 Climate scientists from around the world urged delegates at UN-led talks in Bali on Thursday to make deeper and swifter cuts to greenhouse emissions to prevent dangerous global warming. In a declaration, more than 200 scientists said governments had a window of only 10-15 years for global emissions to peak and decline, and that the ultimate goal should be at least a 50 percent reduction in climate-warming emissions by 2050. "We appreciate this is a significant challenge for the world community," Professor Andy Pittman, from the University of New South Wales in Australia, told reporters in Bali. "But it is what is required to reduce the risks of dangerous climate change, and that is what we are all trying to do here." The meeting in Bali, involving about 190 nations, aims to initiate a two-year dialogue leading to a broader climate pact by 2009 to replace or upgrade the Kyoto Protocol. The goal is to find a formula that will bring outsiders such as the United States, China and India into a global compact to fight growing emissions of carbon dioxide, which is produced from burning fossil fuels in power stations, industry and transport. The United States, the world's top carbon emitter, has come under intense pressure from all sides at the Bali meeting to curb its emissions and on Wednesday US lawmakers moved a step closer to approving caps. A Senate committee approved legislation outlining a cap-and-trade system for industry, power generators and transport. The bill is headed for debate in the full Senate. "The United States simply has to take a leadership role," Senator John Warner, a Virginia Republican and the bill's co-sponsor told the committee. "We are the superpower in the world and we've got to utilise our status to try and help correct a situation I think all of us acknowledge is causing hardships ... that are really without precedent." TIME TO ACT US President George W. Bush pulled America out of the Kyoto Protocol saying it threatened the economy and unfairly excluded big developing nations such as China and India from binding emissions cuts. In turn, China and India say rich nations must do more to cut emissions and that caps would hurt their economies as they try to lift millions out of poverty. "If we don't act, China and India will simply hide behind America's skirts of inaction," Warner said. A group of US scientists in Bali welcomed the committee's move. "This is a very welcome development. It shows the increasing isolation of the US administration," said Alden Meyer of the US Union of Concerned Scientists. Professor Diana Liverman of Britain's Oxford University said the world was already seeing substantial impacts from global warming, but a warming of 2 degrees Celsius would have severe impacts in Africa, Australia, the polar regions and the Pacific Islands. The UN climate panel, which released a series of reports on climate change this year, says the world is at risk from rapidly melting glaciers, vanishing sea ice and loss of icesheets. Polar bears have become an iconic symbol of climate change because the area of Arctic sea ice they rely for hunting has shrunk to record lows during the summer. Outside the Bali conference centre, eight activists dressed as polar bears added a twist to the climate debate by holding banners reading: "Humans need help too". Separately, the WWF conservation group said that 55 percent of the Amazon rain forest could be wiped out or severely damaged by 2030 by a "vicious feedback loop of climate change and deforestation". It said the effects of warming could cut rainfall and aggravate current trends in farming, fires, droughts and logging in the world's largest tropical forest. The Amazon's forests are a giant store of carbon dioxide -- trees soak up the main greenhouse gas as they grow and release it when they rot or are burnt. -- For Reuters latest environment blogs click on: http://blogs.reuters.com/environment/