My response there:
No one is in fact saying that a nightingale’s song is worth £5.
What we’re trying to get to is a set of relative values.
So, we start with, well, people act as if a nightingale’s song is worth £5 to them. They also seem to act as if their own lives are worth around £2 million (not that far off the real figure). Bluebell woods at £300. Salt water marshes at £1,5 million.
Absolutely no one is saying that you can sell the marshes for £1.5 million. Take the nightingale’s song to the bank and get a fiver.
However, now that we’ve got some numbers, these valuations of what people seem to value things at by what they do, now we can begin to make trade offs.
To be absurd, imagine that 1,000 nightingale songs would cure a child of cancer. Five grand? It’s a bargain, start liming those twigs so we can capture them.
Now let’s not be absurd. Those salt water marshes near Cardiff, they’re worth £1.5 million as the home of those wading birds. They’re also worth £1 billion as the shores of the Severn Barrage (note, please, these are imaginary numbers, just for illustration).
So, do we build the barrage or do we keep the home for the birdies? And is our decision different if the tweeties’ mudflats are worth £1 billion and the energy system £1.5 million?
We aren’t at all saying that any of these things are worth £x. We are saying that people seem to value that over there at x times what they value that over here, or some /th of what they value some other thing at. £ is only used so that we have one unit to play with.
Now that we know the relative values (note again, not the absolute values) we can begin to make decisions. So, what do people actually want? Bluebell woods or houses for the homeless in a former bluebell wood? Oystercatchers or energy?
To try and approach this problem any other way would be insane.