Todd Stern, the chief American climate change negotiator, said Thursday that the flawed and incomplete agreement reached last month in Copenhagen could provide significant benefits if countries followed through on its provisions.

The three-page Copenhagen Accord is not legally binding, and the 192 nations that took part in the December talks did not formally accept it. But a sizable group of those countries said they would accept its terms and provide plans to reduce greenhouse gas emissions by Jan. 31.

Wealthy countries also said they would follow through on promises to come up with $30 billion over the next three years to help developing countries adapt to global climate changes.

“It is incredibly important that those things happen,” Mr. Stern told investors gathered for a conference at the United Nations in New York, in his first public comments since the Copenhagen talks ended on Dec. 19. “The accord is lumbering down the runway, and now it needs to get speed so it can take off.”