# The CO2 concentration graph: Guesses solicited for its future shape and consequences **URL:** \ **Category:** Great Debates\ **Created:** [August 14, 2009, 11:27am UTC](https://boards.straightdope.com/t/the-co2-concentration-graph-guesses-solicited-for-its-future-shape-and-consequences/506391 "2009-08-14T11:27:28Z")\ **Posts on this page:** 20\ **Page:** 7
**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\ **Post date:** [August 27, 2009, 6:54am UTC](https://boards.straightdope.com/t/the-co2-concentration-graph-guesses-solicited-for-its-future-shape-and-consequences/506391/121 "2009-08-27T06:54:03Z")
> [@Sablicious](#): > > The sheeple may regret hopping aboard the ‘nouveau environmentalist’ bandwagon once they feel the painful \*\*$\*\*ting of what would once have been a garden variety, facile refrigerant gas leak repair in their humble home fridge or A/C, become a write-off level expense as a direct result of sky-rocketing hydrocarbon production costs. > > Hmmm… yes. ~\_~ This thread is sufficiently rancorous without silly and insulting interjections of partisan fluff. Take this sort of thing to the **Pit**. [/Moderating] ---
**Author:** ![intention](https://avatars.discourse-cdn.com/v4/letter/i/e95f7d/32.png) [@intention](https://boards.straightdope.com/u/intention)\ **Post date:** [August 27, 2009, 8:04am UTC](https://boards.straightdope.com/t/the-co2-concentration-graph-guesses-solicited-for-its-future-shape-and-consequences/506391/122 "2009-08-27T08:04:16Z")
tomndebb, thanks for the mid-course corrections. ---
**Author:** ![SentientMeat](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@SentientMeat](https://boards.straightdope.com/u/SentientMeat)\ **Post date:** [August 27, 2009, 10:49am UTC](https://boards.straightdope.com/t/the-co2-concentration-graph-guesses-solicited-for-its-future-shape-and-consequences/506391/123 "2009-08-27T10:49:58Z")
> [@intention](#): > > Despite the large error estimates, I applaud their work, and use it in my own estimates of historical total CO2 emitted … The fact that the overall sequestration rate has not been affected by the processes in the paper you cited is clear evidence that wherever the extra CO2 is being sequestered, it is the atmospheric concentration which is the main factor. OK, so the terrestrial sequestration rate _has_ been falling in the US since 1960, but the _overall_ sequestration rate is not affected because non-terrestrial sequestration, and terrestrial sequestration elsewhere, has _increased_ since 1960? Am I reading that correctly? If so, surely it is not _just_ CO2 concentration which limits sequestration rate either? For terrestrial mechanisms, is there not also a limit set by the nutrients in the soil, such that above a certain CO2 concentration, the plant simply cannot grow or metabolise any faster and sequester ever more CO2? And for non-terrestrial ocean systems, does increased CO2 dissolved in the water not make the shells of sea creatures like formanifera _thinner_, such that an increase in CO2 concentration does not yield a _proportional_ increase in sequestration rate? (By the way, I’m very impressed that you know the authors of these studies personally – I feel I am indeed getting the Straight Dope.) > [@](#): > > The amount sequestered will equal the amount emitted when the atmospheric CO2 level is high enough that the sequestration rate equals the emission rate. Careful – I made the mistake of talking about _amounts_ when I should have been talking about _rates_ or _annual_ amounts and I’d just like to check you’re not doing the same. The _annual_ amount sequestered will equal the _annual_ amount emitted when the atmospheric CO2 level is high enough that the sequestration rate equals the emission rate. The _total_ amount sequestered will equal the _total_ amount emitted \*many years **after** the sequestration rate has **overtaken** the emission rate \*. Am I right? > [@](#): > > Currently, we are emitting on the order of 8 GtC (gigatonnes of carbon) per year. This means that if emissions magically stayed stable at today’s rate, the eventual atmospheric excess burden will be 8/2.6%, or 308 GtC. Since 1 ppmv =2.13 GtC, this give an atmospheric excess of 145 ppmv. 145 ppmv plus the historical level of ~285 ppmv gives an equilibrium level of 285 + 145 = 430 ppmv. Thanks, those are very helpful numbers which I might well make use of with friend **Blake** (is there a sufficiently respectable citation that might convince him the numbers are correct?). However, all of it still depends on the sequestration rate increasing in proportion to the CO2 concentration, does it not? How much greater do you calculate the sequestration rate to be (_ie._ what slope does the orange line in your graph have) in order for this to occur? > [@](#): > > Well, since 1960 (see the CDIAC data I posted on Page 2 of this thread), the increase has been very linear at about 0.11 GtC per year. If this continues for 50 years (“business as usual”) and then levels off there, the eventual emissions would be 8 + 50\*.11, or 13.5 GtC annually. This corresponds to an equilibrium CO2 level of about 530 ppmv … a long way from the feared 800 ppmv. Again, just help me out here – apologies for being a little slow. This still assumes that the sequestration rate will _still be increasing even in 50 years time_, (_ie._ the orange line will continue to _curve upwards_ for 50 years) yes? ---
**Author:** ![SentientMeat](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@SentientMeat](https://boards.straightdope.com/u/SentientMeat)\ **Post date:** [August 27, 2009, 10:56am UTC](https://boards.straightdope.com/t/the-co2-concentration-graph-guesses-solicited-for-its-future-shape-and-consequences/506391/124 "2009-08-27T10:56:50Z")
> [@Blake](#): > > Talk about that all you like, but until you have some evidence that they are all that is required then there’s for me to discuss. OK. **intention** seems to have some pretty solid evidence that the _current_ sequestration rate is easily enough to decrease atmospheric CO2 concentrations by 60 ppmv within a century. This current sequestration rate is split into terrestrial and non-terrestrial portions which look _eminently feasible_ in terms of measuring how much carbon, say, a square kilometre of trees or a cubic kilometre of plankton sequester and scaling up (the Nature report cited 2.2 Gt per year into oceans and 2.6 Gt per year into forests). What precisely is your _problem_ with this evidence, exactly? > [@](#): > > Are you seriously asking if a fantastic example used for dramatic effect is more likely than the mechanisms you propose? Well, _yes_, since it seemed like you considered them both as likely. Like I said – it’s Ockham’s Razor: start with the mechanisms you know about, and ask whether further entities are _necessary_. You seem to be suggesting they _are_, but I’m not sure why. > [@](#): > > Bollocks. When it was pointed pout that current sequestration rates could be maintained by the missing sink that maintained high sequestration rate sin the past you responded “How, if there are fewer trees, more acidic oceans and all the rest?” And I’ve since accepted that current sequestration rates _could_ largely be maintained despite deforestation, so long as ocean-based sequestration keeps up. I don’t accept that natural sequestration rates will _increase massively in future_, as they would have to to prevent peak CO2 concentrations of 500-800 ppmv, given the 8 GtC we are demonstrably adding each year. > [@](#): > > And you think that’s alright? Yep. > [@SentientMeat](#): > > Actually, no, [**intention**] says that future emission rates are impossible to predict, and accepts that an increasing emission rate (from China and India’s future contributions, say) would lead to upper levels of double or even triple the 1800 level. > > > [@Blake](#): > > > > Umm, do you understand that would and could are different words? Look at his reply above: _“would”_ is perfectly accurate. > [@](#): > > How the hell does this support your claim that global forest cover was higher at the timeof the last glacial maximum? I never claimed that. I claimed that there are fewer trees than there used to be before humans came along. By the way, do you question whether humans are largely responsible for this 40% loss in 11,000 years as well? > [@](#): > > The historic low point was 1600, not 1800. 