LOUISVILLE, Ky—When the six smokestacks of the Cane Run Generating Station came tumbling down in a cloud of dust last weekend as part of a controlled implosion by its utility owner, nearby resident Kathy Little was flooded with emotion.

"I was in tears," said Little, a grandmother, who with her neighbors joined a Sierra Club campaign called Beyond Coal that successfully pressured the plant to curb toxic ash from blowing into their community. "It was so symbolic to me because of all the work we have done."

The 1,000-megawatt coal plant on the banks of the Ohio River hadn't produced toxic ash—or electricity—since it was retired by its owner, LG&E, in 2015. But its demise, which took less than a minute, symbolized the broader decline of coal in both generating capacity and the production of electricity.

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A recent report by the Federal Energy Regulatory Commission shows that U.S. electrical generating capacity by renewable energy sources has surpassed that of coal by a hair. And in April, the renewable sector was projected to generate more electricity than coal-fired plants for the first time, according to researchers at the Institute for Energy Economics and Financial Analysis, a think tank which works toward a sustainable energy economy.

To further those trends, billionaire Michael Bloomberg—who had bankrolled the Sierra Club's Beyond Coal effort—announced that he was giving a half-billion dollars to a new effort, "Beyond Carbon," that seeks not only to close all remaining coal-fired power plants in 11 years, but to block new natural gas plants replacing them.

Bloomberg, a philanthropist, media mogul and former New York City mayor, said in a June 7 commencement address at Massachusetts Institute of Technology that climate change "is now first and foremost a political problem, not a scientific quandary, or even a technological puzzle."

He compared the climate challenge to the 1960s goal of going to the moon and said his new campaign would work to mobilize the electorate to oust politicians who don't take climate change seriously. Climate change is such an urgent threat to humanity, he said, that "we can't put this mission off any longer."

The Sierra Club Wants 240 More Coal Plants Closed

In Louisville, Kathy Little and other residents advocating the cleanup or closure of the Cane Run Generating Station used video cameras to document how the coal ash was blowing into their neighborhoods, resulting in six-figure fines. They had joined forces with activists across the country as part of Beyond Coal, which the Sierra Club started back in 2002 after the administration of George W. Bush put forth a "coal rush" plan to build 150 new coal plants across the country.

In the years since, as cheap natural gas from a fracking boom flooded the market and undercut coal economically, and as the Obama administration cracked down on pollution from coal mining and burning coal, plants like Cane Run have been retired.

To date, the Sierra Club counts 290 coal plants retired since Beyond Coal began, with 240 to go. At Cane Run, which operated for 61 years, a new gas plant was built on the LG&E property.

The Sierra Club, which will extend its partnership with Bloomberg, welcomed Bloomberg's latest largess.

"We're doubling down on the work we've been doing for years because the most important part of the struggle—the endgame—is yet to come," said the Sierra Club's Mary Anne Hitt, in a written statement.

In West Virginia, where coal has slid and natural gas has risen amid talk of a new Appalachian plastics hub, the billionaire coal baron governor, Jim Justice, on Monday described Bloomberg's pledge as a threat to the state's economic future.

"His goal is to extinguish fossil fuels," Justice told reporters, attacking Bloomberg as "a New York super liberal that lives in an absolute bubble" who is going after the livelihoods of West Virginians. "I can't see in any way, shape, form or fashion that we need to let some bubble boy that is in New York that is donating a fraction of his money to destroy us."

For his part, Bloomberg said that "we intend to succeed not by sacrificing things we need, but by investing in things we want—more good jobs, cleaner air and water, cheaper power, more transportation options, and less congested roads."

Renewables Surpass Coal in Generating Capacity

The implosion of Cane Run came as America reached a milestone in the way it generates electricity. Ken Bossong with the Sun Day Campaign, which supports a transition away from fossil fuels and nuclear energy, cited the FERC report as a key point of inflection: U.S. electrical generating capacity by renewable energy sources, such as biomass, geothermal, hydropower, solar, and wind, has now edged past that of coal: 21.56 percent to coal's share at 21.55 percent.

Capacity doesn't mean how much energy was actually produced, an important caveat, Bossong acknowledged.

But "if you have capacity," he said, "at some point the electricity generation will follow. It's just a question of lag time."

Researchers at the Institute for Energy Economics and Financial Analysis, meanwhile, noticed at the end of April that the renewable energy sector was projected to generate more electricity than coal-fired plants for the first time.

The final numbers for April aren't in yet, but even if renewable generation falls short, it's only a matter of time now before that happens, with coal on the decline and renewables on the rise, said Dennis Wamsted, an IEEFA analyst and editor.

One reason is that coal power is falling farther down the pecking order of the different types of energy tapped by grid operators because it's more expensive, he said. That fact, he said, shows up in what are called capacity factors, or measures of how much energy is produced by a plant compared to its maximum possible output.

The overall capacity utilization for coal plants is declining while those for wind and solar are rising, according to the latest Department of Energy figures.

That change itself could be putting some still-operating coal plants at risk.

Coal plants were typically designed to run most of the time, and have been "the old reliable pickup truck of energy generation," said Chris Skates, a former coal plant operator and aide to Kentucky Gov. Matt Bevin, at a gathering of the Southern States Energy board last month.

But increasingly, they are being used only intermittently. That threatens to cause coal plants to break down, adding to their operational costs, and putting them at further risk of being retired, Skates said.

"He's right," Wamsted said.

Cane Run's Closure Led to Cleaner Air

On Saturday in Louisville, after much preparation, several blasts could be heard and flashes of light could be seen. A dust cloud billowed and the Cane Run smokestacks tilted in different directions, crashing to the ground.

"It's bittersweet for our company, employees and retirees who worked at Cane Run to see the last remaining portions of the facility come down today," said Paul W. Thompson, chairman, CEO and president of LG&E, part of PPL Electric Utilities, which has committed to reducing its carbon emissions 70 percent from 2010 levels by 2050. (By then, scientists say worldwide emissions from energy systems should be approaching zero to avoid the worst climate risks.)

Little said she wasn't sad. From her front yard, she can still see the now-closed landfill and a capped ash pond where LG&E dumped a mountain of coal ash over six decades. But the plant is gone and the air is cleaner, she said.

"Coal is definitely on its way out," Little said. "I am so happy, and not for the individuals who have lost their jobs and culture. I understand that and respect that. But from my perspective, green energy won't hurt children."