In a gutsy move, New York Mayor Michael Bloomberg today announced that his Bloomberg Philanthropies has pledged $50 million to the Sierra Club to fight coal plants.

He didn't do it quietly, either. Bloomberg chartered a boat to take about 100 Sierra Club activists, friends, TV cameras and reporters out onto the Potomac River for a press conference in front of an Alexandria, Va., coal plant that environmentalist have been try shut, so far without success. Fittingly, he came to D.C. on a day when the heat was sweltering and authorities declared a "Code Orange," an alert meaning that the air is too dirty for kids to play outside.

"The burning of coal does terrible harm to mothers, children and families across the country," Bloomberg declared, calling coal a "self-inflicted public health risk."

Bloomberg and Mike Brune, the Sierra Club's executive director, set an ambitious goal for the group's "Beyond Coal" campaign: They want to shut down about one-third of the nation's coal plants and replace them with clean energy as quickly as possible.

"If we succeed, and I believe we will," Bloomberg said, "we will save millions of lives and we will help millions of children avoid asthma and its debilitating effects."

For those who care about climate change, air pollution and public health, this is the best news out of Washington, D.C., in some time. It comes in stark contrast to the goings-on on Capitol Hill, where House Republicans are doing everything they can to tame the EPA.

Shutting down 30% of America's coal-burning capacity with be hard, but the anti-coal campaigners have some winds at their back. Natural gas prices are low, and the EPA wants to require older coal plants to put on expensive, pollution control technology, over industry objections. And about 10% of the aging fleet of coal plants is already scheduled to close.

Meanwhile, construction of new coal plants have all but come to halt, in part because of opposition from groups like the Sierra Club, which claims to have blocked more than 150 of them.

Brune, who came to Sierra Club after a successful run as leader of the hard-hitting Rainforest Action Network, said the $50 million, spread over the next four years, will enable the club to expand its Beyond Coal campaign from 15 to 46 states and double the number of people working full-time against coal plants, from 100 to 200. The Sierra Club, which is America's oldest and largest grass-roots environmental group, has an annual budget of about $80 million and about 1.4 million members.

Mike (Brune) told me that the club has been talking with Bloomberg since 2007 when his predecessor, Carl Pope, met the mayor during international climate talks in Bali. It's significant that Bloomberg–who made his fortune in the media and is business-savvy–chose to make the donation to the Sierra Club, as opposed to more mainstream or business-friendly groups like the Environmental Defense Fund.

"He likes to take on big fights," Mike said. "He took on tobacco. He took on guns."

In his remarks aboard ship, Bloomberg said little about climate change and instead talked about public health, a longtime passion of his. (He's the major donor to the Johns Hopkins Bloomberg School of Public Health.)

Banning smoking in New York City's bars and restaurants was controversial, he recalled, but protecting people from second-hand smoke turned out to be popular.

Coal, he said, may appear to be a source of cheap electricity but "the real price tag is hidden" in medical costs. Coal pollution, he said, causes $100 billion in annual health costs.It's also responsible for mining deaths and water pollution caused by mountaintop mining.

"This is about the air we breathe, the water we drink, our health, today," Bloomberg said.

Still, while climate wasn't on his mind today, his Bloomberg Philanthropies has become a leading backer of the C40 Cities Climate Leadership Group (C40), which attempts to drive action to curb global warming at the local level. In New York, meanwhile, he has promoted a range of environmental initiatives in New York City, ranging from bike lanes to solar power at city landfills to his failed effort to impose a congestion tax on private cars entering Manhattan.

This being Washington, Bloomberg's appearance set off some chatter about a third-party presidential bid. There's a whole lot to like about him besides his record on environmental and public-health issues: his business experience and success as an innovator and job-creator, his determined effort to improve New York City's schools and the fact that he has effectively managed a big bureaucracy.

On the other hand, as a vertically challenged New Yorker and a Jew who supports gay marriage, well, let's just say that Bloomberg is not conventional presidential timber.

The Sierra Club probably has a better chance of shutting down a third of the nation's coal plants than Bloomberg does of reaching the White House, and that task won't be easy. Bruce Nilles, who led the Beyond Coal campaign before turning it over to West Virginia activist Mary Anne Hitt last year, said the campaign will use the courts to enforce existing environmental laws against older plants and campaign in state legislatures for renewable energy mandates that typically require utilities to replace fossil fuel plants with wind or solar power.

He's also counting on help from EPA, where administrator Lisa Jackson is pushing rules to regulate emissions of toxic chemicals like mercury from coal plants. "She is our favorite federal official," Nilles told me.

In response, the American Coalition for Clean Electricity -- yes, that's what this utility and coal industry group is called, believe it or not -- said on its website that "the 'Beyond Coal' campaign actually would move America beyond jobs. Mayor Bloomberg's millions will be spent on a plan that would result in higher electricity rates for millions of Americans, fewer jobs, and less competitive American businesses."

Well, yes, replacing dirty coal plants with wind or solar power will modestly increase electricity prices, while delivering public health and climate benefits. But as we should all know by now, there's no such thing as a free lunch.

_{Top photo CC-licensed by Sean McGrath.}