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The crepuscular planet part I: A model for the exhausted atmosphere

Abstract:

The second law of thermodynamics imposes a cost to any transformation in nature. As a consequence, the increased fluxes of materials between the atmosphere, lithosphere and hydrosphere caused by human activities leave a perennial footprint on our planet. The crepuscular earth represents a planet towards we are inexorably approaching, as mineral resources are extracted and dispersed, fossil fuels are burned, and waters are polluted by humankind. By knowing the crepuscular planet we can for the first time visualise and quantify a thermodynamic limit of the earth, which serves as a reference to calculate the exergy of any state of earth's resources. The present work estimates the state of the atmosphere when all remaining fossil fuels are burnt and its carbon is released, leading to a change in atmospheric composition. In order to estimate these effects we use updated fossil fuels stocks (conventional and nonconventional) and emissions projections in a simple model of the carbon cycle. The mixing ratio of carbon dioxide and other greenhouse gases will rise, as well as that of some trace gases, while the oxygen concentration will decrease slightly. This modification of atmospheric composition is expected to result in a temperature rise of the earth's surface and substantial climate change. The water content of the atmosphere is expected to increase, although significant change in relative humidity is unlikely to occur. The availability of freshwater is likely to be reduced due to direct pollution and precipitation changes. Thus, the crepuscular planet appears as having a warmer atmosphere and ocean with a higher content of materials formerly appearing in the lithosphere