ROBERT SIEGEL, HOST:
Tomorrow, most of the world's governments are set to sign the most sweeping climate agreement in history. Their signatures will codify promises they made in Paris last December to reduce emissions of greenhouse gases. The largest sources of those gases are the U.S. and China. NPR's Christopher Joyce reports on their progress in keeping those promises.
CHRISTOPHER JOYCE, BYLINE: For years, the world's nations failed to agree on how to slow climate change. Then just months before the Paris Summit on climate, President Obama and China's Xi Jinping stood side-by-side at the White House and said, we've got this.
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BARACK OBAMA: We're the world's two largest economies, energy consumers and carbon emitters come together like this, then there's no reason for other countries whether developed or developing to not do so as well.
JOYCE: Obama highlighted his clean power plan to cut carbon dioxide from power plants. The Chinese promised to slow the growth of their omissions. That joint declaration paved the way, and the rest of the world made similar pledges in Paris. But since then, the president's clean power plan has fallen from grace.
Kate Larsen is with Rhodium Group, a policy and economics think tank. She says climate experts thought the plan was a sure thing because it didn't require congressional approval.
KATE LARSEN: It was something that looked like a slam dunk, that was really important to show that the U.S. was making progress.
JOYCE: The plan's opponents sued to stop it, and the U.S. Supreme Court has agreed to put it on hold. Obama's Paris pledge would reduce emissions 26 to 28 percent by 2025. The Rhodium Group did the math and concludes that with the clean power plan, the U.S. will come up short, without it, way short.
But Larsen says there are other options beside the clean power plan. Renewable energy is growing way faster than energy experts predicted. That's due largely to Congress, many of whose members don't even believe in climate change.
LARSEN: Congress gave the renewables industry a huge Christmas gift with an extension of the tax credits for solar and wind power.
JOYCE: Those tax breaks enacted last December have helped make solar and wind the leading source of new electricity. So it's tough to say if the U.S. will actually make its goals, but Larsen says the U.S. goals were a stretch anyway, and the rest of the world should understand that.
Now, China - China is the world's leading source of emissions. The government has pledged that emissions there will continue to rise but peak in 2030 and then decline. In fact, they may be way ahead of schedule if you believe the emissions numbers from Chinese officials. Those stats show their emissions have actually declined.
ROB JACKSON: I think that decline is real.
JOYCE: Rob Jackson is a greenhouse gas guru at Stanford University. His research shows that for the past two years, China's emissions flattened and even fell. He says even if China's statistics are off a bit - as they often have been - they signal a shift away from relentless emissions growth.
JACKSON: Emissions are changing in China. Will they peak this year or last year? I don't think so, but I do expect them to increase only a little bit more. They may peak within five years or so.
JOYCE: That depends, of course, on China's economy. It's been tepid lately. If it rebounds, so will omissions. The weather could be a factor, too. China depends a lot on hydropower. A drought could push the country back to coal. So China may be looking good for now, but that could change.
What the U.S. and China do is important, but it won't be enough to stop climate change. Other countries matter as well, in particular India. Its emissions are growing fast. And while its government pledged in Paris to shift to renewable energies as fast as it can, it's not giving up fossil fuels like coal either, not with hundreds of billions of people still without electricity. India could surpass both the U.S. and China in emissions.
JACKSON: What pathway India takes will go a long way to saying where we end up in 10 or 20 years, along with what the U.S. and the EU does and what China does.
JOYCE: Christopher Joyce, NPR News.