A man puts advertising on the the Climate Express in Brussels on Saturday. (Peter Dejong/Associated Press)The Climate Express rolled into Copenhagen's central train station Sunday from Brussels, carrying hundreds of delegates for the 12-day UN summit to reach a climate agreement that would replace the Kyoto Protocol in 2012.

About 450 people, including delegates and journalists, arrived in the Danish capital by train for the start of the conference Monday, to show their commitment to reducing greenhouse gas emissions that contribute to global warming.

More trains were leaving from other European capitals to symbolize efforts to reduce the convention's carbon footprint. However, most of the 15,000 people expected at the conference will arrive by plane from opposite ends of the globe.

'I think a lot of people are skeptical about this issue in any case.'—Yvo de Boer, UN official

Climate negotiators and political leaders from 192 countries, including Canada, will be attending the summit. Canada has been criticized internationally for reneging on the Kyoto Protocol, which expires in 2012, and refusing to sign on to a new deal limiting greenhouse gases unless developing nations are included.

In an interview published Sunday in the Danish daily newspaper Berlingske Tidende, UN Secretary General Ban Ki-moon said he was "very optimistic" delegates would reach an accord for controlling emissions.

U.S. climate negotiator Jonathan Pershing called the science on global warming "very robust, very substantial."

Even so, he worried that emails pilfered from a British university would fuel skepticism among those who believe that scientists exaggerate global warming.

"I think a lot of people are skeptical about this issue in any case," the UN's top climate official, Yvo de Boer, told The Associated Press. "And then when they have the feeling ... that scientists are manipulating information in a certain direction, then of course it causes concern in a number of people to say, 'You see I told you so, this is not a real issue."'

Emails stolen from the climate unit at the University of East Anglia appeared to show some of world's leading scientists discussing ways to shield data from public scrutiny and suppress others' work.

Those who deny the influence of man-made climate change have seized on the correspondence to argue that scientists have been conspiring to hide evidence about global warming.

With files from The Associated Press