For CO2 to be considered a driver of Earth’s temperatures, changes in CO2 that uni-directionally correlate with temperatures should not be an exceptional occurrence. Yet a causal link from CO2 radiative forcing to temperature changes could hypothetically be inferred for just 2.6% of the last 425 million years.
A detailed analysis (Davis, 2017) of temperature and CO2 proxies over the Phanerozoic Eon by environmenalist Dr. W. Jackson Davis finds that for 77.9% of the record there was a non-discernible correlation between CO2 and temperature.
On the occasion there was a correlation between CO2 and temperature, most (60%) of the correlation instances were negative. In other words, when a correlation could be discerned, temperatures fell as CO2 rose or CO2 fell as temperatures rose more often than CO2 and temperature rose and fell with a semblence of synchronicity.
If we assume temperature changes are radiatively forced or amplified by CO2, this cause-effect link could be correlationally established for just 2.6% of the 4.25 million-year record.
As Dr. Davis concludes, “changes in atmospheric CO2 concentration did not cause temperature change in the ancient climate.”
Image Source: Davis, 2017
No discernible correlation between CO2 and temperature for the last 80,000 years either
Some newly published papers also contradict the claim CO2 is a driver of Earth’s temperature changes.
Li and Born (2019) document 8-16°C climate warmings (D-O events) in Greenland that extended to both hemispheres between about 80 and 15 thousand years ago. (Though global in scope, temperature changes were less pronounced outside Greenland.)
These abrupt warmings occurred within decades (or less), and they occurred without any CO2 fluctuation before or after the change.
CO2 hovered around 190 ppm to 200 ppm throughout each warming and cooling event.
Even more fascinating, it’s been suggested that these warm-ups may have required no external forcing, as they’re considered an “unforced oscillation”.
The climate system can warm by 8-16°C within decades via internal variability.
Image Source: Li and Born (2019)
Throughout the last glacial, when CO2 remained effectively unchanged at about 200 ppm, there were warming periods that exceeded the Holocene’s thermal maximum by 2-6°C in locations ranging from Southern Europe to Russia to California.
Of course, none of these warming and cooling climate transitions could be associated with changes in CO2 either.