Guardian: Scientists may have to turn back time and clean the atmosphere of all man-made carbon dioxide to prevent the worst impacts of global warming, one of Europe’s most senior climate scientists has warned. Professor John Schellnhuber, director of the Potsdam Institute for Climate Impact Research in Germany, told the Guardian that only a return to pre-industrial levels of CO2 would be enough to guarantee a safe future for the planet. He said that current political targets to slow the growth …