In 2008, standing in front of a substantially larger Berlin crowd than he faced on Wednesday, President Obama claimed that the United States would "reduce the carbon we send into our atmosphere" to prevent "a world where the oceans rise and famine spreads and terrible storms devastate our lands."

Five years later, it looks like he is finally ready to make good on his promise. His administration is planning to make the most ambitious environmental policy move of Obama's tenure, senior White House officials tell The New York Times, including a cap on carbon emissions for existing power plants.

"To paraphrase Joe Biden, this is a big deal," Daniel F. Becker, director of the Safe Climate Campaign, told the Times. "Nothing he can do will cut greenhouse gases more."

The move is such a big deal because the power plants that provide our electricity also produce 40 percent of the country's carbon dioxide emissions, making them the number one emitter of greenhouse gases in the United States.

Obama's plan would also include new energy efficiency standards for appliances and encourage clean-energy production on public lands, according to Bloomberg.

Of course, Obama has promised to take action on climate change before. His last major attempt at curbing carbon emissions sputtered in Congress in 2010. And during the 2012 debates with Mitt Romney, his liberal supporters blasted him for barely mentioning climate change while touting his record on oil drilling.

Now, with no election to think about, Obama looks to be in full legacy mode. He might not even have to reach out to Republicans thanks to a Supreme Court ruling that the EPA can regulate pollutants that contribute to climate change under the Clean Air Act, writes Kevin Drum in Mother Jones:

The EPA can actually do a fair amount if it decides to. And Republicans know it: It's one of the reasons they've held up the nomination of Gina McCarthy to head up the EPA. This announcement is likely to turn up the heat in that battle another notch or two. [Mother Jones]

Why act now, when McCarthy's nomination can still be blocked? Because, as the Times notes, creating rules governing power plants is a complex process and he wants the regulations in place before he leaves office.

The EPA has already put caps on carbon emissions for new power plants. Obama could have done the same for existing power plants during his first term, but then he would have had to explain to voters why he instituted strict new environmental regulations without consulting Congress.

With that concern out of the way, "the White House is heading into this in the full expectation that the GOP will mount a wall of opposition to everything and that the only way headway will be made is via executive action," writes The Washington Post's Greg Sargent. "That will up the hysteria quotient significantly, but so be it."