# CO2 emissions change our atmosphere for centuries

## What the science says...

Individual carbon dioxide molecules have a short life time of around 5 years in the atmosphere. However, when they leave the atmosphere, they're simply swapping places with carbon dioxide in the ocean. The final amount of extra CO2 that remains in the atmosphere stays there on a time scale of centuries.

## Climate Myth...

CO2 has a short residence time

"[T]he overwhelming majority of peer-reviewed studies [find] that CO2 in the atmosphere remained there a short time." (Lawrence Solomon)

The claim goes like this:

(A) Predictions for the Global Warming Potential (GWP) by the IPCC express the warming effect CO2 has over several time scales; 20, 100 and 500 years.

(B) But CO2 has only a 5 year life time in the atmosphere.

(C) Therefore CO2 cannot cause the long term warming predicted by the IPCC.

This claim is false. (A) is true. (B) is also true. But B is irrelevant and misleading so it does not follow that C is therefore true.

The claim hinges on what life time means. To understand this, we have to first understand what a box model is: In an environmental context, systems are often described by simplified box models. A simple example (from school days) of the water cycle would have just 3 boxes: clouds, rivers, and the ocean.

A representation of the carbon cycle (ignore the numbers for now) would look like this one from NASA.

In the IPCC 4th Assessment Report glossary, "lifetime" has several related meanings. The most relevant one is:

“Turnover time (T) (also called global atmospheric lifetime) is the ratio of the mass M of a reservoir (e.g., a gaseous compound in the atmosphere) and the total rate of removal S from the reservoir: T = M / S. For each removal process, separate turnover times can be defined. In soil carbon biology, this is referred to as Mean Residence Time.”

In other words, life time is the average time an individual particle spends in a given box. It is calculated as the size of box (reservoir) divided by the overall rate of flow into (or out of) a box. The IPCC Third Assessment Report 4.1.4 gives more details.

In the carbon cycle diagram above, there are two sets of numbers. The black numbers are the size, in gigatonnes of carbon (GtC), of the box. The purple numbers are the fluxes (or rate of flow) to and from a box in gigatonnes of carbon per year (Gt/y).

A little quick counting shows that about 200 Gt C leaves and enters the atmosphere each year. As a first approximation then, given the reservoir size of 750 Gt, we can work out that the residence time of a given molecule of CO2 is 750 Gt C / 200 Gt C y^{-1} = about 3-4 years. (However, careful counting up of the sources (supply) and sinks (removal) shows that there is a net imbalance; carbon in the atmosphere is increasing by about 3.3 Gt per year).

It is true that an individual molecule of CO2 has a short residence time in the atmosphere. However, in most cases when a molecule of CO2 leaves the atmosphere it is simply swapping places with one in the ocean. Thus, the warming potential of CO2 has very little to do with the residence time of CO2.

What really governs the warming potential is how long the extra CO2 remains in the atmosphere. CO2 is essentially chemically inert in the atmosphere and is only removed by biological uptake and by dissolving into the ocean. Biological uptake (with the exception of fossil fuel formation) is carbon neutral: Every tree that grows will eventually die and decompose, thereby releasing CO2. (Yes, there are maybe some gains to be made from reforestation but they are probably minor compared to fossil fuel releases).

Dissolution of CO2 into the oceans is fast but the problem is that the top of the ocean is “getting full” and the bottleneck is thus the transfer of carbon from surface waters to the deep ocean. This transfer largely occurs by the slow ocean basin circulation and turn over (*3). This turnover takes 500-1000ish years. Therefore a time scale for CO2 warming potential out as far as 500 years is entirely reasonable (See IPCC 4th Assessment Report Section 2.10).