1600 was unambiguously lower than 1800. But if we’re _fitting an anthropogenic curve_ to that graph, one need not have its tail coincide precisely with the 1600 data points. I’m not arguing that natural factors cannot affect CO2 concentration, and would accept that the fall from 1500 and the rise from 1600 to 1700 is largely natural (though medieval European and Chinese deforestation might have some influence). But I cannot see how such a _gentle_ exponent is evidence that the _very steep_ exponent after 1800 must be natural. Like I said, you might be correct that a small natural increase would have occurred since 1600 without human activities. But the _huge_ observed increase is easily explained by the 500 Gigatons of CO2 _demonstrably added_ by human activities. When you hear hoofbeats, think horses, not zebras – especially when a horse is standing _directly in front of your very eyes, stamping its feet_. > [@](#): > > I have no idea. Nor do you. Well, the idea I have is _all of it_, since we can _see the coal being loaded into the power stations and burned_. > [@](#): > > So what is your point? That when you fit a curve to the Law Dome data, the error bars on the later data points are smaller. This means that there is more latitude in the way you fit the curve to the earlier data points since they have larger error bars. I’m not sure why you’re extrapolating from this that I consider pre-1960 data _unreliable_. > [@](#): > > Huh? Are you even following your own argument? You stated that the current lag between CO2 and temperature was different “Compared to the clear and obvious temperature rises that preceded the CO2 rises in the past”. I asked how you know that, and you claim that I said it was different. No, I claim that you said it was _so_. Look through the thread: in numerous places _you yourself_ state that temperature rises preceded CO2 rises in past events. I really don’t know why you’re asking me to provide suppt for a position that _you yourself share_. > [@](#): > > You are arguing that that this time the atmospheric CO2 can’t be sequestered rapidly because it comes from buried carbon. Not rapidly enough to prevent a large peak, no, because the carbon _we’re_ adding is _over and above_ any natural souces. > [@](#): > > At no stage did anyone suggest that there is no evidence that humans haven’t burned fossil fuels. What you have been called on is your claim that the mechanisms that rapidly sequestered gigatonnes of CO2 in the past won’t work this time because the CO2 comes from fossil fuels. They won’t work _fast enough_ to prevent a large peak. In my correspondence with **intention** , I’ve agreed several times that _after[_ this peak, natural sequestration mechanisms like trees, soils, plankton and so forth will bring down the CO2 concentration quicker than I thought. That still makes the next couple of centuries very uncomfortable for many in high CO2 concentrations have negative impacts. > [@](#): > > Yeah, I’m sure evidence of benevolent aliens would put your mind at rest too. Actually, yes it would. Do you have any evidence for them? > [@](#): > > No. Wanting negative impacts on humanity does _not_ evidence a dislike for humanity. Gotcha – thanks for straightening that out. > [@](#): > > We do not know what the mechanism is, We simply lack that information. As scientists we therefore cannot talk about the mechanism. It’s not a case of reluctance. It is a case of lacking sufficient information to engage in this conversation. But we _do_ know the mechanism by which 500 Gt are added: _burning hydrocarbons and clearing forests_. > [@](#): > > We do know that gigatonnes of CO2 have been rapidly added to the atmosphere numerous times in the past and that this has had no long term impact on CO2 concentrations. We know this lack of impact was because of some massive, rapid sequestration mechanism that removed the CO2 almost as rapidly as it was added. But “a few centuries” is _not_ rapid on a human timescale. That high CO2 concentrations won’t remain the case on a geological timescale is little comfort for those being born as we speak if those high concentrations, _which are demonstrably anthropogenic in origin_, end up having negative impacts on their lives. > [@](#): > > The atmosphere neither knows nor cares where those gigatonnes of carbon came from. Well, _I_ do. You seem to be complaining that a stamping horse is obscuring your view of the magic zebras. > [@](#): > > I neither know not care. It’s total red herring, as I’ve pointed out numerous times. But if the 500 Gt _is_ accurate, we can then ask what effect this would have on concentration, yes? > [@](#): > > And your point in quoting this would be would be what? You made a claim which has no basis in evidence, when I pointed out that exactly the opposite could conclusion could be equally true base don the evidence you constructed massive strawman. How does any of this prove otherwise? Well, I _asked you a question_, and it’s a perfectly reasonable one. You seem to think that human activity in the past few centuries could have prevented a natural CO2 rise being even bigger. I’m asking you how that’s even _possible_ given the CO2 we are demonstrably _adding_. > [@](#): > > If you like. So burning 1 Gt of lignite emits 2.8 Gt of CO2, agreed? > [@](#): > > The doomsaying is entirely your province my friend. Well, I wouldn’t say my OP spelt _doom_ exactly, just a few hundred million refugees here and there. Of course, I hope I’m wrong, but you’re not setting my mind at rest much. > [@](#): > > When the absorption from growth is less than the emmissions from loss then hw can they be a sink? Ah, _net_ sink, no. **intention** said “Google ‘missing carbon sink’. I did, and found a claim that it was no longer missing. That it is not a _net_ sink reinforces my point that natural sequestration mechanisms cannot cope with the sheer quantities of CO2 we are demonstrably emitting. > [@](#): > > If you still don’t understand this then I certainly will. But, you see, here we are _discussing_ the mechanism. I don’t see how you can discuss the mechanism while maintaining that we can’t. > [@](#): > > I neither know nor care. The whole thing is massive red herring. _How_ can 500 Gt of carbon be _irrelevant_? I could understand if you thought this was a gross overestimate, or if you thought that the volume of the atmosphere has been _underestimated_ such that 500 Gt barely affects its composition. But this is like me taking you into a room, taking a CO2 measurement, burning a piece of coal, taking another CO2 measurement, and then you telling me that the act of burning the piece of coal was a red herring in figuring out why the second measurement was higher than the first. > [@](#): > > Yep, that’s good science. I must have happened, therefore I believe it. OK, I’ll phrase it thus: How could adding 500 Gt of CO2 **not** increase CO2 concentration? What other _realistic possibility_ is there? > [@](#): > > Look, SentientMeat, I’m on the verge of giving up on you … If you have anything to add in terms of facts or a coherent argument or facts then lay it out clearly in your next post … If you can’t do that I’ll bow out. Well, I’m not giving up on you, **Blake** – I value your contributions here. I hope this post, and **intention** ’s posts directed at you, are enough to keep you engaged. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [August 27, 2009, 11:36am UTC](https://boards.straightdope.com/t/the-co2-concentration-graph-guesses-solicited-for-its-future-shape-and-consequences/506391/125 "2009-08-27T11:36:11Z")
SentientMeat, I’ll say it one last time: If you have anything to add in terms of facts or a coherent argument or facts then lay it out clearly in your next post. Trying to snip quote my posts is clearly leaving you confused and struggling to follow your own argument, much less mine. To give a blatant example of this: > [@](#): > > How the hell does this support your claim that global forest cover was higher at the timeof the **last glacial** maximum? > > > [@](#): > > > > I never claimed that. Compare with: > [@Blake](#): > > Data from ice cores suggest that **Late-glacial** and early Holocene atmospheric CO2 variations were rather conservative > > > [@Blake](#): > > > > …such a belief has been adopted despite a gross ignorance of the carbon cycle and precisely what mechanism has allowed the atmosphere to remove such massive fluxes rapidly **in thepast**. > > > > > [@SentientMeat](#): > > > > > > But there surely is evidence that the current situation is simply different to those past events? There simply aren’t as many forests > > > > > [@Blake](#): > > > > > > You are joking, right? There are more forests now than at the **last glacial** maximum? Can we have a cite for this claim? You quite clearly stated that there are not as many forests today as during rapid CO2 sequestration events. And we established very early on and in numerous later posts that such previous events included the last glacial maximum. I even challenged you to provide a reference that forest cover has declined since the last glacial maximum and you responded. For you to now state baldly that you never claimed that global forest cover was higher at the time of the last glacial maximum is extraordinary. You quite clearly did state precisely that, and attempted to provide references to support same. Your last post includes numerous similar provable examples that you have lost track of your own argument, including your continuing strawman claim that I stated that the current lag between CO2 rises and temperature are different to those in the past, a statement which I clearly never made. All the while you to fail to provide the requested evidence that the current lag is different, as you claimed. Were you almost any other poster I would at this stage declare you to be deliberately dishonest and walk away. However I know you are not like that. So instead I will instead assume that your snip and quote posting style has resulted in you losing track of your own argument. That almost every factual assertion made in the OP has since been proven to be incorrect has presumably not helped the issue. You have so badly lost track of the argument we have been engaging to date that there is no longer any coherence to your posts. You are arguing positions completely different to those you originally started with and have failed to inform me of this. (eg “I’ve since accepted that current sequestration rates could largely be maintained despite deforestation.” Well you never conceded that to me.) So to avoid this I ask you to simply state your current argument in coherent form, along with any factual support for the same. If you still claim that the current lag between CO2 and temperature is different to past events then present the evidence. Don’t claim that I made such a claim unless you can quote where I said it was different. If you still claim that forest cover is less now than at the last glacial maximum then provide the evidence. And so on and so forth. If you fail to present any previous claims in the post I will assume that you have conceded that point. However I have no intention of continuing to point out where you have made claims that you now deny having made. ---
