WASHINGTON - For the first time, more than 200 of the world's leading climate scientists, many of them losing their patience, have urged government leaders to take radical action to slow global warming.

They say time is running out.

A petition from at least 215 climate scientists, including a Canadian, calls for the world to cut in half greenhouse gas emissions by 2050. It is directed at a conference of diplomats meeting in Bali, Indonesia.

They are there to negotiate the next global warming treaty.

The appeal from scientists follows a petition last week from more than 150 global business leaders also demanding the 50-per-cent cut in greenhouse gases. The goal is in line with what the European Union has adopted.

In the past, many of these scientists have avoided calls for action, leaving that to environmental advocacy groups.

That dispassionate stance was taken during the release this year of four separate reports by the Nobel Prize-winning Intergovernmental Panel on Climate Change.

But no more.

"It's a grave crisis, and we need to do something real fast,'' said petition signer Jeff Severinghaus, a geosciences professor at the Scripps Institution of Oceanography in La Jolla, California.

"I think the stakes are way, way too high to be playing around.''

The unprecedented petition includes scientists from more than 25 countries and shows that "the climate science community is essentially fed up,'' said signer Andrew Weaver of the University of Victoria.

It includes many co-authors of the intergovernmental climate change panel reports, directors of major American and European climate science research institutions, a Nobel winner for atmospheric chemistry and a winner of a MacArthur "genius'' award.

"Action needs to be taken and needs to be taken now,'' said Marika Holland, a scientist at the National Centre for Atmospheric Research. "The longer we wait, the worse it's going to become.''

Negotiators in Bali are working on the initial groundwork for a treaty that would take effect after 2012, the expiration date of the Kyoto Protocol, a climate treaty the United States did not sign.

However, no-one expects concrete results at the closed-door sessions.

NASA scientist Gavin Schmidt, who signed the petition, said "the time for half-measures and the time for voluntary agreements and the time for arguing about one per cent here and one per cent there -- those things are no longer relevant.''