Independent: Lord Stern, the economist who produced the single most influential political document on climate change,says he underestimated the risks of global warming and the damage that could result from it. The situation was worse than he had thought when he completed his review two-and-a-half years ago, he told a conference yesterday, but politicians do not yet grasp the scale of the dangers now becoming apparent. “Do politicians understand just how difficult it could be, just how …