**Author:** ![intention](https://avatars.discourse-cdn.com/v4/letter/i/e95f7d/32.png) [@intention](https://boards.straightdope.com/u/intention)\ **Post date:** [August 27, 2009, 9:09pm UTC](https://boards.straightdope.com/t/the-co2-concentration-graph-guesses-solicited-for-its-future-shape-and-consequences/506391/126 "2009-08-27T21:09:32Z")
> [@SentientMeat](#): > > OK, so the terrestrial sequestration rate _has_ been falling in the US since 1960, but the _overall_ sequestration rate is not affected because non-terrestrial sequestration, and terrestrial sequestration elsewhere, has _increased_ since 1960? Am I reading that correctly? No, unfortunately you’re reading it backwards. The paper lists net carbon emissions, and then only from changes in land use/land cover. The US emissions from LU/LC went down below zero in ~ 1960, indicating that it became a net carbon sink. Curiously, this is because of the increasing efficiency of agriculture. As less and less land produced more and more food, marginal lands were left fallow. Many of these have returned to forest, increasing carbon sequestration. However, there is a huge caveat on this number. It is an estimate from LULC changes only. It does not include other factors such as increased CO2 use by plants when the CO2 levels are higher. > [@](#): > > If so, surely it is not _just_ CO2 concentration which limits sequestration rate either? For terrestrial mechanisms, is there not also a limit set by the nutrients in the soil, such that above a certain CO2 concentration, the plant simply cannot grow or metabolise any faster and sequester ever more CO2? And for non-terrestrial ocean systems, does increased CO2 dissolved in the water not make the shells of sea creatures like formanifera _thinner_, such that an increase in CO2 concentration does not yield a _proportional_ increase in sequestration rate? Again, the answer to your questions in specific is … we don’t know. All that we have numbers on is the net atmospheric concentration and the net sequestration, not numbers for any given mechanism. However, the fact that the e-folding time has not changed despite a large growth in atmospheric CO2 indicates that there has been no reduction to date in the ability of the earth to sequester carbon. It is often naively assumed that an increased in dissolved carbon in the ocean will automatically make calcium using organisms (e.g. diatoms, coral reefs) grow more slowly. However, these are not ruled by simple chemistry, as they are living creatures. > [@](#): > > (By the way, I’m very impressed that you know the authors of these studies personally – I feel I am indeed getting the Straight Dope.) I met Joey Hackler when he was a Peace Corps Volunteer in the Solomon Islands … one of the few researchers I know personally. However, I correspond with a number of the researchers online. [QUOTE=SentientMeat] Careful – I made the mistake of talking about _amounts_ when I should have been talking about _rates_ or _annual_ amounts and I’d just like to check you’re not doing the same. The _annual_ amount sequestered will equal the _annual_ amount emitted when the atmospheric CO2 level is high enough that the sequestration rate equals the emission rate. The _total_ amount sequestered will equal the _total_ amount emitted \*many years **after** the sequestration rate has **overtaken** the emission rate \*. Am I right? [/QUOTE] Yes. [QUOTE=SentientMeat] Thanks, those are very helpful numbers which I might well make use of with friend **Blake** (is there a sufficiently respectable citation that might convince him the numbers are correct?). However, all of it still depends on the sequestration rate increasing in proportion to the CO2 concentration, does it not? How much greater do you calculate the sequestration rate to be (_ie._ what slope does the orange line in your graph have) in order for this to occur? [/QUOTE] It’s not a question of the sequestration rate increasing, that appears to be constant. It’s a question of the emission rate decreasing. And until the emission rate stops increasing, the atmospheric levels will continue to increase. Hope this helps, ask more questions if you have them. w. ---
**Author:** ![SentientMeat](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@SentientMeat](https://boards.straightdope.com/u/SentientMeat)\ **Post date:** [August 28, 2009, 8:55am UTC](https://boards.straightdope.com/t/the-co2-concentration-graph-guesses-solicited-for-its-future-shape-and-consequences/506391/127 "2009-08-28T08:55:58Z")
**Blake** , that’s the _only_ part of my previous post that you feel like engaging me on here? _Sheesh_, so be it. This specification of the last Ice Age as the _single_ event in the past that we’re comparing the current situation to is something of a shift in the goalposts, so apologies for not reading you posts carefully enough to spot this earlier. I thought we were comparing past events _in general_, when a greater forest cover than we currently see seemed a pretty unobjectionable claim. If that’s _still_ an incorrect claim, I’m willing to stand corrected. If there are _more_ trees now than the _specific_ event you’re referring to, I also stand corrected in that specific instance, and would therefore seek to explain the rapid sequestration in that specific event by reference to ocean effects or _tropical_ forests instead. But my argument here, as it has been from the OP onwards, is **not** that natural sequestration wouldn’t eventually bring high CO2 concentrations down. I’ve admitted to **intention** (if not explicitly to you – sorry, it’s tricky to remember what one said to whom when one’s debating two people) that known, natural sequestration mechanisms would do this faster than I thought, and fast enough to bring down past CO2 maxima within a century or two. My argument is that natural sequestration is not fast enough to prevent a high CO2 concentration _this_ time, resulting from humans _demonstrably emitting enough CO2 to raise CO2 concentration_. If you remember, there were three ways in which my concerns could be allayed. I wished to be convinced that: [ul]the CO2 concentration is rising almost entirely naturally, or [li]some natural carbon-sequestering mechanism will kick in cause a level off of 500 ppmv or less, or [\*]500+ ppmv concentrations won’t have significant consequences any old how. [/ul][/li] The second point is what I’ve been discussing with **intention** , and as you can see it seems we’re coming to a consensus that unless the emission rate stays constant while the sequestration rate increases pretty dramatically (_both_ of which are pretty questionable _assumptions_, though that is not to say that either is _impossible_), that is highly unlikely. The third point has not been discussed much, and I’m happy to accept climate sensitivity to large increases in IR-absorbing gases as being so uncertain that negative impacts on humanity _might_ not be forthcoming – it is, if you like, my best hope for the future despite it not allaying my concerns completely. But my main argument with you is the first point: [Quote=Blake] you cannot demonstrate any human impact on the pattern of increase of atmospheric CO2 levels. [/quote] I am seeking to _engage_ you on this point, but all I’m encountering is a form of the Monty Python Argument Sketch. Let me try again. We seek to explain the shape of the CO2 graph over the last few centuries. Yes, there have been dramatic _natural_ rises in CO2 concentration in the more distant past. If a climate scientist proposed an explanation like “well, we think that increased solar warming caused the CO2 concentration to rise a bit, and the IR-absorbing properties of this extra CO2 _amplified_ the temperature rise, and this feedback loop continued until the CO2 concentration peaked, after which natural sequestration mechanisms dragged CO2 concentrations back down again within a few centuries” I would have no problem broadly accepting it, while also accepting that there are important details which are understood very little. But in seeking to explain the _current_ rise, there is an elephant-sized fact sitting right in front of us. Thoughout all those past events, huge stores of carbon were sitting undisturbed, underground. Humans have dug up vast amounts of these stores and burned them, as well as clearing forests, making cement, and all the other things we do which **demonstrably release Gigatons of CO2 every year**. Ockham’s Razor is a useful guiding principle in science: when seeking an explanation, don’t introduce extra explanatory entities unless they are **necessary**. I wish to debate with you whether or not any explanation beyond these **demonstrable human emissions** is _necessary_. Ockham’s Razor can be restated thus: When you hear hoofbeats, think horses, not zebras – _especially when a horse is standing directly in front of your very eyes, stamping its feet._ In order to debate this, we need to agree on roughly how much CO2 _has_ been emitted by human activity: X Gigatons, let’s say. **If** we find that this figure is not enough to significantly affect CO2 concentrations, **then** we can propose further explanatory entities. But you keep saying that this number is _irrelevant_, a _red