Agence France-Presse: The economic impact of global warming has been grossly underestimated and scientists must warn that inaction will spell disaster, top economist and climate change expert Nicholas Stern said on Thursday. Stern told 2,000 climate scientists meeting here that they had failed to clearly tell humanity what it faces if global temperatures reach the upper range of forecasts made by the UN’s Intergovernmental Panel for Climate Change (IPCC). “There has been lots of scientific …