The Ability of the Planet to Recycle Carbon

An important factor about anthropogenic climate change is the ability of the planet to recycle carbon. It does this recycling using three major carbon reservoirs. These comprise the oceans, the shallow water sediments and the biosphere comprising plants (including trees) and soils. If humans inject more carbon dioxide into the atmosphere than the planet can recycle then the atmosphere becomes another carbon reservoir.

At one time it was thought by some that the oceans, being so vast, could absorb all the carbon dioxide that humanity could throw into the air, through the surface of the planet, which after all comprises 70% water. Others thought that carbon dioxide would stay in the atmosphere for thousands of years.

We know from measurements taken in places with very clean air and very far from industry and where there are few vehicles like Maua Loa in Hawaii that the proportion of carbon dioxide in the atmosphere is rising and in the past sixty years has risen by about a quarter. The argument has probably been settled by these measurements which show that the oceans cannot absorb all the excess carbon dioxide. Certainly the biosphere cannot absorb it all, as the biosphere is shrinking as humanity grows, releases carbon dioxide by chopping down and burning trees and disturbing the soil, releasing carbon dioxide sequestrated there.

There have been other means of tracking anthropologically produced carbon dioxide. When you release carbon dioxide by burning fossil fuel, you release carbon that is too old (because it comes from burning very ancient fossil fuel) to have any of the radioactive isotope carbon-14. By measuring and tracking this isotope we can see how much carbon dioxide in the atmosphere has been produced by fossil fuel.

The ocean absorption of carbon dioxide is not an infinite process because by absorbing carbon dioxide the surface of the ocean becomes more acidic and the more acidic an ocean the less carbon dioxide it is capable of absorbing. Also, you have to take into account that while some of the carbon dioxide dissolved in sea water is properly sequestrated by being taken into the ocean floor where it eventually settles in the form of carbon, most of it is released back into the atmosphere by the simple process of sea water evaporating.

Best estimates of the carbon cycle indicate that the plant can only sequestrate about a half of the carbon dioxide released into the atmosphere each year. If that estimate is true and you do the maths taking into account the cumulative effect of carbon dioxide in the atmosphere you arrive at the rather depressing conclusion that if we cut back carbon dioxide production to 50% of the present amount, the global warming effect of atmospheric carbon dioxide would continue for at least another fifty years.