Unveiled in August 2015, the plan envisioned a 32 percent reduction of carbon-dioxide emissions from power plants across the nation by 2030, relative to 2005 levels.
But when the Environmental Protection Agency published its guidelines implementing the plan several months later, a consortium of 27 states sued in a case that went all the way to the U.S. Supreme Court.
The high court then temporarily blocked the plan's implementation until lower courts had a chance to weigh-in on the merits of the states concerns. The legal challenge is currently before a federal appeals court in Washington, D.C.
In the face of that ruling, states that support Obama's goals have sought to adopt the plan on their own, often against stiff opposition from Republicans.
In their letter, the attorneys general, led by New York Attorney General Eric Schneiderman, write that "Our states and local governments are on the front lines of climate change.”
“We see firsthand the significant human and economic costs inflicted by unchecked carbon pollution: whether it is harms from severe drought in California, catastrophic storm surge in New York City, a record deluge on the Front Range in Colorado, routine high tide flooding in Hampton Roads, Virginia and in South Florida, or diminished shellfish harvest in Oregon or Washington State,” the letter continues.
"The Clean Power Plan builds on that successful work and is a blueprint for the critical action needed to fight climate change's devastating environmental, economic and public health impacts," Schneiderman said.
The other attorneys general signing the Dec. 28 letter represent California, New Mexico, Oregon, Hawaii, Rhode Island, Illinois, Vermont, Iowa, Virginia, Maine, Maryland, Massachusetts, Washington and the District of Columbia.
The mayors and city attorneys of New York City, Boulder, Colo., and South Miami, also signed on, as did their counterparts in Broward County, Fla.
The letter was a rebuttal to one sent by Republican officials from 22 states, and Democrats from the coal-producing states of Kentucky and Missouri, urging Trump to issue an executive order immediately upon assuming office declaring the Clean Power Plan unlawful and prohibiting the U.S. Environmental Protection Agency from enforcing it.
Under Democratic Gov. Andrew Cuomo's Clean Energy Standard, established this year, 50 percent of New York state's electricity must come from renewable energy sources like wind and solar by 2030.
New York and eight other states are part of the Regional Greenhouse Gas Initiative, a cap-and-trade program that has reduced carbon dioxide emissions from electrical generation in the region by 40 percent from 2005 levels.
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