Business Green: Lord Stern has this week warned that the cost of avoiding dangerous levels of global warming has doubled since he published his influential report on the economics of climate change in late 2006. In the report, Stern concluded that one per cent of global GDP would have to be invested in transitioning towards a low-carbon economy if levels of carbon dioxide are to be kept between 450 and 550 parts per million (ppm) – the level scientists claimed would be required to reduce the risk of …