The alliance includes California, Colorado, Connecticut, Delaware, Hawaii, Massachusetts, Minnesota, New York, North Carolina, Oregon, Rhode Island, Vermont, Virginia and Washington; plus Puerto Rico. All but two states are led by Democratic governors.
Yet there’s a caveat to this announcement: Because the states in the alliance only represent 36 percent of the nation’s population, the United States as a whole is still expected to fall short of Mr. Obama’s pledge. A previous Rhodium Group analysis estimated that total United States emissions would likely drop just 15 to 19 percent by 2025 as Mr. Trump dismantled federal climate policies.
For the country to meet its commitments under the Paris agreement, further action by states would be needed. The alliance could try to persuade other governors to ratchet up their ambitions, though those prospects are uncertain, since barriers to climate policy in Republican-leaning states are often as much political as technical. Or the alliance states could pursue even deeper cuts themselves. But here, experts say, they may face practical limits on how far they can go to tackle global warming on their own.
What States Can, and Can’t, Do
In theory, state governments have plenty of ways to cut emissions without federal help. They can require electric utilities to use more renewable power, modify building codes and impose tougher efficiency standards on appliances. They can shape transportation infrastructure. California is allowed to require automakers to sell more electric vehicles, and any state can join its program, as several in the Northeast have done.
Within the climate alliance, most of the efforts to date have focused on cleaning up electric grids. Collectively, emissions from electricity in the alliance states are expected to drop by half between 2005 and 2025, the Rhodium Group analysis found.
But many experts consider these changes in the power sector the low-hanging fruit of climate policy, aided by a boom in natural gas production that has forced many coal plants into early retirement. The real test, analysts say, will come as states try to juggle ever-greater shares of intermittent renewable power and tackle other, harder-to-decarbonize sectors like transportation and industry.
Here, the outlook is murkier. According to the Rhodium Group, emissions from cars and trucks in the alliance states are expected to fall just 18 percent by 2025. By contrast, emissions from sectors like buildings, heavy industry and agriculture are hardly expected to decline at all. These sectors are expected to make up more than 60 percent of alliance states’ emissions by 2025.
That hints at one limit states may face in pursuing further climate action. New technologies — like better batteries to help integrate wind and solar, or carbon capture for cement plants — could make the task of deeper decarbonization easier. But historically, the federal government has led the way in researching and developing these technologies. And with the Trump administration proposing deep cuts in federal energy research, it is unlikely that process will speed up anytime soon.
“I see state action as important, but ultimately, if we’re serious about deep decarbonization, the federal government needs to get back involved,” said David M. Hart, who studies energy policy at the Information Technology and Innovation Foundation.
There are other risks to a states-only approach. According to Christopher Clack, chief executive of the grid-modeling firm Vibrant Clean Energy, the best way to fully decarbonize the United States electricity system with renewable energy would be through a national grid that allows optimally placed wind and solar resources from far-flung regions to balance each other out in the face of weather fluctuations. But such a system would most likely require federal planning.
“Right now, solar and wind are still a relatively small slice of electricity, so this isn’t a big problem yet,” Mr. Clack said. But as these sources grow, he said, individual state efforts to build out their own renewable bases without broader coordination could lead to a system that is less well-suited to handling large quantities of wind and solar.
‘A Virtue of Necessity’
For their part, the alliance states are trying to overcome these hurdles. New York, for instance, is trying to nurture energy innovation on a small scale through a state “green bank” that helps companies bring riskier new technologies to market. While this is no substitute for basic energy research at the national labs, state officials say it can help advance incremental innovation around technologies that are closer to market.
“We’re trying to make a virtue of necessity,” said Richard Kauffman, Governor Cuomo’s chairman of energy and finance. “In an ideal world, it would be fantastic if we had the federal government providing leadership and investing in R&D and energy infrastructure. But that’s not only not the world we’re in — with this administration, it’s not even close to the world that we’re in.”
States also face the risk that the Trump administration could try to thwart their efforts. Officials in California, for instance, are preparing to challenge any effort by the federal government to pre-empt their electric vehicle mandate on automakers.
And it remains to be seen if the climate alliance can keep adding members. “There was already heavy political pressure in these states to move forward on clean energy,” said David G. Victor, a climate policy expert at the University of California, San Diego. “But just because these states demonstrate that it can be done doesn’t mean the politics suddenly shift in places like Kentucky or Kansas.”
The ultimate significance of these state efforts, Dr. Victor said, may be to help prevent international climate efforts from collapsing, by reassuring other countries that the United States has not totally abandoned the issue.
“Now that the rest of the world is over the initial reaction to Trump, they’re trying to figure out what’s still real and what’s not in U.S. policy,” he said. “And these states can offer a starting point for other countries to gauge U.S. climate action, even when what’s happening in Washington is chaotic.”
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