Guest Post by Willis Eschenbach
There’s a new study out claiming that tropical forests are losing their ability to sequester carbon dioxide. Bad forest, no cookies for you! The study is entitled “Asynchronous carbon sink saturation in African and Amazonian tropical forests”, and is available through Sci-Hub here. In their press release it says:
In the 1990s intact tropical forests removed roughly 46 billion tonnes of carbon dioxide from the atmosphere, declining to an estimated 25 billion tonnes in the 2010s.
The lost sink capacity in the 2010s compared to the 1990s is 21 billion tonnes carbon dioxide, equivalent to a decade of fossil fuel emissions from the UK, Germany, France and Canada combined.
Overall, intact tropical forests removed 17% of human-made carbon dioxide emissions in the 1990s, reduced to just 6% in the 2010s.
Now, the first thing I noticed was that this study falls under what I modestly call “Willis’s Rule Of Authors”, which states that
Q ≈ 1/N2
Where “Q” is the quality of a scientific study, and N is the number of study authors. In English, this means that the quality of a study decreases in proportion to the inverse of the square of the number of authors … which in this case is … wait for it … no less than one hundred and six authors.
So … how did the one hundred and six authors determine that the tropical forest are no longer sequestering as much as they used to sequester?
According to the study, they used both observations and models. How much of each? Well, a clue is that the word “model” appears 158 times in their study, while “observations” appears only 44 times … here’s a typical comment.
A statistical model including carbon dioxide, temperature, drought, and forest dynamics accounts for the observed trends and indicates a long-term future decline in the African sink, whereas the Amazonian sink continues to weaken rapidly.
Now, it turns out that we can actually measure roughly how much human-generated CO2 is sequestered each year. The calculation is not all that complex. We know how many gigatonnes (“GT”, 109 metric tonnes) of carbon are emitted each year from the burning of fossil fuels plus cement manufacture. We know that for every 2.13 GT of carbon emitted, the atmospheric carbon dioxide level increases by one part per million by volume (ppmv). We routinely measure the atmospheric carbon dioxide level at the Mauna Loa Observatory.
So we take a look at how much carbon is emitted in a given year and we calculate how much the CO2 level should have increased. We subtract from that the actual increase in CO2 during that year, and the difference is the amount sequestered in that year by various carbon sinks around the planet.
Using that calculation, Figure 1 shows the amount of CO2 sequestered by year since 1959.
Figure 1. Percentage of anthropogenic CO2 sequestered by year.
There are some interesting things about this graphic. First, the amount sequestered varies widely year by year. This depends on two factors, the amount of natural emissions of CO2, and the variations in the natural carbon sinks. These are weather-driven. Some years there’s a lot of green growth on land and at sea, and other times there’s much less, which varies the amount of the carbon sinks. On the other side of the ledger, El Nino years like 1998 show an increase in natural CO2 emissions, so the percentage sequestered is smaller. With very large El Ninos, the amount of CO2 released may actually overwhelm the sinks, as in 1967.
Next, the smoothed value (blue/black line) varies between about 40% and 50%. It has hit both 40% and 50% twice in the past and most recently is about in the middle. There is no statistically significant long-term trend in the data (a least-squares analysis shows sequestration increased by 9% over the period, but the p-value is 0.20, far from significant).
Of interest for our purposes is the average for the 1990s and the 2010s mentioned in the study. In the 1990s the average sequestered was 49.8%. In the 2010s the average was 46.0%. The difference indicates the reduction in sequestration is 3.8%, but again it is not statistically significant …
But the one hundred and six authors say that forest loss reduced the amount sequestered by 11%. Hmmm …
Ah, well, I guess we shouldn’t expect models to actually agree with reality, that would be far too boring. In any case, we’re left with several possibilities, which include:
- The new paper is correct, forest sequestration has decreased by 11%, and coincidentally some other unknown carbon sink has increased by 7.2%, or …
- The new paper is wrong, or …
- The uncertainty is too great to come to any conclusion.
My conclusion? I’m not taking firm sides in this question, although option 2) seems most probable, followed by option 3). In any case, there’s no indication of a long-term reduction in the sequestration rate. And finally, I find it … well … discouraging that the authors didn’t include the actual sequestration calculations and discuss the implications of reality as opposed to models.
My best to everyone from a very dry hillside near the ocean in Northern California,
w.
As Usual: I politely request that you quote the exact words you are discussing, to avoid at least some of the misunderstandings that are the bane of the internet.
Technical Note: As you might imagine, there is a lag between when CO2 is emitted at the surface and when that surface CO2 affects the background CO2 as measured at Mauna Loa. This lag is on the order of ten months, and it has been adjusted for in Figure 1 above.
Discover more from Watts Up With That?
Subscribe to get the latest posts sent to your email.
Good statement-Sign me up as a co writer -We will outnumber them 😉
older trees use less carbon
so remove n plant new ones
listen for the screams
Willis
I was quite sure you were going to demonstrate the falsity of the claim in the paper by first graphing the % of human emissions absorbed, thus showing it was about constant, followed by the slam-dunk graph showing the tonnage which of course has increased enormously since 1950.
Sure the fraction of CO2 we emit through various activities we emit (grossly underestimated because of the increase in farming) but the total has varied during the time covered by the graph, always upwards.
If the core claim of the modeller-scientists is that the capacity of the forests is falling, they expressed it in absolute terms, not %. So what is important is the two line chart of mass emitted and the mass absorbed.
That chart will show that the core claim is nonsense – the mass absorbed has been rising, and rising exponentially.
That they come to the opposite conclusion doesn’t surprise me at all. In the ocean of human knowledge and skill, they lurk out of sight in the deep trenches, which is an appropriate place for their paper.
