President Barack Obama proclaimed a new day for U.S. policy on climate change early Thursday, declaring, "In the past, the United States has sometimes fallen short of meeting our responsibilities. So let me be clear: Those days are over."

But by day's end, world leaders wrapped up climate talks at a familiar impasse.

Leaders of the Group of Eight nations declined prompt action to curb greenhouse gas emissions in favor of the high-sounding goal of reducing their own emissions by 80 percent and worldwide emissions by 50 percent by 2050 -- without pledging to take any specific steps to get there. China, India and other major developing countries, who had wanted action in the next decade, reacted by rejecting the G-8 package.

And a side meeting that Obama convened Thursday to bring together the developing and developed nations most responsible for greenhouse emissions ended with only general pronouncements.

The discussions yielded a consensus declaration that the world should try to limit warming to 3.6 degrees, a level scientists say would minimize the dangers of the most catastrophic warming effects.