The Top 10 Forms of Complexity in Earth Surface Systems

When we (scientists) talk and write about complexity in recent years, the focus is on complex nonlinear dynamics, and related phenomena such as deterministic chaos, dynamical instability, some forms of self-organization, fractal geometry, etc.  These are forms or sources of complexity that are intrinsic to the structure of dynamical systems, but these are hardly the only things that make systems complex. So, to make sure we don’t forget the elements of complexity that transcend so-called “complexity science,” I present the Top 10 Forms of Complexity in Earth Surface Systems (ESS). ESS is a blanket term that includes geomorphic systems, landscapes, ecosystems, soil systems, etc.  Even though the items are numbered, they are actually in no particular order. Many ESS may exhibit only a few of these forms, and still be quite complex!

The list I was gonna do has already been done ( 

Forms of Complexity in Earth Surface Systems

1. Number of components.  Earth surface systems may have a very high number of components (landforms, soils, chemical components, organisms, species, microclimates, etc.).

2. Degrees of freedom. The large number of components and dense network of connections and relationships between them means that ESS have many different ways or modes of responding to change, and multiple alternative configurations for a given set of boundary conditions.

3. Mutual adjustments.  Due to feedback relationships, ESS components often feature mutual adjustments, whereby components both affect, and are affected by, each other.

4. Changing interconnections. The existence or presence, rates, and intensities of interconnections and feedbacks change. The components are also dynamic.

5. Multiple Scale Causality.  ESS phenomena are not controlled primarily by either bottom-up (microscale to macroscale) or top-down causality. Rather they are determined by multiple processes and controls acting at a range of spatial and temporal scales both larger and smaller.

6. Variability I.  Extrinsic factors that influence ESS are strongly heterogeneous in space and time.

7. Variability II. ESS themselves are strongly heterogeneous in space and time.

8. Nonequilibrium.  ESS are often in states not in, near, or approaching steady-state, thermodynamic equilibrium, or other equilibria.

9. Historical contingency. The direction and magnitude of change is influenced by pre-existing conditions and past events. ESS development is path-dependent.

10. Nonlinearity.  ESS are nonlinear, which enables the possibility of complex phenomena such as dynamical instability and deterministic chaos. 

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