Immoderate institutional focus on CO2 emissions tends to obscure the energy-density challenge implied by the low-carbon economy transition. Such an attention deficit is often apparent in the sustainability transitions literature in general and in the multi-level perspective (MLP) in particular. The latter characterises the comparatively “benign” conditions of industrial societies which, riding the upside of the energy-density curve, did not have any historical concern for sustainability. Yet, understanding the down slope of the energy-density curve is the urgent imperative in policy decisions and social dialogue around sustainability today.