Imagine a surface of constant, but very low, nitrogen concentration that encloses Earth. That surface is closed and it bounds the Earth System.
While that surface is closed, it does not mean that there are no fluxes across it. Mass crosses in both direction: incoming mass includes meteorites, but also, depending on what nitrogen concentration is chosen to define the surface, a selection of space junk; outgoing includes helium and space probes. The energy balance across that surface determines, among other things, Earth's room temperature.
The scale of that surface defines the largest scale in the hierarchy of Earth systems. The fluxes across that surface connect the Earth System to the Solar System and other systems beyond. That is clearly a loose coupling, but it is just the sort of thing that allows a hierarchical scale to be defined.
Within the Earth System, there are many subsystems. Those subsystems include the carbon cycle, international economics, my body and the computer on which these ideas are being composed. Many of those subsystems are linked and the links between them can be stronger or weaker. The link between the carbon cycle and international economics is reasonably strong; for better or worse the link between the carbon cycle and international politics is weaker than that with economics.
Our challenge then is to work out the connections and workings of subsystems of the Earth System and in so doing find levers we can pull to ensure that the possible futures for our planet include a reasonably large set that are satisficing.
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