David Ellard provides a thorough and timely explanation of the carbon cycle from first principles. His essay meets the standard for all speeches or papers: “A presentation should be like a woman’s dress–long enough to cover the subject but short enough to be interesting.” (OK I’m dated and not PC: the long enough part is passé).
Since the subject is to describe the carbon dioxide fluxes and atmospheric residence timescales, the essay is necessarily long. It is made more lengthy by the need to untangle confusions, deceptions and obfuscations of CO2 science by IPCC partisans pushing CO2 alarms. To completely remove the wool from your eyes takes a full reading and pondering. I will attempt a synopsis here to encourage interested parties to take the lesson for themselves. The experience reminded me of college classes I took majoring in Organic Chemistry, though in those days CO2 was anything but contentious.
Several posts here (links below) have danced around Ellard’s subject, but his exposition is the real deal. Getting to the bottom of this issue, he explains how Henry’s law works regarding CO2 in the real world, makes an important distinction between CO2 molecules and ions, and factors in an accounting of the CO2 output from rising populations of humans and animals.
Some Highlights from Carbon Dioxide, A tale of two timescales from the blog Energy Matters
From the Executive Summary
One of the most controversial topics in understanding the build-up of carbon dioxide in the atmosphere is the question of timescales – the effect of the build-up depends not only on the amounts being released by human(-related) activities but also on how long the gas stays in the atmosphere.
In fact much of the controversy/confusion stems from the fact that there are two relevant timescales, one which determines how the amount of carbon dioxide in the atmosphere equilibrates with other reservoirs (notably physical exchange with the oceans, and biological exchange via photosynthesis and respiration), and another which determines the exchange of carbon atoms.
By analysing the amounts of a marker carbon isotope (carbon-13) it is possible to calculate these two timescales. The timescale for the amount of carbon dioxide is approximately twenty years, a significantly shorter timescale than often claimed (e.g. by the IPCC). From these figures, we can also deduce that the increased carbon dioxide in the atmosphere since the industrial revolution has led to a noticeable increase in the photosynthetic rate of the Earth’s plants and green algae (about 8%). This has clear implications for the on-going discussions on the costs, and indeed benefits, of increasing carbon dioxide levels.
The reasons why the IPCC’s (and others’) estimates of carbon dioxide timescales in the atmosphere are overestimated are analysed – notably because no account is taken of changes in net respiration rates (ever more people, and domesticated animals, and animal pests that depend on them), because hydrocarbon usage by UN member states is underreported (quite possibly for reasons of political prestige), and finally because the models ignore the key empirical evidence (the carbon-13 isotope measurements).
Excerpts from Ellard’s Article
The purpose of this post is to try and explain the nature of the two timescales, and pin down using actual physical measurements (rather than computer games) the size of both.
What Henry’s Law is telling us, then, is that when we add molecules of carbon dioxide to the atmosphere, these molecules will ultimately partition themselves (leaving aside the effects of the biota) in an approximately fixed ratio between atmosphere and ocean (the solvent).
Three questions arise: what is the dilution of carbon dioxide in the oceans? what does ‘ultimately’ mean? and what actually is the value of the fixed ratio? In order of asking: very dilute (the oceans are approximately 500 times undersaturated in molecular carbon dioxide), it depends on the mixing processes both within and between the atmosphere and ocean (discussed further on), and:
To rephrase then, for every six molecules of CO2 that are introduced into the atmosphere, five of the six (again ignoring biological processes) will end up in the oceans, only one of them will hang around in the air. Not only that but, as noted above, molecular CO2 is a very dilute solute in the oceans. At current rates, it would take tens of thousands of years for mankind to achieve saturation.The partition ratio 1:5 will continue to apply for the foreseeable future!
