Check: CO2 emission fingerprint on atmospheric CO2

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- v.1.6 by Tim88 - Overview article: Check: Effects of CO2 emissions on nature

We can estimate the theoretical man-made CO2 increase from historical carbon emission estimations and compare the resulting atmospheric CO2 concentration with the estimated or measured CO2 concentration.

Commonly the CO2 concentrations are plotted in linear graphs, such as on the site While that is what we are commonly used to, here we will plot the concentration in logarithmic graphs, as those more clearly reveal the relevant characteristics for this analysis.

The following illustration shows the effect of adding 60% of the estimated total emitted CO2 to an assumed constant natural CO2 concentration. About half (in this illustration 40%) is assumed to be absorbed by the oceans and the biosphere.

Estimation of man-made atmospheric CO2 increase (logarithmic scale)
Measured atmospheric CO2

Compared to the measured CO2 concentrations we see a reasonably good match, especially from the time that continuous direct CO2 concentration measurements were done at Mauna Loa.

The “human fingerprint” in increased CO2 concentrations looks quite convincing, the graphs are a match especially at high emission levels. The clear increase around 1960 of emitted CO2 is also visible in the atmospheric CO2 measurements. However, the earlier record is subject to debate.

We can notice some short term dips in atmospheric CO2 (e.g. around 1915-1920) that are clearly NOT due to human emissions; they can be attributed to a change in natural climate variation. For example, natural cooling results in more natural CO2 absorption, and natural warming results in more natural CO2 emission. On short time scales of months and a few years, atmospheric CO2 variations generally follow temperature variations. Consequently, also the less good match before 1950 may be due to natural warming, and the dip around 1950 may be due to a slight natural cooling. That complicates the analysis somewhat. Similarly the yearly the CO2 concentrations fluctuate, as plants inhale less CO2 in winter and the oceans can't hold as much CO2 in summer - most plants are in the Northern hemisphere, and most water is in the Southern hemisphere.

A few scientists such as Salby, Humlum and Harde see such observations as evidence that nature drives atmospheric CO2 concentrations and that human overall CO2 emissions make only a small contribution. Indeed, over the last century the world has warmed; warmer water tends to outgass CO2 and that increases CO2 in the atmosphere. However, overall the oceans absorbed CO2 while atmospheric CO2 concentrations increased. At the same time nature has been greening [reference to add], which tends to lead to more natural CO2 absorption. That points to CO2 emissions driving most of the recent increase of CO2. And it would still be a great coincidence if nature was responsible for the long term increase of atmospheric CO2 while it so well matches human CO2 emissions.

According to greenhouse gas theory, the increased emissions in the period 1900-1960 and even more so in the period 1960-2018, resulted in an increase of atmospheric CO2 concentrations, which we here grant to be very likely correct. It is thought that this caused significantly more warming of the planet which in turn increased the rate of sea level rise, due to sea water expansion and increased melt water from glaciers.

change of strength of greenhouse gas effect on warming

On a logarithmic scale is the speed of CO2 increase in the period after 1980-2018 at least 5 times that of the period before 1960.
In theory this should cause also 5 times faster warming.

Downloadable files:
File:GlobalCO2emissions1751 2013.ods
File:CO2-mole fraction in air.ods

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