BALI, Indonesia (AP) _ Top scientists jumped into the political battle over global warming at a climate conference Thursday, urging mankind to make deep cuts in carbon dioxide and other heat-trapping gases. The United States, however, refused to back away from its opposition to mandatory cuts, despite mounting international and domestic pressure.
More than 200 experts issued a declaration at the four-day-old international gathering on Bali island calling for a 50 percent reduction in such emissions by 2050 _ a rare policy prescription by scientists who usually limit themselves to presenting evidence and leaving the politicians to choose which remedies to take.
The scientists aimed to spur talks here over launching negotiations, to extend over the next two years or so, on an emissions-cutting agreement to succeed the Kyoto Protocol, which expires in 2012. The current pact requires 36 industrial nations to reduce the gases by a modest 5 percent below 1990 levels. The United States is the only industrial nation to reject it.
``What this declaration is about is delivering a clear message. It's got the weight of the scientific community behind it,'' said Australian climatologist Matthew England, a group spokesman. ``It means we have to have a radical change to the way we power this planet. We have to start reducing greenhouse gas emissions as soon as we possibly can.''
Delegates from nearly 190 nations are attending the two-week conference.
It has broken into a tense standoff between two camps, with a majority supporting mandatory emissions cuts on one side, and opponents such as the United States on the other, delegates said. Failure to act, experts say, would allow rising temperatures to trigger devastating droughts, flooding and other environmental damage.
The United States, the world's largest producer of climate-warming gases, resisted calls for strict limits on emissions, even as the U.S. Senate Environment and Public Works Committee passed a bill Wednesday to cut pollutants by 70 percent by 2050 from electric power plants, manufacturing and transportation. The bill now goes to the full Senate.
U.S. officials said neither the Senate action nor the decision earlier this week by Australia to sign the Kyoto Protocol _ after years of standing with the U.S. in opposition _ would have an impact on Washington's stance at the Bali conference.
Top American negotiator Harlan Watson shrugged off the latest scientific declaration, suggesting it lacked the weight of the Intergovernmental Panel on Climate Change, or IPCC, the scientific group that shared this year's Nobel Peace Prize with former Vice President Al Gore.
``There are thousands of scientists involved in the IPCC. This is the opinion of 200,'' he told reporters. ``I haven't seen the statement and its content, so, no, I can't endorse something that I haven't seen.''
On Thursday, the Australian delegation said Canberra supported a U.N. document that mentioned cutting greenhouse gas emissions by between 25 percent and 40 percent below 1990 levels by 2020. The government has already proposed 60 percent cuts by 2050.
However, Australian Prime Minister Kevin Rudd refused on Thursday to commit to the 2020 figures, saying it was premature to set firm targets before he receives a comprehensive report he has commissioned on the issue, due next year.
The U.S. Senate action cheered environmentalists and others in Bali clamoring for dramatic action to stop global warming. U.N. climate chief Yvo de Boer led off his daily briefing Thursday by hailing the ``encouraging sign'' from the United States.
David Waskow, of the Oxfam humanitarian agency, said the Senate legislation suggested that many in the U.S. were eager to assume leadership in the fight against global warming.
``It does show the seriousness of the U.S. Congress in addressing these issues, and really sends a positive signal to developing nations in particular that the United States Congress is not going to sit idly by,'' he said. ``That is quite distinct from ... the Bush administration.''
The United States and ally Japan are proposing that the post-Kyoto agreement favor voluntary emission targets, arguing that mandatory cuts would threaten economic growth which generates money needed to fund technology to effectively fight global warming.
Indonesian Environment Minister Rachmat Witoelar, the host of the conference, said the mood in the closed-door negotiations was ``serious, apprehensive,'' but that there were hopes the U.S. would slowly change its stance.
``I think the United States will be judicious enough to accept the changes of atmosphere,'' said Witoelar, who took over as president of the U.N. climate change conference this year.
``I don't think we should pressure them, they will come by themselves,'' he said. ``We should not demonize anyone. We still have another week.''