Drawing down atmospheric CO2 – part 3

I finally have some time to write the third, and final, of my posts on drawing down atmospheric CO2. There were a few things that I was wanting to stress, that I’ll repeat below.

  • There is a difference between the residence time for a single CO2 molecule (years) and the time over which an enhancement in atmospheric CO2 would decay (centuries, or longer).
  • CO2 continually cycles between different resevoirs (atmosphere, oceans, biosphere, lithosphere) and there are a number of different cycles, with different timescales.
  • The most rapid process involves the cycling of CO2 between the atmosphere and oceans, and the atmosphere and the biosphere (hundreds of years). The slowest cycles involve reactions with calcium carbonate (10s of thousands of years), weathering (hundreds of thousands of years) and the emission of CO2 back into the atmosphere through volcanic activity.
  • The long-term, quasi-stable atmospheric CO2 concentration is essentially set by the slowest of the carbon cycles. Hence, the time it will take to return to equilibrium, after an enhancement in atmospheric CO2, is hundreds of thousands of years.
  • Even though the time it would take to return to equilibrium after an ehancement is hundreds of thousands of years, the initial decay – if we stopped emitting – would be quite fast. However, that new CO2 has been added to the system means that some fraction will remain in the atmosphere for a very long time.
  • Given what we’ve already emitted, and expect to emit in the future, it is likely that at least 20% of our emissions will remain in the atmosphere for thousands of years.

So, the last point above is what I wanted to discuss here. We’ve currently emitted about 550GtC since the mid-1800s. We’re currently emitting just under 10GtC per year. If we carry one as we are, we could reach 1000GtC by the middle of this century. We would expect 20-25% of this to remain in the atmosphere for millenia (although, this doesn’t mean 20-25% of the specific molecules, but that the enhancement in atmospheric concentration would be equivalent to 20-25% of what we’ve emitted).

Currently, about 45% of what we’ve emitted remains in the atmosphere and atmospheric CO2 is at about 400ppm. If we were to halt all emissions now, we would expect (over a few hundred years), the enhancement in atmospheric concentration to approximately halve (i.e., go from 400ppm to about 340ppm). If we get to the point where we’ve emitted 1000GtC and then stopped emitting, atmospheric CO2 would decay (again over a few hundred years) from around 550ppm to around 380ppm. If we emit even more than 1000GtC, then the atmospheric concentration would remain even higher than 380ppm for thousands of years.

Credit : Solomon et al. (2008)

Credit : Solomon et al. (2008)

An important point, which is discussed in this paper on irreversible climate change, is that the radiative forcing depends logarithmically on atmospheric CO2. If halting all emission reduces the enhancement in CO2 by a factor of 2, it doesn’t mean that it reduces the forcing by a factor of 2. Consequently, what is expected (as shown by the figure on the left) is that if we halt emissions, the CO2 concentrations will drop, but the temperature will not.

This is essentially because if CO2 concentrations were fixed at the peak, then we’d continuing warming to equilibrium. Halting emissions leads to a reduction in atmospheric CO2, but does not lead to much of a reduction in temperature; we’d essentially remain at – or close to – the transient response to the peak CO2 concentration. The significance of this is that, without some additional way to remove atmospheric CO2, the most we can do is halt all emissions, which would be expected to simply stop future warming, but not lead – on average – to any cooling; on century timescales, at least. Also, as the bottom panel in the figure shows, even though warming may stop, thermal expansion of the oceans does not.

What the above also implies that even if we reduce emissions substantially, but not halt it completely, we’d expect continued warming; simply fixing the concentration at the peak would probably require reductions of 80-90%. So, we would expect 20-25% of our total emissions to remain in the atmosphere for thousands of years and – without finding a way to draw extra CO2 out of the atmosphere – the best we can do is to halt all emissions, which would essentially prevent future warming, but would not produce any cooling.

Okay, this post isn’t as fluent and clear as I would have liked. Should probably not have started it late last night, but I’ll post it as is. I should credit Tom Curtis for bringing the Solomon et al. (2008) paper to my attention. I should also highlight Eli’s post that also discusses this topic and has a very nice animation at the end. Comments and corrections welcome.

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131 Responses to Drawing down atmospheric CO2 – part 3

  1. I should probably add the kind of comment that I normally do when discussing this issue. If we halted emissions completely, we would expect atmospheric concentrations to drop, but global temperatures to remain almost constant (i.e., at the transient response to the peak CO2 concentration). However, it’s probably more complex than this, given that the Northern Hemisphere (with more land) will probably be close to actual equilibrium than the Southern Hemisphere (with more ocean). Hence, what we might expect is for the NH to cool slightly as concentrations drop, and the SH to continue warming as the oceans continue to take up energy.

  2. Also check out:

    Irreversible Does Not Mean Unavoidable
    http://www.sciencemag.org/content/340/6131/438.short

    And this blog post by Steve Easterbrook:

    How Big is the Climate Change Deficit?
    http://www.easterbrook.ca/steve/2013/02/how-big-is-the-climate-change-deficit/

  3. today,
    Thanks, I’ll have a look at the paper. I’ve referred to Steve Easterbrook’s post quite regularly myself (there’s a similar Realclimate post too).

    There’s also this Ricke & Caldeira paper which makes the point that the fast cycle will draw down CO2 from a specific emission quite quickly and that the warming due to that emission will peak only about a decade after the emissions takes place (essentially the same point as here; we warm to the transient response of each emission). Consequently, any reduction in emission has an impact, and does so on relatively short timescales; decades.

  4. bill shockley says:

    ATTP,

    The Ricke/Caldeira paper has no relevance for an instantaneous cessation of emissions because there is no corresponding dramatic/instantaneous change in forcing as there is with an instantaneous doubling or quadrupling of CO2 concentration — the scenario on which the R-C paper is predicated.

    The transient response of the atmosphere is rapid; the equilibrium response of the earth system is slow. Therefore, the more dramatic the change in forcing, the more these two responses will diverge in short-term magnitude. That is the “trick” being played in the Caldeira paper. In the real world of plausible scenarios, their conclusions have no relevance. And even for the implausible scenario of an immediate cessation of emissions, their conclusions don’t apply. Only if you instantaneously remove a large amount of CO2 would their conclusions be relevant. Unfortunately, this is even more implausible than an instantaneous large increase in CO2

  5. bill,
    I disagree. The Ricke & Caldeira paper is essentially analagous to the instantaneous cessation of emissions. They’re treating each pules of emission independently and showing that the warming associated with a pulse (say our annual emissions) happens within a decade. What their conclusions indicate is that any reduction in emissions will have an impact and will have that impact within decades. Of course, internal variability could mask this, but that doesn’t invalidate their result. I think the strength of the Ricke & Caldeira paper is that it is a response to those who argue that their can be no impact on decadal timescales.

  6. bill shockley says:

    ATTP,

    Caldeira switched from 40 years response time to 10 years based on the results of that paper. So he’s saying if we stop emitting CO2 today, then we achieve maximum warming 10 years from now. We know that can’t be true, because we know there’s at least half a degree in the pipeline, and the system doesn’t warm that fast.

  7. bill,

    So he’s saying if we stop emitting CO2 today, then we achieve maximum warming 10 years from now. We know that can’t be true, because we know there’s at least half a degree in the pipeline, and the system doesn’t warm that fast.

    Ahh, but that’s the point. We only have at least half a degree in the pipeline if we fix the concentration at 400ppm. If we stopped emitting today, then atmospheric CO2 would start dropping straight away and there would very little – if any – warming in the pipeline (apart from a NH-SH adjustment). Look at the middle panel of the figure in the post.

    In a sense, this is a crucial issue. If we halt all emissions, then we won’t continue warming (well, apart from some initial adjustment). However, if we reduce emissions by anything less than 80-90%, then we will. Getting atmospheric CO2 to decrease would require emission reductions of – probably – more than 80%. If you look at the Steve Easterbrook post that todaysguestis linked to, fixing atmospheric CO2 at around 400ppm, would require an almost instant reduction in emissions of about 50%, and an overall reduction of about 90% within a few decades.

  8. Nick Stokes says:

    “The slowest cycles involve reactions with calcium carbonate (10s of thousands of years), weathering (hundreds of thousands of years)”

    Actually, reaction with calcium carbonate is fast. On a decade-century scale, we live in a large scale acid/base buffer, in which CaCO3 participates, and acts as a huge back-up store. Atmospheric CO2 is the expression of the state of this buffer. We shift the buffer state by oxidising C to CO2 (acid). The increase of CO2 in the air resulting from burning a gigamole of C is about the same, medium-term, as you would get from releasing a gigamole of HCl. It’s a shift in the buffer, and to sequester the CO2 as CaCO3 requires shifting it back. The availability of base is the limiting factor, not rate of CaCO3 reaction.