Intermediate rebuttal written by Doug Mackie

**Update July 2015:**

Here is the relevant lecture-video from Denial101x - Making Sense of Climate Science Denial

Last updated on 5 July 2015 by skeptickev. View Archives

Tom Curtisat 01:26 AM on 27 June, 2011Such an interpretation would be a misinterpretation, however, for by 'uptake' Archer and Brovkin mean the process whereby equilibrium is established between the deep ocean and the ocean surface/atmosphere. Because of the slow transfer of CO2 from surface to the deep ocean, the rate at which equilibrium is established with the deep ocean is indeed governed by the cumulative excess above equilibrium levels accumulated by the surface of the ocean, and the atmosphere. (Because the surface and atmosphere equilibriate over a very short time span, Archer and Brovkin, they mention only the atmosphere.) In contrast, establishing equilibrium between ocean surface and the atmosphere is governed annual emissions. On your interpretation of Archer and Brovkin, they flat out contradict themselves within two paragraphs by claiming that Now you may require something more than the fact that on your interpretation of Archer and Brovkin that the ocean surface and atmosphere will equilibrate within a year, but that 'uptake' will "come and fade on a time scale of a few centuries to millennia". That fact should be enough to see that my interpretation of Archer and Brovkin is correct. But to drive home the point, we see in an earlier passage that they definitely use 'uptake' to refer to the slow, centennial scale process of equilibrating between ocean surface/atmosphere and the deep ocean rather than the rapid process of equilibrating between ocean surface and atmosphere:Eric (skeptic)at 13:17 PM on 27 June, 2011KRat 13:39 PM on 27 June, 2011Dikran Marsupialat 17:31 PM on 27 June, 2011Eric (skeptic)at 21:24 PM on 27 June, 2011Dikran Marsupialat 21:47 PM on 27 June, 2011Eric (skeptic)at 23:02 PM on 27 June, 2011Dikran Marsupialat 23:21 PM on 27 June, 2011Response:(DB) Dikran, I was referring to something which came up on Dr Franzen's first post several months ago that, as CO2 level stabilize and then fall, that the oceans will begin to outgas CO2 themselves, going from sink to source & preserving elevated CO2 levels (& temps) at elevated levels compared to preindustrial; look in the comments in that post for the direct discussion (I'd link to it but we're camping out in the bush& I barely have a cellphone signal).[Dikran Marsupial] Cheers DB, I thought it would be something like that. It's swealteringly hot in my office, I wish I were outdoors! ;o)Eric (skeptic)at 23:28 PM on 27 June, 2011KRat 23:35 PM on 27 June, 2011"KR, I must have insinuated something I didn't mean to ("50 year time cycle for full equalization")."You're quite correct, Eric, my apologies. I misread your post, which clearly refers to 50 years as thehalf-life. Sorry about that. That's fairly reasonable - my back of the envelope check on this indicated a half-life of ~40 years assuming absorption rate was proportional to excess over pre-industrial levels. Although, given the 340-350GT we've added to the carbon cycle from sequestered fossil fuels, and themultipleabsorption paths with different equalization times, I don't think it's as simple as a single half-life. The rise in temperature from the added GHG's will mean an equilibrium level of ocean absorbed CO2lowerthan in pre-industrial times, for example. Oops! Reading the past few posts, it appears Dikran has beaten me to these points with much better information...Rob Paintingat 23:37 PM on 27 June, 2011BobCat 03:38 AM on 12 July, 2011Carbon-14page, is that the CO2 adjustment time in the atmosphere is ~10-12 years (stated as a half-life). Compare the plot shown on this page with the theoretical plots (from box models) posted by Dikran Marsupial @ 93. If you want to dispute this, you shouldn’t argue with me about it, but rather the thousands of scientists and engineers (and published papers) that use the well known and tested method of tracer measurement. (Google "tracer" and "measurement" for a huge list -- start anywhere you like.)Response:[Dikran Marsupial] minor edit (as discussed with author)Dikran Marsupialat 17:25 PM on 12 July, 2011Martin Aat 06:31 AM on 17 May, 2012"Individual carbon dioxide molecules have a short life time of around 5 years in the atmosphere. However, when they leave the atmosphere, they're simply swapping places with carbon dioxide in the ocean. The final amount of extra CO2 that remains in the atmosphere stays there on a time scale of centuries."Can you let me have a reference where I can look this up please? When I write down the differential equations for a simple two-box model, with