  The notion that the whole is more than the sum of its parts has a long
tradition in science. This, of course, also applies to the Earth system. With
its myriad of processes, spanning from purely physical to life and human
activity, the Earth is a vastly complex system. It may thus seem that there is
nothing simple and general to say because of this overwhelming complexity. What
I want to show here is that by formulating the Earth as a thermodynamic system,
one can identify general directions and infer simple functioning because
thermodynamics imposes fundamental limits on the dynamics. At the center of
this description are energy conversions and states of disequilibrium, which are
at the core of the dynamics of Earth system processes, from convection cells to
living organisms and human societies. They are linked to each other and
interact by their exchanges of energy and mass, and ultimately affect how much
of the input of low entropy solar radiation from the Sun is converted into free
energy, energy able to perform work, before the energy gets re-emitted by the
Earth as high entropy terrestrial radiation. The emergent thermodynamic
behavior of the Earth then becomes simple because the dynamics evolve to and
operate at thermodynamic limits. Such behavior of Earth system processes
operating at the edge of their limit can then be linked to previously described
holistic theories, such as the Gaia hypothesis, with similarities in the
described emergent behavior. Such a thermodynamic view, however, can go
further, as it can also be used to understand the role of human societies in
the Earth system and the potential pathways to a sustainable future.
Thermodynamics taken together with the energy conversions and interactions
within the Earth system can thus provide a basis to understand why the whole
Earth system is more, and simpler, than the sum of its spheres.
