Gore called Obama "the greenest person in the room" for making environmental funding a big chunk of the $819 billion economic stimulus bill passed by U.S. lawmakers this week.
"I think it's important for the world leaders gathered here to fully appreciate the magnitude of the change in U.S. leadership," Gore said.
The former U.S. vice president and environmental advocate, speaking at the World Economic Forum in Davos, referred to frustration in many countries at the Bush administration's refusal to sign international pacts on reducing emissions of carbon, blamed for global warming.
Questions remain over the new U.S. government's position on the Copenhagen meeting, which is seen as crucial.
Gore remained upbeat. "The new administration is very serious about this," he said. "We need an agreement this year, not next year or some other time."
The panelists acknowledged that the financial crisis will be a key challenge to getting agreement on a climate pact.
Danish Prime Minister Anders Fogh Rasmussen, who will host the Copenhagen meeting, urged countries to agree to reduce global emissions by 50 percent by 2050, and said industrialized countries should reduce by 80 percent.