    That is where the rock weathering comes in. It’s the only real source of new base to undo our acidification.

  9. Actually, reaction with calcium carbonate is fast.

    Yes, but the timescale over which this reaction reduces atmospheric CO2 is long (thousands of years), isn’t it? That’s what I was referring to, not the reaction rate itself. I was thinking of what is illustrated in the figure in Tom Curtis’s comment.

  10. Nick Stokes says:

    I see that Tom made the same point about restoration of the buffering system. It seems to me that the availability of base, from whatever source, determines the rate of CaCO3 formation here. Rock weathering is the ultimate source – I don’t know what source he has in mind for the middle dark grey part of the curve.

    In the sea, CO2 first reacts with CO3– to give HCO3-. As a solubility product matter, that then dissolves CaCO3 – this is the ocean acidification story. In the longer term, what can then happen is that the more acid buffer diffuses to the depths. This gets CO2 away from the air, but doesn’t form CaCO3. Only the introduction of a stronger base than CO3– can do that, which is where the weathering of igneous rock comes in.

  11. Nick,
    I think that the middle dark grey area is associated with CaCO3 from shells, or reactions with CaCO3 that is already in the oceans, rather than with CaCO3 added via weathering.

  12. This paragraph from Archer et al. (2009) may explain the different regions of the figure.

    The sediment response is composed of two components: a fast pH-neutralizing reaction of CO2 with CaCO3 on the sea floor (a process called chemical erosion), followed by a longer timescale reaction of CO2 with carbonates on land (weathering) (Archer et al. 1997, Ridgwell&Hargreaves 2007). The amount of CaCO3 on the sea floor available to dissolve is limited by the formation of a clay layer on the sea floor, the nonreactive material remaining after CaCO3 dissolves, which impedes further CaCO3 dissolution (Broecker & Takahashi 1978, Archer et al. 1997). The 5000 Pg C CO2 release is close to enough to deplete the available CaCO3 stock of the ocean, leaving excess weathering over CaCO3 burial to drive the CO2 neutralization.

  13. Nick Stokes says:

    ATTP,
    I’m surprised that is considered such a slow process. In fact, large parts of the ocean are currently supersaturated with CaCO3. And there is plenty of coral, shell material etc around near the surface. And even limestone.

  14. Nick Stokes says:

    ATTP,
    Thanks for the Archer quote. I wasn’t aware that it was thought that access of the sea to limestone could be limited by clay overlay.

  15. Also Figure 1 in Archer (2005) seems to also suggest that non-weathering CaCO3 cycle has a timescale of thousands of years.

  16. bill shockley says:

    ATTP,

    Point taken on constant composition vs 0-emissions scenarios. I keep needing reminding of this and how this applies to what is meant by pipeline heating. But I don’t think there’s as much a difference as you think. I spent a good amount of time creating my own CO2 model. Here’s a relevant pic, showing atmospheric CO2 up to 2008 (the years for which I had good data), and what happens when emissions stop at that point. The upper panel shows the decay profile I’m using. I think the profile is pretty realistic, but you may disagree. It’s adjustable, so let me know…
    https://googledrive.com/host/0B6KqW0UlivnVMWN5eVU4UlpneE0
    (I know this pic won’t embed, but I’ve about had it with tinypic)

  17. Bill,
    It looks reasonable. If we halted emission now, then we expect it to remain above about 340 ppm for hundreds/thousands of years. If you calculate the radiative forcing of 340ppm, it’s about 1Wm-2. If the ECS is 3C, then that would produce an equilibrium warming of about 0.85C, which is about what we’ve experience to date. So, even your figure seems consistent with that basic idea.

  18. bill shockley says:

    https://googledrive.com/host/0B6KqW0UlivnVS0lVQWdxbzhEQVE
    I’ve added a green line at 2048, which shows we’re still at 370 at that date. But that’s stopping emissions in 2008. Add another 8ppm to that, so we’re still at 378ppm, mid-century.

    Hansen says we need to get to 350ppm to zero the energy imbalance, so we’re still warming at 378ppm, 40 years from now, and even in 2100 we’re not there.

  19. Tom Curtis says:

    Anders, what is missing from your discussion is why the temperature remains near constant with the cessation of all emissions. The reason is that the timescale for the rapid reduction in atmospheric CO2 associated with oceanic uptake is approximately that of the transition from the transient response to the Charney equilibrium climate response, ie, the response excluding slow feedbacks such as icesheet melt and changes of vegetation patterns. Further, the timescale of the slow drawdowns is also approximately that for the transition from Charney equilibrium to Earth System Equilibrium, ie, the full response including all slow feedbacks. Clearly the flat temperature response also depends on the ratios of Transient Climate Response (TCR) to (Charney) Equilibrium Climate Sensitivity (ECS) to Earth System Sensitivity (ESS). The flat temperature after cessation of emissions arises with TCR =~= 2, ECS =~= 3, and ESS =~= 5.

    There are substantial uncertainties as regards both those timescales, and the temperature responses. Higher values of ECS and ESS will result in a gradually climbing temperature, wheras lower values will result in a gradually falling temperature. At one extreme, a TCR =~= ECS =~= ESS such as is believed by Nic Lewis will result in a draw down in temperatures approximately coinciding with the draw down in CO2. (This may be the basis of Nic Lewis’ comments, but given their tenor, I suspect he has failed to recognize the significance of the small retained fraction of anthropogenic emissions, ie, that he is expecting draw down rates similar to those following the emission of a slug of CO2 rather than a phased emission over time.) Conversely if ESS =~= 2*ECS and ECS =~= TCR, temperatures will continue rising for thousands of years into the future with a complete cessation of emissions.

    Mismatch of timescales will result in an uneven temperature history. A more rapid transition to the Charney equilbrium response, for example, will result in an initial short term peak in temperatures followed by a slight decline over a few centuries before temperatures remain near constant in the long term. That would look something like the the scenario shown by Ricke and Caldeira. They show slightly more than 0.2 C reduction in temperatures from that at the cessation of emissions after 100 years, and presumably would continue to show that reduction for the next 200 years if it were included. However, if the ESS is approximately 5, after that there would be a slow rise over the centuries until temperatures approximately matched those at the cessation of emissions, before a long term decline over tens of thousands of years. The potential of that future rise is reinforced by the fact that the rate of the long term reduction in CO2 due to rock weathering is governed by temperature, so that lower initial temperatures will result in a slower draw down.

    (As an aside, as near as I can tell, Ricke and Caldeira use the Joos et al CO2 impulses rather than the historical rise in CO2. Consequently their slight rise is probably an artefact of the high initial CO2 levels and there scenario is not strictly relevant to the cessation of emissions after a long term build up in emissions.)

    The upshot of all this is that the long term picture is uncertain. At a best guess tempertures will remain near constant for thousands of years after the cessation of all anthropogenic emissions, and they certainly will not rapidly decline. That last point is the take home, rather than any specific projection of future temperatures.

  20. Tom Curtis says:

    A related issue is just how much emissions can we allow ourselves and still remain on an essentially flat temperature trajectory. Based on some experiments with the stripped down Bern model Archer used for an MOOC, it turns out that even 10% of peak emissions will result in ongoing increases in CO2 and hence a rise in temperatures to the full Charney Equilibrium response. Even at 5% peak emissions, CO2 values could still rise in the short term (next 300 years) and will certainly rise in the long term.

    As some anthropogenic emissions, such as those from cattle and rice production, are unavoidable (though potentially reducible) that means that to stabilize the climate we will need some deliberate sequestration of CO2.

    In the mean time, any policy that does not aim at near zero net emissions within 35 years fails to address the issue.

  21. Tom,

    Anders, what is missing from your discussion is why the temperature remains near constant with the cessation of all emissions. The reason is that the timescale for the rapid reduction in atmospheric CO2 associated with oceanic uptake is approximately that of the transition from the transient response to the Charney equilibrium climate response, ie, the response excluding slow feedbacks such as icesheet melt and changes of vegetation patterns.

    Yes, and that is roughly what I was going to say in response to Bill’s latest comment, but you’ve done it better than I would have done.

    Bill,

    Hansen says we need to get to 350ppm to zero the energy imbalance, so we’re still warming at 378ppm, 40 years from now, and even in 2100 we’re not there.

