by F. Engelbeen, Nov 2022

In climate skeptics circles, there is rather much confusion about historical/present CO2 measurements. This is in part based on the fact that rather accurate historical direct measurements of CO2 in the atmosphere by chemical methods show much higher values in certain periods of time (especially around 1942), than the around 280 ppmv which is measured in Antarctic ice cores. 
280 +/- 10 ppmv is assumed to be the pre-industrial amount of CO2 in the atmosphere during the current interglacial (the Holocene) by the scientific community. This is quite important, as if there were (much) higher levels of CO2 in the recent past, that may indicate that current CO2 levels are not from the use of fossil fuels, but a natural fluctuation and hence its influence on temperature is subject to (huge) natural fluctuations too and the current warmer climate is not caused by the use of fossil fuels.

To be sure about my skepticism: I like to see and examine the arguments of both sides of the fence, and I make up my own mind, based on these arguments. I am pretty sure that current climate models underestimate the role of the sun and other natural variations like ocean oscillations on climate and overestimate the role of greenhouse gases and aerosols. But I am as sure that the increase of CO2 in the atmosphere since the start of the industrial revolution is mainly from the use of fossil fuels.

There are several reasons why the hypothesis of large non-human CO2 variations in recent history is wrong (see my comment on the late Ernst Beck’s compilation of historical measurements) and that most of the recent increase in CO2 in the atmosphere indeed is mainly man-made, but that needs a step-by-step explanation. Follow the steps: 

  1. Evidence of human influence on the increase of CO2 in the atmosphere.

    1. The mass balance
    2. The process characteristics
    3. The 13C/12C ratio
    4. The 14C/12C ratio
    5. The oxygen use
    6. The Ocean’s pH and pCO2
    7. The processes involved
  2. Conclusion

  3. Extra: how much human CO2 is in the atmosphere?

  4. Reference