WASHINGTON (CBSNewYork/AP)Former Mayor Michael Bloomberg on Wednesday announced that he is donating an additional $30 million to a Sierra Club initiative working to reduce the nation’s use of coal.

The Sierra Club has a goal of replacing half the nation’s coal plants with renewable energy by 2017.

Bloomberg, who served three terms before leaving office at the end of 2013, donated $50 million to the program in 2011. The latest donation, along with $20 million from others, will be spent over the next three years. He says that reducing the number of coal plants will save lives and that job growth in solar, wind and natural gas can offset coal-related jobs.

“Coal’s days are numbered. It is an outdated technology,” Bloomberg said during a rally at the Sierra Club’s offices in Washington. “It’s holding back our economy and it’s hurting our health.”

The American Coalition for Clean Coal Electricity, a trade group, says that every time the Sierra Club helps shut down a coal plant, workers are sent to the unemployment lines and electricity rates for consumers increase.

“Sierra Club’s effort is purely a political campaign that ignores the energy realities and needs of our nation,” said Laura Sheehan, a spokeswoman for the group. “The notion that 5 percent of the energy our country gets from wind and solar can somehow replace the 40 percent of electricity Americans get from coal is simply absurd.”

The number of coal-fired power plants in the United States has dropped by more than 100 over the past decade. The Sierra Club uses the donations from Bloomberg and others to fund campaign ads, hire lawyers and mobilize local support against opening new coal-powered plants and to retire older plants.

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