    Tom’s largely explained this. The timescales happen to match. The rate at which CO2 is drawn down is roughly the same as the rate at which we’d be warming to equilibrium if CO2 was remaining constant. So, ultimately global temperatures remain roughly constant.

    There is, however, a subtlety that I was trying to get at in the first comment. More land-mass in the northern hemisphere means that it will be probably be closer to equilibrium than the southern hemisphere. So, what will probably happen is that the northern hemisphere will cool slightly as CO2 is drawn down, while the southern hemisphere will warm slightly as the ocean continues to take up energy.

  22. bill shockley says:

    Thanks guys… some food for thought.

    I forgot I have a backtested, excellent-fit decay profile. It’s a little more aggressive and puts 2055 at about 370ppm (adjusted for 2015 vs 2008).
    https://googledrive.com/host/0B6KqW0UlivnVTFUySTVHbVY5b2M

  23. Joel Snape says:

    When I clicked on this 3 part series I was expecting it to be very thorough; it’s been a little dissapointing. Apart from what Archer says about the different removal times (which may or may not be correct) how do we know that the increase in atmospheric CO2 is mainly caused by our emissions today?

  24. Joel,
    Sounds like you were disappointed because it didn’t do what you were hoping it would do, rather than because it didn’t do what I was intending to do.

    I’ve spent a good deal of time explaining to people why the increase in atmospheric CO2 is anthropogenic. It’s almost always been a waste of time. Any reason why doing so again wouldn’t also be a waste of time?

  25. Joel Snape says:

    Not at all. When I saw that this had been split up into a 3-part series I naturally thought that it must have been split up because it was so comprehensive that whatever you were saying couldn’t have easily been said in one single post (and not a particularly long one either).

    You say “Any reason why doing so again wouldn’t also be a waste of time?” If think that explaining these things to me would be waste of time (I can only imagine because people don’t end up agreeing with what you are saying) that’s fine by me. I won’t lose any sleep.

  26. Joel,
    It only became 3 because they each turned out longer than I was intending.

    You could read these 10 reasons as to why it’s virtually certain that the increase in atmospheric CO2 is anthropogenic.

  27. verytallguy says:

    Joel, or you could just look at this.

    [Image fixed. -W]

  28. dikranmarsupial says:

    Joel asks “how do we know that the increase in atmospheric CO2 is mainly caused by our emissions today?”

    If the natural environment were a net source of carbon into the atmosphere, then atmospheric CO2 would be rising faster than the rate of anthropogenic emissions as both nature aned mankind would be contributing to the increase. However we observe that this is not the case, and atmospheric CO2 is actually only rising at about half the rate of anthropogenic emissions. This means that the natural environment must be a net carbon sink and hence is opposing the rise, rather than causing it. That is the most basic argument that shows that the increase is down to our emissions, the page ATTP gives provides an excellent summary of the others.

    Like ATTP, I have also spent a lot of time explaining this most basic fact (I even wrote a journal paper about it). Even though we know beyond reasonable doubt that the rise is anthropogenic, it still gets raised again and again on climate “skeptic” blogs and I don’t think anything is going to change that anytime soon. Sadly there are some that cannot accept *any* part of AGW, regardless of how strong the evidence may be. It is time we moved on to more complex issues (such as the one discussed in these three articles) and take the basics as read.

  29. Michael Hauber says:

    ‘ If we halted emissions completely, we would expect atmospheric concentrations to drop, but global temperatures to remain almost constant ‘

    I think uncertainty is an important issue here. With a bit of luck and long term feedbacks in the lower range of what is expected temperatures may start dropping if emissions were halted. With some bad luck and long term feedbacks in the upper range we may see temperature continue to climb, in which case technologies such as BECCS and biochar or whatever other tweaking of the carbon cycle we can manage may be important. They may not do enough to be a major factor on the decades to century or two timescale, but in the centuries to millenia timescale that we would take to approach a possible high end equilibrium sensitivity they may make the difference between a large portion of the planet becoming too hot for human habitation (35 degree wet bulb limit) or not.

  30. Willard says:

    > With a bit of luck […]

    How much?

  31. mt says:

    If the spike is not anthropogenic, where did the emitted carbon go?

    If we argue this point it absolutely constitutes sacrificing public rationality to a filibuster. Whether this filibuster is driven by stupidity or malice is the only interesting question. For myself, I find it hard to believe that anyone understands the physical world that badly.

    But in case I am wrong, look, if you can’t find your socks, they are probably under the bed. They did not disappear. Socks do not work that way.

  32. Michael Hauber says:

    ‘a bit of luck’ – something that has about a 30% chance of happening.

    A further thought – does anyone know what would happen if we follow say RCP 4.5, have the bad luck of both an upper end climate sensitivity, and a lower end combined ability of natural and anthropogenic processes to remove Co2 from the atmosphere. How much of the earth’s surface would exceed the 35 degree wet bulb limit when we reach equilibrium under such a scenario?

  33. Willard says:

    > something that has about a 30% chance of happening

    Where does that number come from, and what drop should we expect?

    I want to know what’s the payoff to bet on that bit of luck.

  34. Mark Bahner says:

    “Given what we’ve already emitted, and expect to emit in the future, it is likely that at least 20% of our emissions will remain in the atmosphere for thousands of years.”

    Only if economic growth stops:

    http://markbahner.typepad.com/random_thoughts/2013/04/global_warming_is_not_irreversible-1.html

    …which is unlikely:

    http://markbahner.typepad.com/random_thoughts/2005/11/why_economic_gr.html

  35. JCH says:

    They did not disappear. Socks do not work that way. …

    BS!

  36. Mark,
    Yes, sure, the magical future technology that will save us.

  37. Michael,

    How much of the earth’s surface would exceed the 35 degree wet bulb limit when we reach equilibrium under such a scenario?

    I’m not sure that any would. I suspect the maximum possible likely warming from RCP4.5 would be around 4oC above pre-industrial. Wet bulb rises at around 0.7C per 1C of warming. The maximum we have at the moment is around 31C, so potentially we could reach wet bulb temperature of 34C under an RCP4.5 scenario if ECS is higher than we currently expect. To be clear, that would severe impacts on those who experience it, but I don’t think we’d quite get to 35C.

  38. Michael Hauber says:

    RCP 4.5 gets to roughly one doubling of CO2 at roughly 550ppm. If earth system equilibrium is as high as 8 degrees (which I believe Hansen has claimed somewhere as an upper limit) and no Co2 is drawn down then ultimately (1,000’s of years) we could see warming of roughly 8 degrees. Assuming 1C wet bulb/1C warming that would put where I live in Brisbane Australia in the zone of very rare wet bulb temps above 35 degrees(highest dew point I’ve personally experienced here is 27), and so I’d imagine all of the tropics and a big slice of the subtropics. Reduce this by however much Co2 is drawn down in a worst case scenario (could it be as low as 0? Earth system sensitivity includes carbon feedbacks so it should not be negative)

    Is the 0.7 ratio of wet bulb:global warming for transient warming while the oceans cool slower than land? Or is there something I’m missing?

  39. verytallguy says:

    MT

    If the spike is not anthropogenic, where did the emitted carbon go?
    If we argue this point it absolutely constitutes sacrificing public rationality to a filibuster. Whether this filibuster is driven by stupidity or malice is the only interesting question. For myself, I find it hard to believe that anyone understands the physical world that badly.

    I’ll see your public rationality and raise you a contrarian Curry:

    I think it unlikely that 100% of the increase in atm CO2 is caused by humans. It is not unreasonable to start from a point of 50-50 (Fred’s conclusion) and see if you can falsify natural variability as large as 50%

    http://judithcurry.com/2015/05/06/quantifying-the-anthropogenic-contribution-to-atmospheric-co2/#comment-700829

    Perhaps even worse:

    Has anyone read AR5 Ch 6 on the carbon cycle lately? Their main conclusion:
    With a very high level of confidence, the increase in CO2 emissions from fossil fuel burning and those arising from land use change are the dominant cause of the observed increase in atmospheric CO2 concentration…

    …Dominant does not mean all or 100%. Seems like 70-80 anthro is perfectly consistent with ‘dominant’. Fred’s 50% would be outside this range, but not by a huge amount.

    http://judithcurry.com/2015/05/06/quantifying-the-anthropogenic-contribution-to-atmospheric-co2/#comment-703425

    Filibuster is an excellent description of that thread. The congruence of surreal content and a well qualified participant makes it one of the all time most illuminating climateballs I’ve participated in.

