Determining the value of environmental assets is notoriously difficult, and one of the reasons that the environmental movement has largely relied upon emotional appeals.  But people are starting to get more serious about trying to quantify the benefits that the natrual ecosystem gives us.

A recent study by a group of European economists has been the latest to try to quantify the value.  The study put the estimated cost of environmental destruction at $2-5 trillion.  Obviously, this is a lot, but it is not necessarily wrong.  There are many variables involved, and up for interpretation, so none of these studies are unanimously received.  But many natural systems are extremely valuable, such as the water-purification of forests and wetlands, pollination by bees and insects, and erosion prevention by plant roots.

Recently New York City has had to expand their land preservation program in the Catskill watershed in order to prevent the need to build additional treatment facilities, which can cost billions of dollars.  Land preservation is a fraction of that cost.

While there may not yet be consensus about how much things like deforesation and over-fishing cost, there is a consensus that they cause serious economic harm, and the better we get at being able to count the value, the better we will get at integrating preservation of ecosystems into our world economy.