Climate scientists call for urgent emission cuts

• Alison Benjamin and agencies
• Guardian Unlimited,

Greenhouse gas emissions must be urgently cut, with reductions of at least 50% by 2050, climate scientists warned today.

More than 200 leading international climate scientists attending the UN climate change conference in Bali called for emissions to peak and decline within the next 10 to 15 years.

If emissions are not limited, millions face extreme events such as droughts, flooding and rising sea levels, the scientists said.

In the "Bali declaration" published today, the scientists say that a new international deal on climate change must ensure global warming does not exceed a 2C rise above pre-industrial levels.

Today's declaration said: "The amount of carbon dioxide in the atmosphere now far exceeds the natural range of the past 650,000 years and it is rising very quickly due to human activity.

"If this trend is not halted soon, many millions of people will be at risk from extreme events such as heat waves, drought, floods and storms, our coasts and cities will be threatened by rising sea levels, and many ecosystems, plants and animal species will be in serious danger of extinction."

Negotiations on a new treaty have to begin now and be completed by 2009, with targets of keeping warming below 2C by reducing global emissions by 2050 and ensuring they peak and decline in the next 10 to 15 years, they said.

"As scientists, we urge the negotiators to reach an agreement that takes these targets as a minimum requirement for a fair and effective global climate agreement," the declaration said.

Corinne Le Quere, of the University of East Anglia and the British Antarctic Survey, is one of the scientists who have signed up to the initiative, which is under the auspices of the Climate Change research centre at the University of New South Wales, Australia.

She said: "Climate change is unfolding very fast. There is only one option to limit the damages: stabilise the concentration of CO2 and other greenhouse gases in the atmosphere.

"There is no time to waste. I urge the negotiators in Bali to stand up to the challenge and set strong binding targets for the benefit of the world population."

The warning comes after the Intergovernmental Panel on Climate Change assessment this year, drawing on work by thousands of scientists, which said that warming was "unequivocal" and was at least 90% likely to be mostly caused by humans.