Examining the Global Carbon Project’s Estimates of CO2 Sources and Sinks, 1959-2023
March 30th, 2025 by Roy W. Spencer, Ph. D.
Summary of Main Points
By choosing the “best” models and estimates of CO2 fluxes (those which best explain year-to-year changes in atmospheric CO2 content as measured at Mauna Loa, HI) for the period 1959-2023 as provided by the Global Carbon Project, a multiple linear regression of yearly Mauna Loa CO2 changes against those “best” estimates of sources and sinks leads to the following alterations to the “official ” Global Carbon Project estimates of the sources and sinks leading to the observed rise in atmospheric CO2. (NOTE: being a statistical exercise, this does not constitute “proof”… these are just some areas that carbon budget modelers might want to look into when tweaking their models):
Global anthropogenic CO2 emissions appear to be 30% larger than reported (I find this hard to believe… again, statistics are not necessarily proof).
The Land Sink of CO2 has been underestimated by an average of about 25%
The Ocean Sink of CO2 has been overestimated by about 20% (I don’t know whether they include CO2 outgassing).
The Land Use source of CO2 (primarily biomass burning) has been overestimated by about a factor of 2 (very uncertain)
The cement carbonation sink has been underestimated by about a factor of 7 (very uncertain)
There is a remaining unknown CO2 sink that has averaged 0.2 ppm/yr during 1959-2023 (this could just be a residual of other statistical errors).
https://www.drroyspencer.com/2025/03/examining-the-global-carbon-projects-estimates-of-co2-sources-and-sinks-1959-2023/