an injected mass of CO2, in addition to an ongoing equilibrium exchange between atmosphere and sink, the result I get does not agree with your explanation. I want to resolve the difference.KRat 07:37 AM on 17 May, 2012(relatively simple)mid-term carbon cycle modeling. Generally speaking, a two-box model will not be sufficient to examine ocean sequestration. The Bern model(not the most complex out there)uses one atmospheric box, four ocean boxes, plus an additional four for the biosphere.Tom Curtisat 08:49 AM on 17 May, 2012Dikran Marsupialat 17:14 PM on 17 May, 2012Martin Aat 05:29 AM on 18 May, 2012KR:Thank you for the Bolin and Eriksson 1958 reference. The link does not lead to the paper itself and I did not manage to locate the paper. (I don't have access to library facilities.) I am aware of the Bern model but my query is related to understanding the fundamentals, not the details of the results used by the IPCC and predicted by the Bern model.Tom Curtis:I have not considered volcanic CO2. But, as I said above, at present I am trying to understand the basic principles, I am not attempting to produce realistic results.Dikran Marsupial:Thank you for the link to the abstract of your paper. I read the words which seem to reiterate the statement at the head of this page but, as I said before, my calculations seem to differ from this and I am trying to resolve the discrepancy. The SkS comment is:"Individual carbon dioxide molecules have a short life time of around 5 years in the atmosphere. However, when they leave the atmosphere, they're simply swapping places with carbon dioxide in the ocean."My understanding is that this means that it takes much longer for the system to reach equilibrium than the residencetime of molecule. My calculations give the same average lifetime in the atmosphere for a CO2 molecule in an injected mass of CO2 as the average time for atmospheric CO2 to reach its new equilibrium following the injection. This differs from the SkS statement, if I have correctly understood the latter. Here is what I have done. I have taken a very simple case but I am simply trying to understand the basics, not produce realistic results. I have considered a case of two finite boxes, atmosphere and ocean (let's say). I have made assumptions as follows: 1. The rate of diffusion from atmosphere to ocean (Gt/yr) is proportional to the mass of CO2 (Gt) in the atmosphere and is independent of the mass of CO2 in the ocean. 2. The rate of diffusion from to ocean to atmosphere (Gt/yr) is proportional to the mass of CO2 (Gt) in the ocean and is independent of the mass of CO2 (Gt) in the atmosphere. Note: Assumptions 1 and 2 imply that the system is linear. 3. The system is initially in equilibrium, so that, initially, the rate of diffusion from atmosphere to ocean equals the rate of diffusion from ocean to atmosphere. 4. I assumed a significant total mass of CO2 (in ocean and atmosphere) and calculated the equilibrium mass of CO2 in atmosphere from the diffusion rate coefficients. 5. I then assumed that an additional mass M (Gt) of CO2 is injected into the atmosphere. I calculated: - the equilibrium mass in the atmosphere and in the ocean when the system once again reaches equilibrium, with the additional M Gt in the system. The equilibrium levels will have changed because I have not assumed the ocean is infinite. - I solved the 1st order differential equation giving the atmospheric CO2 as a function of time, to find the time constant with which the atmospheric CO2 reaches the new equilibrium in the presence of the ongoing equilibrium exchange. Then I repeated the calculation, but this time assuming that initially there waszeroCO2 in the atmosphere and zero in the ocean. So, physically, the injected molecules of CO2 leaving the atmosphere cannot be being replaced by CO2 from the ocean - there was none in there. I solved the differential equation to find the average time for an injected mass of CO2 to reach the new equilibrium (for a system containing no other CO2), and it was the same as for the initial calculation of the average time to reach equilibrium (for a system with CO2 present in atmosphere and ocean much greater in mass than the injected CO2). This was not unexpected, as the differential equation is linear, so the response to an input (the injected mass) should be independent of the response to other inputs (such as the ongoing equilibrium interchange)simultaneously present. I hope the foregoing makes sense. What I am still hoping to find, is a paper that explains (using mathematics, rather than verbal reasoning) how it is that the average lifetime of an injected CO2 molecule differs greatly (or differs at all) from the average time it takes for the system