Capitalism is obsessed with growth. Growth in a closed system means siphoning resources from other areas of the system. With the exception of solar energy, the Earth is a closed system.

It stands to reason that if capitalist subsystems are always seeking growth, then they will eventually exhaust the energy of the parent system. Indeed, the entire model of "capital" centers around the exploitation of the parent system's resources and converting them to profit.

Grassroots degrowth (ie, people being actually conscious of their energy useage and trying to reduce it) cannot succeed on its own without dissolution (whether by governance or violence) of existing energy vorices.