There's a long way to go, but new power plant rules from the White House are a huge step in the fight against global warming

Barack Obama ran for president six years ago promising to end a "dumb war" in Iraq and save a planet in peril. After last week, when the president was forced to send 300 troops back to Iraq, it would be easy to think he would break both those promises before leaving the White House.

But in his second term, Obama is building a real legacy on global warming and environmental protection. He is doing so despite resistance from Congress, conservative groups and business lobbies, many of whose members refuse to accept that climate change is even occurring.

New rules proposed this month would for the first time set limits on the amount of carbon dioxide that power plants can spew into the atmosphere, tackling America's single largest source of planet-warming emissions. And Obama has also unveiled plans to use his executive authority to establish a huge marine conservation area in the Pacific, to protect coral reefs, whales, dolphins, sharks, sea turtles and a number of fish species

The power plant regulations are arguably the most important US environmental initiative in 40 years, the pinnacle of Obama's agenda. On their own, though, they are not enough to keep warming below the 2C threshold for catastrophic climate change. And Obama has waffled on key environmental decisions such as the Keystone pipeline, a project to expand production from Canada's tar sands that scientists say would be a disaster for the planet. His "all of the above" energy strategy has aggressively promoted oil and gas drilling, while America's greenhouse gas emissions rose last year after several years of decline because of the economic downturn.

But even taking all that into account, Obama is steadily delivering on the grand promises of his 2008 election campaign. He has shaken off the failures of his first term – the inability to get a climate change law through Congress or reach a global deal at the Copenhagen summit – and avoided the examples set by the UK, Australia and Canada, which have reined in their ambitions or in the case of Tony Abbott, reversed course entirely on climate change.

By the time of his re-election in 2012, after a summer of wildfires and drought, and the shock of Superstorm Sandy, Obama seized his moment. In his first State of the Union address, the president pointed to the extreme weather events as evidence of global warming and gave Congress an ultimatum: act on climate or I will.

On 25 June last year, Obama did exactly that, asserting that he would use his executive authority to set new standards for future and existing power plants. He also made it easier for his fellow Democrats to talk about climate change. In the last 18 months, Obama has regularly mentioned climate change in interviews and speeches and taken shots at Republicans for climate denial, likening that view to believing the moon was made of cheese.

The approach could turn Republican climate denial into a liability in the midterm elections in November. Meanwhile, there is optimism the power plant rules could have a knock-on effect on the painfully slow efforts for a global climate deal in 2015. Diplomats have long said climate change negotiations would go nowhere unless America was willing to show real leadership. Now, with the new power plant rules redefining Obama's climate agenda, America has the credibility to lead. And that could be good news for all of us.