Thermodynamics and environmental constraints make the biosphere predictable – a response to Volk

Authors:

Axel Kleidon

Abstract:

In his critique of Kleidon (2004), Tyler Volk concludes that maximum entropy production (MEP) has no great relevance for biological evolution and the time history of life on Earth. I think that most of his points are not justified but rather reflect (a) a lack of appreciation of the central importance of entropy production as the “universal currency” that measures what keeps systems working, including the biosphere, (b) a misunderstanding of how biotic activity is embedded in the global entropy budget, and (c) a lack of distinction between optimal environmental conditions that maximize productivity and result from environmental tradeoffs versus optimal function of organisms to some internal tradeoffs. The examples that he uses to support his conclusions show flaws in that these mostly discuss single environmental effects and immediate system responses. Optimal environmental conditions, however, requires at least two effects that result in a trade-off, so it is not surprising that his examples seem to contradict optimality and MEP. And the immediate response of a system to change can be very different than the response in steady state, for which MEP applies. This is specifically important to be considered in the context of the “cheater” problem. In summary, I do not think that Volk makes convincing arguments that contradict MEP, although I certainly agree that there is a lot more work to be done to fully recognize the great importance that thermodynamics and MEP play in shaping the Earth’s biosphere and its evolutionary history.

Reference:

  • Climatic Change, 85 (3-4), 259-266.
  • Weblink to publisher's web page.
  • Postprint of this manuscript (accepted version of the paper formatted by author).
  • BibTex entry.

Figure 1: Sensitivity of land averaged global mean temperature and precipitation rate to vegetation parameters (stomatal conductance, canopy roughness, root-shoot partitioning) and its effect on terrestrial productivity (colored shades). Each symbol represents one simulation with different vegetation parameters. The white star denotes the ”Control” simulation, the black star the simulation of a ”Desert world”. After Kleidon (2006).