The crepuscular planet. A model for the exhausted atmosphere and hydrosphere

The Crepuscular Earth presented here is a guess reference model of the planet in which all mineral resources have been extracted and dispersed and fossil fuels have been burnt. It serves as a realistic limit of resources to assess the Earth’s non-renewable exergy capital.Under such conditions we estimate a state of the atmosphere and hydrosphere using updated fossil fuels stocks (1925 GtC for proven reserves, rising to about 16,224 GtC when including estimated additional reserves) and emissions projections in a simple model of the carbon cycle. We consider the BAU-I scenario as the most likely to occur, corresponding to an atmospheric injection of about 2000 GtC. Accordingly, we propose a crepuscular atmosphere having a carbon dioxide content of 683 ppm, a mean surface temperature of 17 °C (peak carbon dioxide induced warming of 3.7 °C above pre-industrial temperatures), a pressure of 1.021 bar, and a composition in volume basis of 78.8% N2, 20.92% O2, 0.93% Ar, and 0.0015% of trace gases. Considering that oceans account for 97.5% of the whole hydrosphere, the crepuscular hydrosphere is assumed to have the current chemical composition of the oceans at an average temperature of 17 °C.