overall to reach equilibrium following the injection of a mass of CO2. Thank you for any help you can give me.Response:[DB] KR's link itself had a further link to Bolin and Eriksson 1958.Tom Curtisat 08:43 AM on 18 May, 2012learn from other peoples mistakes, for you will not live long enough to make them all yourself. To that end, I recommend purchasing "Global Warming: understanding the forecast" which is the best general introduction to the science of the green house effect and carbon cycles available. It is doubly useful because it has an associated, free online course with associated video lectures and models. The model which will most interest you is the Geocarb model, described as "an on-line zero-dimensional descendent of the Berner & Kothavala (2001) GEOCARB III model".Dikran Marsupialat 22:34 PM on 18 May, 2012Martin Aat 23:26 PM on 18 May, 2012DBThank you for the link. I've downloaded the Bolin and Eriksson paper and I'm now reading it. It's often the earliest papers that give the deepest insight, perhaps because they had to sort things out from basics.Tom CurtisThank you for the Archer recommendation. I have sent for a copy. From a quick peek via Amazon, if seems to be a descriptive introduction, avoiding the use of mathematics. It's quite true that life is to short to do everything but I'm determined to get to the bottom of the point I'm trying to understand in this case. So far as I can see, injecting a mass of CO2 into the atmosphere results in an exponential approach to a new equilibrium with a time constant equal to the avererage atmospheric residence time of a CO2 molecule. This seems to conflict with what I've seen in several places, including the statement at the top of this page.Dikran MarsupialThank you. "the adjustment time is essentially independent of the residence time" This is the key point that I believe this SkS page makes, and which I have not been able to reconcile with my own intuition nor with my calculations of a simple model. I believe I have correctly formulated the differential equation, for my simplified case where there are zero emissions other than a one-off injection. [dx/dt = rate CO2 exits ocean - rate CO2 exits atmosphere, where x = CO2 in atmosphere]. I've emailed you a request for a reprint of your paper and maybe it will help me pin down the discrepancy between my understanding and what I've seen stated here and elsewhere.KRat 01:46 AM on 19 May, 2012total concentration(not individual molecular identities)changes. If you(from your intuitions)get this point wrong, you're going to obtain wildly wrong answers. As a rather brain-dead computation(an example - please do not consider this authoritative, as it skips: Currently oceans and the biosphere are absorbing ~2ppm of our slightly greater than 4ppm emissions. If the equilibrium for oceans and atmospheric CO2 is 285 ppm, we're currently at 395, and absorption rates are scaled by the imbalance from equilibrium, then 2/110 =somany factors)~1.8% of the imbalance is absorbed every year. That's thedifferencebetween ocean absorption and ocean emission via CO2 exchange. If we were to stop emitting right now, with that simple 1.8% decrease per year, we're looking at ane-fold. Not 5. Again - the residence time is not directly related to the sum flow into and out of climate compartments, the adjustment time. That comes from the(1/e)decay time of about 55 yearsdifferencesbetween flow rates.Martin Aat 03:49 AM on 19 May, 2012KR"The important thing to remember is that regardless of residence time, the vast majority of CO2 molecules entering the ocean are simply swapped with another molecule."Yes, completely agree. And if the system were in equlibrium, 100% of entering molecules would be swapped for an exiting molecule."The rate of importance is how fast total concentration (not individual molecular identities) changes."Completely agree with this too. (...) At present I'm trying to understand simple idealised cases - I'm avoiding realistic situations as there are too many extra things to cause confusion. I'm working through DM's paper at the moment."Again - the residence time is not directly related to the sum flow into and out of climate compartments, the adjustment time. That comes from the differences between flow rates."Again, I agree. Yet something does not add up for me and I reach a different final conclusion. I'm going to track it down - I promise.IanCat 04:48 AM on 19 May, 2012provided that you interpret the results with care. Using X for atmospheric CO2, and Y for ocean CO2. The differential equations are dX/dt= -F(X) + G(Y) dY/dt= F(X) - G(Y) With F(X) and G(Y) being fluxes out of the atmos and ocean respectively. In your scenario, you initially assumed that the system is