herring_. I could understand if you thought that the X Gt amount I propose is a gross overestimate, or if you thought that the volume of the atmosphere has been _underestimated_ such that X Gt barely affects its composition. But to say that X is _irrelevant_ is like me taking you into a room, taking a CO2 measurement, burning a piece of coal, taking another CO2 measurement, and then you telling me that the act of burning the piece of coal was a red herring in figuring out why the second measurement was higher than the first. > [@Blake](#): > > I ask you to simply state your current argument in coherent form, along with any factual support for the same. I contend that the amount of CO2 humans have _demonstrably emitted, and demonstrably continue to emit_ is vast enough to explain the current CO2 concentration. I contend that a vast [500 Gigatons](http://www.realclimate.org/index.php/archives/2004/12/how-do-we-know-that-recent-cosub2sub-increases-are-due-to-human-activities-updated/) is not a gross overestimate for “X”, and that this amount is increasing by 8 Gt per year is a **fact** which can be demonstrated by adding up all the hydrocarbons we burn each year, forest we clear each year, cement we make each year and so on. If you disagree with these numbers, we can discuss them in more detail. **intention** also has access to respectable data in this regard, so if you don’t like something I set forth we might ask him to provide something you find more convincing (since he certainly is _not_ an “AGW patsy”). Thanks for your continued contribution here. ---
**Author:** ![SentientMeat](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@SentientMeat](https://boards.straightdope.com/u/SentientMeat)\ **Post date:** [August 28, 2009, 9:01am UTC](https://boards.straightdope.com/t/the-co2-concentration-graph-guesses-solicited-for-its-future-shape-and-consequences/506391/128 "2009-08-28T09:01:39Z")
> [@intention](#): > > No, unfortunately you’re reading it backwards … It does not include other factors such as increased CO2 use by plants when the CO2 levels are higher. So the claim on page (iii) that “the terrestrial sequestration rate has been falling in the US since 1960” is _not_ justified, in your opinion, because the increased CO2 concentration means that sequestration has increased enough to **more than counteract** the drop attributable to land use change? > [@](#): > > It is often naively assumed that an increased in dissolved carbon in the ocean will automatically make calcium using organisms (e.g. diatoms, coral reefs) grow more slowly. However, these are not ruled by simple chemistry, as they are living creatures. Actually, I was thinking less of “[will](http://www.nature.com/nature/journal/v437/n7059/abs/nature04095.html)” and more of “[has already](http://adsabs.harvard.edu/abs/2009BGD.....6.1811D)” if the measurements in this second report are accurate. > [@](#): > > It’s not a question of the sequestration rate increasing, **that appears to be constant**. It’s a question of the emission rate decreasing. And until the emission rate stops increasing, the atmospheric levels will continue to increase. OK, this is where I have genuine trouble understanding you. The bolded sentence suggests that you believe the sequestration rate to be **constant** , and I accept that, to date, “there has been no **reduction** to date in the ability of the earth to sequester carbon.” But what I’m saying time and time again here is that **even if** the emission rate remains **constant** (and _yes, yes, yes_ it might well increase, but let’s leave that aside for now), then if the **sequestration rate remains constant, too** , then the atmospheric CO2 concentration **will continue to increase**. I simply do not see how this can possibly fail to occur: if we add 1 litre to a vessel per second, and 500 ml per second leaks out, the vessel fills by 500 ml per second. The leakage rate must _double_, not just stay constant, to prevent the vessel filling up. On your graph, the current emission rate is higher than the current sequestration rate: the blue line is **steeper** than the orange line. In order for atmospheric CO2 to stop increasing, the **sequestration rate must increase** , _not_ merely remain constant, until it **equals** the emission rate. Apologies for badgering you, but if we could explicitly talk about the gradients of your graph lines, that will be the easiest way fo me to understand your apparent contention that the CO2 concentration will peak around 500 ppmv **even if both rates remain constant**. (If that _isn’t_ your contention, an explicit disavowal of it would also be very helpful.) Many thanks **intention**. And yes, you’ve correctly identified the key issue I’m discussing with **Blake** , and any further help on that score would be welcome - why do _you_ believe that humans are responsible for the current CO2 concentration? ---
**Author:** ![intention](https://avatars.discourse-cdn.com/v4/letter/i/e95f7d/32.png) [@intention](https://boards.straightdope.com/u/intention)\ **Post date:** [August 28, 2009, 9:59pm UTC](https://boards.straightdope.com/t/the-co2-concentration-graph-guesses-solicited-for-its-future-shape-and-consequences/506391/129 "2009-08-28T21:59:32Z")
SentientMeat, as always, your collegial tone is greatly appreciated. Onwards to the questions. > [@SentientMeat](#): > > So the claim on page (iii) that “the terrestrial sequestration rate has been falling in the US since 1960” is _not_ justified, in your opinion, because the increased CO2 concentration means that sequestration has increased enough to **more than counteract** the drop attributable to land use change? In general, we don’t know the answer to that question. We have estimates of the carbon either sequestered or emitted through land use change, but they are just that — estimates. They depend (as does so much of climate science) on imperfect understanding of the processes involved. How much CO2 is released in the conversion of forest to brushland, for example? We can only make rough estimates. So we look at how much forest is cleared … but much of that doesn’t turn into carbon unless the entire forest is burnt. Some fraction of the wood is used for building, so the carbon stays locked up. How much of the wood cut in say 1922 to clear a forest was used to make railroad ties, and how much was burnt, and how much rotted? … Hard to tell, so we make educated guesses. However, there is a lot left out. Here’s what Houghton says about the [study](http://cdiac.ornl.gov/trends/landuse/houghton/houghton.html) (emphasis mine): > [@](#): > > Changes in land use included the expansion and contraction of croplands and pastures, plantation establishment, and harvest of wood. Carbon budgeting included **only those ecosystems** converted to other uses or harvested; unmanaged ecosystems **were not considered**. Further, rates of growth and decomposition were ecosystem specific and \*\*did not vary \*\*in response to variations in climatic factors, CO2 concentrations, or other elements of environmental change. This points to the larger problem, which is that we have much less information about the other sinks. Yes, I know that you found people claiming on the intarweb that they’ve found the missing carbon sink … and others who claim that they’ve found the Loch Ness Monster. I would encourage you to read the studies. Perhaps they have, and perhaps they haven’t. The “missing sink”, however, if found, would only roughly balance the books for the carbon cycle. It would not indicate, for example, how much more limestone is formed when CO2 goes from e.g 280 to 380 ppmv, or how much extra plant life will arise from the same change. Here’s another example. The ocean is a huge source and sink, absorbing an estimated 92GtC and emitting an estimated 90 GtC per year. We estimate that the ocean is a net sink for ~ 2GtC annually. But the error bars on that are huge, because there is absolutely no way to measure the total CO2 either emitted or absorbed by the ocean. So it might be absorbing 6 GtC, or emitting 2 GtC … we don’t know. So I fear that the only real hard evidence is our measurements of anthropogenic CO2 emissions, and the atmospheric levels. By comparing the two we can get a good idea of total sequestration … but that doesn’t tell us where or how it is being sequestered. > [@SentientMeat](#): > > OK, this is where I have genuine trouble understanding you. The bolded sentence suggests that you believe the sequestration rate to be **constant** , and I accept that, to date, “there has been no **reduction** to date in the ability of the earth to sequester carbon.” > > But what I’m saying time and time again here is that **even if** the emission rate remains **constant** (and _yes, yes, yes_ it might well increase, but let’s leave that aside for now), then if the **sequestration rate remains constant, too** , then the atmospheric CO2 concentration **will continue to increase**. I simply do not see how this can possibly fail to occur: if we add 1 litre to a vessel per second, and 500 ml per second leaks out, the vessel fills by 500 ml per second. The leakage rate must _double_, not just stay constant, to prevent the vessel filling up. > > On your graph, the current emission rate is higher than the current sequestration rate: the blue line is **steeper** than the orange line. In order for atmospheric CO2 to stop increasing, the **sequestration rate must increase** , _not_ merely remain constant, until it **equals** the emission rate. Apologies for badgering you, but if we could explicitly talk about the gradients of your graph lines, that