Pay for Nature?

There is an interesting proposal from the UN's Economics of Ecosystems and Biodiversity project (http://www.guardian.co.uk/environment/2010/may/21/biodiversity-un-report). It is argued that the costs resulting from losses of natural organisms that 'do jobs' for we humans (e.g. fertilise 'our' plants, recycle materials and control flood waters) are a magnitude greater than the costs involved in attempting to conserve them. It is consequently argued that preventing extinctions may be even more important than curtailing global warming (in a financial sense, assuming we are still here). All this may well be true but it does seem slightly dodgy that these things have to be converted into pounds, euros and dollars before they interest politicians and the voters. I have no 'beef' with the idea, however, that destructive agencies should be taxed at a rate commensurate with the environmental damage they cause.