Evidence from changing 13C/12C isotopic ratio for human generated increases in carbon dioxide

[@whirrrl3349]

Extremely edifying. Thanks. I had not known there was such compelling evidence. It is obvious that humans contribute to CO2 increase, but here is a very specific and important explanation of evidence based on changing carbon isotope ratios. Fascinating, really.

[@ncdave4life]

Your overall point is correct, but you made a couple of errors. 2:20 The air bubbles are not trapped in Antarctica as liquid water freezes. The Antarctica Plateau is below -40°, so it never thaws, and there's never any liquid water. Instead, the snow is compressed (by the weight of snow above it) into firn, and then into solid ice, trapping air in tiny bubbles. (That introduces a well-known delay in the sequestering of air bubbles, so the trapped air is "newer" than the ice which encases it, with the lag time depending on the site's snow accumulation rate.) 3:35 You said "when a plant encounters 13C CO2 it is rejected. The biochemistry of the plant does not use 13C carbon dioxide." Also, at 4:42 you said that coal, oil and natural gas have "only carbon-12," and at 5:24 you said that no 13C is added to the atmosphere by burning fossil fuels, and at 5:47 you said something similar. That is incorrect. Plants use both 12C and 13C (and also 14C). Their preferential selection of 12C over 13C (and 14C) is slight, on average reducing plants' 13C content by only about 2.4% relative to its abundance in the atmosphere (i.e., average δ13C in plants is roughly -24‰, though C4 plants aren't as 13C depleted). So burning fossil fuels increases the amounts of both 12C and 13C in the atmosphere, but it decreases the percentage of 13C.

[@CrashChemistryAcademy]

Interesting, thanks for the clarification. Unfortunately youtube does not allow for much of any editing of posted videos. I may at some point replace this. My email has a follow-up comment regarding C3 versus C4 plants from you, but it is not here, not sure why. At any rate, my understanding is that C4 will much more readily use C13. However, the evolution of C4 plants was relatively recent and far to short a time to become fossil fuel, so our fossil fuels all come from C3 plants.

[@ncdave4life]

​@@CrashChemistryAcademy, I agree that fossil fuels are from C3 plants, not C4. Not only were there no C4 plants in the carboniferous, when the great coal deposits were created, even now C4 plants are basically irrelevant w/r/t carbon sequestration. The prevailing wisdom is that even most brown coal (which is relatively recent) was laid down before there were very many C4 plants. Both trees and sphagnum moss (which sequester carbon for a relatively long time) are C3. AFAIK, all C4 plants (including crops like corn and sugarcane) are grasses. If there are any exceptions, they're pretty obscure. C4 grasses can take up CO2 at a prodigious rate, but they don't hold onto it for long. E.g., on a still, sunny day a healthy cornfield can deplete nearly all the CO2 from the air by noon! But within a few years, at most, nearly every trace of that corn has rotted away or been digested by something, and virtually all the carbon has been released back into the air as CO2. (BTW, be thankful C4 plants are grasses, and there're no C4 trees! In the long term C4 trees could drive CO2 levels so low that C3 plants [i.e., most plants!] would be driven into extinction. So if you ever encounter a plant geneticist trying to engineer C4 trees, STOP HIM!!!)

[@ncdave4life]

BTW, if you want to dive deeper down the rabbit hole, look up "Suess Effect" dilution.

[@ncdave4life]

​@@CrashChemistryAcademy, w/r/t the inability to see some comments, youtube has been cracking down against comments with substantive content. Some they delete, some they shadowban. They do it less of you change the "Sort by" setting to "Newest first." However, there's no way to make that the default. I just posted a comment on another of your videos, but it is hidden unless you change "Sort by" to "Newest first."

[@CrashChemistryAcademy]

Do you remember which video? I have not found any comment by you in another video.

[@BertWald-wp9pz]

5:42 So the graph shows CO2 increasing from 280ppm to about 350ppm so x1.25. At the same time C13 is diluted from about 1.6% down to about 0.4% - about a quarter. I wondered what the detailed explanation of the dilution effect. My attempt starts by saying that 1.6% of 280 is about 4.5 parts per million but when a further 70ppm is added the 4.5ppm should still be present in which case it would represent about 1.2% of 350ppm not 0.4%. Where did the rest of the C13 go? Hopefully someone more knowledgable will be able to put me right.

[@CrashChemistryAcademy]

While I did not check out if the math works, I assume your error is in the fact that the 0.4% is the change in C13 in atmospheric CO2; it is not the change of C13 in the atmosphere, which is what it sounds like you are thinking.