in equilibrium and then perturb X to determine the response. Suppose the system is initially in equalibrium (X*,Y*), i.e. F(X*)=G(Y*). Linearising the above system I'll get d(X-X*)/dt= -F'(X*)(X-X*) + G'(Y*)(Y-Y*) d(Y-Y*)/dt= F'(X*)(X-X*) - G'(Y*)(Y-Y*) The implication is if you want to treat the problem as a linear one, the time constants are actually given by derivatives of the fluxes with respect to concentration, i.e. how sensitive the fluxes are to a change in CO2.The equilibration time scale is given by 1/F'(X*).On the other hand, the residence time or lifetime is defined as as capacity divided by the flow rate, in our case at equilibrium is given by X*/F(X*). Intuitively this is sensible: if we have 100 tons of CO2 in the atmosphere, and it is entering the ocean at a rate of 100tons/day, it'll take about a day to clear the atmosphere of CO2. Now if the flux F(X) is linear in X as in your model, the residence time and equilibration time is exactly the same! The fact that you can't get a separation between the two timescales is due to your choice of F(X) and G(Y).IanCat 04:56 AM on 19 May, 2012Martin Aat 09:25 AM on 19 May, 2012IanC:Thank you for clarifying. Yes, I had been assuming linearity. None of the statements I had seen (eg "the adjustment time is essentially independent of the residence time") mentioned that they no longer apply if you assume linearity. Dikran M's paper uses linear systems as examples (if I have understood his paper correctly). He uses an example of a wash basin to explain the principle. I worked out the equations that describe it, assuming its outflow is proportional to the volume of water it contains. We have a wash basin, with: *ilitres per minute flowing into it. *v(t)litres in the wash basin at time t minutes. * Outflowk v(t)litres per minute. (Note: outflow proportional tov(t)for linearity.) The equation forv(t)is thendv(t)/dt = -k v(t) + iResidence timeIn equilibrium(ie at t=infinity), dv(t)/dt = 0, so0 = -k v(infinity) + isov(infinity)/i=Residence time = 1/k.Adjustment timeConsider the wash basin in equilibrium and then, att = 0, dump an additionalDlitres of water into it att = 0.The equation forv(t)is, as before,dv(t)/dt = -k v(t) + i, but withv(0) = D. This has solutionv(t) = i/k + D exp (-k t)so the deviation from the equilbrium isd(t) = D exp(-k t). This means that the adjustment time (ie for the transient to decay to1/eof its initial value) is 1/k.So it seems that in the case of a linear model, at least one with a 1st order differential equation, residence time = adjustment time. And presumably, with some nonlinear models this may also apply? If you assume finite volume for the ocean, even with a 1st order linear model, the equilibrium changes after the injection of a mass of CO2 into the atmosphere. This means that a proportion of the released CO2 remains in the atmosphere forever (according to the model) - but I think that is different from saying that the residence time and the adjustment time are not equal.Adjustment time = 1/k.Dikran Marsupialat 03:23 AM on 20 May, 2012IanCat 09:15 AM on 20 May, 2012F(X) is precisely AX+B for all X.A model linearised about (X*) meansF(X) ~ C(X-X*) + D for points near X*. Typically X* is chosen to be be an equilibrium point so D is usually 0. 1/A and 1/C give you the adjustment time, but only in the linear model will 1/A give you the resident time as well. The reason is that because the residence time depends on the X and magnitude of the flow, which is explicitly given in thelinear model(|AX| and B). On the other hand, information about the absolute magnitude of inflow and outflow is not readily available in a linearised model. It is of course possible that there is some nonlinear F(X) such that upon linearising, 1/C happens to give you the resident time, but unless you know F(X)a prioriyou cannot assume such a thing.Martin Aat 00:25 AM on 21 May, 2012Dikran M, IanC:Thank you. I need to try and work out some examples for simple models with significant nonlinearity so I can get a feeling for what's really going on.IanCat 02:14 AM on 21 May, 2012Dikran Marsupialat 02:33 AM on 21 May, 2012IanCat 02:08 AM on 22 May, 2012Dikran Marsupialat 03:15 AM on 22 May, 2012IanCat 15:31 PM on 22 May, 2012in the absence of a source, which is just X divided by the flux of X out of the box. I believe this is the standard definition of the residence time. To clarify, in 131 are you referring to the residence time and adjustment time of CO2 or C14? I might have misunderstood you.Martin Aat 04:16 AM on 23 May, 2012Dikran Marsupialat 17:12 PM on 23 May, 2012IanCat 04:07 AM on 24 May, 2012Martin Aat 23:59 PM on 24 May, 2012Dikran M:Thank you - I'll go back and look more carefully at your paper. I had