US to pledge up to 28% emission cut
The United States has pledged to cut its greenhouse gas emissions up to 28% as part of a global treaty aimed at preventing the worst effects of climate change.
The White House's contribution to the treaty, which world leaders expect to finalise in December, codifies a commitment President Barack Obama first made late last year in Beijing.
He announced a joint US-China climate deal that raised global hopes that developed and developing nations can come together to fight climate change.
The US proposal has drawn intense interest around the world. Most nations will miss today's informal deadline to convey their contributions to the UN - only the EU, Switzerland and Mexico unveiled their pledges before the US.
By announcing its commitment early, the US hopes to dial up the political pressure on other countries to take equally ambitious steps to cut emissions.
White House senior adviser Brian Deese said that, along with the US pledge, countries that account for more than half of total carbon pollution from the energy sector have submitted or announced what they will do to combat climate change beginning after 2020.
"That's a big deal, because truly global challenges demand global solutions," he said. "Climate change is real, it is being driven by human activity, and it is not a problem any one country can solve on its own."
In the works for years, the treaty is set to be finalised in Paris in December. If successful, it will mark the first time all nations - not just wealthier ones - will have agreed to do something about climate change.
As part of its proposal, known to climate negotiators as an Intended Nationally Determined Contribution, the US is also asserting that its contribution is both ambitious and fair.
It was unclear what metrics the US would use to back up that claim. But the proposal is expected to emphasize that the Obama administration has accelerated the rate of emissions reductions nearly twofold.
Early in his presidency, Mr Obama committed to cut US emissions 17% by 2020, his subsequent goal for 2025 pushes it to between 26% and 28%.
How will the US meet its goal? The Obama administration has avoided putting hard numbers on the size of emissions reductions it expects from specific steps.
In its submission, the EU listed specific economic sectors - such as transportation, energy and manufacturing - where it expects major reductions, and named the specific greenhouse gases it plans to cut.
In contrast, the US is expected to point broadly to the steps Mr Obama is taking through executive action, such as pollution limits on power plants, stricter vehicle emissions limit, and initiatives targeting specific gases.
Many of those steps face major legal challenges and intense political opposition, raising the risk that they could be undermined or even discarded once Mr Obama leaves office in 2017.
"Considering that two-thirds of the US federal government hasn't even signed off on the Clean Power Plan and 13 states have already pledged to fight it, our international partners should proceed with caution before entering into a binding, unattainable deal," said Senate majority leader Mitch McConnell, a Republican.