The international conference on climate change opens Monday in Copenhagen, Denmark, hosting thousands of participants and observers hoping to reach a deal to combat global warming.  Initial expectations have been scaled back, but pressure remains for a substantive political agreement.

For the next two weeks this city plays host to experts, officials, activists and eventually world leaders as they try to clinch a deal.

Speaking to journalists on the eve of the conference, top U.N. climate official Yvo de Boer said it is time to act.

"Time is up," said Yvo de Boer. "Over the next two weeks, governments have to deliver a strong and long-term response to the challenges of climate change."
The goal was to reach a legally binding agreement to reduce greenhouse gas emissions, blamed for heating up the atmosphere.  But big questions remain over who cuts, by how much, who pays and what it will cost.

Initial expectations for Copenhagen have been scaled back to try to reach political agreement on a framework, with a detailed, binding treaty to follow.

More steps will be needed, said Yvo de Boer, but he remained confident.

"Never in the 17 years of climate change negotiations have so many different nations made so many firm pledges together," he said.

That, said de Boer, makes this conference a turning point already.  Certainly many Copenhagen residents hope that is true and they see climate change as a crucial issue.

MAN:  "I think the most important thing we can politically is to force the leaders to take seriously the problems we are facing."

MAN:  "The issue is important for my future and my children's future as well."

COUPLE:  "It is very important.  Super important - it involves all of us whether we live here in Denmark or whether we live in Asia or in North America, for that matter."

MAN:  "I think it is very important for the people in the world that we do something about it right now."

Copenhagen has embraced the conference - with posters and reminders of what is at stake at almost every corner.  One exhibit has taken a different tack - with large posters of some of the world's beauty spots - remaining wilderness and wildlife. 

The exhibit is meant as a message to world leaders, when they come here, to make sure such beauty remains for future generations.