In a bleak finding for environmentalists, Larsen and his colleagues found that a future “worst-case” scenario far exceeded the “best case.” Even if President Trump does not succeed in fully dismantling every Obama-era climate policy, the United States will still fail to make its Paris target, cutting greenhouse-gas pollution by only 20 percent by 2025.

But if the White House succeeds in totally destroying U.S. climate policy, and renewable energy does not mature as quickly as anticipated, then U.S. emissions could far undershoot their target, declining by only 12 percent, according to the report. That would mean the U.S. will not even come halfway to making its Paris goals.

If the United States fails to make its Obama-era climate targets, it will not be alone. Germany will not meet its 2020 climate goals, though it aimed for reductions far more ambitious than the United States.

Even if all the countries of the world managed to make their Paris targets, the world would still fail to prevent the world’s average temperature rising by two degrees Celsius. Countries have simply not pledged to reduce their greenhouse-gas emissions fast enough to meet that goal.

“The Rhodium Group is a serious outfit that does really impressive work,” said Zeke Hausfather, a research scientist at Berkeley Earth who was not connected to the report.

He said the study reached the same conclusions as most energy analysts. “Cheap natural gas and renewables will continue to force out coal, leading to reducing emissions in the power sector. But emissions will stay mostly flat in the transportation sector.”

Still, faced with these lackluster findings, climate advocates have turned to two more hopeful storylines. First, they argue that states and cities are beginning to pass climate laws of their own. They have formed We Are Still In, which claims to represent 171 million people and 34 percent of the U.S. economy.

Larsen said that state action was good—but there needed to be more of it. “California’s doing everything it can do. They’re going to keep trying new stuff, but they’re in their own league,” he told me.

States in the Northeast could be far more aggressive, he said. They could try encouraging public-transit use or promoting electric-car ownership. And in New England—where many homes still run oil-burning furnaces through the winter—local governments could subsidize the purchase of new electric heaters.

“States, whether or not they succeed, need to try to get at this stuff,” Larsen said. “By trying new stuff in the hope that something works, it’s laying the groundwork for the next wave of federal action.”

Second, climate advocates argue that renewable energy is getting cheaper faster than anyone has anticipated.

“There’s this idea in the power sector that technology is going to save us, that renewables are getting cheaper way faster than predicted,” Larsen said. “What we find is: Yes, emissions could go down faster and more dramatically than anybody expected. However, there is a limit to that success.”