will be the easiest way fo me to understand your apparent contention that the CO2 concentration will peak around 500 ppmv **even if both rates remain constant**. (If that _isn’t_ your contention, an explicit disavowal of it would also be very helpful.) I see the problem, which is (as is often the case) the lack of clarity in my writing. Let me attempt to distinguish clearly between the e-folding time, and how much is sequestered. When I have said that the sequestration rate is constant, I have meant that there is no observable change in the e-folding time. If the e-folding time is constant at say 38 years, each year about 2.5% of the atmospheric excess CO2 is sequestered. Now, as you can imagine, the amount of CO2 sequestered is not constant even though the e-folding time is unchanged. The amount sequestered is 2.5% of the excess CO2 (the amount above the historical equilibrium level of ~ 280 ppmv). As the excess CO2 amount changes, so does the amount sequestered, despite the fact that the sequestration rate (2.5% of excess/annum) is unchanged. Sorry for my lack of clarity on this question. [QUOTE=SentientMeat] Many thanks **intention**. And yes, you’ve correctly identified the key issue I’m discussing with **Blake** , and any further help on that score would be welcome - why do _you_ believe that humans are responsible for the current CO2 concentration? [/QUOTE] I think that humans are responsible for the recent (last couple hundred years) increase in CO2 because: 1. The curve of calculated human emissions and the curve of increasing atmospheric CO2 are highly correlated. 2. The ratio of atmospheric C12/C13 has changed in the direction that we would predict from the burning of fossil fuels. 3. Atmospheric CO2 is known to increase with increasing temperature. This is because CO2 is less soluble in warmer water. However, if the ice core data is correct, the recent temperature change (about 0.6°C in the 20th century) is an order of magnitude too small to explain the recent CO2 rise. I hope this clarifies my position, but as always, if there are more questions I’m happy to answer them. ---
**Author:** ![Captain\_Lance\_Murdoch](https://avatars.discourse-cdn.com/v4/letter/c/47e85d/32.png) [@Captain\_Lance\_Murdoch](https://boards.straightdope.com/u/Captain_Lance_Murdoch)\ **Post date:** [August 29, 2009, 5:05am UTC](https://boards.straightdope.com/t/the-co2-concentration-graph-guesses-solicited-for-its-future-shape-and-consequences/506391/130 "2009-08-29T05:05:34Z")
> [@intention](#): > > Even if that were true (it isn’t), it still wouldn’t be appropriate. Among other things, it is an insult to those who died in the Holocaust … some of us still care about that, although I suppose YMMV. > > w. So the University of Illinois is full of it then? [http://www.ens-newswire.com/ens/jan2009/2009-01-20-02.asp](http://www.ens-newswire.com/ens/jan2009/2009-01-20-02.asp) > [@](#): > > climatologists who are active in research showed the strongest consensus on the causes of global warming, with 97 percent agreeing humans play a role. And I have seen you refer to those who accept the general scientific consensus as “warmers” so your offense at “deniers” rings very hollow. ---
**Author:** ![intention](https://avatars.discourse-cdn.com/v4/letter/i/e95f7d/32.png) [@intention](https://boards.straightdope.com/u/intention)\ **Post date:** [August 29, 2009, 6:04am UTC](https://boards.straightdope.com/t/the-co2-concentration-graph-guesses-solicited-for-its-future-shape-and-consequences/506391/131 "2009-08-29T06:04:20Z")
**Captain** , thanks for raising interesting issues. > [@Captain\_Lance\_Murdoch](#): > > So the University of Illinois is full of it then? > [http://www.ens-newswire.com/ens/jan2009/2009-01-20-02.asp](http://www.ens-newswire.com/ens/jan2009/2009-01-20-02.asp) This was an poorly designed survey. I would rank the rate of agreement like this: 1. The earth has been warming since about 1650. There is wide agreement on this. 2. Humans are responsible for some part of the warming. Again, wide agreement. However, that’s where the wide agreement ends. When we get to how much of the warming humans are responsible for, opinions start to diverge radically. And when we get to what the mechanisms are, there is even less agreement. Some scientists say that half or more of the Arctic warming is due to black carbon. Others say no, it’s mostly CO2. Others say it is mostly natural swings, with only small human contribution. Is that a consensus? So I fear that the citation you give does not clarify the question much. It is full of waffle words. The questions were: > [@](#): > > “Have mean global temperatures risen compared to pre-1800s levels?” and, “Has human activity been a significant factor in changing mean global temperatures?” 90% agreed with the first question, as I said, wide agreement. 82% agreed with the second question … but what is “a significant factor”? Does that mean humans are responsible for 25% of the warming since 1800? 50% of the post 1800 warming? 75% of the post 1800 warming? Most scientists that I read say the warming up until about 1975 was mostly from natural causes, with the post 1975 warming ascribed to partly or mostly human causes. So the total amount of “post 1800” warming caused by humans can’t be much, only the latest bit … but 82% of them called it “significant”. So what does “significant” mean to them in this context? I also note that only 2/3 of meteorologists believe that there is human involvement. As to whether people doing active research in the climate field believe in AGW, that’s no surprise, they would have a very hard time getting funding if they didn’t. It’s the called the “Willie Sutton Effect”. Willie Sutton was a bank robber. When a reporter asked him why he robbed banks, he famously replied “Because that’s where the money is” … So no, I don’t think the University is “full of it” … I think they have asked poorly designed questions, and misunderstood the answers. Finally, science is not decided by consensus. Albert Einstein famously remarked, “No amount of experimentation can ever prove me right; a single experiment can prove me wrong.” Or as Abraham Lincoln said ““If the end brings me out all right, what is said against me won’t amount to anything. If the end brings me out wrong, then ten angels swearing I was right would make no difference.” I would recommend Michael Crichton’s speech on the subject entitled [“Aliens Cause Global Warming”](http://www.michaelcrichton.net/speech-alienscauseglobalwarming.html). > [@Captain Lance Murdoch](#): > > And I have seen you refer to those who accept the general scientific consensus as “warmers” so your offense at “deniers” rings very hollow. “Deniers” is an attempt to connect scepticism about AGW with Holocaust denial. Perhaps you could explain the pejorative connotation of “warmers”? In any case, although I’ve used the term in the past, I do not do so now. I say “AGW supporters”. Why did I change terms? Well, you called me on it back in August 2007, saying: [QUOTE=Captain Lance Armstrong] “Warmers” is that your pet insult or something? [/QUOTE] to which I courteously replied [QUOTE=intention] Didn’t realize that “warmers” was an insult … please replace “warmers” with “AGW supporters” as necessary. [/QUOTE] So I’m not clear why you are bringing it up again. I thought we settled that two years ago. ---
**Author:** ![intention](https://avatars.discourse-cdn.com/v4/letter/i/e95f7d/32.png) [@intention](https://boards.straightdope.com/u/intention)\ **Post date:** [August 29, 2009, 7:16am UTC](https://boards.straightdope.com/t/the-co2-concentration-graph-guesses-solicited-for-its-future-shape-and-consequences/506391/132 "2009-08-29T07:16:49Z")
Sorry, misquoted your user name as “Lance Armstrong”, my bad … ---
**Author:** ![jshore](https://avatars.discourse-cdn.com/v4/letter/j/b5e925/32.png) [@jshore](https://boards.straightdope.com/u/jshore)\ **Post date:** [August 29, 2009, 9:30pm UTC](https://boards.straightdope.com/t/the-co2-concentration-graph-guesses-solicited-for-its-future-shape-and-consequences/506391/133 "2009-08-29T21:30:01Z")
intention, Good to see you here as always. I’ve taken a long break from this thread…and don’t want to get too involved, but thought that I should address a few points that you have brought up. First, it is important to note that your modeling of the decay of excess CO2 released as a simple exponential process is not the accepted scientific understanding of what is physically going on. For a view into the scientific literature, see [this](http://www.realclimate.org/index.php/archives/2005/03/how-long-will-global-warming-last/) RealClimate thread or, better yet, read David Archer’s book “The Long Thaw”. His basic picture is summarized as: > [@](#): > > When you release a slug of new CO2 into the atmosphere, dissolution in the ocean gets rid of about three quarters of it, more or less, depending on how much is released. The rest has to await neutralization by reaction with CaCO3 or igneous rocks on land and in the ocean [2-6]. These rock reactions also restore the pH of the ocean from the CO2 acid spike. My model indicates that about 7% of carbon released today will still be in the atmosphere in 100,000 years [7]. I calculate a mean lifetime, from the sum of all the processes, of about 30,000 years. That’s a deceptive number, because it is so strongly influenced by the immense longevity of that long tail. If one is forced to simplify reality into a single number for popular discussion, several hundred years is a sensible number to choose, because it tells three-quarters of the story, and the part