Earlier today, Bloomberg Philanthropies announced a $50 million grant to the Sierra Club's Beyond Coal Campaign, aimed at giving the organization enough additional heft to focus on its effort to get one third of the nation's aged coal-fired power fleet to retire by 2020 and replace it with renewable energy.

The four-year financial commitment plumps up the campaign's four-year budget to $150 million.

The campaign also seeks to reduce mercury pollution from coal 90 percent by 2020.

Sierra Club Executive Director Michael Brune called the grant a "game changer."  Among other things, it will allow the organization to increase the number of people working on the campaign from 100 to 200.

Part of the plan calls for increasing pressure on plants to comply or close, and bringing community pressure to bear as well.

"Coal relentlessly dirties our water, air, and lungs and fixing the problem cannot be left to Washington," said Brune in a press release. "Nor can coal's contributions to climate disruption be left to international bodies. Mike Bloomberg's strong clean air agenda as Mayor of New York, and his Chairmanship of the C40 Cities Climate Leadership Group, shows that he understands that actions are being taken, and that the most significant ongoing successes will be won city by city, by dedicated people across America."

"If we are going to get serious about reducing our carbon footprint in the United States, we have to get serious about coal," Bloomberg said in the press release. "Ending coal power production is the right thing to do, because, while it may seem to be an inexpensive energy source, the impact on our environment and the impact on public health is significant. Coal is a self-inflicted public health risk, polluting the air we breathe, adding mercury to our water, and the leading cause of climate disruption."