[jackcosgrove]

Earth's biome gets most of its energy from the sun. I think that's what the GP was getting at.

[js8]

The physics definition of closed system allows exchange of energy. If neither matter nor energy can be exchanged, that's called an isolated system.

[jackcosgrove]

Thanks for the clarification. I'm not sure in what sense the others are using the term. The mechanism of collapse in the paper, exhaustion of fossil fuels, relies on not enough energy in the system, so I assumed energy was part of the calculation.