  40. Michael,
    Fair point, although I think the 8C ESS is based on data from glacials. I think today (with smaller ice sheets) we’d expect it to be lower.

    Is the 0.7 ratio of wet bulb:global warming for transient warming while the oceans cool slower than land? Or is there something I’m missing?

    I think this is related to the assumption of constant relative humidity which then leads to a 0.7C rise in wet bulb temperature for a 1C rise in temperature. However, if you look at Figure 2 in Sherwood & Huber it seems that its 0.75C per 1C globally, but can be as high as 0.96C per 1C for the tropics.

  41. Judith seems to think that the Global Warming Policy Foundation using their own Academic Advisors to review their reports is somehow less pally than normal peer review. Will wonders never cease.

  42. verytallguy says:

    ATTP,

    I should expect it, but Judith continually surprises. That “report” is pure propaganda with a great set of reviewers acknowledged – “Craig Idso,Will Happer, and other reviewers… …Andrew Montford”

    The idea that these reviewers are anything than the biggest of pals, or that such content would ever pass muster in an actual scientific publication is risible.

  43. dikranmarsupial says:

    Regarding the IPCC quote

    “With a very high level of confidence, the increase in CO2 emissions from fossil fuel burning and those arising from land use change are the dominant cause of the observed increase in atmospheric CO2 concentration…”

    The reason it only says “dominant” is (a) because fossil fuel and land use change emissions are only the two most dominant components of anthropogenic emissions, but not all of it (for instance it doesn’t include cement production) and (b) so as not to exclude the possibility of some change in e.g. ENSO giving rise to a trend in atmospheric CO2 in the short to medium term. I know this, because I asked them (the IPCC), it is amazing what you can find out if you ask politely! ;o)

    Reason (a) seems pretty straightforward, and it fully explains why the report says that fossil fuel and land use changes are the dominant causes of the rise in atmospheric CO2, and that is perfectly consistent with the rise being 100% anthropogenic.

    Reason (b) seems a little more complex. I would argue that if the oceans and terrestrial biota are both net carbon sinks (when averaged over a few years), then just because some component part may become on average more source than sink, that does not mean the rise in atmospheric CO2 is in any way a natural phenomenon, as the other components must have become more sink than source. Likewise I don’t regard the decrease in ocean solubility due to rising ocean temperatures as explaining any of the rise because the rise in solubility due to increasing atmospheric CO2 is even greater, and so the oceans have been taking steadily more CO2 from the atmosphere each year than it puts in (in other words it is more and more strongly opposing the rise). Any short-to-medium term trend due to ENSO is going to be rather small in magnitude anyway, so it isn’t going to change the overall picture very much.

    However by the time I had found this out, there was no longer any point trying to discuss it on that particular thread, given that Prof. Curry wrote:

    “Bart, have you done any quantitative analysis on this topic? I agree with you that the mass balance approach is naive zeroth order. I would welcome a guest post on this

    It may be “zeroth order”, but conservation of mass is a hard constraint, and any model of the carbon cycle that substantially violates it is obviously wrong (and even in a Boxian sense useless).

  44. Mark Bahner says:

    “Yes, sure, the magical future technology that will save us.”

    You mean “magical future technologies” like those that have been used to remove CO2 from air in submarines for the last 70+ years, or from spaceships for the 50+ years?

    Or like the prototype that Carbon Engineering ran for more than 1000 hours in 2013?

    http://www.researchgate.net/publication/269901472_Outdoor_Prototype_Results_for_Direct_Atmospheric_Capture_of_Carbon_Dioxide

    Note: They’re building a much larger version of this “magical future technology” (probably with access to some sort of time machine):

    http://carbonengineering.com/updates/

  45. Mark,
    I was being sarcastic, in case that wasn’t obvious. It was your certainty that I was mocking, not the general concept. Could we develop technology that will help in the future? Sure, I’d be surprised if we didn’t. However, if we carry on as we are, we’ll be talking about removing 100s of GtC, which is no small amount. There are certainly valid arguments as to why it might be better to have to not do that, rather than simply carry on as we are in the hope that we will develop something that will accelerate CO2 drawdown sometime in the future.

  46. anoilman says:

    Mark Bahner: There’s way more going out there besides Carbon Engineering. But I often quote them myself.

    A) The last I read on Carbon Engineering was that it cost $120 a ton to extract. That is a godawful expensive number. Even if it works, its a big bill, and of course a lot more ever popular drilling, the bill for a household with 4 people in it is a good $8000 in Canada.
    https://en.wikipedia.org/wiki/List_of_countries_by_carbon_dioxide_emissions

    B) Their tech is still early and prototype. You need to consider that fact when quoting future technology that is currently unavailable. There are many mitigating factors in the uptake of any new, hitherto completely unavailable technologies. Like… it won’t work in some places, like Alberta where we have too many leaky oil wells.

    Just so you know… I’m an engineer. I’ve been the first to do many many things. None of which ever saw the light of day for various reasons even though the tech worked. I was the first human to walk around on a wide area wireless data network receiving streaming video. Paul Allen received the demo after I got it working. The companies involved folded shortly afterwards due to the fact that the networking costs had quadrupled during roll out. (Yes… 5-10 years later cell phones started doing this, and we all take it for granted now.)

  47. Willard says:

    > You mean “magical future technologies” like those that have been used to remove CO2 from air in submarines for the last 70+ years, or from spaceships for the 50+ years?

    The technological magic involved relates to “if the world spent 10 percent of its GDP on removing CO2 from ambient air in the year 2100.” The world is not an economic agent — it’s the whole system.

    The first magic trick is therefore to abstract away the CO2 market needed to make sense of this investment. Unless of course we’re willing to assume that everyone but the “world” is a freerider in that gimmick.

    The second magic trick is the “10%” – it does not sound like a lot, it’s the size of the whole GDP of Japan and Germany together:

    https://en.wikipedia.org/wiki/List_of_countries_by_GDP_(nominal)

    A third magic trick is to assume that because it’s technologically possible to reduce from (say) 900 to 300 ppm, a world with 900 ppm is so rosy as to have no effect on GDP. Even if we accept that we could reduce 900 ppm to 800 ppm by using these calcs, the process takes 60 years.

    The fourth magic trick is to assume Grrrowth.

    ***

    The whole exercise amounts to wonder what the Stern Review would look like if we used twice its rates or more:

    According to the Review, without action, the overall costs of climate change will be equivalent to losing at least 5% of global gross domestic product (GDP) each year, now and forever. Including a wider range of risks and impacts could increase this to 20% of GDP or more, also indefinitely.

    https://en.wikipedia.org/wiki/Stern_Review

  48. verytallguy says:

    Mark,

    That it is possible to scrub CO2 from the atmosphere is entirely unremarkable. The technology you link to doesn’t seem particularly novel either.

    However, given the extremely low concentration of cO2 in the atmosphere, that it is possible to remove at lower cost than either scrubbing at source or not emitting in the first place would astonish me.

    I’m not saying it can’t be done, but thermodynamics is against it.

    Do you have a cite for the economics of their proposition?

    On a much wider level, regardless of the exact future technology, it’s all limited by thermodynamics. Those laws are well understood and are not going to change any time soon. Which is why appeals to cutie technological breakthroughs deserve to be treated skeptically.

  49. bill shockley says:

    We could spend $12 trillion per 100GtC in 2100 and be too late.

    Or we could spend a few commons cents now.

    Google: What an Energy-Efficiency Hero Gets Wrong about Carbon Taxes

    Nice breakdown on a carbon tax model.

    An ounce of prevention…

    WordPress seems to be blocking the Carbon Tax Center URL

  50. Tom Curtis says:

    Mark, the key paragraph of your cited paper reads:

    “Estimates of the total cost for air capture of CO2 are disputed, in part because technologies for CO2 air capture are still being devel-oped (Lackner et al., 2012).Holmes and Keith (2012)have estimated the cost of air contacting (regeneration costs not included) at $60 per tonne of CO2 for a functional prototype (Holmes et al., 2013). Cost estimates that include regeneration range broadly, from ~$20 to $1000 per tonne of CO2 (Goeppert et al., 2012).To remove 10 Tg CO2 y1 at this range of costs, the corresponding expense would amount to $0.2e10 billion per year.”

    To start, regeneration returns the sorbant to its original condition, ie, releases the CO2 from it. Ergo costs with regeneration are irrelevant for mitigating climate change (though relevant for maintaining breathable air in enclosed spaces).

