The Scientific Method at Work: The Carbon Cycle Revisited, Again

In a previous post, I demonstrated how a new model of the carbon cycle, described in a 2020 preprint, is falsified by empirical observations that fail to confirm a prediction of the model. The crucial test of any scientific hypothesis is whether its predictions match real-world observations. But a newly publicized discussion now questions the foundations of the model itself.

The model in question, developed by U.S. physicist Ed Berry, describes quantitatively the exchange of carbon between the earth’s land masses, atmosphere and oceans. Berry argues that natural emissions of CO₂ into the atmosphere since 1750 have increased as the world has warmed, and that only 25% of the increase in atmospheric CO₂ after 1750 is from humans.

This is contrary to the CO₂ global warming hypothesis that human emissions have caused all of the CO₂ increase above its preindustrial level in 1750 of 280 ppm (parts per million). The CO₂ hypothesis is based on the apparent correlation between rising worldwide temperatures and the CO₂ level in the lower atmosphere, which has gone up by 49% over the same period.

Natural CO₂ emissions are part of the carbon cycle that includes fauna and flora, as well as soil and sedimentary rocks. Human CO₂ from burning fossil fuels constitutes less than 5% of total CO₂ emissions into the atmosphere, the remaining emissions being natural. Atmospheric CO₂ is absorbed by vegetation during photosynthesis, and by the oceans through precipitation. The oceans also release CO₂ as the temperature climbs.

In a recent discussion between Ed Berry and the CO₂ Coalition, the Coalition says that Berry confuses the 5% of CO₂ emissions originating from fossil fuels with the percentage of atmospheric CO₂ molecules that actually come from fossil fuel burning. This percentage is very small, because the molecules are continually recycled and thus “diluted” with the much larger quantity of CO₂ molecules from natural emissions.

Physicist David Andrews amplifies this comment of the CO₂ Coalition in a 2022 preprint, by pointing out that total CO₂ emissions into the atmosphere from human activity over time exceed the rise in atmospheric CO₂ over the same interval. So all the modern CO₂ increase (from 280 to 416 ppm) must come from human emissions. Adds Andrews:

… we know immediately that land and sea reservoirs together have been net sinks, not sources, of carbon during this period. We can be sure of this without knowledge of the detailed inventory changes of individual non-atmospheric reservoirs. … Global uptake is simply what is left over after atmospheric accumulation has been subtracted from total emissions. If more carbon was injected into the atmosphere by fossil fuel burning than stayed there, it had to have gone somewhere else.

The arguments of both Andrews and the CO₂ Coalition are at odds with Berry’s calculations, depicted in the figure below; H denotes human and N natural CO₂.

This figure shows that the sum total of human CO₂ emissions (blue dots) exceeds the rise in atmospheric CO₂ (black dots), at least since 1960, in agreement with Andrews’ comment. Where Berry goes astray is by claiming that natural emissions, represented by the area between the blue and red solid lines, have not stayed at the same 280 ppm level over time, but have gone up as global temperatures have increased.

Such a claim is extremely puzzling, as the model requires the addition to the atmosphere of approximately 100 ppm of CO₂ from natural sources since 1840 – an amount far in excess of the roughly 10 ppm of CO₂ outgassed from the oceans as ocean temperatures rose about 1 degree Celsius (1.8 degrees Fahrenheit) over that time. Berry acknowledges the problem, but only proposes unphysical explanations, such as mysteriously adding new carbon to the carbon cycle.

The falsified prediction of his model, on the other hand, involves the atmospheric concentration of the radioactive carbon isotope ¹⁴C, produced by cosmic rays interacting with nitrogen in the upper atmosphere. The concentration of ¹⁴C almost doubled following above-ground nuclear bomb tests in the 1950s and 1960s, and has since been slowly dropping. At the same time, concentrations of the stable carbon isotopes ¹²C and ¹³C, generated by fossil-fuel burning, have been steadily rising. Because the carbon in fossil fuels is millions of years old, all the ¹⁴C in fossil-fuel CO₂ has decayed away.

Although Berry claims that his model’s prediction of the recovery in ¹⁴C concentration since 1970 matches experimental observations, Andrews found that Berry had confused the concentration of ¹⁴C with its isotopic or abundance ratio relative to ¹²C, as I described in my earlier post.

As a result, Berry’s carbon cycle model does not replicate the actual measurements of ¹⁴C concentration in the atmosphere since 1970, as he insists it does. Needless to say, he also disputes the arguments of Andrews and the CO₂ Coalition about the very basis of his model.

Next: Challenges to the CO2 Global Warming Hypothesis: (7) Ocean Currents More Important than the Greenhouse Effect