“Consensus” climate science has for decades assumed that the vast majority of the increase in atmospheric concentration of carbon dioxide (from about 280 parts per million by volume [ppmv] before the Industrial Revolution to about 400 today) has come from burning fossil fuels for energy. On that assumption, “consensus” scientists have alleged that human activity has driven all or most global warming over that time.
Most criticism of that thinking has focused on “climate sensitivity”—how much warming comes from added atmospheric CO2, with “skeptics” opting for “climate sensitivity” in the range of 0.5–2.0 deg. C while “alarmists” opt for 1.5–4.5 or even higher. More recent studies increasingly lean toward the lower range as they note that observed warming has been considerably less than predicted.
But what if far less of the increase in CO2 has come from human activity? If that’s so, then human contribution to global warming would be far less, too—regardless what “climate sensitivity” turns out to be.
And what if CO2 added to the atmosphere remains there not for hundreds of years but for only a few? That, too, would reduce human contribution to global warming.
That’s the implication of a new paper in Global and Planetary Change by Hermann Harde, “Scrutinizing the carbon cycle and CO2 residence time in the atmosphere,” which concludes that human activity has contributed only about 4% of total atmospheric CO2 and 15% of the ~120 ppmv increase in CO2 concentration since the Industrial Revolution, and that CO2 added to the atmosphere stays there for only about 4 years.
Here’s the abstract:
Climate scientists presume that the carbon cycle has come out of balance due to the increasing anthropogenic emissions from fossil fuel combustion and land use change. This is made responsible for the rapidly increasing atmospheric CO2 concentrations over recent years, and it is estimated that the removal of the additional emissions from the atmosphere will take a few hundred thousand years. Since this goes along with an increasing greenhouse effect and a further global warming, a better understanding of the carbon cycle is of great importance for all future climate change predictions. We have critically scrutinized this cycle and present an alternative concept, for which the uptake of CO2 by natural sinks scales proportional with the CO2 concentration. In addition, we consider temperature dependent natural emission and absorption rates, by which the paleoclimatic CO2 variations and the actual CO2 growth rate can well be explained. The anthropogenic contribution to the actual CO2 concentration is found to be 4.3%, its fraction to the CO2 increase over the Industrial Era is 15% and the average residence time 4 years.