    Second, $60 per tonne of CO2 equals $220 per tonne of Carbon, or $880 billion dollars to absorb current anthropogenic emissions. To that must be added the cost of sequestering the absorbant once used, and the cost for additional emissions. It represents a high end cost for mitigation. It also represents just over 1% of Gross World Product, so it is feasible as a last resort (if the costings are correct).

    Third, while there are many cheaper ways to mitigate emissions, some for of carbon capture and storage will be needed in the long run as the last 10-20% of emissions will not be amenable to elimination by any means. In particular, emissions from agriculture and some transport and steel manufacturing means will be unavoidable. In the short term growing new (or renewing existing) forests would likely be a cheaper method of that, but there is a limit to how long you can expand forests.

  51. Tom Curtis says:

    dikranmarsupial, if global temperatures were to increase due to natural reasons by 1 C, the CO2 concentration of the atmosphere would increase by about 10 ppmv due to ocean outgassing. As it happens the global temperatures have increased by about 1 C, primarily due to anthropogenic emissions so arguably, while 100% of the increase is anthropogenic, only 92% is directly the result of human activity (with the remaining 8% being an indirect result).

    Because of this, I am uncomfortable saying the rise in CO2 is 100% anthropogenic based on the mass balance argument alone. Rather, I would say that about 90% of the rise in atmospheric CO2 is directly anthropogenic, greater than 100% of the rise in Dissolved Inorganic Carbon (DIC) in the oceans is anthropogenic and that 100% of the increase in carbon in its various forms, summed across all reservoirs is directly anthropogenic.

    From a AGW “skeptic’s” perspective, given these facts, they can claim that about 5% of the increase in atmospheric CO2 is anthropogenic without going full flat-earther and denying basic facts about the climate cycle. I think it is important to recognize this so that we do not turn disagreement about the percentage contribution of human emissions to recent temperature increase into disagreement about the carbon cycle unnecessarily,

  52. http://www.technologyreview.com/news/540706/researcher-demonstrates-how-to-suck-carbon-from-the-air-make-stuff-from-it/

    you’all better invest in C02 removal.

    Not as a primary plan… you can try for another 20 years to forge a global agreement
    But, when that fails, or when that agreement is violated
    or when we discoever that ECS is more like 4 or 4.5…
    Then you better have a back up plan.

    precautionary principle and all that.

  53. Steven,
    A back-up plan may well be necessary. Certainly if we’re relying on CCS to allow us to continue using fossil fuels, then we may need some kind of plan if that doesn’t work as well as we’d hope or – as some have suggested – might work at the 10s/100s of MtC level, but not at the 10GtC level.

    However, according to this, we’re producing about 300 Million tons of plastic in 2013. That’s still quite a bit less than the roughly 10GtC we emitted.

  54. Tom, I agree it is not completely straightforward, perhaps because the idea of causation is not that well defined in everyday (rather than scientific/statistical) usage. Personally I would say that the rise in ocean temperature had reduced its ability to oppose the rise in atmospheric CO2, rather than that it was a cause, and so am comfortable with saying it is 100% anthropogenic. It seems a bit odd to me to suggest that the oceans are causing some of the rise in atmospheric CO2, when they are acting as an increasing large net sink. However I don’t want to be particularly dogmatic about it.

    “From a AGW “skeptic’s” perspective, given these facts, they can claim that about 5% of the increase in atmospheric CO2 is anthropogenic without going full flat-earther and denying basic facts about the climate cycle.”

    I assume you meant 95% rather than 5%? If so, I agree.

  55. Dikran’s view seems similar to what Archer et al. (2005) suggest when they regard the temperature response as a feedback that influences how the CO2 is drawn down. See the right-hand panels of Figure 1, for example.

  56. Eli Rabett says:

    So many dead ducks, so little time.

    Here is a finger exercise for Joel Snape.

    We measure an increase in the atmospheric fraction of CO2
    We measure a decrease in the pH of the ocean which means the mixing ratio of oceanic dissolved inorganic carbon has increased
    You tell us that increased carbon dioxide increases net primary production so there is more carbon tied up in plants and soils.

    Explain where all this excess carbon is coming from.

  57. Tom Curtis says:

    dikran, yes – 95%, not 5%.

    Anders, there is, as dikran mentions, an ambiguity about causal talk. On one, intuitive way of looking at things, a thing causes only that which would not have occurred in its absence, all else being equal. On that basis, absent the reduced solubility of DIC with increased temperature, anthropogenic emissions would have resulted in approx 5-10% less of an increase in atmospheric CO2; and absent anthropogenic emissions, a 1 C increase in GMST would have resulted in that 5-10% increase. Ergo the temperature increase has caused 5-10% of the increase in temperature. Correspondingly, from this perspective, 90-95% of the increase is due to anthropogenic emissions.

    That said, given that the 1 C increase in temperature is almost entirely anthropogenic, the Archer/dikran description is equally appropriate. It is just one of those cases where the same situation can have two apparently different but in fact equivalent descriptions. I prefer my description primarily because in discussion with “skeptics”, it allows my two isolate two issues and (potentially) convince them about the facts of the carbon cycle while leaving the issue of climate sensitivity and attribution aside. In particular, it leaves it open to me to show that the temperature impact on CO2 concentration is known, and cannot explain any more than a small fraction of the recent rise. Archer (I suspect) prefers his because he is not debating with “skeptics” and his is a more economical way of expressing it.

  58. Tom Curtis says:

    Steven Mosher, the process you link to involves the direct electrolyctic splitting of oxygen from carbon. With 100% efficiency, that process uses as much energy as the original combustion of the carbon in the first place. Even allowing that substantial energy comes from combustion of hydrogen in methane and oil based products, it is dubious that the round cycle eficiencies of fossil fuel combustion would leave any surplus power if we employed this method to sequester CO2. That is evident in the estimate that using solar cells to power the process, and with just 10% of the Sahara’s surface area, the process could be used to restore preindustrial CO2 levels*. As it happens, just 5% of the Sahara’s surface area is required to supply 100% of current global energy needs from all sources.

    In sum, if the method is economic as a source of carbon fiber, fantastic. That will help mitigate climate change. But if not, then it can only have a niche role at best in mitigating climate change.

    * This calculation was not performed as part of the original study, and I suspect is extremely optimistic. As the actual calculation is not presented, however, I cannot comment further.

  59. Mark Bahner says:

    “It was your certainty that I was mocking, not the general concept.”

    You said CO2 would stay in the atmosphere for thousands of years. I stated that would require economic growth to stop, which is unlikely.

    Which of us is being falsely confident? It seems clear to me that your statement that CO2 would remain in the atmosphere for thousands of years is much more likely to be falsely confident. What evidence do you have that economic growth will stop?

    P.S. I guess I should have said that economic growth stopping was unlikely…”barring thermonuclear war or takeover by Terminators.” But I assumed that was understood.

  60. Kevin O'Neill says:

    Steven – the process also uses (requires?) lithium carbonate. While we currently sit at high levels of lithium reserves and resources, if EVs and PowerWalls become the norm ‘peak lithium’ will become as talked about as peak oil 🙂

    This seems a reasonable estimate Is There Enough Lithium to Maintain the Growth of the Lithium-Ion Battery Market?, while this analysis by Tim Worstall is a bit wanting; he doesn’t consider increased demand going forward whatsoever.

  61. Mark,

    Which of us is being falsely confident? It seems clear to me that your statement that CO2 would remain in the atmosphere for thousands of years is much more likely to be falsely confident. What evidence do you have that economic growth will stop?

    Are you actually being serious? Really? Economic growth is guaranteed to lead to the development of something that will allow us to remove 100s of GtC from the atmosphere sometime in the future? That seems like a remarkable leap of faith. Did you read the other – more thoughtful – responses to your earlier comment?

    Okay, at least 20% of what we’ve emitted will remain in the atmosphere for thousands of years unless we find some way of removing CO2 from the atmosphere. As I had thought was obvious (but clearly isn’t to some) these posts were mainly a response to those who seem to think that it can be drawn down naturally and that only a small fraction will remain for thousands of years, even if we don’t develop some technology to remove CO2 from the atmosphere.

  62. Willard says:

    > I stated that [CO2 would stay in the atmosphere for thousands of years] would require economic growth to stop, which is unlikely.

    So let me get this straight, MarkB: unless economic growth completely stops, CO2 will not stay in the atmosphere for thousands of years?

    I thought it was the other way around.

