COPENHAGEN — As President Obama prepared to visit the historic climate conference here, there were signs Wednesday of a break in the impasse between rich and developing nations.
The United States and Japan agreed to make major contributions to the developing world to keep a deal alive. And the leader of a bloc of African nations said they would accept a smaller — though still sizable — package of financial aid in return for going along with an agreement.
But tear gas hung in the air outside the conference center as protesters demanding faster and more stringent cuts in greenhouse-gas emissions clashed with police. And inside, talks were slowed by disagreements within the developing world — which has proved an unexpectedly powerful and fractious force.
Some environmentalists expressed hope that Obama's appearance Friday, the final day of the 12-day talks, could help conclude these two chaotic weeks with a global deal.
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"If the pieces are here, President Obama is the only person who can pull them together into an agreement," said Fred Krupp, president of the Environmental Defense Fund. "We expect him to do so."
Even before the United Nations-led talks began, it was clear they would not deliver what environmental groups had initially hoped for: a global treaty on climate change, with high-emitting countries formally pledging to reduce their greenhouse-gas emissions in the coming decades.
Instead, the goal was to sign a "political agreement," in which nations would pledge to tackle emissions but without making a binding commitment under international law. The understanding was that a formal treaty would come in 2010.
That goal still seemed within reach Wednesday, one day before Secretary of State Hillary Clinton arrives to take part in the negotiations.
White House press secretary Robert Gibbs told reporters that it is typical of global conferences that some differences remain when heads of state arrive. Obama, who has made phone calls this week to the leaders of developed nations such as Germany and France and developing countries such as Bangladesh and Ethiopia, will join 118 other world leaders in the Danish capital.
"I think you've seen in some ways people say that... some of this is just going to get hashed out when leaders of these countries get here to start hashing it out," Gibbs said. "I think that's in many ways how some of this stuff happens. "