The classic book Natural Capitalism quotes a Pew study done in the 1990s that determined (p. 154) “the annual value of seventeen ecosystem services: $36 trillion on average, with a high estimate of $58 trillion (1998 dollars).” The study was published in 1997. In today’s (2007) dollars, these numbers translate into $28T and $45T respectively.
If the world started consuming the means of production of these services in 1990 (the capital has the same value as the services), then we’ve been depleting them since then by the amount of growth in our Gross World Product. In 1990, the services would have been worth $37T to $54T (2007 dollars, estimating inflation). Based on my consumption model’s projections of GWP, we will exhaust the supply of natural services between 2013 and 2020. Interestingly, the earlier date corresponds to when I expect populations of other species to crash (2014) and the later date corresponds to the year that I project our population will peak.
These facts imply that our planet is a closed economic system, with a fixed value that is the sum of humanity’s economic production and the rest of Nature’s ecological production. If true, the total value is between $77T and $94T.