The Copenhagen agreement would require developing countries to curb their emissions growth, but it was unclear how their plans would be enshrined in the accord and what would happen if their promises were broken.
White House aides said Sunday that a fully binding legal agreement would be put off until a December 2010 meeting in Mexico City, even though the new agreement must be ratified and in force when the Kyoto pact expires at the end of 2012.
Together, the U.S. and China emit 40 percent of the world's greenhouse gases, and a new study said the recent growth of emissions during the economic downturn was almost entirely driven by China. Worldwide carbon emissions jumped 2 percent last year, said the study, published Tuesday in the journal Nature Geoscience, adding urgency to efforts to rein in pollution that traps the Earth's heat.
In a joint statement, Obama and Hu said Copenhagen should produce an agreement that would "include emission reduction targets of developed countries and nationally appropriate mitigation actions of developing countries."
Obama administration officials are pushing for Copenhagen negotiators to tackle specifics on the major issues such as financing for poor nations, technology cooperation and some commitments among developing nations – though not legally binding – on emission reductions.
That is what Obama was referring to when he said in Beijing that whatever comes out of Copenhagen should have "immediate operational effect," according to administration and congressional officials with knowledge of the administration's preparation for the climate talks.
In Washington, Carol Browner, the White House adviser on energy and climate, said the United States is ready to participate in a commitment by developed countries to help poor countries deal with the impacts of climate change. Browner declined to say how much the United States might contribute, but indicated those details would be worked out in Copenhagen.
U.N. estimates say about $150 billion a year will be needed by 2020.
The summit's Danish hosts and other European leaders understood Obama's comments on his Asian tour as a signal that he will deliver specific pledges of U.S. action on carbon emissions and financing in Copenhagen – even at the risk of moving faster than Congress would let him.
U.S. negotiators have persistently resisted pressure to commit to figures for emissions reductions or financing until Congress completes domestic climate legislation.
The legislative struggle in Congress is now certain to extend into next year. One version, calling for an 80 percent reduction in greenhouse gases by mid-century, has passed the House and a similar version recently emerged from a Senate committee, despite solid Republican opposition.
The administration hopes the U.S. position in Copenhagen will be fortified by evidence of some progress in Congress on climate, along other action the White House has taken to promote clean energy and rein in carbon dioxide emissions. In turn, they believe, some additional commitment from developing countries – even in terms of specific goals – could help get a climate bill through Congress, where opponents have repeatedly argued U.S. action alone won't help solve the climate problem.