Inside the US-China agreement on climate change

President Obama looked on during a press conference at the Great Hall of the People in Beijing.HOW HWEE YOUNG/EPA

The United States and China have agreed to work together to rein in carbon emissions and combat climate change. That announcement, made Wednesday, signals a new partnership between the world’s two largest producers of CO2, and it points towards the possibility of a global agreement in 2015.

However, a lot depends on implementation. It’s one thing to establish long-term goals and quite another thing to meet them, especially here in the United States where climate skepticism is widespread and Republican opposition remains firm.

How will the US meet these goals?

The Obama administration has already taken steps to reduce emissions, including new rules for power plants and tightened fuel efficiency standards. But further initiatives may be necessary to meet the new targets, which raises questions about how this agreement will shape US climate policy and what role the Republican-controlled Congress will play.

If Congress won’t pass legislation to help reduce emissions (and early responses suggest little appetite), there’s only so much the president can do on his own. Partly that’s because the president’s power to set domestic policy is always constrained. But even if Obama could develop an effective action plan, there’s no guarantee that future presidents would follow it.

Just because the president has the power to sign executive agreements with other countries doesn’t necessarily mean he has the power to implement them.

What’s in the new agreement?

The United States would cut its carbon emissions between 26 and 28 percent by 2025. China would expand its use of clean energy and ensure that its carbon production stops increasing by around 2030.

The standards are different, because the countries are at very different points in their economic development. But while some had hoped for even more aggressive action, the cuts do seem to be relatively significant.

Didn’t the US just introduce new carbon cuts?

In June, the Environmental Protection Agency released a plan to cut power plant emissions by 30 percent.

This new agreement is much broader. It deals not just with power plants but with all emissions in the United States, whether from utilities, businesses, cars, or otherwise.

How much carbon do the US and China produce?

China is by far the world’s largest emitter of CO2, not least of all because it is the most populous nation.

Fifteen years ago, the United States was the largest producer of CO2 . But since then, emissions from China have more than doubled.