I have a paper in The Economists’ Voice on “Do Voluntary Carbon Offsets Work?” Bottom line: I am in favour of them as a concept. Summary over the fold. (Actually, this is part of a special issue on climate change with lots of interesting stuff).
Voluntary purchases of offsets for carbon emissions have been criticized as potentially increasing emissions. However, Joshua S. Gans argues that even if offsets do increase the consumption of carbon intensive goods, net emissions will always fall because these goods will become less carbon intensive.