CO2-CH4 Concentrations Over the Last 3 Million Years

April 20, 2026 rjdavison

CSS-81 – CO2-CH4 Concentrations Over the Last 3 Million Years Download PDF

CSS-81 A recent paper (March 2026), “Broadly stable atmospheric CO₂ and CH₄ levels over the past 3 million years” by Marks-Peterson et al was published in Nature. As the title states, atmospheric CO₂ and CH₄ levels have been broadly stable for the last 3 million years (based on ice cores from the Allan Hills Blue Ice Area (BIA) in Antarctica). This is great information (unless you are a Catastrophic Anthropogenic Global Waming (CAGW) alarmist). But the Marks-Peterson et al data is just confirmation of an earlier and more comprehensive data set (Westerhold et al’s benthic foraminifera carbon isotope ratio reconstruction).

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In 2020, Westerhold et al published their paper, “An astronomically dated record of Earth’s climate and its predictability over the last 66 million years”. The general stability in the Marks-Peterson et al data provides a confirmation of the Westerhold et al data (focused on the last 3 million years). The Westerhold et al carbon isotope ratio (δC₁₃ ≡ C₁₃/C₁₂) data, a proxy for CO₂ levels, fluctuates significantly (in conjunction with the Milankovitch cycles visible in the earlier ice core data sets). Those fluctuations correspond to a CO₂ concentration range of roughly 180 to 300 ppm. However, over the last 3 million years, the average CO₂ levels have dropped just ±12 ppm (240 to 228 ppm), consistent with the Marks-Peterson ice core data.

The two data sets effectively provide the same information. The major difference is in their resolution. For the Marks-Peterson data more than one million years old, the data is likely just reflecting the average CO₂ concentration. There is more variability in the Marks-Peterson data from 400,000 to 1,000,000 years ago. That increased variability is likely due to higher resolution data reflecting more of the Milankovitch cycle influence.

The Westerhold et al data also contains the oxygen isotope ratio (δO₁₈ ≡ O₁₈/O₁₆) data, a proxy for temperature. That data shows that temperatures dropped roughly 4.5 °C over the last 3 million years. The current temperature down trend began around 3.5 million years ago when the Panama Isthmus finally closed. Temperatures were already dropping as the Panama Isthmus was closing, just at a lower rate. So, is that ±4.5 °C temperature drop due to the ±12 ppm drop in average CO₂ concentrations? Not a chance! Natural forcings were producing the changes in temperature over the last 3 million years and the CO₂ changes were following that temperature change. A minor portion will be CO2, but the magnitude is dependent on CO2’s climate sensitivity.

The Marks-Peterson and Westerhold et al data shows that CO₂ had, at best, an imperceptible minor influence on our planet’s climate over the last 3 million years. Based on other data sets, that statement also applies over humanity’s existence (the Holocene interglacial warm period). The climate changed vigorously over the last 12,500 years while CO₂ concentration levels remained virtually flat in the 265 to 280 ppm range. Since 1850, our CO₂ levels have increased to 430 ppm. That ±150 ppm CO₂ increase will have contributed to some of the ±1.5 °C temperature increases since 1850. But the natural forcings that have been driving the earth’s climate over the last 3 million years (with little influence from CO₂) are still active. Just not in the IPCC’s climate models.

The contributions of anthropogenic and natural forcings are not settled science. The IPCC uses a CO₂ Equilibrium Climate Sensitivity (ECS) range of 1.8 to 5.7 °C. The climate models self-admittedly run too hot even at the lower end of the IPCC range. Even on the climate realist side, the estimates range from virtually zero to the IPCC’s low end. Not settled science! The IPCC effectively ignores solar activity, using just one out of the 40+ Total Solar Irradiance (TSI) reconstructions. They also ignore the many other solar forcings (Cosmic Ray Flux (CRF), High Energy Particles (HEP), etc.) over and above the relatively minor TSI influence. TSI is more a proxy for solar activity than an absolute value. Again, not settled science!

The links below delve into these general concepts in far more detail. But the climate change picture is far more comprehensive and accurate when solar activity and its influence on ocean cycles, volcanic/seismic activity, etc. are factored into the analysis. Net Zero, the energy transition and other ‘green’ initiatives that are being pushed on society are based on unsettled science that will have no measurable effect on the climate. These unnecessary, dangerous initiatives must be put aside so that we can focus on the real crises (energy, food, financial, crime, etc.) we are already facing. CO₂ emissions are not a problem; the wasted capital directed towards their reduction are!