A group of 1,700 leading scientists called on the US government yesterday to take the lead in fighting global warming. Citing the unprecedented and unanticipated" effects of global warming, the scientists, including six Nobel prizewinners, presented a letter calling for an immediate reduction in US carbon emissions. The letter, issued by the non-profit Union of Concerned Scientists, warns: "If emissions continue unabated, our nation and the world will face more sea level rise, heatwaves, droughts, wildfires, snowmelt, flood risk, and public health threats, as well as increased rates of plant and animal species extinctions." The White House joined in the chorus of gloom when it issued a long-delayed report bringing together research into global warming. The report was issued after environmental groups won a court order last year enforcing a statute that obliges the government to produce an assessment of global warming every four years. Described as "a litany of bad news in store for the US", the report catalogues threats from drought, natural disaster, insect infestation and energy shortages. The scientists call on the government to "reduce emissions on the order of 80% below 2000 levels by 2050." As a first step, the scientists call for a 15-20% reduction on 2000 levels by 2020. "There is no time to waste," the letter concludes. "The most risky thing we can do is nothing." Another group of climate scientists warned yesterday that a "curious optimism ... pervades the political arenas of the G8 and UN climate meetings. The authors are part of the Intergovernmental Panel on Climate Change, but stress in this paper they do not represent the panel.