Source
Kleidon (2009), Naturwissenschaften 96:653–677, LIT-519, read in full in NOTE-423. The model studies the claim rests on (Kleidon 2004a, 2006; Kleidon & Fraedrich 2005) are not in the record and are taken as the review reports them.
What was actually shown
The budget (Fig. 3). In mW m⁻² K⁻¹: absorption of sunlight, 555 at the surface and 258 in the atmosphere; scattering and terrestrial radiative exchange, about 26 each; the hydrologic cycle, 23; the carbon cycle, about 6, 70% of it at photosynthesis; ground heat diffusion, about 1. Turbulent processes are small in the budget and matter because they enhance radiative export. The order of magnitude is strong (C3). Three figures in the text are printed in W where the inputs give mW (NOTE-423, Corrections).
The biotic claim. Biotic activity raises planetary entropy production by enhancing the absorption of sunlight (C5). The support is model studies; the author says it “would still need to be further explored” (p. 670).
The step to Gaia. The implications section proceeds explicitly “under the presumption that MEP is justified sufficiently well” (p. 670). An MEP state answers small perturbations with negative feedback; a change in boundary conditions first gives positive feedback until a new optimum is reached (Fig. 7, schematic). Planetary MEP mediated by life would then give Gaia-like homeostasis, and the Earth may have evolved stepwise toward higher entropy production (C6, weak).
What could have come out otherwise. The cited models could have shown vegetation lowering absorption. They did not, but they are the author’s own sensitivity studies, not tests designed to fail.
What this does not say
- That MEP holds. The account needs it, and the review itself says “no one would argue that MEP is well established” (p. 673).
- That life is a different kind of system. It treats life as the most effective of the Earth’s dissipative processes. It gives no criterion separating a living dissipative system from a convection cell, and does not try to (LIT-519, Standing).
- That the Earth’s history shows the steps. Stepwise increases at the oxidation events are an open question the review raises, not a finding.
- That the feedbacks have been computed. Fig. 7 is a schematic of what MEP would imply.
- That life aims at anything. “Gaia” here is homeostasis as a consequence of a selection principle, not regulation by design.
Connections
- Its premise is maximum entropy production (THEORY-671), with the derivation problems of THEORY-676.
- Forests that degrade more sunlight. Schneider and Kay’s thermal-scanner comparison (THEORY-532) is the same claim at the scale of a stand, and has the same confound: evapotranspiration does most of the degrading.
- Light absorption. Morowitz and Smith (LIT-528) cite a calculation that absorption in place of scattering raises an atom’s heat-transporting capacity by about 10⁹, stated, not shown (THEORY-492).
- Life as dissipation. The “Dissipative Self-Organizing Systems” cluster of definitions in LIT-211 (NOTE-109) is this view’s home among definitions of life. THEORY-072 is the record’s account of where organisms differ from dissipative structures.