include a border adjustment on imports from countries that lack comparable policy.

China’s growing emissions are a big problem. But they should not be another excuse for congressional inaction.