thought the examples I had worked out (including the one above) had shown that residence and adjustment times were the same for a 1st order linear system. I think you are quite right. It makes good sense to reconcile your model and mine before introducing any further complications.Martin Aat 20:26 PM on 29 May, 2012Dikran M:I tried to work through your paper but found I was making slow progress. So I decided to reproduce the results of your "A One-Box Model of the Carbon Cycle". Here is my working - I hope I have not made errors despite my tendency to do so. I've made my notation close to yours, though not exactly the same. If you would clarify the points I am sure of (where I've put questions), I'd be very grateful. I am eager to get to the bottom of this (residence time)/(adjustment time) question. Let:C(t)= total atmospheric carbon at timet, (Gt).Fe(t)= Rate that carbon is absorbed by the reservoir from the atmosphere at timet, (Gt yr^-1). This is taken as being given by the formulaFe(t) = ke C(t) + Fe0whereke = 0.0135 yr^-1 and Fe0 = 182.7 Gt yr^-1. [Please see question 1 below]Fi =rate that carbon leaves the reservoir and enters the atmosphere, assumed constant and equal to the pre-industrial emission rate,= 190.2 Gt yr^-1(calculated from values taken from your figure 1). The differential equation for the carbon in the atmosphere isdC(t)/dt = -ke C(t) - Fe0 + Fi = -0.0135 C -182.7 + 190.2 = -0.0135 C + 7.5.[Please see question 2 below] In equilibrium, the carbon in the atmosphere is given by puttingdC(t)/dt = 0, which givesCeq = 7.5 / 0.0135 = 555.5Gt. The solution for the differential equation, assumingC(0) = Ceq + delta is C(t) = Ceq + deltaexp(-ke t). The time constant for this 1st order equation iske, so theadjustment time is[Please see question 3 below] For residence time, your paper talks about carbon of natural and anthropomorphic origin. I did not see why this was necessary. As you say, nature can't distinguish the origin of CO2 molucules so I did not grasp why it is useful to calculate the lifetime of molecules of specific origin. For arbitrary CO2 molecules, the residence time in equilibrium is (content)/(throughput). So1/ke = 74.07 yr.residence time. General question on linearity - [Please see question 5 below]= Ceq/Fi = 555.5/190.2 = 2.92yrQuestions1a. Does "the size of the atmospheric reservoir" (p18) mean the mass of carbon in the atmosphere? 1b. How are the numbers for (Fi - Fe) calculated, please, (in enough detail I can calculate them myself from the Mauna Loa or other data)? 2. This involves taking differences of largish numbers which I imagine are not precisely known, to get smallish differences. An error of a few percent in the numbers would mean that their difference contained no useful information. Is there reason to believe the difference has meaning? 3. This is slightly different from your value of 74.2 yr - I assume this is a typo. 4. Have I got the residence time right (for CO2 of arbitrary origin)? Or can you help me understand why calculating the residence time of a subset of CO2 molecules is useful? 5. Linearity. In ES09,Fewas given byFe = ke C.You have replaced this with a functionFe = f(C)wheref(C) = ke C + Fe0.This function is the formula for a straight line but that does not make the equation linear, so far as I can see. For the equation dC(t)/dt = f(C) to be linear, the function f(".") must satisfy f(C1 + C2) = f(C1) + f(C2) for any C1, C2, because this is how linearity is defined. In this case, for example f(0 + 0) = f(0) = Fe0. But f(0) + f(0) = 2Fe0. So it does not, so far as I can see, qualify as alineardifferential equation. Does this make sense? Have I missed something? Thank you your help.Dikran Marsupialat 04:11 AM on 30 May, 2012Martin Aat 22:13 PM on 30 May, 2012Dikran M:Commiserations on the exam marking - I can't imagine it's much fun. Thank you for the comments - I'll study them carefully and try to do some calculations with the data. I came across the paperH. Rodhe + A Björkström "Some consequences of non-proportionality between fluxes and reservoir contents in natural systems" (Tellus(1979),31, 269-278)which specifically studies nonlinear equilibrium. It reinforces my conjecture that nonlinearity is necessary for (residence)/(adjustment)< 1.Dikran Marsupialat 00:32 AM on 31 May, 2012Martin Aat 10:22 AM on 1 June, 2012directly proportionalto C ie if you have dC/dt = const.V + F_i then you will get (adjustment time)=(residence time). I'm working on using the Mauna Loa data to reproduce your result and to get an understanding of why your model is a better representation of reality than ES09.KRat 13:39 PM on 13 August, 2013And like a bad penny, this silly argument has risen again. Someone named Gosta Petterson

