But despite going far beyond his predecessors on global warming, Obama's green legacy will face question marks for years. Executive actions such as new EPA regulations lack the certainty of the bedrock environmental statutes Congress passed in the late 1960s and early 1970s.
The particulars of how he's using the Clean Air Act to demand cuts in power-plant pollution are almost certain to wind up before the Supreme Court. And GOP White House contenders, if elected, would seek to dismantle or hamstring the rules, which have already emerged as a top target of congressional Republicans.
Obama's green legacy is not yet set. He has yet to announce a decision on whether or not to approve the Keystone XL pipeline, which environmentalists bitterly oppose, believing Keystone will enable a surge in carbon-spewing oil-sands production in Canada. And greens are still unhappy he is allowing Shell to drill for oil off the Alaskan coast in the Arctic Ocean.
And another legacy item awaits: The United States is heavily involved in negotiations aimed at reaching a major global climate accord at a make-or-break United Nations summit in Paris late this year.
"He really sees this as just an issue that just can't be ducked," said Dan Utech, a White House adviser on energy and climate. "For both today, but also for the sake of his daughters, their kids, and the kids and grandkids of all Americans."
Obama has talked about how, as an undergraduate in Los Angeles, the pollution was so bad that "folks couldn't go outside." And he has blamed rising temperatures for his daughter Malia's asthma attacks when she was 4.
Of course, the sweeping EPA rules weren't the first choice for the administration. An extensive climate-change bill to set up a national cap-and-trade system passed the House in mid-2009 but collapsed in the Senate the next year.
Presidents are often remembered for sweeping actions and bills they signed, like the civil rights and anti-poverty bills that President Lyndon Johnson pushed through Congress. Carol Browner, Obama's former climate-policy director, said Obama doesn't get the credit he deserves for his step-by-step approach on climate change.
"People don't see the arc of it. They see each of these acts as isolated. But when you put them together, they're actually more than the sum of the parts," Browner said. "It all comes together to give you a magnitude of reduction."
The stimulus Obama ultimately signed in 2009 would steer some $90 billion into low-carbon energy initiatives and technologies. Another big win on climate in his first term: rules finalized in 2012 that boost gas mileage standards for cars and light trucks to 54.5 miles per gallon by 2025, a mandate that will make the United States auto fleet much greener.
William Reilly, who led EPA under President George H.W. Bush, strongly praised Obama for his steps to address global warming, especially in the face of strong opposition from congressional Republicans. Reilly credits Obama for tackling a topic that had been "suspended as a presidential priority for the previous eight years" under President George W. Bush.