Speaking in Washington DC on 25 June, President Barack Obama unveiled his plan for cutting US carbon emissions. Credit: whitehouse.gov

Ending months of speculation, US President Barack Obama today called for regulations that would limit carbon dioxide emissions from existing power plants — perhaps the single largest regulatory question the administration has faced on global warming.

Obama unveiled the wide-ranging climate plan in a speech at Georgetown University in Washington DC, pledging to "put an end to the limitless dumping of carbon pollution from our power plants".

The US Environmental Protection Agency (EPA) will work with states, industry and other stakeholders on a power-plant rule that will promote a "common-sense, timely transition to a clean-energy economy", White House officials told reporters yesterday. But the administration, which aims to issue its proposal by June 2014 and finalize it by June 2015, is not committing to specific emissions reductions.

Power plants account for roughly 40% of US greenhouse-gas emissions, and the potential for emissions reductions is huge: a proposal put forth by the Natural Resources Defense Council, an environmental group based in New York, would cut the power sector's greenhouse-gas output to 26% below 2005 levels by 2020. That plan relies on setting up a complex regulatory framework that gives power companies flexibility to reduce emissions through paths such as mechanical upgrades or even consumer energy-efficiency programmes.

But some legal experts say that the Clean Air Act was not designed to regulate ubiquitous pollutants such as carbon dioxide. On one hand, there is a risk that an aggressive policy to stem emissions would be vulnerable to legal challenges, says Jeff Holmstead, an attorney at Bracewell and Giuliani, a law firm in Washington DC, who served at the EPA under former president George W. Bush. On the other hand, Holmstead says that the administration could stick with a relatively straightforward, safer rule that requires basic equipment upgrades across the industry, but such an approach would reduce emissions by much less — perhaps only a few per cent.

The White House plan also includes initiatives targeting domestic energy efficiency, climate resilience and international climate diplomacy. But it conspicuously avoids calling for policies that cannot be implemented without assent from Congress. Obama’s nominee for EPA administrator, Gina McCarthy, has yet to be confirmed, and the administration faces continued opposition on Capitol Hill to any kind of comprehensive climate policy.

Ticking clock

Environmentalists generally applauded the president's message while underscoring the need for urgency, given the time it takes to push complex rules through the regulatory process. The public comment period on the administration's proposal to regulate emissions from new power plants ended a year ago, for example, and that rule has not yet been finalized. Obama's speech comes six months into his second term and more than two years after his last major address on climate change.

"President Obama has a little more than three years to cement a lasting legacy on climate change, and he'll need every last second," says Alden Meyer, director of strategy and policy at the Union of Concerned Scientists, an advocacy group based in Cambridge, Massachusetts.

The president's plan also proposes a new round of fuel-economy standards for heavy-duty vehicles manufactured after 2018, building on regulations established in 2011. The plan includes funding for advanced fossil-fuel projects, a new round of efficiency regulations for household appliances and further commitments to generate renewable energy on federal lands. To nudge these plans along, Obama is backing calls for a 'Quadrennial Energy Review' designed to assess progress and help to establish a national energy strategy.

On the international front, Obama said that the United States will push for lower international tariffs on climate technologies and an end to international financial aid for coal-fired power projects in developing countries, except where no other energy options are feasible. Officials say that Obama remains "firmly committed" to the country's international pledge to reduce greenhouse-gas emissions to 17% below 2005 levels by 2020.

Tom Peterson, president of the Center for Climate Strategies, a think tank in Washington DC, says that the administration deserves credit for building "a more holistic" climate plan. Nonetheless, he said that it will be difficult for the United States to meet its emissions commitments. "This gets us much closer, but there’s still more work that needs to be done," Peterson says.