WASHINGTON AND L'AQUILA, ITALY — Addressing leaders of the world's most important economies early Thursday, President Obama wasted no time in proclaiming a new day for U.S. policy on climate change.
"I know that in the past, the United States has sometimes fallen short of meeting our responsibilities," he said. "So let me be clear: Those days are over."
But by the end of the day, when the Group of 8 summit in L'Aquila, Italy, wrapped up its deliberations on climate, Obama found himself stymied by many of the same roadblocks that plagued previous efforts to tackle global warming.
Leaders of the most developed nations again declined to commit themselves to any specific actions now or in the immediate future to curb the greenhouse gas emissions that contribute to global warming -- actions that would require increasing energy prices, raising taxes or imposing other unpopular economic measures on their people.
Instead, they embraced the high-sounding goal of reducing their own emissions by 80% and worldwide emissions by 50% by 2050 -- without pledging to take any specific steps to get there. China, India and other major developing countries, which pressed for action in the next decade by the G-8 countries, reacted by rejecting the package.
And a side meeting Obama convened Thursday to bring together the nations most responsible for greenhouse emissions ended with only general pronouncements, and no firm financial commitments, to work against warming and share emissions-curbing technologies in the future.
Paying the economic and political costs for effective action against climate change has always been a problem. But it was especially difficult this time because of the global recession, even with a popular new leader such as Obama seeking to forge ahead.
"There's always a high expectation for what the U.S. can deliver, and higher expectations for Obama, because he's Obama," said Jake Schmidt, international climate policy director for the Natural Resources Defense Council. "Those are difficult expectations to meet."
Schmidt and other activists said that Obama, by bringing the United States to the table on global warming after what they called foot-dragging by the Bush administration, has given new steam to negotiations that will culminate at a United Nations climate conference in Copenhagen in December.
The Italy talks represented small but important progress in the debate, they said.
The environmental group Greenpeace, by contrast, derided the package as a "missed opportunity" for more aggressive emissions reductions and a failure of leadership by Obama and the G-8.
Obama convened the 17-nation climate meeting at a giant circular table, inviting fellow leaders to speak openly about their hopes and concerns. Several acknowledged the new leadership from the U.S., administration officials said.
The discussions yielded a consensus declaration that the world should try to limit warming to 2 degrees Celsius (3.6 degrees Fahrenheit) above preindustrial temperatures, a level scientists say would minimize the dangers of the most catastrophic warming effects.
The 17 major emitters -- the most advanced economies that make up the G-8, plus the nine biggest emerging economies -- also agreed to partner in research on energy technologies that would reduce emissions, such as solar power and the capture and storage of carbon from coal.
They set broad principles for financing the effort, but did not pledge specific contributions.
After the meeting, Australian Prime Minister Kevin Rudd praised the American president for his role in the sessions.
"Can I say on behalf of so many of us," he told Obama, "how welcome it is to see the return of U.S. global leadership on climate change under your presidency."
The warm words did not change the fact that, with the global economy racked by recession and even the wealthiest countries struggling with unemployment and other economic pain, considerable obstacles remain for moving against climate change now -- in the United States and elsewhere.
Reflecting the challenge on the home front, Sen. Barbara Boxer (D-Calif.), head of the committee drafting the centerpiece of Obama's climate change legislation, announced that she was pulling back from a promise to act swiftly and would not finish work on a bill until at least September.
The House last month passed a climate bill that would gradually impose carbon emissions limits and set up a "cap and trade" system to encourage industries to reduce pollution. Europe has already created such a system.
During the climate talks, Obama aides said, some developing nations asked why they should sacrifice when other countries have caused more of the damage. Analysts said Obama would have more leverage in dealing with such objections from other countries if the Senate approved a climate bill.
The president's clear call for action in Italy could help down the road, too, they said.
Michael Oppenheimer, a Princeton University geoscientist and longtime participant in the Intergovernmental Panel on Climate Change, said that the G-8 meeting was "a chance for the heads of state to look at each other in the eye and say, 'Yeah, we agree about this' -- and then the word goes down to the negotiators."
"That kind of signal then reverberates," he said, "and then a deal that seems impossible can be done."
The climate discussions dominated a day at the G-8 that saw little other action.
Leaders did agree to work toward completing a long-stalled global trade agreement, and Obama became the first U.S. president to shake hands with Libyan leader Moammar Kadafi, whose country has won favor in Washington in recent years since he abandoned its nuclear program.