Costanza et al [1] estimated the value of the non-marketed contribution of the world’s ecosystem services to human welfare at US$16-54 trillion per year (with a mean of US$33 trillion) in $1994.  This figure was significantly larger than the corresponding global GNP at $18 trillion per year and was considered to be an underestimate.  Toman [2] suggested that "economic assessment of ecosystem benefits and opportunity costs [are] one important element of the information set that must go into social decision making, even though a simple cost-benefit test cannot determine what actions are appropriate". He states that "a default value of zero for a difficult-to-measure ecological value, as is used (explicitly or implicitly) in a number of cost-benefit analyses, is no more defensible scientifically than a default value of infinity" which only reinforces the need to appreciate the context of the analysis.  He then concludes that the fundamental problem with the analysis in [1] is "that there is little that can be usefully done with a serious underestimate of infinity"!

Imhoff and Bounoua [2] report that the human species constitutes around 0.5% of the total biomass of organisms that require organic compounds to get carbon for growth and development, yet globally they consume 20% of the net primary production from the land, i.e. the supply of food energy. Kern [3] has summarised the debate about food, feed, fibre, fuel and industrial products.

References

1. Robert Costanza, R d'Arge, R de Groot, S Farber, M Grasso, B Hannon, K Limburg, S Naeem, RV O'Neill, J Paruelo, RG Raskin, P Sutton and M van den Belt,
   The value of the world's ecosystem services and natural capital  Nature, 15 May 1997, 387(6630), 253 - 260. University of Vermont free download. The Encyclopaedia of Earth, 2007.
2. Michael Toman, Why not to calculate the value of the world's ecosystem services and natural capital, Ecological Economics, April 1998, 25(1), 57-70.
3. ML Imhoff and L Bounoua, Exploring global patterns of net primary production carbon supply and demand using satellite observations and statistical data, Journal of Geophysical Research, 2006, 111, D22S13 (extended abstract as 9.15MB PDF file.
4. M Kern, Food, Feed, Fibre, Fuel and Industrial Products of the Future: Challenges and Opportunities. Understanding the Strategic Potential of Plant Genetic Engineering, Journal of Agronomy and Crop Science, 2002, 188 (5), 291–305.

Advanced Composites Manufacturing Centre School of Engineering Faculty of Technology University of Plymouth Plymouth  PL4 8AA  United Kingdom