Guardian: The vast majority of schemes that sell carbon credits to offset pollution are delivering 30% less than they promise, a report published today claims. The study will be unveiled by Lord Stern at the launch of a service offering ratings similar to those on financial products for the carbon-credit market – which is expected to be worth £160bn-£400bn by 2020. The scale of problems found with existing credit schemes, most operated under United Nations projects, will fuel criticism …