22 Aug 2022
22 Aug 2022
Status: this preprint is currently under review for the journal ESD.

Working at the limit: A review of thermodynamics and optimality of the Earth system

Axel Kleidon Axel Kleidon
  • Max-Planck-Institute for Biogeochemistry, Hans-Knoell-Str. 10, 07745 Jena, Germany

Abstract. Optimality concepts related to energy and entropy have long been proposed in Earth system science, yet they remain obscure, seem contradictory regarding their goal to either maximize or minimize, and have so far only played marginal roles. This review aims to clarify the role of thermodynamics and optimality in Earth system science by showing that it plays a pivotal role in how, and how much, work can be derived from the solar forcing, and that this imposes a major constraint to the dynamics of dissipative structures of the Earth system. This is, however, not as simple as it may sound. It requires a consistent formulation of Earth system processes in thermodynamic terms, including their linkages and interactions. Thermodynamics then constrains the ability of the Earth system to derive work and generate free energy from the solar radiative forcing, which limits the ability to maintain motion, mass transport, geochemical cycling, and biotic activity. It thus limits directly the generation of atmospheric motion and other processes indirectly through their need for transport, such as hydrologic cycling or biotic activity. I demonstrate the application of this thermodynamic Earth system view by deriving first-order estimates associated with atmospheric motion, hydrologic cycling, and terrestrial productivity that agree very well with observations. This supports the notion that the emergent simplicity and predictability inherent in observed climatological variations can be attributed to these processes working as hard as they can, reflecting thermodynamic limits directly or indirectly. I discuss how this thermodynamic interpretation is consistent with established theoretical concepts in the respective disciplines, interpret other optimality concepts in light of this thermodynamic Earth system view, and describe its utility for Earth system science.

Axel Kleidon

Status: open (until 10 Oct 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on esd-2022-38', Anonymous Referee #1, 20 Sep 2022 reply

Axel Kleidon

Axel Kleidon


Total article views: 419 (including HTML, PDF, and XML)
HTML PDF XML Total BibTeX EndNote
297 115 7 419 3 2
  • HTML: 297
  • PDF: 115
  • XML: 7
  • Total: 419
  • BibTeX: 3
  • EndNote: 2
Views and downloads (calculated since 22 Aug 2022)
Cumulative views and downloads (calculated since 22 Aug 2022)

Viewed (geographical distribution)

Total article views: 407 (including HTML, PDF, and XML) Thereof 407 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
Latest update: 28 Sep 2022
Short summary
The second law of thermodynamics has long intrigued scientists, but which role does it play in the Earth system? This review shows that its main role is that it shapes the conversion of sunlight into work. This work can then maintain the dynamics of the physical climate system, the biosphere, as well as human societies. The relevance of it is that apparently many processes work at their limits, so that they become predictable by simple means.