The author of an authoritative study on climate change says he underestimated the dangers of global warming. In 2006, the British economist Lord Stern wrote the Stern Review on the Economics of Climate Change, which argued the costs of fighting climate change would amount to one percent of annual global GDP by 2050. By contrast, the report said the cost of doing nothing would amount to up to 20 percent of world GDP. But speaking at a UN meeting in Copenhagen, Stern revised the latter figure, saying the cost of inaction could be up to a third of the world’s wealth.