Any delay in reaching an agreement to tackle global warming would be disastrous, leading climate scientists said yesterday.

More than 200 scientists signed a declaration urging politicians at the United Nations climate change conference in Bali to reach agreement on how to reduce greenhouse gas emissions by more than half. The declaration was drawn up amid fears that delegates would try to delay taking action or weaken the measures necessary to combat climate change.

The signatories said that temperature rises brought about by global warming must be no higher than 2C (3.6F) and that emissions of greenhouse gases must start falling within 15 years. They were particularly concerned that politicians from the 180 countries represented at the conference would argue that they needed more time to assess the impacts of global warming before signing up to a deal.

The Bali Climate Declaration by Scientists, due to be released this morning, was organised by researchers from the University of New South Wales. It is based on the results of three major studies carried out this year and highlights the costs of inaction.

The declaration echoes the conclusion of the Intergovernmental Panel on Climate Change (IPCC) that the world’s weather is “warming rapidly” and that it is virtually certain that the increases have been caused largely by human activities, notably through carbon dioxide being pumped into the atmosphere.

“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,” the declaration says.

“Global greenhouse gas emissions need to be reduced by at least 50 per cent below their 1990 levels by the year 2050 . . . In order to stay below 2C, global emissions must peak and decline in the next ten to fifteen years, so there is no time to lose.”

Among the signatories were experts from Britain, the United States, Russia, India, Japan, South Africa, Brazil, Indonesia, Australia, New Zealand and several European countries.

Professor Corinne Le Quéré, of the University of East Anglia and the British Antarctic Survey, said that the declaration was intended to remind delegates of their duty and to prevent compromise and shilly-shallying.

“We have as scientists done our jobs in doing the IPCC reports earlier this year. Now other people have to take over, but we are concerned they will not realise the urgency of the actions which are needed,” she said.

“There might be a lot of argument among delegates about, for example, restricting temperature rises – they might argue for 3C or 4C. The declaration is trying to emphasise 2C. They might try to gain time and let things go for a decade or two to see what happens. We don’t have time for that.

“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 conference is not expected to set targets for reducing greenhouse gas emissions, but delegates are hopeful that a “road map” can be agreed, setting out the dates by which consensus needs to be reached. If successful, the road map will chart a pathway to a final agreement on targets to be signed in 2009, ready to be put into effect by 2013.

The conference in Bali started on Monday and will continue next week, when environment ministers from around the world will arrive in the Indonesian resort.

Hilary Benn, the Environment Secretary, and Phil Woolas, the Environment Minister, will be among the British delegation at the conference next week.

The Bali Declaration

— The 2007 IPCC report, compiled by several hundred climate scientists, has unequivocally concluded that our climate is warming rapidly, and that we are now at least 90 per cent certain this is mostly due to human activities. The amount of carbon dioxide in our 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.

— The next round of focused negotiations for a new global climate treaty (within the 1992 United Nations Framework Convention on Climate Change process) needs to begin in December 2007 and be completed by 2009. The prime goal of this new regime must be to limit global warming to no more than 2C [3.6F] above the preindustrial temperature, a limit that has already been formally adopted by the European Union and a number of other countries.

— Based on current scientific understanding, this requires that global greenhouse gas emissions need to be reduced by at least 50 per cent below their 1990 levels by the year 2050. In the long run, greenhouse gas concentrations need to be stabilised at a level well below 450 parts per million (measured in CO2-equivalent concentration). In order to stay below 2C, global emissions must peak and decline in the next ten to fifteen years, so there is no time to lose.

— 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.

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