[@ncdave4life]

Well spotted, Bert! The disparity is due to an error in this video. Plants use both 12C and 13C. Their preferential selection of lighter 12C over heavier 13C is slight, on average reducing plants' 13C content by only about 2.4% relative to its abundance in the atmosphere (i.e., δ13C in plants is -24‰, though it's reduced less than that in C4 plants). So burning fossil fuels increases the amounts of both 12C and 13C in the atmosphere, but it slightly decreases the percentage of 13C.

[@stubmow1567]

This just saved my ass for a test in ERSC. I'm a visual learner, and this really helped me grasp the concept of how C13-C12 ratios provide evidence for human-caused climate change. Thank you so much!

[@andersondacostaalves3474]

Excelente vídeo, parabéns pelo trabalho!!!

[@CrashChemistryAcademy]

Obrigado por assistir!

[@jonasdarilek5775]

Great video! I actually enjoyed watching this one. Keep it up:)

[@fsledge2222]

Thanks so much for posting. Very interesting studies.

[@rivisulakan]

when new video

[@CrashChemistryAcademy]

Hopefully soon. Too much to do at work!

[@rivisulakan]

@@CrashChemistryAcademy alright

[@yixuanliu1394]

Great vid 👍👍

[@CrashChemistryAcademy]

Thanks Yixuan!!

[@philoadriensson9850]

Great video! Thanks for posting.

[@eddiestone9966]

So important, great video!

[@CrashChemistryAcademy]

🙂

[@DanielSMatthews]

There is a fact that breaks the "link" hypothesis, so it may require modification before it can support a theory capable of accurate quantification. Subduction of an oil or gas field will see that material oxidized to CO2 and vented from "hot smokers" on the ocean floor as well as other volcanic phenomena. This can happen without being noticed on the surface as it is dissolved into the seawater and released in a more diffuse manner into the atmosphere during the annual cycles of warming and cooling of seawater. You may also need to cross check your data against known measures of economic activity and the Keeling Curve dataset because a direct link is not apparent for the recent significant downturn due to covid response measures. If all of the facts fail to support the hypothesis then it can't stand, without those apparent contradictions being accounted for.

[@davidsegal186]

Using processes occurring in geologic time frames to discredit a 200 year process (the video's time frame), or a 65 year process (your Keeling Curve data) is a false argument. It in fact supports what was said in the video: Geologic time frame processes cannot possibly account for the 200 year diminishing percent of 13C, especially given its exact reflection of the data in the upper graph as well as Keeling Curve data.

[@pasdpasse439]

Thanks for the video. Many people deny the impact of human beings on climate change

[@juandv77]

Well, the evidence of human impact on CO2 levels is undeniable, I will not discuss that. But, I don't understand how a plant can reject CO2 with 13C and not CO2 with 14C. Because I always thought that the presence of 14C in living organisms was because it was assimilated by plants and entered in the food chain. 14C would remain constant while the organism stays alive but would start decaying the moment it dies. I just don't see why this won't happen with 13C too. I think there might be another reason why 13C is less abundant in fossil fuels. This premise has been assumed but there is not a reference for it (I am sure this can be easily measured but I don't see any reference of it neither in the presentation). Are you sure that 13C cannot decay to 12C? Because that would explain the less abundance of 13C in fossil fuels, just thinking.

[@CrashChemistryAcademy]

