"President Obama's commitment to dealing with global warming has changed the political dynamic for our negotiations," United Nations Secretary General Ban Ki-Moon told ABC News here at the Copenhagen Climate Summit.
"Everybody is looking to the U.S. for leadership and commitment in dealing with global warming," he said. "It has helped that he has repeated his commitment many times."
President Obama is expected to speak at the final plenary session of the conference after he arrives here early Friday.
Standing next to Ban was Achim Steiner, the Brazilian-born head of the United Nations Environment Program.
"Obama has improved humanity's efforts to fight climate change by bringing America back to the table," Steiner told ABC News, contrasting it to the attitude of the administration of President Bush.
Some speakers, including former Vice President Al Gore, have called on the U.N. to move up its next climate meeting from December 2010 to July, so that binding limits on greenhouse-gas emissions can be agreed upon more quickly. Steiner would not be specific about dates, but said speeding it up could have a good impact on world finance.
Meeting Sooner Would 'Have a Good Effect on Markets'
"Moving the date up would not only have a good effect on the climate," he said, "but also on markets."
"Hundreds of billions of dollars will be triggered or redirected once we have an agreement," Steiner said, adding his belief that "the world is immensely impatient" to make this transition to a carbon-restricted economy.
"Many of the world's markets and companies are waiting for a clear signal to tell if the world is going to move into a low-carbon era," he said.
The enormous meeting room was still filled with the many delegates and other attendees who had listened to an unusually intense and animated description by Secretary Ban of the climate issue and the "very difficult" negotiations to deal with it.
Many of the heads of United Nations organizatons -- the United Nations Development Program, the World Meteorological Organization, the World Food Program -- stood behind him as he spoke to the crowd.
"The U.N. has the widest and the deepest and the longest experience and know-how in helping people -- certainly in the developing world," he said, and affirmed that this entire "U.N. System", as it is called, has been working for two years on ways to provide aid to people as the apparently inevitable damages of global warming accelerate.
"We are user friendly!" said a smiling Ban to the capacity crowd.
Vietnam's New Woes; Small Islands' Pleas for Help
Descriptions of human suffering that has already started worldwide as a result of human-induced global warming are heard throughout the day on the in-house monitors scattered throughout this vast convention complex.
One after another, delegates from poor and developing countries appear at a podium or microphone. They talk of the beginnings of mass migrations, long predicted by some scientists, of "climate refugees" looking for food or water. They describe the losses increasingly suffered from flood or drought that are now linked to worsening weather patterns produced by the rising average global temperature.
"For us, your disagreements are about our right to exist!" declared one man from one of the 37 "small island nations" at the summit.
His home island, he said, is expected to disappear under rising sea level in the coming decades.
"We are here to fight for our human right to exist," he said.
Many islanders say their nations will die if the average global temperature rises two degrees Centigrade, a number considered a safe upper limit by many delegates. They say the limit should be reduced to 1.5 degrees above the levels at the beginning of the Industrial Revolution.
A man from Vietnam, which has enormous areas of land near sea level along the Mekong River and its delta, reminded the delegates that his largely-rural country's 86 million people "have not been one of the big greenhouse gas emitters."
Unnoticed Amid the Crowds....
In a hall near one of the vast rooms where journalists from all over the world working intensely on their laptops, climatologist Stephen Schneider of Stanford University went largely unnoticed.
With him was his wife, Terry Root, a Stanford ecologist who did some of the first widely accepted work assessing global warming's enormous impacts on ecosystems and species extinction rates.
Steve Schneider had seen the coming dangers in the year 1975 when he readjusted some computer models (using computers that were primitive by today's standards) to determine that the excess greenhouse gas humanity was pouring into the air would not be part of a cooling of the planet, as he had briefly thought, but of a potentially catastrophic rise in global temperature.
Copenhagen Climate Talks: United Nations Chief Waits for Obama
Schneider now looked out across a swirling assembly of thousands of people from every country, all still wrestling to figure out how they - and everyone - might agree on unified action to control the planetary changes he had predicted a quarter of a century ago.
We asked him for his thoughts.
He paused and said, "After two decades of special interests blocking planetary sustainability, we are haltingly moving forward at last."
In another part of the complex, Princeton scientist Michael Oppenheimer watched, bemused, as a speaker decried the slow progress of the negotiations.
Today the scientific journal Nature would be publishing the latest of Oppenheimer's articles -- this one written with colleagues at Princeton and Harvard -- describing an even greater vulnerability of earth's polar ice sheets to global warming than scientists had previously suspected.
"There are always these ups and downs in U.N. Climate summits," he told ABC News. "In the end, the world's leaders are going to live up to their responsibilities and set us on a path to solving this."