Greenpeace activists have climbed halfway up the Colosseum in a protest to press for a historic climate deal at the Copenhagen conference.

As the sun rose Wednesday over Rome's ancient arena, eight members of the pro-environment group used ropes and their hands to reach the top of the second tier of the monument's four tiers.

On the cobblestones below, some 50 activists lay down to spell out, with their bodies, the message "act now."

The activists, dressed in orange jump suits, unfurled a yellow banner saying "Copenhagen: make history now."

Police watched but did not intervene.

Spokesman Francesco Tedesco predicted that if action isn't taken immediately to reduce carbon dioxide emissions, mass migration and starvation will result.