“If humanity were to replace the ‘free’ services of the natural economy with substitutes of its own manufacture, the global GNP would have to be raised by at least $33 trillion.”

E.O. Wilson, 2003.

Three types of accounting for ecological impacts:

True cost | Net cost | Assimilative cost

True cost accounting

include what the true or actual costs are in terms of externalities,

• such as: calculate common health and environmental damages.
• factor in the opportunity costs (what do you give up for this investment)
• eliminate subsidies
• Consider the expenses over the full life of the product; Life cycle accounting.

Net energy accounting

considers, by calculating the costs, or expenses involved in:

1. finding,
2. extracting,
3. transporting,
4. using any fuel [energy] source,
5. cleaning up after the combustion
   

Assimilative capacity accounting

• include the ability of the resource site to absorb the impact without functional collapse.
• calculate the cost of restoring damaged, degraded, or destroyed water, air or land resources.
• The Catskill Mountain watershed is worth $6 to $8 billion to New York City for drinking water.