"I am in no sense writing off legislation over time. And I'm quite sure the president isn't," U.S. climate envoy Todd Stern told a news conference during two days of talks in Geneva among about 45 nations reviewing climate finance.

He said Washington would rely on a combination of regulation by the Environmental Protection Agency (EPA) and future legislation to meet President Barack Obama's goal of a 17 percent cut in emissions from 2005 levels by 2020.

"The EPA will be a piece, an important piece, of the total equation," he said. "There will be legislative progress I can't say when."