The destruction of forests accounts for about 20 per cent of global greenhouse gas emissions. Governments, companies or forest owners should be rewarded for keeping their forests instead of cutting them down. It’s a simple idea. But putting it into practice is proving immensely complicated.

There is currently no international agreement to reduce carbon emissions from forests, but negotiators are working on one. It’s called ‘Reduced emissions from deforestation and degradation’, or REDD for short, and is being developed in the build up to December’s UN climate negotiations in Copenhagen. The problem is, in the words of Marc Stuart, head of UK-based carbon consultancy EcoSecurities, ‘REDD is the most mind-twistingly complex endeavour in the carbon game. It involves scientific uncertainties, technical challenges, heterogeneous non-contiguous asset classes... There’s brutal potential for gaming and getting it wrong means that scam artists will get unimaginably rich while emissions don’t change a bit.’ Nevertheless, Stuart is in favour of financing REDD through carbon trading. Since he made his fortune through, er, carbon trading, perhaps we shouldn’t be too surprised.