Early this year, a journal called Health Physics published a paper on World Atmospheric CO2, Its 14C Specific Activity, Non-fossil Component, Anthropogenic Fossil Component, and Emissions (1750–2018). The paper concluded that
Our results show that the percentage of the total CO2 due to the use of fossil fuels from 1750 to 2018 increased from 0% in 1750 to 12% in 2018, much too low to be the cause of global warming.
As you can imagine, this gained some traction amongst those who dispute that anthropogenic emissions drive global warming.
In the June edition of the journal there were 4 letters criticising the article, the authors of which included Pieter Tans, Ralph Keeling and Stephen Schwartz. The July edition then included a letter from myself, Gunnar Schade and Mark Maslin.
The letters point out that the paper’s assumptions about 14CO2 are inconsistent with observations, that it ignores the impact of the bomb tests in the 1950s and 1960s, and ignores that there are large exchange fluxes between the atmosphere, ocean, and terrestrial biosphere. It’s very obvious that the increase in atmospheric CO2 since the mid-1700s is almost entirely due to anthropogenic emissions and it’s rather surprising that a bunch of physicists don’t get that if you want to consider the detailed evolution of atmospheric CO2 concentrations, you really do need to consider all of the fluxes.
The authors of the original paper, of course, think that the criticisms don’t actually address their assumptions, methodology, or results, and they stand by [their] methodology, results and conclusions. Somewhat bizarrely, the authors still seem to think that the increase in atmospheric CO2 can only be anthropogenic if all of the CO2 that makes up this increase has a direct anthropogenic origin, rather than (obviously) the increase would not have happened in the absence of anthropogenic emissions.
The editor of the journal has also responded to say that they stand by their decision to publish the paper and invited readers to examine the original paper, the criticisms in the Letters in this issue, and the authors’ responses to these criticisms and come to their own informed conclusions of this work. This is all good and well, but understanding why the rise in atmospheric CO2 is almost entirely anthropogenic is pretty straightforward, it’s been well established in the relevant field for a very long time, and the only people who dispute this are justifiably described (in my view) as science deniers.
I don’t expect the letters to really change the minds of those who still dispute that the increase in atmospheric CO2 is almost entirely due to anthropogenic emissions, but I do think it’s useful for them to have been published. They at least provide something to highlight when people promote the original paper. Since ours isn’t fully public, if you’re interested in reading it, you can download the accepted version here.
I should have acknowledged that there were some who provided useful comments on drafts of the letter. So, thanks to Dikran, Bob L. and A.N. Other for their comments that helped to improve what we submitted.