Belt and Road

Even if China's domestic climate program is strong, those gains could be erased if the net effect of its infrastructure investments abroad is to establish coal-fired power.

China is in the midst of a massive global infrastructure and trade project known as the Belt and Road Initiative (BRI) that plans $1 trillion to $4 trillion in investment in regions from South Asia and Africa to the European Union.

Kevin Gallagher, a professor of global development policy at Boston University, calls the program "a Marshall Plan on steroids."

"If it could globalize some of its domestic policies through the Belt and Road Initiative, it would really be a great benefit for climate and social inclusion," he said.

But his research shows that the BRI is poised to explode emissions globally, not to limit them.  Almost 80 percent of planned investment from China's overseas development banks has gone to large hydropower plants and coal plants, he said.  Chinese-backed coal plants overseas emit as much carbon dioxide annually as the entire economy of the United Kingdom.

And more is on the way.  Urgewald, a German environmental group, reported earlier this year that Chinese corporations are planning 700 new coal plants in China and abroad — nearly half of what is in the pipeline globally.

In fact, reductions in Chinese coal-fired power at home might create an incentive for Chinese corporations to look for foreign customers to buy their coal and power plant components.

"There's this huge fork in the road," said EDF's Keohane.  If developing countries in Asia and elsewhere follow the Chinese example and modernize on the back of coal, "we're totally hosed," he said.  "We're going to blow through 2 degrees."  The Paris Agreement set that Celsius threshold to avoid catastrophic warming.

Here again, the loss of U.S. leadership could lighten pressure on China to contain its emissions, said Nakano.  Last year, Xi stated as part of his final joint statement on climate change with Obama that "China is taking concrete steps to strengthen green and low-carbon policies and regulations with a view to strictly controlling public investment flowing into projects with high pollution and carbon emissions both domestically and internationally."

Now that calculus might be changing.

"I think now there's no pressure on China to really deliver on that particular commitment," said Nakano.

Read more at Will Xi Help Trump Re-Enter the Paris Agreement?