The U.S. and China announced new carbon-emissions targets Tuesday following talks between President Obama and Chinese President Xi Jinping, steps the White House called part of an effort to "achieve the deep decarbonization of the global economy over time."
China, where emissions are surging, offered a first-time pledge to achieve a peak in its carbon emissions by 2030, although the White House expressed hope that China could reach the target more quickly.
The U.S. pledged to cut its greenhouse-gas emissions by 26 to 28 percent below 2005 levels by 2025, building on the years-old White House commitment of a 17 percent cut by 2020.
The pledges, which follow months of talks between the two countries, come amid delicate United Nations-hosted talks aimed at finalizing a new global climate-change accord in Paris late next year.
The unveiling of the U.S. pledge while Obama is in China is something of a surprise, because nations are not formally scheduled to offer post-2020 emissions targets to the U.N. talks until the first quarter of next year.
China is the world's top greenhouse-gas emitter and the U.S. is No. 2. The White House, in a statement, expressed hope that the actions would "inject momentum" into the negotiations. The two nations together produce roughly 40 percent of global greenhouse-gas emissions.
In September, China's Vice Premier Zhang Gaoli told a United Nations climate conference in New York that his nation would seek to have its emissions peak "as soon as possible," but Tuesday's announcement marks the first commitment to a specific deadline.
United Nations Secretary-General Ban Ki-moon sought to cast the announcements as a turning point in talks over a new global climate deal. Negotiators will meet in Peru late this year ahead of the make-or-break talks in Paris in late 2015.
"This leadership demonstrated by the governments of the world's two largest economies will give the international community an unprecedented chance to succeed at reaching a meaningful, universal agreement in 2015," a spokesman for the U.N. leader said late Tuesday night.
The announcements arrive as the White House is expanding its use of executive actions on climate change that do not require action by Congress. Emissions-cutting legislation has been a nonstarter for years, and now ascendant Republicans are planning to attack EPA's regulations and other parts of Obama's agenda.
Republican Sen. Mitch McConnell, who will be majority leader when Republicans take control of the upper chamber next year, quickly attacked the U.S. pledge of deeper emissions cuts.
"This unrealistic plan, that the president would dump on his successor, would ensure higher utility rates and far fewer jobs," McConnell said. "Easing the burden already created by EPA regulations will continue to be a priority for me in the new Congress."
The White House said the U.S. commitment can be met without winning new authorities from Congress, calling them "grounded in intensive analysis of cost-effective carbon pollution reductions achievable under existing law."
Environmentalists cheered the actions while also signaling that they believe stronger steps are needed. Natural Resources Defense Council President Frances Beinecke called them "landmark" commitments but added: "We look forward to working with both governments to strengthen their efforts—because we are confident that both can achieve even greater reductions."
The Center for Climate and Energy Solutions, a U.S. group that's heavily involved in international global-warming policy, similarly welcomed the pledges while noting they fall short of some advocates' hopes.
"Even if the targets aren't as ambitious as many might hope, the world's two largest carbon emitters are stepping up together with serious commitments. This will help get other countries on board and greatly improves the odds for a solid global deal next year in Paris," said Bob Perciasepe, the group's president who was the second in command at EPA until earlier this year.
Activists are calling for stronger steps as scientists offer fresh warnings that soaring emissions will result in a suite of dangerous effects. Climate experts warn that the prospect of limiting the global temperature increase to 2 degrees Celsius above pre-industrial levels—the target of international talks—is slipping away as emissions keep rising.
"Continued emission of greenhouse gases will cause further warming and long-lasting changes in all components of the climate system, increasing the likelihood of severe, pervasive and irreversible impacts for people and ecosystems. Limiting climate change would require substantial and sustained reductions in greenhouse-gas emissions which, together with adaptation, can limit climate change risks," the U.N.'s Intergovernmental Panel on Climate Change warned in a major report in early November.
In a joint statement with the U.S., China said it would make its "best efforts" to have its emissions peak before the 2030 target, and also said the country plans to boost the share of its energy from nonfossil fuels to around 20 percent by 2030.
"Both sides intend to continue to work to increase ambition over time," the countries said.