(You get a cookie for showing readers how to evade the paywall.)
The planet is greening, but sequestering is down. Gotcha. /sarc
Excellent article (as usual), Willis!
Figure 1 also shows that the percentage of CO2 sequestered seems to have varied less since about 2005 than in previous years. This may be due to an improved tracking of CO2 emissions in recent years, whereas in earlier years people in third-world countries didn’t bother measuring CO2 emissions, so estimates of their emissions were less accurate, and could result in large variations of the (delta ppm) / (emission rate) ratio.
It’s also interesting that the (time-smoothed) sequestration ratio hasn’t changed much since 2005, while global anthropogenic CO2 emissions have increased significantly (particularly from China). The sequestration ratio calculated in Figure 1 does not distinguish between sequestration by photosynthesis or by absorption into the ocean, but both processes are known to accelerate when CO2 concentrations in the air increase (plant growth rates increase with higher CO2 concentrations, and Henry’s Law would force more CO2 into the ocean at higher CO2 concentrations for a given temperature).
The 106 authors of the original study seemed to concentrate on forests in the Amazon and tropical Africa, but it is possible that increased forest growth in other areas is balancing out any losses in the Amazon basin.
If the sequestration ratio hasn’t varied much while emissions have increased from 2005 to 2020, that means that the total sequestration rate (emissions * ratio) has increased while CO2 concentrations have increased. It would be interesting to plot a graph of sequestration rate (emissions * ratio) as a function of CO2 concentration, to determine whether this is a first-order (linear) relationship, or some other function. This could be used to estimate future CO2 concentrations as a function of predicted emission rates.
This so-called study does not even pass the laugh test.
I’m afraid I don’t get this claim that mature rainforest is a carbon sink. Photosynthesis traps carbon dioxide as sugars, starch and eventually cellulose and lignin. Eventually all this is broken down down by bacteria and fungi and the carbon dioxide (and plant nutrients) released again. If this did not happen there would be a continuous build up of organic matter (wood, leaf litter etc.) I am sure the late lamented David Bellamy considered the whole system was in balance and therefore carbon neutral. In the carboniferous organic matter did accumulate but this may have been because it was trapped in anoxic conditions or the bacteria needed to break down wood (lignin) had not evolved. Perhaps someone more knowledgeable than I could sort this out for me.
Latest data point shows biggest monthly drop in over 20 years https://www.woodfortrees.org/plot/esrl-co2/from:1990/derivative
Curious indeed that climate scientists seem almost embarrassed by trees and plants and always try to downplay their significance. I read something interesting today that could put the cat among the pidgeons. Rising CO2, we are admonished to believe, traps IR in the lower atmosphere causing warming. However there is a parallel effect of CO2 in enhancing – for obvious reasons of the photosynthesis reaction – plant growth worldwide.
Thus global leaf area has recently increased – not decreased – by an amount in the tens of percent. Specifically because of CO2 enhancement of photosynthesis.
But that’s well known – the interesting thing I learned today is that recent infrared spectroscopy research has found that plants’ leaves are surprisingly good at backscattering and re-emitting incident near infrared light. Indeed – trees and plants look unexpectedly bright in IR camera images (see below).
This points to yet another feedback working against warming by CO2. The increased leaf area caused by CO2 rejects an increasing percentage of ground incident IR back upwards – effectively increasing near IR albedo.
Could this be one of the factors causing CO2 warming to have been less than expected? I always suspected and felt that the great efforts to conceal and down-play global CO2 greening are unhelpful to a full scientific understanding of the total effects of rising CO2.
As usual I like your thoughtful and well expressed critique, Willis. I’m a biochemical engineer (at least my diploma says I am). One thing that has served me well in my career is to focus on the variables that significantly impact the system I am trying to understand, and set aside the variables that have a minor impact. That is why, for example, when sizing an evaporative cooling tower for a large plant the variables that I used to correctly purchase, install, and run the cooling system were 1. The total heat the tower needed to dispate, 2. The range of heat dissipation rates the plant could expect over a typical year, 3. The temperature of the incoming cooling fluid (water), 4. The desired temperature of the out flow cooling fluid, 5. The desired efficiencies, and costs to operate various cooling systems having various coolants, etc. The most efficient large scale cooling towers all rely on water as the coolant. As you know water not only has an unusually large heat capacity, but it also can absorb an incredible amount of heat because it can change phase. Water also scrubs gases out of the air! Including CO2.
In your analysis, it is my opinion (not worth much I know, but I’m going to give it anyways) that by far the largest sink (and source) of sequestered CO2 is not forests, but rather the living flora and fauna in the oceans, coupled with all the CO2 scrubbing done by water in the storm layer (second ocean layer). This sink/source of CO2 sequestration so dominates the movement of CO2 into and out of the air it effectively buffers ALL other mass transfers of CO2 planet wide by several orders of magnitude. Am I way off in my thinking?
Current estimates of land and ocean carbon sinks are that the land absorbs about 60% and the ocean about 40% of the sequestered carbon.
Thanks,
w.
Dear Mr. Eschenbach,
Allow me to tell you that I enjoy your articles hugely, and as an editor of the only skeptical climate web site in Denmark, I have taken the liberty of translating some of your articles (partly or in full) into Danish (an obscure incomprehensible language) for our site, and they have been very well received. The last one I published was your story about the paleo climate model work, which based on 58 variable parameters basically concluded nothing. I loved it.
Best regards,
Soren Hansen
Soren, thank you for your kind words. Please feel free to use any of my posts, past or present, at your convenience. There is an index to my work here, over 900 posts … enjoy.
w.