Mr de Boer said nations had an opportunity to aim higher
The head of the UN Framework Convention on Climate Change says he has seen "encouraging developments" in recent climate change negotiations.
His comments come as the first "negotiating text" for the UN's December climate change conference is published on the UNFCCC website.
Yvo de Boer said this document marked "an important point on our road".
The text collates discussion proposals from all of the nations that will take part in the December talks.
Mr de Boer said the publication of the 53-page document was the first time "real negotiating text" had been put on the the table.
He said it could "serve as a basis for governments to start drafting... an agreed outcome" to the long-awaited Copenhagen conference.
"We have an almost complete list of industrialised nations' pledges to cut emissions after 2012, so governments can see now, more clearly, where they are in comparison to each other, and can build a higher ambition on that basis," he said.
He added that the US had committed to a Copenhagen agreement and a "clean energy future".
"In response to the financial crisis, many national stimulus packages have been launched that include green economic objectives," he added.
"With only 200 days before Copenhagen, time gets tighter but the world is not standing still on climate change."