(a professor emeritus of biochemistry and specialist in reaction kinetics, not atmosphere or carbon cycle)is once again claiming thatindividual molecular residence time(one way)is somehow identical toCO2 concentration change time(with most CO2 molecules simply exchanging for another from a different climate compartment), a much slower process.There's a good discussion of this topic and the errors involved on SkS, under The Independence of Global Warming on Residence Time of CO2.

Sadly, this appears to be yet another example of an emeritus professor wandering out of his specialty, and with little perspective proclaiming an entire field of science invalid. And of long-debunked myths being recycled over and over again...

Ashbyat 01:56 AM on 27 June, 2014"Biological uptake (with the exception of fossil fuel formation) is carbon neutral: Every tree that grows will eventually die and decompose, thereby releasing CO2. "

I can see how that would be true for the portion of a tree above ground (assuming the wood isn't used to make a house or something that locks up the wood for 100+ years), but my impression is that the roots are probably as large a carbon sink as the above ground tree and that the smallest tendrils will constantly grow and die back and essentially become part of the soil, fixing their carbon for a long time. Do you have a paper that supports your assertion that trees/plants are carbon neutral? (Preferably one that actually measures the carbon fixing of below ground material over time.) It seems unlikely to be carbon neutral.

This paper argues that organic carbon stored in forest soils are a reservoir roughly the same size as the atmosphere, so we aren't talking about a small effect. http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0006/389859/Principles-and-Processes-of-Carbon-Sequestration-by-Trees.pdf

Dikran Marsupialat 02:16 AM on 27 June, 2014Ashby, there are fungi and bacteria in the soil that break down the roots of dead trees as well. I suspect how fast this happens depends on the moisture and oxygen availability. If this were not true, we would be digging up the roots of dead trees everytime we dig a hole in the ground, which is not the case.

Tom Curtisat 02:25 AM on 27 June, 2014Ashby @145, according to Melin et al (2009), root systems apparently account for only 20% of the biomass of a tree (citing Hakilla, 1989). Further, for Norway Spruce, 4.6% of the subterainian biomass decomposes per year, so that 50% is lost in 15 years, and 95% in 64 years. That is faster than the 3.8% of soil carbon respired to the atmosphere each year (see diagram in main article), but not sufficiently so as to expect a large increase in the soil reservoir from reforestation relative to the increase in the vegetation reservoir from the growth of the trees.

Bob Loblawat 06:05 AM on 29 June, 2014Below-surface carbon in forest can be quite complex. I say "below-surface" because there is not only roots, but also carbon in other soil micro-organisms, plus carbon from decaying roots, etc., as well as the carbon that is carried into the soil from surface litter and such.

Roots do decay over periods of years to centuries, depending on size (and what forect type you are talking about). Tree trunks and branches fall to the forest floor, and then slowly rot - but the more persistent carbon compounds produced will work their way into the soil.

In tropical forests, soil carbon and surface litter are rapidly decayed, so soil carbon content is low - root mass will be the dominant store. In the boreal forest, soild carbon often exceeds (per hectare) the carbon stored in trees above ground, due to cooler temperatures and slow decay rates.

Fire obviously returns carbon rapidly back to the atmosphere, as biomass is burned. Removal of above-ground mass (burning, logging, etc.) will often lead to a rapid drop in soil carbon, as the soil is exposed to sunlight and warmer temperatures. The loss of soil carbon often exceeds the uptake by new growth, so a rapidly-growing forest in a recently-disturbed area can still be a source of carbon (loss to atmosphere), not a sink.

