A group of more than 1,700 prominent scientists and economists yesterday urged US lawmakers to take urgent action to curb carbon emissions, citing the prospect of "sea level rise, heatwaves, droughts, wildfires, snowmelt, flood risk and public health threats" if emissions continue to grow unabated.

The warning comes just days before the Senate debate on the Climate Security Act, which proposes the adoption of a US-wide cap-and-trade scheme designed to curb emissions by up to 70 per cent on 2005 levels by 2050.

In an open letter to Senators, the group, including six Nobel Prize winners and organised by the Union of Concerned Scientists (UCS), said that "the strength of the science on climate change" had compelled the signers to warn policymakers of climate change's growing risks.

"There is a strong consensus that we must do something about reducing the emissions that cause global warming," said James McCarthy, president of the American Association for the Advancement of Science and one of the letter's authors. "The debate right now is about how much we need to cut. The fact that so many scientists and economists have spoken out and signed this letter should give policymakers the confidence that we can avert serious adverse climate impacts."

The group calls for deeper cuts than those proposed under the Climate Security Act, also known as the Lieberman-Warner bill, concluding that the US should reduce greenhouse gas emissions "on the order of 80 per cent below 2000 levels by 2050" and that the first step should be reductions of 15 to 20 per cent below 2000 levels by 2020.

Some US business groups have been lobbying extensively for the Lieberman-Warner bill to be dropped, warning that the legislation would damage the economy. Meanwhile, pro-business lobby group the Club for Growth this week launched a series of adverts urging citizens to contact their Senator and urge them to oppose the bill.

However, Columbia University economist Geoff Heal, another signatory of the UCS letter, said there was a strong business case for supporting efforts to cut emissions, arguing that the cost of cutting emissions to safe levels would be between one and two per cent of GDP, while the costs of allowing climate change to proceed unabated would be on the order of 10 to 20 per cent of GDP.

"Limiting global warming emissions is a great investment," he said. "When you compare the cost of acting to the cost of not acting, cutting emissions would give the world a return of 10 to 1. That's attractive even to a venture capitalist."

The letter came on the same day as former British prime minister Tony Blair wrote in the Washington Post urging the Senate to support the Climate Security Act, arguing that such a move would represent a "hugely important signal of intent on behalf of US legislators".

"If the US commits to the 50 per cent global target for a reduction in emissions by mid-century and to legislation that mandates action, it will transform the prospects for effective change," he said.