The discovery of fire is acknowledged as one of the essential steps in the development of our current society. However, fire now stands accused of threatening to destroy that society, since the burning of carbon-based fuels emits carbon dioxide as an unavoidable product; and, that carbon dioxide is suspected of causing global climate change.

The combustion of carbon stored as coal, oil and natural gas releases carbon dioxide in excess of the carbon dioxide released each year as the result of natural processes and geologic events. These emissions are described as anthropogenic emissions, since they result directly from human activities. Various sources differ on details. However, it appears that global atmospheric concentrations of carbon dioxide began increasing in about 1750, from a concentration of approximately 270-280 ppm, with inflection points at approximately 1850 and again at approximately 1950. Atmospheric carbon dioxide concentrations have now reached approximately 390 ppm.

Various sources have estimated that approximately one half to two thirds of annual anthropogenic carbon dioxide emissions are removed from the atmosphere by natural processes, primarily by absorption into the world’s oceans. Some have suggested that global annual anthropogenic carbon dioxide emissions would therefore have to be reduced by roughly one third to one half to halt the increase in atmospheric carbon dioxide concentrations. I believe the history of the increase in global atmospheric carbon dioxide concentrations suggests that the percentage reduction in global annual carbon dioxide emissions would have to be far greater, arguably total, to halt the accumulation of anthropogenic carbon dioxide in the atmosphere.

For example, if natural processes remove half of anthropogenic emissions at current rates and would continue to do so at reduced emissions rates, all other things being held equal, then a 50% global annual emissions reduction would directly match the natural removal rate, stabilizing the atmospheric concentration at the concentration when the 50% reduction was achieved. However, that logic would also suggest that the atmospheric carbon dioxide concentration would have remained unchanged through history until the global annual emissions rate reached 50% of the current global annual emissions rate, at which point the atmospheric carbon dioxide concentration would have increased far more rapidly than the historic record indicates, until it achieved the current concentration. Since global annual emissions have approximately doubled since 1950, that would suggest that the proxy record of atmospheric carbon dioxide concentration should have recorded no concentration increase until around 1950, then a rapid ramp-up to current concentrations. That is clearly not the case, as both the proxy records and the instrument records indicate.

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Rather, the proxy record suggests that atmospheric carbon dioxide concentrations began increasing in approximately 1750, when global annual emissions were approximately 0.05% of current emissions levels. That then suggests a process controlled by the concentration difference between the carbon dioxide concentration in the atmosphere and the concentration in the natural systems, such as the oceans, which absorb carbon dioxide from the atmosphere. The significance of such a process is that, as global annual carbon dioxide emissions decreased, the percentage of the annual anthropogenic carbon dioxide emissions absorbed through natural processes would remain at or near 50% in this example. Therefore, atmospheric carbon dioxide concentrations would not stabilize until incremental annual carbon dioxide emissions ceased, although the rate of growth would be progressively diminished.

That construct has major implications for any effort to control climate change by stabilizing atmospheric carbon concentrations. It has even greater implications for any effort to not only stabilize atmospheric carbon dioxide concentrations, but also reduce atmospheric carbon dioxide concentrations from current levels to some lower level, such as 350 ppm, which some believe is the maximum safe long term concentration; or, to 270 ppm, the approximate pre-industrial atmospheric carbon dioxide concentration. While atmospheric carbon dioxide concentration would be expected to decay over a multi-decadal period, once global annual anthropogenic carbon dioxide emissions ceased, that decay could be partially offset by desorption of carbon dioxide from the oceans and other natural systems as the atmospheric concentration declined. More rapid decrease of atmospheric carbon dioxide concentration would require extraction of carbon dioxide from the atmosphere. While several technologies exist for such extraction, their implementation on a global scale would be both investment intensive and time consuming.