Turning lumber into houses and such does represent a moderate-term carbon sink. Carbon budget models of the forest will account for these factors, such as the Canadian Carbon Budget Model.

I'm most familiar with the dynamics of boreal forests. One major study from 20 years ago was the BOREAS project. A Google search for "BOREAS soil carbon" gives megahits.

Forests do represent major carbon storage, and that is where some of the carbon from burning fossil fuels is going, but by and large they do not represent a long-term permanent sink.

Zadamsat 14:02 PM on 30 June, 2015Hi, the question I have is how do we know that global CO2 emissions weren't increasing at a rate of 3.3x back before the industrial revolution? (Sorry forgot the units). If so, how did the process of figuring that out work?

Thank you.

Response:[Rob P] - There are multiple lines of evidence, but the simplest to understand is that tiny bubbles of air are trapped in snow on the giant ice sheets of Antarctica and Greenland. As this snow is slowly compacted to form ice, the air trapped inside is sealed off from the atmosphere. The ice that has survived for hundreds of thousands of years is therefore a continuous record of the Earth's atmosphere. Core samples are obtained by drilling down into the ice with specialized drilling rigs, and the ice core is later painstakingly analyzed to determine atmospheric CO2 concentration.

Consider the last 10,000 years for instance.......

Tom Curtis' Climate Change Cluedo is also a worthwhile read if you want to learn more.

Tom Curtisat 18:56 PM on 30 June, 2015Zadams @149, I assume you are asking how do we know that atmospheric CO2 was not increasing by 3.3 Gigatonnes of Carbon per annum (1.56 ppmv) prior to the industrial revolution?

Well, to start with, the increase in CO2 concentration observed at Hawaii shows an accelerating trend:

Decade Total Increases Average Annual Rates of Increase

2005 – 2014 21.06 ppm 2.11 ppm per year

(4.47 GtC per year)1995 – 2004 18.67 ppm 1.87 ppm per year

(3.96 GtC per year)1985 – 1994 14.24 ppm 1.42 ppm per year

(3.01 GtC per year)1975 – 1984 14.40 ppm 1.44 ppm per year

(3.05 GtC per year)1965 – 1974 10.56 ppm 1.06 ppm per year

(2.25 GtC per year)1960 – 1964 3.65 ppm 0.73 ppm per year (5 years only)

(1.55 GtC per year)Second, CO2 data from icecores, and C13 data from icecores, speliothems, corals, and mollusc shells show CO2 levels to have been near constant prior to 1750 going as far back as the end of the last glacial. I discuss these in a post here that canvasses the wide range of evidence showing the recent increase in CO2 to have been anthropogenic (see in particular points 1, 5 and 10).

However, the most fundamental reason is arithmetic. The atmosphere currently has about 400 ppmv of CO2 (848 GtC). If atmospheric CO2 had been increasing continuously by 3.3 GtC per annum into the past, just 257 years ago, the atmosphere would have had no CO2 (at which point there could be no photosynthesis, and hence no plants on which we live). Even an increase of as little as 0.09 GtC per year would mean that at the start of the phanerozoic, at the time humans were inventing agriculture, there would have been no CO2 and hence no possibility of our wheat, rye, rice or maize growing. So, even if we had no CO2 records going back into the past, we would know that the current rate of increase is much greater than fifty times the long term average rate of increase leading into the industrial revolution.

So, if we want to believe that the increase in CO2 is natural in origin, we need to believe that just as the industrial revolution kicked of, the long term natural rate of net emissions suddenlty increased by a factor of 10 or more, and then continued to increase over the following 250 years in almost perfect sync with know human emissions until they rose to their current level of well over fifty times the previous long term rate of increase. Further, at the same time we have to believe their is an independent natural sink that did not previously operated that increased at the same rate as human emissions to nullify them, and which is triggered by those emissions so that it should not be included in the net natural emissions, is also incapable of stabilizing net natural emissions (which on this scenario are anything but stable). Put simply, that is not an elegant hypothesis.

Finally, FYI, from icecore data we know that the long term increase in CO2 over the holocene up to the industrial revolution was actually about 0.004 GtC per annum; and there is good reason to think that most of that was driven by deforestation driven by the expansion of agriculture (ie, that it was anthropogenic).