    ***

    It seems to me that 10% of the global GDP is a bigger number than the 1-2% Stern suggested:

    The Review proposes that one percent of global GDP per annum is required to be invested to avoid the worst effects of climate change. In June 2008, Stern increased the estimate for the annual cost of achieving stabilisation between 500 and 550 ppm CO2e to 2% of GDP to account for faster than expected climate change

    https://en.wikipedia.org/wiki/Stern_Review

    In fact, considering that 2% in 2008 was twice the estimate of 2006, we might wonder about the margins of error for the 10% in 2100, a figure that is only stipulated:

    Then I calculated what would happen if the world spent 10 percent of its GDP on removing CO2 from ambient air in the year 2100

    http://markbahner.typepad.com/random_thoughts/2013/04/global_warming_is_not_irreversible-1.html

    “Calculated” sounds a bit too certain for that kind of estimation.

    In any case, investing 2% of the global GDP may not prevent our grandchildren’s grandchildren to spend 10% of their GDPs.

    ***

    Speaking of irreversibility, here’s what we can read in the very first paragraph of MarkB’s reference:

    Understanding how decreases in CO2 emissions would affect global temperatures has been hampered in recent years by confusion regarding issues of committed warming and irreversibility. The notion that there will be additional future warming or “warming in the pipeline” if the atmospheric concentrations of carbon dioxide were to remain fixed at current levels (1) has been misinterpreted to mean that the rate of increase in Earth’s global temperature is inevitable, regardless of how much or how quickly emissions decrease (2–4). Further misunderstanding may stem from recent studies showing that the warming that has already occurred as a result of past anthropogenic carbon dioxide increases is irreversible on a time scale of at least 1000 years (5, 6). But irreversibility of past changes does not mean that further warming is unavoidable.

    http://www.sciencemag.org/content/340/6131/438.full

    This of course does not imply “technologically impossible to reverse” (ibid.):

    If technological investments and innovation increase the availability of reduced-carbon sources of energy that are competitive in price, development can continue to improve the lives of people in emerging economies without driving global climate change to increasingly dangerous levels. If reduced-carbon energy sources are not advanced rapidly, a great deal of carbon-intensive infrastructure is likely to be put in place in the developing world, implying a large and ongoing societal commitment to further global CO2 emissions and consequent climate warming.

    If one could engineer carbon-neutral coal mines, say by coupling them with Dyson trees, then this would qualify as a “technological investment and innovation that increase the availability of reduced-carbon sources of energy,” assuming the Dyson trees can suck carbon as efficiently as vacuum cleaners with the same name.

    The “competitive in price” is far for being plausible compared to a carbon-dumping coal power plant, however. Some regulations might be required. Or at least Leprechauns.

  63. verytallguy says:

    Wow. Do I have this right? What’s suggested is:

    Emit now. Sequestrate from atmosphere later. Because Growth ?

    That is properly batshit crazy.

    Or, to put it more delicately, even if technologically possible, is likely to infringe the laws of both economics and thermodynamics.

  64. anoilman says:

    vertallguy: Yes that is batshit crazy. You nailed it. 🙂 Why does that word come to mind so often when looking at what these guy’s think?

    In the mean time a Carbon tax would sort through a lot of the short term issues. As Tom Curtis mentioned it may be cheaper to do other things first, like not emitting it in the first place. Carbon tax and let the free market sort it out. With a Carbon tax the easiest and cheapest to do things will get done first.

    After all we do know that constraining carbon emissions has little impact on growth, so I’d start here before we start worrying about ‘ouch time’, and actually changing things. First thing’s first.
    http://www.theglobeandmail.com/globe-debate/the-insidious-truth-about-bcs-carbon-tax-it-works/article19512237/

  65. The most rapid process involves the cycling of CO2 between the atmosphere and oceans, and the atmosphere and the biosphere (hundreds of years).

    Since the rate of uptake has increased by 500% in 55 years, this would not appear to be correct.

    An important point, which is discussed in this paper on irreversible climate change, is that the radiative forcing depends logarithmically on atmospheric CO2.

    Earth has had climate fluctuations on a wide spectrum of time scales. All have reversed.
    What hubris do you invoke in using the adjective ‘irreversible’?

  66. TE,

    Since the rate of uptake has increased by 500% in 55 years, this would not appear to be correct.

    The timescale over which 1/e of our emissions would be sequestered in the fast climate sinks is – according to the IPCC – somewhere between 50 and 200 years. Archer et al. (2009), however, suggest 250 +- 90 years.

    What hubris do you invoke in using the adjective ‘irreversible’?

    Do you want to think about what I’m actually saying in that sentence: “a paper on irreversible climate change” (hint, follow the link in the post).

  67. anoilman says:

    Turbulent Eddie says: I really don’t think I want an ocean full of CO2.. er… Carbonic Acid.
    https://en.wikipedia.org/wiki/Ocean_acidification

  68. izen says:

    @-TE
    “Earth has had climate fluctuations on a wide spectrum of time scales. All have reversed.”

    None have reversed, although the fluctuations may establish conditions SIMILAR to previous conditions.

    That such fluctuations are possible should give cause for concern over what further fluctuations we may cause by altering a key component of the climate on a decadal timescale, but at a magnitude that has only been seen over geological timescales in the past.

    @-“What hubris do you invoke in using the adjective ‘irreversible’?”

    All macroscopic physical processes beyond the quantum level are irreversible.
    You can’t step into the same river twice…
    And once you open the box the cat is either dead or alive.

  69. For a scientifically literate but mathematically challenged layperson like myself (and other laypeople), it seems to me a very strong argument can be made on the difficulties of carbon sequestration and storage just from the sheer quantities involved. The idea that at some hypothetical time in the future we will find some physical space warp to put all that stuff, or somehow otherwise sidestep the laws of physics (which are, largely, about reality unless you start adding dimensions, which works for math and apparently has deeply practical applications, but not anywhere I can see of think of) seems impractical at best. Gummy, sorry about the messy loops in that overlong parenthesis.

    The idea that it is realistic to imagine an idealized future seems dangerous to me if it is used to delay and/or prevent every available practical measure being put in place now. The expense does not get less with time, it gets to be more.

  70. izen says:

    Fifty years ago there was around 3Kg (6lb) of CO2 above every square meter of the Earth.

    Today there is about 4Kg (8lb).
    That extra 1Kg of atmospheric CO2 would form a block of chalk approx 20cm (8in) square.

    So to remove the CO2 already added would involve forming around 70 blocks of chalk, (limestone, nanofibres) per person.
    Globally.

    (numbers approximate, and there may be an order of magnitude error? any corrections welcome)

  71. Rachel M says:

    I don’t think many people, outside of climate blogs, understand that we’ve already committed ourselves to more warming even if we stopped emissions today. This is something that hasn’t been communicated very well to the general public. I wish more people read your blog 🙂

    On a positive note I was pleased to see the Canadians got rid of Harper. Hopefully science will have a voice in Canada now.

    (p.s. I’d probably delete Joel Snape’s comments)

  72. anoilman says:

    Susan Anderson: We’ve already determined that we can’t sequester in Alberta. We’ve drilled too much and left too many holes all over the place. We have leaks into the ground water all over the place, and its coming up the the surface. The following papers would give you and idea about the scope of the issues. We also haven’t developed ‘forever’ concrete yet. Concrete breaks down over time and that means, this stuff will try to escape pretty much forever.

    http://www.ucalgary.ca/wasp/Well%20Integrity%20Analysis.pdf
    http://www.albertasurfacerights.com/upload/files/SBachuTWatson%20%20Potential%20Wellbore%20Leakage.pdf

    Rachel M: Harper’s gone… crazy right wing Libertarian policies were a total flop in Canada. If they weren’t Harper would get votes. I’m hopeful that the Liberals will end censorship and application of political minders for scientists.

  73. Jim Eager says:

    Tom Curtis wrote: “if global temperatures were to increase due to natural reasons by 1 C, the CO2 concentration of the atmosphere would increase by about 10 ppmv due to ocean outgassing.”

    True, once the ocean came into full equilibrium with the atmosphere, but less than two hundred years on we’re no where near full equilibrium. At present the ocean is still absorbing almost half of our annual CO2. That absorption will have to drop to zero before the ocean can become a net emitter. To put it another way, humans are responsible for over 200% of the increase, with the ocean and land biosphere absorbing over half of of what we emit.

  74. Jim Eager says:

    And to put that in terms that even Joel Snape should be able to understand, every year the ocean and land biosphere absorb 100% of all natural CO2 emissions, *plus* ~60% of ours. In short, that is how we know that the increase in atmospheric CO2 is mainly caused by our emissions today.

  75. Mark Bahner says:

    “So let me get this straight, MarkB: unless economic growth completely stops, CO2 will not stay in the atmosphere for thousands of years?”