of the story which applies to our own lifetimes. > > However, the long tail is a lot of baby to throw out in the name of bath-time simplicity. Major ice sheets, in particular in Greenland [8], ocean methane clathrate deposits [9], and future evolution of glacial/interglacial cycles [10] might be affected by that long tail. A better shorthand for public discussion might be that CO2 sticks around for hundreds of years, plus 25% that sticks around forever. > [@intention](#): > > Of course, this leads to another puzzle. During the ice ages, a 100 ppmv change in CO2 is associated with about a 10°C temperature change … which casts huge doubt on the idea that the changes in CO2 are causing temperature change. It also supports my claim that there is a cap on the global temperature. I believe there are several problems with such a simple analysis: (1) The 10°C temperature change is accurate for the polar regions but the estimates of global temperature change are about half of this, say about 5-6°C. (2) As you know, the dependence on CO2 concentrations is expected to be approximately logarithmic, so each additional 100 ppmv change will have somewhat less effect than the last. And, of course, the most natural way to discuss things is in terms of fractional changes in CO2 levels (since a logarithmic function like y = A log(x) + B has the property that a given fractional change in x leads to the same absolute change y, independent of the initial value of x). (3) In fact, it is generally understood from estimates of relative forcings that only about 1/3 of the global temperature change between the last glacial maximum and now should be attributed to CO2. The rest is attributed to changes in the albedo (due to the ice sheets and vegetation changes), changes in aerosol loading, and changes in the concentration of other greenhouse gas like methane. [The changes in orbital forcings…i.e., the Milankovitch oscillations…are understood to be the initiator of the glacial - interglacial cycles although the direct change that they produce in the GLOBAL forcing is very small. Their role is instead to change the distribution of the solar forcing (both in location and time of year) so that they cause the growth or decay of the ice sheets, which then leads to the albedo forcing changes.] ---
**Author:** ![intention](https://avatars.discourse-cdn.com/v4/letter/i/e95f7d/32.png) [@intention](https://boards.straightdope.com/u/intention)\ **Post date:** [August 30, 2009, 6:09pm UTC](https://boards.straightdope.com/t/the-co2-concentration-graph-guesses-solicited-for-its-future-shape-and-consequences/506391/134 "2009-08-30T18:09:50Z")
> [@jshore](#): > > intention, > > Good to see you here as always. I’ve taken a long break from this thread…and don’t want to get too involved, but thought that I should address a few points that you have brought up. > > First, it is important to note that your modeling of the decay of excess CO2 released as a simple exponential process is not the accepted scientific understanding of what is physically going on. For a view into the scientific literature, see [this](http://www.realclimate.org/index.php/archives/2005/03/how-long-will-global-warming-last/) RealClimate thread or, better yet, read David Archer’s book “The Long Thaw”. His basic picture is summarized as: > > I believe there are several problems with such a simple analysis: > > (1) The 10°C temperature change is accurate for the polar regions but the estimates of global temperature change are about half of this, say about 5-6°C. > > (2) As you know, the dependence on CO2 concentrations is expected to be approximately logarithmic, so each additional 100 ppmv change will have somewhat less effect than the last. And, of course, the most natural way to discuss things is in terms of fractional changes in CO2 levels (since a logarithmic function like y = A log(x) + B has the property that a given fractional change in x leads to the same absolute change y, independent of the initial value of x). > > (3) In fact, it is generally understood from estimates of relative forcings that only about 1/3 of the global temperature change between the last glacial maximum and now should be attributed to CO2. The rest is attributed to changes in the albedo (due to the ice sheets and vegetation changes), changes in aerosol loading, and changes in the concentration of other greenhouse gas like methane. [The changes in orbital forcings…i.e., the Milankovitch oscillations…are understood to be the initiator of the glacial - interglacial cycles although the direct change that they produce in the GLOBAL forcing is very small. Their role is instead to change the distribution of the solar forcing (both in location and time of year) so that they cause the growth or decay of the ice sheets, which then leads to the albedo forcing changes.] jshore, good to see you as well. Using your numbers does not change my point, which is that the 20th century change of temperature is not enough to cause the change in CO2 levels seen during the 20th century. Thus, it is probable that the change is from fossil fuel burning. Regarding exponential decay, what is usually used is the “Bern Model”. This model posits three different decay times which operate on different fractions of the airborne CO2. The three decay times are 171, 18, and 2.6 years. I do not agree with this model, and I use (as I cited above) the simpler model of Jacobson. Since you are here, perhaps you could explain how the Bern model is supposed to work. The claim is that the three different decay times operate on separate parts of the airborne CO2 … but I know of no physical process which can operate that way. Your explanation of that would be greatly appreciated. ---
**Author:** ![jshore](https://avatars.discourse-cdn.com/v4/letter/j/b5e925/32.png) [@jshore](https://boards.straightdope.com/u/jshore)\ **Post date:** [August 31, 2009, 1:24am UTC](https://boards.straightdope.com/t/the-co2-concentration-graph-guesses-solicited-for-its-future-shape-and-consequences/506391/135 "2009-08-31T01:24:31Z")
> [@intention](#): > > jshore, good to see you as well. Using your numbers does not change my point, which is that the 20th century change of temperature is not enough to cause the change in CO2 levels seen during the 20th century. Thus, it is probable that the change is from fossil fuel burning. Well, I certainly agree with you on that. But, what I thought you were also implying in the sentence that I quoted (although it wasn’t completely clear) was that the sensitivity to CO2 determined from the glacial - interglacial cycles was much larger than what has been observed so far in the past century (i.e., when you said that a change of 100ppmv of CO2 was associated with a 10 C increase in temperature). So, I was explaining the various ways in which this estimate that each 10ppmv would lead to a 1 C temperature increase is erroneous. The real estimate, as worked out by Hansen and others, is that a doubling of CO2 (which, from pre-industrial values would be an increase of ~280 ppmv) should lead to about a 3 C temperature increase. [Although, Hansen has pointed out that this “Charney sensitivity” estimate considers any ice sheet albedo changes to be a forcing and not a feedback. And, from the glacial - interglacial cycles, he estimates that the feedback on the timescale that the ice sheets can disintegrate (which he believes might be quite a bit more rapid than current ice sheet modeling generally indicates) would be about 6 C per doubling. It seems that others like James Annan and William Connolley are skeptical that there is enough ice to melt in our current interglacial state to increase the climate sensitivity by that much above the 3 C “Charney sensitivity” estimate.] > [@](#): > > Since you are here, perhaps you could explain how the Bern model is supposed to work. The claim is that the three different decay times operate on separate parts of the airborne CO2 … but I know of no physical process which can operate that way. Your explanation of that would be greatly appreciated. I am not sure about the details of the Bern Model which may just be a fit to the results obtained from a more mechanistic modeling of the carbon cycle. However, as David Archer explains in Chapter 8 of his book, the carbon cycle is quite complicated because of the buffering reactions that occur in seawater. These buffering reactions allow the water to absorb a lot more CO2 initially than one would otherwise expect, but eventually the buffering saturates (due to the acidification of the ocean which reduces the availability of the carbonate ion that reacts with the CO2 and water in the buffering reaction to produce bicarbonate ions) and this leads to 20-40% of the released CO2 not being absorbed by the oceans. Hence, this CO2 has to wait until calcium carbonate dissolved from the land neutralizes the increased acidity in the oceans (or, to put it equivalently, increases the availability of the carbonate ion) thus allowing further absorption of CO2 or until the CO2 reacts with igneous rocks on land. ---
