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Max Planck Institut for Biogeochemistry

Motivation

Our research uses a combination of thermodynamics, which is motivated by the fundamental importance of the second law of thermodynamics, and an Earth system perspective, which jointly describes processes as well as their interaction with the conditions at the boundary.

The thermodynamic view

Water flows downhill, mountains erode, and wood decomposes. In the absence of other processes, sooner or later, water would collect in the world’s oceans, mountains would be eroded down to the seafloor, and wood would decompose to its raw ingredients. The outcome would constitute a “dead” state of the Earth system, without atmospheric dynamics, hydrologic and biogeochemical cycling, and it would be unable to sustain life. The present Earth is nowhere near such a “dead” state, yet energy and mass balances, which form the central basis for many models of Earth system components, are insufficient to explain this difference.

The key to understand the highly dynamic nature of the Earth system is that it is a system maintained far from a state of thermodynamic equilibrium. To understand how this state of disequilibrium is being maintained requires the description of Earth system processes in thermodynamic terms, in terms of the form of thermodynamic disequilibrium, and in terms of the processes being dissipative, thereby producing entropy. Thermodynamics thus provides the key answer to understand why the Earth is not in such a “dead” state.

The Earth system context

In practice, this view requires to think about the different forms of energy that Earth system processes relate to, in terms of their conversions, where these forms of energy come from, where they go to, and these energy conversions relate to the processes and functioning of the whole system. Many processes interact within the Earth system, thereby making it highly complex and dynamic. To identify general directions and limits in these dynamics, we look at how the Earth generates various forms of energy out of the incident solar radiation. These forms of energy maintain the winds in the atmosphere, the currents in the oceans, and the global cycling of water and other elements.

We use this approach to describe how the land surface interacts with the atmosphere, how these interactions are altered by vegetation, and quantify the natural limits of how much renewable energy is generated by the Earth system.

Planetary thermodynamics of the Earth system. A planetary thermodynamic view of the Earth system, with its cascades of energy conversions (left, solid lines) and its effects (right, dashed lines). The thermodynamic description of this planetary view and the quantification of thermodynamic limits of the conversion rates are the main objectives of this book. (after Kleidon 2010, 2012, 2016).


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