Former New York Mayor Michael Bloomberg speaks at the Democratic National Convention in Philadelphia, Pennsylvania, on July 27, 2016. Credit: Lucy Nicholson | Reuters

The Sierra Club is expanding its campaign to retire U.S. coal power plants with a $64 million contribution from former New York Mayor Michael R. Bloomberg, as the environmental group aims to blunt efforts by the Trump administration to rescue coal.

Bloomberg, the founder and majority owner of Bloomberg LP, parent of Bloomberg News, announced the gift from his charitable organization, Bloomberg Philanthropies. It came a day after the Trump administration began a formal effort to repeal Obama-era curbs on greenhouse gas emissions from power plants. Compared to other sources of electricity, including natural gas, wind, the sun and nuclear power, coal generates more carbon dioxide for each unit of electricity generated.

“The Trump administration has yet to realize that the war on coal was never led by Washington — and Washington cannot end it,” Bloomberg said in a prepared statement.

“It was started and continues to be led by communities in both red and blue states who are tired of having their air and water poisoned when there are cleaner and cheaper alternatives available, cities and states that are determined to clean their air and reduce their costs, and businesses seeking to lower their energy bills while also doing their part for the climate,” Bloomberg said.

President Donald Trump, who has dubbed climate change a hoax, campaigned on promises to pull the U.S. out of the Paris climate agreement and to jettison the Obama-era Clean Power Plan. He has now taken steps to do both.

On Tuesday, Trump’s Environmental Protection Agency issued a formal proposal to repeal the Clean Power Plan, kicking off a long process of scrapping the regulation, and, possibly, replacing it with more modest curbs.

The Sierra Club’s Beyond Coal campaign claims credit for helping to drive the closing or announced retirement of 259 U.S. coal plants since the effort began in 2010. The initiative has helped galvanize grassroots opposition to coal-fired power, and worked out settlements with state regulators and utility owners to shutter the plants.

In 2011, Sierra Club announced a $50 million, four-year gift from Bloomberg Philanthropies to its campaign against coal. Bloomberg Philanthropies also pledged $15 million to back operations of the United Nations Framework Convention on Climate Change earlier this year after Trump said he would abandon the Paris agreement. That gift effectively underwrites the U.S. portion of the convention’s operating budget.

In total, Bloomberg has committed more than $100 million to reduce the nation’s reliance on coal through support for the Beyond Coal campaign.

Coal plants are facing lots of pressure beyond the Sierra Club. Flat electricity demand and cheap natural gas has depressed wholesale power prices, curbing the profits of coal plants. And installations of solar and wind are leading to competition from those carbon-free electricity sources.