**Author:** ![intention](https://avatars.discourse-cdn.com/v4/letter/i/e95f7d/32.png) [@intention](https://boards.straightdope.com/u/intention)\ **Post date:** [August 31, 2009, 5:34am UTC](https://boards.straightdope.com/t/the-co2-concentration-graph-guesses-solicited-for-its-future-shape-and-consequences/506391/136 "2009-08-31T05:34:17Z")
jshore, thanks for the reply. You say: > [@jshore](#): > > Well, I certainly agree with you on that. But, what I thought you were also implying in the sentence that I quoted (although it wasn’t completely clear) was that the sensitivity to CO2 determined from the glacial - interglacial cycles was much larger than what has been observed so far in the past century (i.e., when you said that a change of 100ppmv of CO2 was associated with a 10 C increase in temperature). So, I was explaining the various ways in which this estimate that each 10ppmv would lead to a 1 C temperature increase is erroneous. The real estimate, as worked out by Hansen and others, is that a doubling of CO2 (which, from pre-industrial values would be an increase of ~280 ppmv) should lead to about a 3 C temperature increase. [Although, Hansen has pointed out that this “Charney sensitivity” estimate considers any ice sheet albedo changes to be a forcing and not a feedback. And, from the glacial - interglacial cycles, he estimates that the feedback on the timescale that the ice sheets can disintegrate (which he believes might be quite a bit more rapid than current ice sheet modeling generally indicates) would be about 6 C per doubling. It seems that others like James Annan and William Connolley are skeptical that there is enough ice to melt in our current interglacial state to increase the climate sensitivity by that much above the 3 C “Charney sensitivity” estimate.] The numbers still come out too high, although not as much, when we use your numbers. If we divide the figures I used by six, per your estimate (1/3 of the rise due to CO2, temperature change of 5°C instead of 10°C), we get a sensitivity of 2.3°C/doubling. In 1990, the CO2 levels were about 290 ppmv. They are now about 385 ppmv. During that time the earth has warmed about 0.6°C. Somewhere around a quarter to a half of that rise is generally ascribed to factors other than CO2. Let’s call the “CO2 caused” rise 0.3°C. That gives a sensitivity of 0.8°C/doubling. Even if we use the full 0.6°C observed, making the illogical assumption that 100% of it was from CO2, that’s still only a sensitivity of 1.6°C/doubling, about half of your 3°C and also below the numbers from the Vostok ice data. You’re still in a cleft stick with this one, however. If we take your numbers for the ice age, it implies that a temperature change of 0.6°C would lead to an increase of some 60 ppmv since 1900… which only leaves 30 ppmv which can be ascribed to human emissions … > [@jshore](#): > > I am not sure about the details of the Bern Model which may just be a fit to the results obtained from a more mechanistic modeling of the carbon cycle. However, as David Archer explains in Chapter 8 of his book, the carbon cycle is quite complicated because of the buffering reactions that occur in seawater. These buffering reactions allow the water to absorb a lot more CO2 initially than one would otherwise expect, but eventually the buffering saturates (due to the acidification of the ocean which reduces the availability of the carbonate ion that reacts with the CO2 and water in the buffering reaction to produce bicarbonate ions) and this leads to 20-40% of the released CO2 not being absorbed by the oceans. Hence, this CO2 has to wait until calcium carbonate dissolved from the land neutralizes the increased acidity in the oceans (or, to put it equivalently, increases the availability of the carbonate ion) thus allowing further absorption of CO2 or until the CO2 reacts with igneous rocks on land. My problem with the Bern model is that it assumes something that I don’t understand. This is the idea that a quarter of the CO2 is subject to 171 year e-folding time, 28% is subject to an 18 year e-folding time, and so on. I don’t understand how this works in a physical sense, since all CO2 molecules are identical. As you say, this may just be a convenient fit to a more complex model. However, given the fact that this fit does not represent any known physical principles, we are left depending once again on a complex, untested model which has not been subjected to V&V and SQA … and yes, before you say it, I know that most scientific models are not subjected to that kind of testing. But most scientific models are not used as the basis for multi-billion dollar decisions, either. Once again, I refer you to [Jacobson](http://www.stanford.edu/group/efmh/fossil/ClimRespUpdJGR%201.pdf). Finally, do you have a citation for the “20-40% of the released CO2 not being absorbed by the oceans”? I ask because the numbers I’ve seen have been much smaller. This is called the “Revelle factor”. Revelle’s original paper on the subject is [here](http://uscentrist.us/about/issues/environment/docs/Revelle-Suess1957.pdf), and is well worth reading. It doesn’t say the things that it is usually cited to uphold. ---
**Author:** ![jshore](https://avatars.discourse-cdn.com/v4/letter/j/b5e925/32.png) [@jshore](https://boards.straightdope.com/u/jshore)\ **Post date:** [August 31, 2009, 4:58pm UTC](https://boards.straightdope.com/t/the-co2-concentration-graph-guesses-solicited-for-its-future-shape-and-consequences/506391/137 "2009-08-31T16:58:32Z")
Thanks, intention, for your reply. > [@intention](#): > > In 1990, the CO2 levels were about 290 ppmv. They are now about 385 ppmv. During that time the earth has warmed about 0.6°C. Somewhere around a quarter to a half of that rise is generally ascribed to factors other than CO2. Let’s call the “CO2 caused” rise 0.3°C. That gives a sensitivity of 0.8°C/doubling. Even if we use the full 0.6°C observed, making the illogical assumption that 100% of it was from CO2, that’s still only a sensitivity of 1.6°C/doubling, about half of your 3°C and also below the numbers from the Vostok ice data. There are two main problems here: (1) Your estimate that only 0.3°C of temperature rise could be attributed to CO2 is almost certainly too small. And, in fact, there is nothing illogical about assuming that 100% of the rise is due to CO2…In fact, it could be more than 100% of the rise (the best estimate of which is now ~0.7°C, by the way) since there were also negative forcings during that period, most notably anthropogenic aerosol contributions. The truth of the matter is that because of the uncertainty in the aerosol forcing and also to some degree because of internal variability, the 20th century temperature rise does not provide good constraints on the climate sensitivity…i.e., within uncertainties it is compatible with a wide range of sensitivities. Better constraints are provided by looking at the change from the last glacial maximum (plus other things such at the cooling from the Mt Pinatubo eruption). (2) To correctly obtain the equilibrium climate sensitivity from the temperature rise, one would have to know how much temperature rise is “still in the pipeline”…i.e., how much additional rise would be expected if we froze greenhouse gas concentrations at their current values. The best estimate that I have seen for this is something like 0.5°C of additional warming, although admittedly with fairly large error bars. > [@](#): > > You’re still in a cleft stick with this one, however. If we take your numbers for the ice age, it implies that a temperature change of 0.6°C would lead to an increase of some 60 ppmv since 1900… which only leaves 30 ppmv which can be ascribed to human emissions … I lost you. For one thing, the argument that only about 1/3 of the warming is due to CO2 is not reversible if you are going to try to determine how much of the CO2 rise is due to warming. Hence, a more reasonable estimate is that 0.6°C of global temperature rise should result in ~15 to 20 ppmv rise in CO2. However, even this is only true over the long term. I.e., the often-noted fact that initial changes in CO2 levels often lag the initial change in temperatures by several hundred years implies that the process by which increasing temperature causes increasing CO2 levels (and vice versa) takes several hundred years to play out. And, it has been suggested that this corresponds with the time it takes to overturn the oceans. > [@](#): > > Finally, do you have a citation for the “20-40% of the released CO2 not being absorbed by the oceans”? I ask because the numbers I’ve seen have been much smaller. It comes from Chapter 8 of Archer’s book “The Long Thaw”. He references David Archer, “Fate of fossil fuel CO2 in geologic time,” Journal of Geophysical Research Oceans (2005); David Archer and Victor Brovkin, “Millenial atmospheric lifetime of anthropogenic CO2,” Climatic Change (2007); Timothy Lenton, “Enhanced carbonate and silicate weathering accelerates recovery from fossil fuel CO2,” Global Biogeochemical Cycles (2006); Philip Goodwin et al., “Ocean-atmosphere partitioning of anthropogenic carbon dioxide on centennial timescales,” Global Biogeochemical Cycles (2007); and Andrew Ridgwell and J. Hargreaves, “Regulation of atmospheric CO2 by deep-sea sediments in an Earth system model,” Global Biogeochemical Cycles (2007). ---
