From Dr. Roy Spencer’s Blog

by Roy W. Spencer, Ph. D.

This is an update of my CO2 budget model that explains yearly Mauna Loa atmospheric CO2 concentrations since 1959 with three main processes:

1. an anthropogenic source term, primarily from burning of fossil fuels
2. a constant yearly CO2 sink (removal) rate of 2.05% of the atmospheric “excess” over 295 ppm
3. an ENSO term that increases atmospheric CO2 during El Nino years and decreases it during La Nina years

The CO2 Budget Model

I described the CO2 budget model here. The most important new insight gained was that the model showed that the CO2 sink rate has not been declining as has been claimed by carbon cycle modelers after one adjusts for the history of El Nino and La Nina activity.

If the sink rate was really declining, that means the climate system is becoming less able to remove “excess” CO2 from the atmosphere, and future climate change will be (of course) worse than we thought. But I showed the declining sink rate was just an artifact of the history of El Nino and La Nina activity, as shown in the following figure (updated through 2022).

The model also showed how the eruption of Mt. Pinatubo caused a large increase in rate of removal of CO2 from the atmosphere (not a new finding) due to enhanced photosynthesis from more diffuse sunlight. This contradicts the popular perception that volcanoes are a major source of atmospheric CO2.

I attempted to get the results published in Geophysical Research Letters, and was conditionally accepted after one review. But the editor wanted more reviewers, which he found, who then rejected the paper. The model is straightforward, physically consistent, and agrees with the observed Mauna Loa CO2 record, as shown in the following plot.

2022 Update: CO2 continues to Rise Despite Renewable Energy Transition

As I have pointed out before, the global economic downturn from COVID had no measurable impact on the Mauna Loa record of atmospheric CO2, and that is not surprising given the large year-to-year variations in natural sources and sinks of CO2. Atmospheric CO2 concentrations continue to rise, mainly due to emissions from China and India whose economies are rapidly growing.

The following plot zooms in on the 2010-2035 period and shows the Mauna Loa CO2 rise compared to my budget model forced with 3 scenarios from the Energy Information Administration (blue lines), and also compared to the RCP scenarios used by the IPCC in the CMIP5 climate model intercomparison project.

The observations are tracking below the RCP8.5 scenario, which assumes unrealistically high CO2 emissions, yet remains the basis for widespread claims of a “climate crisis”. The observations are running a little above my model for the last 2 years, and only time will tell if this trend continues.

But clearly the international efforts to reduce CO2 emissions are having no obvious impact. This is unsurprising since global energy demand continues to grow faster than new sources of renewable energy can make up the difference.