Speaking after talks in Washington with EU officials, he said they agreed they should create a framework for progress.
The Copenhagen talks are aimed at negotiating a follow-on agreement to the Kyoto Protocol.
Meanwhile, former US Vice President Al Gore says he believes President Obama will attend the talks in Copenhagen.
He said the president would want to emphasise his administration's commitment to safeguarding the environment.
But Mr Obama's allies in Congress are struggling to push through legislation to reduce greenhouse gas emissions, and it is unlikely that any bill will be passed before the December talks.
Mr Obama said climate change had been discussed "extensively" with EU leaders on Tuesday.
"All of us agreed that it was imperative for us to redouble our efforts in the weeks between now and the Copenhagen meetings to ensure that we create a framework for progress in dealing with what is a potential ecologic disaster," he said.
European Commission President Jose Manuel Barroso said the talks with Mr Obama had made him more confident about progress.
"With the strong leadership of the United States we can indeed make an agreement," he said.
The Kyoto Protocol required 37 industrial nations to cut carbon emissions by an average 5% from 1990 levels by 2012, when it expires.
However, UN Secretary-General Ban Ki-moon has said world leaders are unlikely to agree on a comprehensive treaty in Copenhagen. He said it was more likely there would only be agreement on principles.
UN officials have also recently declared there is no chance of agreeing all elements of a new legally-binding UN treaty before the end of the year.
But Mr Gore, a leading environmental campaigner, said it wouldn't be a disaster if the conference produced only a framework agreement, and not a binding deal.