Global warming talks in Paris next year have a better chance of reaching a productive conclusion now that the two biggest economies in the world, which also happen to be the two biggest climate polluters, have promised to curb greenhouse gases dramatically by 2030. But the questions other nations will be asking as they analyze the forward-looking agreement reached by U.S. President Barack Obama and Chinese President Xi Jinping are exactly how they intend to achieve these ambitious goals and, indeed, whether they will be able to carry out their promises.

The latter question applies especially to Obama, who already faces opposition to the deal from Republican lawmakers, who will soon control both houses of Congress. Though the president has been accelerating the nation’s battle against climate change, particularly targeting emissions from coal plants, there are limits to what he can achieve through executive action without cooperation from Congress. What’s more, there are no guarantees that future presidents will adhere to his nonbinding commitments.

It is in ways easier for China, which is now by far the biggest emitter of greenhouse gases, to meet its goals. The country is already under pressure from its own citizens to clean up its terrible air pollution problems. And it has been building solar energy capacity at a fast pace, so meeting its goal of 20 percent renewable power by 2030 should be achievable. It would also have to cap greenhouse gas emissions by that year.

Xi also has more flexibility than Obama; China is not a democratic power, which means that Xi doesn’t contend with term limits or open elections. That may not make for good government, but it does make his job easier.

On this side of the Pacific Ocean, incoming Senate Majority Leader, Mitch McConnell, who represents the coal-producing state of Kentucky, already is complaining that China doesn’t have to do anything for 16 years under the deal, while the U.S. is making more immediate commitments. That’s neither fair nor accurate. It will take tremendous planning for China, which has been increasing its reliance on coal along with its commitment to solar, to start applying the brakes to that momentum.

Conservative Republicans seem to see the battle against climate change as a costly and unnecessary war on cheap and plentiful energy. (Then, of course, there’s Republican Sen. Jim Inhofe of Oklahoma, who has called the very idea of man-made climate change a hoax, and who is about to take the chairmanship of the Senate Environment and Public Works Committee.) In truth, there is a dollar cost either way, and studies estimate that the price of ignoring climate change in the form of flood, drought, crop loss and so forth is far higher than that of doing something about it.