**Author:** ![intention](https://avatars.discourse-cdn.com/v4/letter/i/e95f7d/32.png) [@intention](https://boards.straightdope.com/u/intention)\ **Post date:** [September 1, 2009, 3:38am UTC](https://boards.straightdope.com/t/the-co2-concentration-graph-guesses-solicited-for-its-future-shape-and-consequences/506391/138 "2009-09-01T03:38:12Z")
> [@jshore](#): > > Thanks, intention, for your reply. > > There are two main problems here: > > (1) Your estimate that only 0.3°C of temperature rise could be attributed to CO2 is almost certainly too small. And, in fact, there is nothing illogical about assuming that 100% of the rise is due to CO2…In fact, it could be more than 100% of the rise (the best estimate of which is now ~0.7°C, by the way) since there were also negative forcings during that period, most notably anthropogenic aerosol contributions. The truth of the matter is that because of the uncertainty in the aerosol forcing and also to some degree because of internal variability, the 20th century temperature rise does not provide good constraints on the climate sensitivity…i.e., within uncertainties it is compatible with a wide range of sensitivities. Better constraints are provided by looking at the change from the last glacial maximum (plus other things such at the cooling from the Mt Pinatubo eruption). You say that there is “nothing illogical” about saying that all of the 20th century changes are from CO2. The obvious conclusion is that the IPCC list of other forcings as black carbon, fluorocarbons, LULC, methane, and a host of other things is illogical … [QUOTE=jshore] (2) To correctly obtain the equilibrium climate sensitivity from the temperature rise, one would have to know how much temperature rise is “still in the pipeline”…i.e., how much additional rise would be expected if we froze greenhouse gas concentrations at their current values. The best estimate that I have seen for this is something like 0.5°C of additional warming, although admittedly with fairly large error bars. [/QUOTE] Gosh, funny how that hasn’t come out of the pipeline in the last decade … during that decade we should have had both CO2 forcing, and “pipeline warming”. But we’ve seen no sign of either. “It’s all natural variability” is what the AGW supporters say now … but they must be wrong, because you tell me it’s reasonable that natural variability had absolutely nothing to with the 20th century changes, since it’s logical to ascribe it entirely to CO2. [QUOTE=jshore] It comes from Chapter 8 of Archer’s book “The Long Thaw”. He references David Archer, “Fate of fossil fuel CO2 in geologic time,” Journal of Geophysical Research Oceans (2005); David Archer and Victor Brovkin, “Millenial atmospheric lifetime of anthropogenic CO2,” Climatic Change (2007); Timothy Lenton, “Enhanced carbonate and silicate weathering accelerates recovery from fossil fuel CO2,” Global Biogeochemical Cycles (2006); Philip Goodwin et al., “Ocean-atmosphere partitioning of anthropogenic carbon dioxide on centennial timescales,” Global Biogeochemical Cycles (2007); and Andrew Ridgwell and J. Hargreaves, “Regulation of atmospheric CO2 by deep-sea sediments in an Earth system model,” Global Biogeochemical Cycles (2007). [/QUOTE] Thanks for the references, much appreciated, although I get nervous when Archer cites Archer citing Archer … ---
**Author:** ![SentientMeat](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@SentientMeat](https://boards.straightdope.com/u/SentientMeat)\ **Post date:** [September 1, 2009, 8:55am UTC](https://boards.straightdope.com/t/the-co2-concentration-graph-guesses-solicited-for-its-future-shape-and-consequences/506391/139 "2009-09-01T08:55:30Z")
Well, real life has caught up with me again so I’ll be saying au revoir to the SDMB once more. There were 3 ways my concerns for the future might have been allayed here. To summarise: [ul]The CO2 concentration is rising almost entirely naturally[/ul] This is clearly not the case, as attested to by **Blake** ’s resounding silence since I set forth the argument in the way he requested a few days ago. Human emissions are _right there in front of us_ in volumes easily vast enough to explain the current level _and_ the current annual increase, such that to even _seek_ another explanation is a grave violation of Ockham’s Razor. [ul]Some natural process will prevent CO2 levels rising past about 500 ppmv[/ul]This is what I have been discussing with **intention**. Yes, the annual emission rate due to humans might rise further, confounding any hope of a natural limiting mechanism. However, even if this rate stays constant at around 8 Gt CO2 per year, I consider the possibility of a roughly 500 ppmv level-off to be remote. **intention** has now identified what I see as the problem here: > [@intention](#): > > When I have said that the sequestration rate is constant, I have meant that there is no observable change in the e-folding time. If the e-folding time is constant at say 38 years, each year about 2.5% of the atmospheric excess CO2 is sequestered. > > Now, as you can imagine, the amount of CO2 sequestered is not constant even though the e-folding time is unchanged. The amount sequestered is 2.5% of the excess CO2 (the amount above the historical equilibrium level of ~ 280 ppmv). As the excess CO2 amount changes, so does the amount sequestered, despite the fact that the sequestration rate (2.5% of excess/annum) is unchanged. Calling _this_ the “sequestration rate” is unhelpful and confusing, IMO. If the emission rate is measured in Gigatons per year, so should the sequestration rate. And since the excess is **increasing so dramatically** , then proposing a ‘constant’ sequestration rate of 2.5% \*of the excess \* per year actually implies a dramatic **increase in the sequestration rate**. I simply cannot see how this will continue to happen indefinitely, given the obvious limiting mechanisms which prevent ever more CO2 being sequestered as atmospheric CO2 rises: [soil fertility](http://www.ncbi.nlm.nih.gov/pubmed/11373677), [ocean acidification](http://www.nature.com/nature/journal/v437/n7059/abs/nature04095.html) and so on, all in _addition_ to the tropical deforestation and desertification which continue apace. In **intention** ’s [graph](http://homepage.mac.com/williseschenbach/.Pictures/atmospheric_CO2_exponential_decay.jpg), the orange line will have to become _as steep as_ the blue line - _ie._ 2.5% of excess will have to be sequestered every year even when that excess has increased _dramatically_ as the steeper blue line continues to pull away from the orange. I might be optimistic enough to accept a small increase in the sequestration rate ove the next few decades, but I cannot see how it can continue to eat up 2.5% of a dramatically increasing excess. Of course, I _hope_ **intention** is right in this regard, but I hope he would also consider my concerns to be reasonable. Finally: [ul]CO2 concentrations of 500-800 ppmv won’t have particularly negative impacts anyway[/ul]If there is hope, it lies here. Maybe **intention** ’s increased cloud cover will kick in and reflect the heat which the extra CO2 would otherwise have captured. If so, well, those extra clouds better start measurably forming pretty soon. Maybe the climate is sufficiently insensitive to extra IR-absorbing gases that large temperature rises are not forthcoming. If so, it would have to be the bare minimum sensitivity allowed for the Greenhouse Effect to exist at all, and even a modest sea level rise would surely have highly negative impacts on countries like Bangladesh. But both of these are _possible_, even though in my admittedly amateur eyes they don’t seem all that _likely_. So I guess these are what I’ll have to Believe in, since the consequences of large temperature rises do not bear thinking about. Is this mere _positive_ thinking on my part, or positively _wishful_ thinking? Again, I’m not sure I wish to examine that question too closely lest my optimistic bubble bursts. Many thanks to all who contributed here, and all who spent time reading those contributions. ---
**Author:** ![jshore](https://avatars.discourse-cdn.com/v4/letter/j/b5e925/32.png) [@jshore](https://boards.straightdope.com/u/jshore)\ **Post date:** [September 1, 2009, 6:37pm UTC](https://boards.straightdope.com/t/the-co2-concentration-graph-guesses-solicited-for-its-future-shape-and-consequences/506391/140 "2009-09-01T18:37:25Z")
> [@intention](#): > > You say that there is “nothing illogical” about saying that all of the 20th century changes are from CO2. The obvious conclusion is that the IPCC list of other forcings as black carbon, fluorocarbons, LULC, methane, and a host of other things is illogical … My point is not that there weren’t any other forcings but rather that the NET forcings of all the other components other than CO2 could be close to zero, or even negative. I’m not saying that is definitely the case but, within the error bars on the aerosol forcing, it is certainly a reasonable possibility. > [@](#): > > Gosh, funny how that hasn’t come out of the pipeline in the last decade … during that decade we should have had both CO2 forcing, and “pipeline warming”. But we’ve seen no sign of either. “It’s all natural variability” is what the AGW supporters say now … but they must be wrong, because you tell me it’s reasonable that natural variability had absolutely nothing to with the 20th century changes, since it’s logical to ascribe it entirely to CO2. Noone is saying that natural variability had noting to do with the 20th century changes, but rather that it is unlikely to account for very much of the change (and is as likely to have been negative rather than positive). In fact, I noted that internal variability is one of the contributing uncertainties when one uses the 20th century temperature record to try to constrain the climate sensitivity. > [@](#): > > Thanks for the references, much appreciated, although I get nervous when Archer cites Archer citing Archer … Well, experts in an area do have a tendency to cite their own work in the area. But, 3 of the 5 cites are to papers that he is not an author on. [Previous page](https://boards.straightdope.com/t/the-co2-concentration-graph-guesses-solicited-for-its-future-shape-and-consequences/506391.md?page=6) [Next page](https://boards.straightdope.com/t/the-co2-concentration-graph-guesses-solicited-for-its-future-shape-and-consequences/506391.md?page=8)