Thanks for many thoughtful questions. I have looked into some of this several years ago when I came across the papers listed in the description, and this is what I found (not much): 1) It is not known why plants differentiate between 13C and 12C. One article ventured to say it was because of the difference in mass, which does not really explain anything, in particular your question about 14C, which is heavier and thus one would assume even less likely to be absorbed by plants, which makes no sense given the fact that carbon dating is reliable in plants and animals. Most stable isotopes have little to no changes in their physical & chemical properties. One interesting exception is water, in which H2O with the isotope 2H has higher bond energy with the H-O bond than water with the 1H isotope, an unusual consequence for an isotope, but I was thinking if that is the case for 13CO2, that is, higher C-O bond energy, then that could explain it-- the Calvin cycle would be unable to break the C-O bond and so the 13CO2 would just diffuse out of the leaf unused. The rate of absorption of 13CO2 into plants is less than 1% of total atmospheric 13CO2 (I did not mention this in the video to keep things simple). Let's say mass really is the issue. If so one might assume 14CO2 would be absorbed at an even lower rate, making carbon dating in animals and plants not possible. Since we know carbon dating in animals and plants is very reliable, there must be some other rejection mechanism specific to 13CO2 but I could not find anything. One thing very interesting that I did find is the differences in 13CO2 absorption in C3 versus C4 plants. C4 plants absorb a more significant proportion of 13CO2 (about 10-20% of total atmospheric 13CO2 if memory serves), however C4 plants did not evolve until ~200 million years ago, about 100 million years short of the 300 million years needed for the production of fossil fuels. So it is the C3 plants that were present 300 million+ years ago from which we get our fossil fuels. This study also further supports the finding that C3 plants take in negligible amounts of 13CO2. So I feel the evidence from people who study these things supports well enough that it is the lack of 13C in (C3) plants that ultimately produces the lack of 13C in fossil fuels. Regarding 13C decaying to 12C: 13C is a stable isotope, so it would not decay. But let’s say it is unstable, what would happen? There are three types of particles emitted from radioactive (unstable) nuclei: alpha, beta, and gamma. A 13C alpha emitter would lose two protons and two neutrons, and so the 13C atom would become a 9Be atom, so that does not work. A 13C beta emitter would emit an electron from a neutron, which turns one of that neutron’s down quarks into an up quark, which turns the neutron into a proton, and the result would be a 13N atom, so that would not work either. (A real example of that is 2H, which, when it loses an electron, becomes 2He.) I’m a little rusty on gamma emission, but I believe it occurs with heavier nuclei after an alpha or beta emission, and does not change the nuclear components. It occurs due to the nucleus being in an excited energy state and so it is able to go to ground state by emitting excess energy as gamma rays. So the bottom line is I do not have a concrete answer for your 13C versus 14C question, but it is a great question! Thanks for asking. By the way, 14C decays regardless of its circumstances (live tissue, dead tissue, a rock…). It is because its decay is so slow we do not have to worry about it as living beings. It is also because its decay is so slow that we can use it for carbon dating. BTW #2: 14C is a beta emitter, and so becomes 14N after beta emission. Hope that helps!

[@DonBrowningRacing]

Interesting! Excellent analysis!

[@CrashChemistryAcademy]

😊 Thanks!

[@b92555]

What happened to the C13? Where did it go. Why was it not replaced by the natural source it came from in the first place? Can C13 eject a neutron and become C12? Why was the graph over such a small increment of time? Lots of questions to answer. Let’s not jump to conclusions.

[@alexlewis2522]

The C13 has not gone anywhere it just now makes up a smaller percentage of the total carbon in the atmosphere as we have emitted C12 carbon dioxide into the atmosphere. Carbon 13 is constant in the atmosphere as it is stable and cannot decay into C12. C13 will therefore be at equilibrium so, the amount of it will not change significantly over time. Finally, the graph doesn’t show a longer period of time because the trend would be the same but would simply become harder to read. Whilst there would be variations if you went further back (ice ages etc) these would not be relevant to anthropogenic carbon emissions and therefore would only serve to complicate the picture.

[@mattlm64]

@@alexlewis2522 The bottom chart doesn't suggest constant at all as the percentage goes to almost zero suggesting it has dramatically decreased which opens questions.

[@ForChiddlers]

@@mattlm64 it is the relative amount, so obviously it goes to zero, when the other rises and it stays the same. If you've got 11 football players in your team, and the other team has 11, then it's 50%. If the other now adds 10.000 players to it's team, then your teams percentage of total players goes to zero

[@mattlm64]

@@ForChiddlers The co2 only went up around a quarter.

[@whatabouttheearth]

In plants there is a carbon ratio that is heavier in the lighter 12C and lighter in the heavier 13C and 14C. But coal, a fossil plant, has the same ratio found in plants but without the 14C isotope because it is radioactive and depletes overtime. So there is a lower level of 13C compared to 12C because that reflects the ratio found in plants, in this case fossil plants that made coal.

[@mattlm64]

Why would C13 go almost to zero?

[@ForChiddlers]

Its the relative amount compared to c12. As explained in the video

[@whatabouttheearth]

In plants there is a carbon ratio that is heavier in the lighter 12C and lighter in the heavier 13C and 14C. But coal, a fossil plant, has the same ratio found in plants but without the 14C isotope because it is radioactive and depletes overtime. So there is a lower level of 13C compared to 12C because that reflects the ratio found in plants, in this case fossil plants that made coal.