    Yes, that comes from very straightforward logical analysis. Excess CO2 (above say, 300-400 ppm) is bad. Therefore, people will eventually want to get the concentration down to 300-400 ppm.

    Right now, the world GDP is about $80 trillion. But if the world real GDP (i.e., adjusted for inflation) increases by about 2.1 percent per year, the world GDP will increase by a factor of 8 every 100 years.

    So we’d have:

    2115 = $640 trillion (year 2015 dollars)
    2215 = $5.1 quadrillion (year 2015 dollars)

    Let’s assume the CO2 concentration in the year 2215 is 700 ppm, and they want to get down to 300 ppm. If the cost of removal is $1000 per metric ton of CO2, that would be $7.81 trillion per 1 ppm of atmospheric CO2 concentrations (since there are approximately 7.81 metric gigatons of CO2 per ppm of CO2 in the atmosphere ). So the cost would be 400 ppm X $7.81 trillion per ppm = $3.1 quadrillion. So if the people of 2215 spent 10 percent of their GDP on removing CO2, they could go from 700 ppm to 300 ppm in 6 years. (Note that the U.S. spent on average approximately 10 percent of its GDP on the military for the 30 years after WWII.)

    Again, this is very straightforward. It demonstrates that, unless economic growth stops, there is virtually no chance that human beings will allow CO2 concentrations in the atmosphere to remain above 300-400 ppm for 1000+ years. So Anders whole analysis is predicated on a situation that is very unlikely to occur.

  76. Tom Curtis says:

    Jim Eager, regardless of whether I offer you a service for 8000 dollars with a 25% penalty for late payment, or a service for $10000 with a 20% discount for early payment, I offer you the same deal. The only difference is in the words used to describe the deal, and neither choice is more accurate than the other. It is the same between your stated position and mine, except on one point, and with one nuance.

    The point of difference is whether the increase of atmospheric CO2 due to increasing temperatures is dependent on full ocean equilibrium or just surface ocean equilibrium. As it happens, the change in atmospheric concentration as a function of change in temperature is approximately the same between the icecore record over the last 400,000 years, and in the modern instrumental record. That suggests that within the uncertainty of the estimate of the temperature response, the difference between equilibriation of the surface ocean (timescale of a couple of years at most) and the deep ocean (timescale of about 300 years), the estimate is effectively the same. From carbon models, the additional production change in atmospheric concentration due to equilibriation with the deep ocean results in the ocean absorbing approx 36% more, so again within accuracy of the determination, there is no significant difference.

    The nuance is that on a molecular level, increasing the pCO2 of the ocean due to the absorption of CO2 from the atmosphere results in an increase of the emission of CO2 from the ocean even though the increase in absorption is greater. If in addition to increasing atmospheric CO2, you warm the ocean, the emission from the oceans surface will increase beyond that due to the change in pCO2, with no corresponding increase in absorption. So, at a molecular level, my description is more accurate; even though when we talk about net effects there is no difference between the descriptions beyond rhetorical effects. In terms of rhetorical effects, my description has the advantage of allowing a discussion of the actual effect of increasing temperature without commitment on the cause of that increase (even though the great majority of it is anthropogenic). The advantage of your method is that it emphasizes that 100% of the total surface system increase in CO2 (ie, the net increase in atmosphere, ocean and biosphere combined) is anthropogenic. I just happen to think that my immediately preceding description is also a better way of saying that as well.

  77. “Steven – the process also uses (requires?) lithium carbonate. While we currently sit at high levels of lithium reserves and resources, if EVs and PowerWalls become the norm ‘peak lithium’ will become as talked about as peak oil 🙂

    This seems a reasonable estimate Is There Enough Lithium to Maintain the Growth of the Lithium-Ion Battery Market?, while this analysis by Tim Worstall is a bit wanting; he doesn’t consider increased demand going forward whatsoever.”

    You missed the point entirely

    If you want to adress the Risks of climate change then you have to adress all the risks

    1. The risk that we’ve estimated ECS to low
    2. the risk that we will never get a global agreement
    3. the risk that people will cheat

    Those risks can be adressed by carbon capture from the air

    I pointed you at one example. There are others

    The argument is this. Pay attention

    1. It makes sense to mitigate
    2, It makes sense to invest in more research into take c02 out of the air
    Because
    a) we might get ECS wrong
    b) we might not get to a global treaty
    c) there is a risk that people will cheat.

    Address the argument.

    You can do that by denying #1
    or take issue with any of 2a-c

  78. Kevin O'Neill says:

    Steven – you missed the point: You pointed to what appears to be an *unfeasible* answer. I.e., no answer at all.

  79. Tom Curtis says:

    With regard to Mark Bahner’s proposal for the reversibility of climate change, I will first note that his calculations assume not oceanic outgassing with the decline in CO2 concentration. That means, of course, that the calculated CO2 concentration has no bearing on the actual CO2 concentration over time, where his proposals implemented. As CO2 concentrations fall, the full amount of CO2 sequested in the ocean and biosphere will be returned to the atmosphere, so to reduce atmospheric CO2 concentrations to 280 ppmv requires sequestering the full cumulative anthropogenic emissions since industrialization.

    Based on that, and based on Bahner’s methodology of projecting 22nd century values as the linear trend of the last three values in the scenario descriptions (2080, 2090 and 2100), I calculated the GTC sequestered as a constant proportion of Gross World Product in trillions of dollars (GWP) that would be required to return to preindustrial conditions by given target dates. From that it was easy to calculate the percentage of GWP required to reach the sequestration targets for a range of assumed sequestration costs (in dollars per tonne of Carbon). The results for the A2 AIM scenario are as follows:

    A2 AIM
    Target Year 2300 2250 2200 2250
    Gigatonnes/$Trillion GWP 0.1375286 0.148287 0.1711968 0.2451972
    $/tonne % GWP
    30 0.41% 0.44% 0.51% 0.74%
    60 0.83% 0.89% 1.03% 1.47%
    100 1.38% 1.48% 1.71% 2.45%
    200 2.75% 2.97% 3.42% 4.90%
    220 3.03% 3.26% 3.77% 5.39%
    500 6.88% 7.41% 8.56% 12.26%
    1000 13.75% 14.83% 17.12% 24.52%

    As you can see, and unsurpisingly given his underestimate of the sequestration target, Bahner significantly underestimates the percentage of GWP needed to return to preindustrial CO2 concentrations. That requires 13.75% to reach preindustrial concentrations by 2300, whereas Bahner shows a return to preindustrial conditions shortly after 2200.

    Even allowing for that, however, his proposal is not altogether unrealistic as an abstract technical excercise. A sequestration cost of @220 per tonne of Carbon has already been estimated for at least one current technology, so sequestration costs for a return to preindustrial concentrations over 100 years are unlikely to be more than 5% of GWP and may be as little as 0.5% of GWP.

    That does not mean the plan is in fact feasible. To begin with, from these back of the envelope costings, the people in 2100 will face a greater relative cost to draw down CO2 than we currently face to mitigate climate change. Further, just as with us, the full benefits of their actions will not be experienced for half a century or more, so the same political dilemma will be faced. It follows that if it is unrealistic economically or politically to mitigate today, it will be equally economically or politically unrealistic draw down CO2 in 2100. Indeed, if Bahner’s argument makes sense economically now, it will make even more sense in 2100 to wait yet another hundred years before sequestering the CO2 as the wait will generate that much more wealth (on his assumptions) with which to pay for that draw down. The argument, therefore, has merit only if never drawing down the CO2 has merit, for at any time x, at x+100 (on Bahner’s assumptions) the economy will have that much more resources to draw down the CO2 so it would be sensible to wait until then to respond.

    Further, the reduction of CO2 to preindustrial levels will not fully reverse climate change. In particular, the significant melting of glaciers and icesheets will result in a significant perturbation of albedo that will not renormalize for centuries to come. Further, the temperature increase between now and 2100 will result in an increase in atmospheric CO2 relative to preindustrial levels due to ocean outgasing that will not be eliminated by CO2 sequestration of anthropogenic emissions. These along with sea level rise mean a return to the status quo ante is not possible by CO2 sequestration, becoming more impossible the longer that sequestration is delayed.

    This does not indicate the temperature effects of these persistent changes will be particularly large, or undesirable. Of more real concern is that the Bahner strategy involves a rapid rise in GMST over the century to come, which will have harmful impacts. Further, as the rate of temperature change is one of the best predictors of harmful impacts, the rapid decline in temperature following the draw down in CO2 will have further harmful impacts.

