Source: Adapted from Kleidon and Fraedrich (2004).

Source: Adapted from Kleidon and Fraedrich (2004).

Notes': a Negative components represent loss of energy from the surface.

b Terrestrial productivity is normalized to give 100% for desert world climatic conditions.

Kleidon (2002) and Lenton (2002), and the criticisms by Kirchner (2002), pointing out weaknesses and offered his own conclusion. Specifically, Volk promoted the idea that the Earth is a 'Wasteworld' built of free by-products from vital processes.

The debate is certainly not at an end (see Kirchner 2003; Lenton and Wilkinson 2003; Lovelock 2003; Volk 2003a, 2003b). To move the discussion forwards, Kleidon and Fraedrich (2004) and Kleidon (2004) applied thermodynamic considerations of non-equilibrium systems to biotic functioning in an Earth system perspective. Kleidon and Fraedrich (2004) argued that two maximum entropy production states are relevant to atmosphere-biosphere interactions at global scale, both of which relate to planetary albedo (Figure 9.3). Planetary albedo varies, mainly according to surface albedo and the extent of

Reflection by polar S snow and ice cover

Reflection by tropical convective clouds

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