This post is about proving that CO2 changes in response to temperature changes, not the other way around, as is often claimed. In order to do that we need two datasets: one for measurements of changes in atmospheric CO2 concentrations over time and one for estimates of Global Mean Temperature changes over time.
Climate science is unsettling because past data are not fixed, but change later on. I ran into this previously and now again in 2021 and 2022 when I set out to update an analysis done in 2014 by Jeremy Shiers (discussed in a previous post reprinted at the end). Jeremy provided a spreadsheet in his essay Murray Salby Showed CO2 Follows Temperature Now You Can Too posted in January 2014. I downloaded his spreadsheet intending to bring the analysis up to the present to see if the results hold up. The two sources of data were:
Temperature…
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Salby claims that the reason for rising atmospheric CO2 levels is not mankind’s CO2 emissions, but, rather, that the oceans are outgassing CO2, because of global warming. He is wrong. I have an article explaining how we can know that he’s wrong, here:
https://sealevel.info/atmospheric_co2_increase_is_not_from_ocean_outgassing.html
Salby has a long lecture on YouTube, making that claim. I critiqued it here:
http://sealevel.info/Salby_CO2_lecture_critique.html
I also posted the critique in comments on YouTube (back before Google’s censorship of YouTube comments got so bad that it became impossible to post substantive information). Salby did not respond.
The most thorough examination of the cause of rising CO2 concentration which I’ve found is this very clear and comprehensive analysis, by Ferdinand Engelbeen:
http://www.ferdinand-engelbeen.be/klimaat/co2_origin.html
We have reliable measurements of year-to-year atmospheric CO2 level changes since 1958.
We also have good data about the amount of “fossil” CO2 mankind produces each year, thanks to the economic data about the production & use of fossil fuels and cement.
From those two datasets we can tell that, every year since at least 1958, the amount of CO2 in the atmosphere has increased by less than the amount of CO2 we’ve added to the atmosphere.
That means nature is removing CO2 from the atmosphere, not adding it, every single year. There are many large natural “sources” and “sinks” of atmospheric CO2, but their sum (counting sources as positive and sinks as negative) has always been negative, every year since 1958.
It should not be necessary to point out that adding CO2 to the atmosphere increases the atmospheric CO2 level, and removing CO2 from the atmosphere decreases the atmospheric CO2 level. Since mankind is adding CO2 to the atmosphere, and nature is removing CO2, we (not nature) are responsible for the increase in atmospheric CO2 concentrations. The only reason that the atmospheric CO2 level continues to rise is that mankind is adding CO2 faster than nature is removing it.
Digression #1: It is essential to use annual figures for such calculations, not monthly, because many of the large natural sources and sinks of CO2, which balance / cancel over an entire year, are seasonal in nature. E.g., grasses and tree leaves grow in the spring and summer, sequestering carbon from CO2, but then rot in the fall and winter, releasing that same carbon as CO2.
Digression #2: It is not correct that “nature… absorb[s] about half of human emissions.” Nature does not absorb any human CO2 emissions. Rather, nature absorbs CO2 from the atmosphere, at a long-term average rate which depends mostly on the CO2 level in the atmosphere. The rate at which nature removes CO2 from the atmosphere does not depend the CO2 emission rate, except through the indirect mechanism of accumulation of emissions in the atmosphere (which Salby denies), through which accumulated emissions minus accumulated net natural removals determine the level. The fact that natural CO2 removals are accelerating as the atmospheric CO2 level rises is simply proof of strong negative feedbacks, which you can read about here:
https://sealevel.info/feedbacks.html#greening
Digression #3: The question of why “in 2020 FF CO2 declined significantly with no discernable impact on rising atmospheric CO2” is easily answered. It is simply that the decline in CO2 emissions was smaller than they typical year-to-year fluctuations in the rate at which net natural fluxes removed CO2 from the atmosphere.
Digression #4: Salby’s “sum of temperatures in previous years” and “the integral of temperature over previous year” are gibberish.
Digression #5: The observation that “For each subsequent year, the co2 level for each month [can be approximated by a formula of the form] ‘a + b × Tempthis month this year + CO2this month last year'” works just as well if you substitute any generally increasing quantity for temperature. E.g., try it with the Consumer Price Index. Do you think the similarity of graphs proves that the CPI determines CO2 level at Mauna Loa?
Digression #6: Salby’s intense focus on the seasonal or month-to-month variation in CO2 at Mauna Loa suggests that he is unaware of the fact that they are not global. Although the annual trend in CO2 levels measured at Mauna Loa approximates the global trend, the seasonal cycle there is particular to Hawaii’s latitude. Here’s what the seasonal cycle in CO2 levels measured at Mauna Loa [MLO] looks like (in green) compared to Cape Grim [CGO] (in blue):
Here’s a map:
Salby’s claim that nature, not mankind, is responsible for raising the CO2 level in the atmosphere, is just plain wrong.
Here’s a spreadsheet, from which you can see that it is not correct to say that that 100% of the rise in atmospheric CO2 level is due to mankind’s emissions:
https:///sealevel.info/global.1751_2014_2019.ems5_v07c.xlsx
The correct figure (since 1958) is about 180%. Since 1958 mankind has added about 180 ppmv of CO2 to the atmosphere, and nature has removed about 79 ppmv of CO2 from the atmosphere.
Fortunately, the scientific evidence is compelling that the rise in atmospheric CO2 level is a Good Thing, not a bad thing. Read about it here:
https://sealevel.info/learnmore.html?0=benefits#benefits
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