Al Gore is now claiming, per Amory Lovins, that the US can alter its economy as he described at no cost. This is way out of line with mainstream economics. Even the Stern Report, which quite probably understimated costs, says early action will cost 1 percent of global GDP. Most studies suggest limiting CO2 concentrations to 550 or 650 ppm – well above the environmentalist favored target of 450 ppm – will cost 2 to 5 percent of global GDP.