[@ncdave4life]

It doesn't go almost to zero. That's just how the axis is scaled on the graph. The 13C isotopic signature is normally expressed as "δ13C," which is parts-per-thousand ("per mille") above or below a standard baseline level. The standard baseline value is a 13C/12C ratio of 0.01123720 called "Vienna Pee Dee Belemnite" (VPDB). Burning fossil fuels has slightly lowered the 13C percentage, so that the average current atmospheric δ13C value is about -8‰ (i.e., 8 parts per thousand below the baseline). (Note: if something had a δ13C value of +1000‰ that would mean that the carbon in it is 2.2% 13C instead of the usual 1.1%, or if its δ13C value were -1000‰ that would mean it contains no 13C at all.)

[@reginaldcornwalingford6210]

Your whole argument rests on their being no alternative explanation for the declining ratio, yet C3 plants are what is likely depleting c13 from the atmosphere given that they are the most widely cultivated plants on Earth (i.e. Corn, Sorghum, grass ect). Industrial activity did not cause c12 to increase, agricultural caused c13 it to decrease. This has been shown to be true by soil sequestration studies demonstrating the concentration of c13 in the soil has increased over the last few centuries.

[@CrashChemistryAcademy]

The most widely cultivated plants are C4 plants, not C3. Corn, Sorghum, other grasses are all C4 plants. C4 plants do indeed use 13CO2, but not indiscriminately, they still favor 12CO2. Further, one can reasonably expect (as you are) fossil fuels derived from C4 plants to add to atmospheric C13. However C4 plants evolved about 30 million years ago, and the agricultural C4 plants much later. The point is that it takes about 300 million years for plant biomass to become fossil fuel, which means our fossil fuels are derived from decomposing C3 plants, which have little to no 13C in them. C4 plants have not been around nearly long enough to decompose and change into fossil fuel.

[@ncdave4life]

@@CrashChemistryAcademy, that is incorrect. Most crops are C3, not C4. The only important C4 crops are corn/maize, sugarcane, sorghum and millet. Also, both C3 and C4 plants use both 12C and 13C. C3 plants typically have 13C levels depressed by at least 2.4% below the atmosphere. C4 plants typically have 13C levels depressed by no more than 1.6%. So fossil fuels have 13C levels that are only about 2.4% below the natural atmospheric abundance of 13C. That is to say, 13C is about 1.103% of the carbon in the atmosphere, but 13C in fossil fuels averages about 1.085% of the carbon in the fossil fuels.

[@scottdorfler2551]

Very well done until the very end. It's hard enough to get science deniers to admit they're wrong. That smartass shot at the end doesn't help. Take the high road. Otherwise, great video.

[@CrashChemistryAcademy]

Thanks for your comment. My wife had the same thought. I’ll see if youtube allows that kind of editing.

[@anndolinko7880]

NICE!

[@whatabouttheearth]

What? Plants have 13C, its just far lower than 12C. In plants there is a carbon ratio that is heavier in the lighter 12C and lighter in the heavier 13C and 14C. But coal, a fossil plant, has the same ratio found in plants but without the 14C isotope because it is radioactive and depletes overtime. So there is a lower level of 13C compared to 12C because that reflects the ratio found in plants, in this case fossil plants that made coal.

[@CrashChemistryAcademy]

Not sure if there is a question there, but to clarify-- C3 plants have 13C but in minute quantities compared to atmospheric 13C. C4 plants have a 13C presence that is roughly equal to that of atmospheric 13C. The crux is that all fossil fuels--coal, natural gas, and oil--take about 300 million years to be produced from decaying plants. Only C3 plants were around 300 million years ago. C4 plants did not evolve until about 30 million years ago, and so only C3 plants produce fossil fuel, and so the 13C presence in fossil fuel is the same as it is in C3 plants, which is negligible.

[@tomc642]

Really like this. It is one evidence that human activity increased CO2 levels in the atmosphere. However, how does this tie in with global warming. So, the CO2 levels stayed stable in the past, but we still had very warm and cool periods during these ages. In this case, there would be no correlation with CO2.

[@CrashChemistryAcademy]

The naturally occurring cooling and warming of the earth over geologic time is tied to naturally occurring changing CO2 levels over those time periods, with other factors at work as well. However there is no time period in the geologic record in which 1) CO2 has been this high (420 ppm currently), and more significantly, had such a steep rise in such a short (non-geologic, 200 yr) time period. Natural changes in CO2 in geologic time are far less variable and are far more gradual and last for much longer (geologic time) periods.

[@tomc642]

@@CrashChemistryAcademy Thank you sir, this all makes sense. I guess, naturally occurring changes in CO2 levels would include volcanic eruptions above and below sea level.