Radiolab had a pretty good podcast explaining where these economic estimates come from and why they are important to have around. It's part 3 at the following l

Radiolab had a pretty good podcast explaining where these economic estimates come from and why they are important to have around. It's part 3 at the following link: http://www.radiolab.org/story/worth/ http://www.radiolab.org/story/worth/ Basically, if you do not make a monetary estimate of the worth of some feature of nature, it's assumed worth is $0 when governments are making decisions about policy and land use.