The basic take home fact is that the ‘dissolved inorganic carbon’ or DIC in the world’s oceans is, in principle, a mixture of molecular carbon dioxide and dissolved carbonates. What is the ratio of molecular to ionic carbon dioxide? The smart among you will already have guessed: there is approximately 9 times as much ionic CO2 dissolved in the oceans as molecular. Only the latter is in Henry’s Law equilibrium with CO2 in the atmosphere. Hence the different ratios of 1:5 (atmospheric:molecular dissolved CO2) and 1:50 (atmospheric:molecular plus ionic dissolved CO2 i.e. DIC).So we can now recap. Before the exchange the atmosphere contained ten surplus marked molecules of carbon dioxide. After the exchange, there were still nine surplus molecules in the atmosphere, but none of them contained the marker! The ocean gained a single extra molecule of carbon dioxide but gained an extra nine atoms of marked carbon (and lost nine unmarked ones).
Since the industrial revolution, the human population of this planet has exploded. Not just humans though. We also have caused an explosion in the number of domestic animals, sheep, pigs, cows and chickens and the like. And not just the intended results of human food production. There are a myriad rats, cockroaches, potato blight funguses and the like out there which depend for their existence on our (unintended) generosity. They are also all busy respiring carbon dioxide into the atmosphere, thanks to us.
We have to take this into account, as well as any changes in photosynthetic fluxes (which have the opposite tendency, to reduce atmospheric carbon dioxide). I would need a whole other post to discuss this in detail, but I am simply going to assume that one third of the ‘excess’ carbon dioxide is not of hydrocarbon origin. The crucial point is that this excess CO2 will not have the distinctive carbon-13 marking. Its carbon-13 profile will be almost identical to (well, pretty similar to, we will ignore the difference for simplicity) that already in the atmosphere.
So we are going to calculate the carbon dioxide adjustment timescale as a function of the deep ocean-surface mixing timescale but reduce the result by a third to take into account non-hydrocarbon anthropogenic CO2 emissions. If you object to this piece of fudging, by all means feel free to do the calculation without it.
If you plot a graph of this using values of the deep ocean-surface mixing timescale of between, say, 0 and 100 years (which really should cover all eventualities), the value of the adjustment timescale varies between 16 and 23 years. Let’s take a happy median, thus:
The current concentration of carbon dioxide in the atmosphere is 400 ppmv and is increasing by 2 ppmv/year. If the atmospheric adjustment timescale is 20 years then it means the oceans and biota are together absorbing 5 ppmv/year of the excess. Three quarters of this absorption is due to the increase in productivity of the biota and one quarter to the Henry’s Law re-equilibration in the oceans.
So we can say that for every seven molecules of CO2 put into the air by mankind, of which just under five are from burning hydrocarbons, two accumulate there, one and a bit is dissolved into the oceans and just under four are reabsorbed by the biota via increased photosynthetic productivity.
But to my mind the most striking result, if we bring the carbon-13 isotope evidence fully to bear, is the increase in photosynthesis that must have taken place over the course of the twentieth century. The Henry’s Law equilibration between atmosphere and oceans is simply too slow to get rid of much of mankind’s excess CO2. The fact that there is not a lot more of this CO2 still lingering in the atmosphere (and therefore that the proportion which is hydrocarbon-derived is not even smaller) shows us that the donkey work of mopping up (most of) the excess has been carried out by the biota – all the phytoplankton, trees, grasses and algae that give wide areas of our planet’s surface its distinctive green colour.
Bio – David Ellard
David Ellard studied Natural Sciences at Kings College Cambridge with specialisations in mathematical and atmospheric chemistry.
Since then he has worked over twenty years in the European Commission in Brussels in various science/technology/law-related areas, notably responsible for the Commission’s proposed directive on the patentability of computer-implemented inventions.
Many thanks to David Ellard for this clear and readable treatise on established CO2 science, which still applies despite climate activists attempting to unsettle it. Before anyone takes a stand on CO2 and global warming, be sure to remove the wool from over your eyes.
Other Reading on CO2 and the Carbon Cycle