https://www.nytimes.com/2017/01/17/business/economy/climate-change-california-new-york.html?_r=1

Is there a more environmentally conscious state than California? It has been at the forefront of climate policy for decades - from demanding stringent fuel economy and emissions standards to wholeheartedly embracing renewable energy from the sun and wind.

It has fighting words for the incoming administration of Donald Trump. "We will not deviate from our leadership because of one election," the State Senate leader, Kevin de Leon, told The New York Times. Last fall, the state legislature committed to cutting its greenhouse gas emissions 40 percent below their 1990 level by 2030. "California is doing something that no other state has done," proclaimed Gov. Jerry Brown.

State policies were always bound to play a central role in the decarbonization of the American economy. But with a president-elect who has asserted that climate change is a Chinese hoax, promised a bright future for fossil fuels and vowed to undo President Obama's climate strategy, their choices have become more important than ever.

And yet for all the pluck of the Golden State's politicians, California is far from providing the leadership needed in the battle against climate change. Distracted by the competing objective of shuttering nuclear plants that still produce over a fifth of its zero-carbon power, the state risks failing the main environmental challenge of our time.

Mark Muro, director of policy at the Metropolitan Policy Program at the Brookings Institution, has compiled a ranking of progress toward decarbonization within the United States. In 2014, he found, California had the third-lowest carbon dioxide emissions per person, behind only the District of Columbia and New York.

Its progress of late, however, has been less than stellar: Despite its aggressive deployment of wind turbines and solar panels, the carbon intensity of California's economy - measured by the CO₂ emissions per unit of economic product - declined by only 26.6 percent between 2000 and 2014. That put it in 28th place. In New York, which came in seventh, carbon intensity declined 35.4 percent.

It is not entirely California's fault. Persistent drought has drastically cut its supply of hydroelectric power. Still, the state's carbon emissions were also driven by its own choices: Added to the hydroelectricity slump, the 2012 closing of the San Onofre nuclear plant north of San Diego left a void in the power supply that even a vast increase in solar and wind generation could not replace. So it was mostly filled with natural gas.

New York, by contrast, left its nuclear plants running. It even offered upstate generators subsidies similar to those available to renewable energy generators, to help them survive the cutthroat competition against cheap power fueled by natural gas.

But even a state like New York still has work to do. An analysis by PricewaterhouseCoopers argued that to ensure that the global temperature does not rise more than 3.6 degrees above its preindustrial average, which world leaders have agreed is the tolerable limit, the carbon intensity of the global economy must decline 6.3 percent per year between now and 2030.

The United States must decarbonize at an annual rate of 4.3 percent under that timetable. But over the last decade and a half, only North Dakota and the District of Columbia have achieved this pace. New York is decarbonizing at about 3 percent per year, California at barely above 2 percent.

What's more, most of the gains in the United States have come relatively easily, not from the deployment of renewables but from the wholesale switch from coal to cheaper and cleaner natural gas. Much of that transition has played itself out, however. Further gains will be more expensive.

"What's critical to think about is, Where are the next savings going to come from?" Mr. Muro told me. "Divergent state dynamics on nuclear energy will become a crucial issue in the next 40 years." Taking nuclear energy off the table has already pushed the nation too far in the wrong way.

Consider this bit of counterfactual history. Environmental Progress, an advocacy group that aggressively supports the deployment of nuclear energy to combat climate change, estimated what California's power sector would look like had the opposition from antinuclear forces - including Governor Brown - not undone the state's deployment of nuclear energy, starting in the 1970s.

The power from San Onofre and the Rancho Seco nuclear generation station near Sacramento, both now shuttered, added to that from the never-built Sundesert nuclear plant in the Mojave Desert and three planned-but-not-built units at Diablo Canyon on the state's central coast, would add a total of 77,000 gigawatt-hours of zero-carbon power to California's supply. Only 27 percent of the power produced in California would come from fossil sources, other things remaining equal, as opposed to 66 percent today. And carbon emissions from power generation would be only 40 percent of what they are today.

Nuclear energy cannot compete with natural gas at current prices, of course. But its woes aren't just about economics. Incorporating the climate costs imposed by fossil fuels would sharply increase the cost of gas generation. But rather than level the playing field, policy makers mostly squeeze nuclear generation further.

There's a reason for that: Alarmed by the prospect of nuclear meltdowns and the potential damage to ecosystems and human health, voters remain decidedly against nuclear reactors. Still, if combating climate change is an imperative, nuclear power and its risks must get a more careful assessment. Climate change will be hard to stop without it.

Consider Germany, which vowed both to replace its nuclear energy with renewable energy sources and to make great strides in combating climate change.

Last year it got less energy from the sun despite having more solar panels than the year before. An 11 percent increase in wind capacity produced a 1 percent increase in wind power. And Germany's carbon emissions from energy rose.

At several moments last winter, a high-pressure system reduced wind and solar power to a small fraction of total demand. What if this happened in 2030? About a third of German power comes from renewables, on an average day. Even if the Germans had three times as much renewable generation capacity, there would be periods when it wouldn't come close to satisfying demand. With no nuclear energy to speak of, the gap would have to be filled with fossil fuels.

"One cannot simultaneously rely on massive amounts of wind and sunshine, dispense with nuclear power plants (for very good reasons), significantly lower the supply of fossil energy, and nevertheless tell people that electricity will definitely be available in the future," noted the German economist Heiner Flassbeck.

Unfortunately, it doesn't look as if America's governors and state legislators will take the lesson to heart.

California is on track to shutter Diablo Canyon, its last remaining nuclear power plant. And in New York, Gov. Andrew M. Cuomo just announced an agreement to close the Indian Point nuclear plant. When that happens, the state will lose almost a quarter of its zero-carbon power.

Maybe New York's carbon emissions won't immediately kick back up. The state government argues that it will fill the gap with renewable energy, gains in efficiency and the like. It has also committed to cutting greenhouse-gas emissions 40 percent below 1990 levels by 2030. And it is promising that half its power will come from renewable sources.

Still, it's hard not to think that the battle against climate change has, once again, been relegated to the back seat.