With carbon markets worth more than €40bn ($63bn) and investment in clean energy in 2007 reaching almost $150bn, it is no wonder people are dreaming up all sorts of ways to cash in on the current vogue for the environment.

The carbon market is one area that has generated a lot of hot air. For example, Environmental Power Corp of the US says it produces “energy that transcends conventional notions of what is possible”. Or put another way, the loss-making company collects cow and pig dung and sells the methane produced. This not only produces revenue but also carbon credits because methane is a greenhouse gas that is 21 times as potent as CO2.