Thread by @ncdave4life

《1/12⟫ Someone asked how we can know the ongoing rise in atmospheric CO2 level is entirely from human emissions, since Earth's climate is so complex.


Fortunately, you don't need a climate model to answer that question. It's as easy as (steps) A, B, C:sealevel.info/co2.html

《2/12⟫ A. The bean-counters keep good track of production & use of fossil fuels and Portland cement, and simple chemistry tells us how much CO2 is produced from them. That's "fossil carbon." (Irrelevant side note: fossil carbon is almost completely depleted of radioactive 14C.)

《3/12⟫ There are also "land use change emissions" (e.g., clearing forests, draining swamps), which produce non-fossil CO2 emissions. They are poorly constrained, but certainly less then 15% of fossil emissions (probably about 10%).
sealevel.info/carbon/Dohner2…

《4/12⟫ B. Precise measurements of well-mixed atmospheric CO2 concentrations allow simple calculation of how the amount of CO2 in the air is changing.

1 ppmv CO2 = 7.8024 Gt CO2 = 2.12940 PgC (petagrams carbon)

To convert from PgC to Gt CO2 multiply by 3.66419

《5/12⟫ C. Subtract (B) from (A) for the time period (# of years) of your choice to get the net rate of CO2 removal by all natural sources & sinks, summed.

《6/12⟫ Let's consider, as an example, the one year period, calendar year 2021.

You can find all the relevant data here:


(You could do this same exercise with any year or span of years since 1958.)sealevel.info/carbon/carbonf…

《7/12⟫ A. Mostly from economic data, we know mankind added between 9.79 PgC and 11.60 PgC to the atmosphere in 2021. The lower figure includes only fossil carbon, the higher figure adds a high-end estimate of land use change emissions.

《8/12⟫ B. In 1Q of 2022 the average CO2 level measured at MLO was 418.760 ppmv, and in 1Q of 2021 the average level was 416.637 ppmv, so the level increased by 2.123 ppmv in 2021, which is:

2.123 ppmv CO2 × 2.1294 PgC / ppmv CO2 = 4.52 PgC (which is 16.56 Gt CO2)

《9/12⟫ C. In other words, the amount of carbon in CO2 in the atmosphere increased by about 4.52 PgC in 2021. But, at the same time, mankind added between 9.79 PgC and 11.60 PgC to the atmosphere.

(9.79 to 11.60) - 4.52 = 5.27 to 7.08 PgC.

《10/12⟫ So natural “carbon sinks” (the terrestrial biosphere & soil, the oceans, rock weathering, etc.) removed a net total of at least 5.27 PgC (=2.47 ppmv of CO2) in 2021.

《11/12⟫ “Nature” (i.e., net summed natural CO2 sources & sinks) removed at least 2.47 ppmv of CO2 from the atmosphere, yet the amount of CO2 in the atmosphere nevertheless increased by 2.12 ppmv.

《12/12⟫ That means the entire increase in atmospheric CO2 in 2021 was from human CO2 emissions. The only reason CO2 level rose in 2021 is that mankind added CO2 faster than nature removed it.

For a deeper dive see Ferdinand Engelbeen's analysis:


𝓠𝓔𝓓ferdinand-engelbeen.be/klimaat/co2_or…

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