– Robert U. Ayres. Paris, 29 October 2014
Photosynthesis was (and is) the biological process that removed carbon dioxide from the primitive atmosphere and left some of the oxygen in the atmosphere and sequestered CO2 in the earth’s crust. That happened as living organisms, such as diatoms, in the oceans attached carbon dioxide to calcium ions to make shells for themselves and left them as chalk or limestone. This went on for billions of years. When the oxygen level in the atmosphere rose enough, the new ozone layer cut the UV radiation level and made life on land feasible. Plants moved onto the land, and thrived spectacularly during the so-called Carboniferous era, several hundred million years ago when the CO2 level was still quite high by present standards. For over a hundred million years immense accumulations of dead plant biomass were covered by silt from erosion of the land surface. Meanwhile the bodies of dead marine organisms accumulated in some places under the sea. These accumulations were gradually compressed and “cooked” (pyrolized) releasing some of the hydrogen and converting the rest of the mass successively into peat, lignite and coal or (in the case of marine biomass) into bitumen and petroleum.
These accumulations constitute an energy (exergy) resource that currently drives industry and human civilization. We humans are now “un-sequestering” those stored hydrocarbons, combining them with oxygen and putting CO2 back into the atmosphere. Moreover, we are doing this at a rate thousands or even millions of times faster than the original accumulation. This ultra-rapid dissipation of stored exergy in the form of hydrocarbons clearly cannot continue indefinitely, not because we will run out of carbon fuels immediately, but because the atmospheric buildup of CO2 cannot continue much longer without catastrophic climatic consequences (IPCC 2007, 2014).