For some time, I've been following the debate on Climate Change and the back and forth on the practicality of removing enough carbon dioxide (CO2) from the atmosphere, soon enough to matter. It's useful to hang some numbers on the problem.
There are two main areas of discussion, Science and Engineering, with much overlap.
The vast majority of the debate to date has been about the Science, to wit the correctness and completeness of the science underlying the various climate models and thus their predictions.
Climate-change science is a very complex field, far exceeding the capabilities of any one individual to follow or fully understand: Currently, about US $20 billion is spent per year globally on Climate-Change related research, yielding an exponentially growing river of paper, at least 10,000 new peer-reviewed articles per year circa 2015, and growing.
Petersen, A.M., Vincent, E.M. & Westerling, A.L. Discrepancy in scientific authority and media visibility of climate change scientists and contrarians. Nat Commun 10, 3502 (2019).
The other area is Engineering, where the predicted levels of atmospheric carbon inventory and flux from the Science debate are simply accepted as true or true enough, proceeding directly to the question of how does one actually remove carbon fast enough to at least stop the increase in carbon inventory, or ideally, to reduce the inventory to pre-industrial levels over time. This is a far simpler question, requiring only first-year chemistry and physics to quantify and predict.
The entire engineering-practicality debate turns on a single number, the mass of carbon in the atmosphere for each part per million by volume (ppmv) of carbon dioxide. People are instinctively suspicious of the very large numbers that result. But unlike climate science and its multitude of computer models, this is practical for an individual to verify.
The source of the 2.133 metric gigatons of carbon at one ppmv value one hears is the CDIAC (Carbon Dioxide Information Access Center) and its FAQ: .
The calculation is quite simple. The official weight of the atmosphere is 5.1480 x 10^18 kilograms, or 5.148 x 10^15 metric tons, or 5.148 million metric gigatons.
If one assumes for simplicity that air and CO2 have the same density (they don't, but never mind), we get 5.148 Gigatons (per ppmv) of elemental carbon, establishing that the order of magnitude (10^18) is correct. The more precise calculation from CDIAC yields the stated
2.133 metric gigatons of elemental carbon per 1 ppmv.
The current level of carbon dioxide in the atmosphere is about 400 ppmv, so the total is 2.133*400= 853 metric gigatons of elemental carbon in the atmosphere.
Joe Gwinn