  80. Mark,

    Again, this is very straightforward. It demonstrates that, unless economic growth stops, there is virtually no chance that human beings will allow CO2 concentrations in the atmosphere to remain above 300-400 ppm for 1000+ years. So Anders whole analysis is predicated on a situation that is very unlikely to occur.

    Firstly, it’s not really my analysis, it’s the generally accepted scientific position. It illustrates that without some kind of technology, a reasonable fraction of our emissions will remain in the atmosphere for a very long time. I don’t know how to respond to the rest of what you say since it simply seems an assertion. Yes, if we do continue to get richer and richer then we may indeed find it straightforward in 100 years time to develop something that could remove CO2 from the atmosphere. This, however, ignores that climate change itself may influence economic growth and you seem to be ignoring all the other responses to your comments.

  81. verytallguy says:

    ATTP (and Mark),

    Yes, if we do continue to get richer and richer then we may indeed find it straightforward in 100 years time to develop something that could remove CO2 from the atmosphere

    No.

    No.

    And thrice no.

    The removal of CO2 from the atmosphere is *not* limited by just by the cleverness of our technology, it is limited by the laws of conservation of mass and thermodynamics.

    Entirely regardless of technology, we still require a certain amount of energy to remove CO2 from the atmosphere. We still require a certain area of contact to maintain the reaction rate. We still require a certain mass of raw materials to use in the process. We still require the carbon emissions from building such a vast engineering enterprise.

    Limitless economic growth, even if achievable, does *not* imply a limitless availablity of energy, raw materials, or dumping ground for waste.

    In the same way that just because we’re richer now, we still can’t harvest more whales than we did in the 19th century.

    In the same way that regardless of how rich we are we won’t be travelling faster than light.

    The belief that constant economic growth allows unconstrained control of the physical world is beyond hubris. It’s denial, in the true sense of the word.

  82. The removal of CO2 from the atmosphere is *not* limited by just by the cleverness of our technology, it is limited by the laws of conservation of mass and thermodynamics.

    Indeed, that is true. As Tom points out, you can’t simply remove what’s in the atmosphere since that will always settle back to being about 20% of what we’ve emitted in total. You need to essenitially remove all of our emissions.

    The belief that constant economic growth allows unconstrained control of the physical world is beyond hubris. It’s denial, in the true sense of the word.

    Yes, I was being too polite.

  83. dikranmarsupial says:

    Just a comment on something Tom wrote earlier “On one, intuitive way of looking at things, a thing causes only that which would not have occurred in its absence, all else being equal.”

    This does indeed make some intuitive sense, but I find this definition of causality unsatisfactory. Consider the familiar analogy of a bank account shared by a husband and wife. The wife decides that she would like the balance to rise by £5 per month (and is able to adjust her deposits and withdrawals to make that happen). The husband decides he would like to deposit £10 per month more than he withdraws. In this case the wife will start to take out £5 per month more than she puts in. Can we really say that in this case the husband is not causing the balance to rise on the grounds that if not for his transactions the balance would have risen by £5 per month anyway? We certainly can’t say that the wife caused the balance to rise as she took more out than she put in. The “all else being equal” does apply here as the rules governing the wife’s transactions had not changed. So who did cause the rise? I find financial analogies to be quite useful as people tend to be naturally quite shrewd when it comes to money in a way that they are not when it comes to scientific theories.

    The real problem is that there are many “skeptics” who think that the temperature sensitivity of ocean solubility is sufficient to explain all of the observed rise; if they are willing to agree that it only explains about 5% (assuming near-instantaneous response), then that is sufficient to move on to more interesting topics.

  84. Tom Curtis says:

    verytallguy, sequestration of CO2 by splitting of the carbon from the oxygen and burying the carbon faces hard thermodynamic limits such that no level of technology can sequester the CO2 without a net energy loss in the round trip of combustion, followed by sequestration. It is not obvious that the same applies for other methods of sequestration. Other methods of sequestration will require either a suitable volume in which to store the CO2 as a high pressure gas or a suitable quantity of the material that acts as an absorbent. There may be limits on the availability of these such that no combination of them could sequester the total human emissions over two to three centuries but that is not proved. Ergo we cannot assume that a Bahner style strategy will fail on those grounds. As a result, the possibility that there are insufficient such reservoirs becomes just another risk for that strategy (of which there are already several very large risks).

    I do agree that unlimited economic growth cannot imply unconstrained control of the real world. I just do not agree that this case is one with proven hard limits.

    In any event, what truly makes that strategy folly is that it involves a large, multi degree spike then fall in temperature over the space of two centuries. The costs of such a temperature trajectory are likely to be equivalent to, and possibly exceed unabated AGW. On top of that, the strategy relies on our descendants seeing the rationality of playing their part when, objectively, their decision matrix does not differ substantially from ours for mitigating now (and hence avoiding the large temperature excursion), and indeed is likely to be relatively more costly. At best, then it is a strategy of allowing ourselves to be moral cowards in the expectation that our descendants will act better than we will.

  85. Tom Curtis says:

    Dikran, in the CO2 case, if the equilibrium pCO2 in a gas over water was independent of the temperature of the water, then the amount of anthropogenic emissions todate would have resulted in an increase in atmospheric pCO2 about 5% less than has occurred (with an matching increase in oceanic pCO2). If the temperature response was as in the real case, with a 1 C increase in GMST and there had been no anthropogenic emissions the pCO2 in the atmosphere would have increased by about 5% of the actual increase. You need both components to infer a cause by the intuitive principal, and the first component has no equivalent in your economic analogue. If you modify the analogy such that, excluding the actions of the wife would have resulted in final savings 5% less, and excluding the actions of the husband, the final savings would be just 5% of the final total; it would be reasonable to say the wife contributed (caused) 5% to (of) the final savings.

  86. verytallguy says:

    Tom,

    without labouring a point, I agree in principle; in practice I suspect it is actually possible to demonstrate the constraints are very likely too high for implementation; I lack the energy to do that for something so obviously barking mad.

  87. Magma says:

    It seems obvious that rather than any hare-brained scheme to reduce the use of Nature’s bountiful coal and oil, research should be done to develop a stable or metastable polymorph of CO2 that is solid at ambient temperatures and pressures, ideally one that comes in a range of pleasing colors and that can be used as a strong, lightweight construction material in less developed countries.

  88. dikranmarsupial says:

    Tom, the problem is agreeing (with climate “skeptics”) on what the environment would have done in the absence of anthropogenic emissions. If they claim that the rise we have observed in the presence of anthropogenic emissions is natural, they are not going to agree that we would only have seen 5% of that rise in the absence of anthropogenic emissions. If someone won’t accept that the mass balance argument shows that the natural environment is a net carbon sink, they are not going to accept more complicated scientific arguments about CO2 solubility either. The real problem is not the science, or the definition of causality (which is ambiguous, but not problematically so, unless deliberately exploited), but with an inability to accept that we exert a significant influence on the climate and that there are negative consequences to fossil fuel use (as well as benefits).

  89. Willard says:

    > It demonstrates that, unless economic growth stops, there is virtually no chance that human beings will allow CO2 concentrations in the atmosphere to remain above 300-400 ppm for 1000+ years.

    The word “demonstrates” is a bit strong, since it’s just a napkin calculation. A stock broker could not show this kind of thing to clients without caveat emptor. He’d need to disclose that it’s just a vulgar display of graphical power, unless getting sued is part of the business plan.

    Also, I think the analysis goes beyond that, and also applies to any economic conditions “barring thermonuclear war or takeover by Terminators.” If allowing CO2 concentrations to skyrocket is not an option, humans will find the resources to get rid of it. If it’s an option, then there’s no need to disallow it. Focusing on the case where we’re so rich we can afford a baseball stadium for everyone is just the usual lukewarm marketing ploy.

    More importantly, this analysis has little to do with Matthews and Solomon’s point. In fact, it is perfectly consistent with it. For instance, they referred to Matthews & Caldeira 2008. Here’s the abstract:

    Current international climate mitigation efforts aim to stabilize levels of greenhouse gases in the atmosphere. However, human-induced climate warming will continue for many centuries, even after atmospheric CO2 levels are stabilized. In this paper, we assess the CO2 emissions requirements for global temperature stabilization within the next several centuries, using an Earth system model of intermediate complexity. We show first that a single pulse of carbon released into the atmosphere increases globally averaged surface temperature by an amount that remains approximately constant for several centuries, even in the absence of additional emissions. We then show that to hold climate constant at a given global temperature requires near-zero future carbon emissions. Our results suggest that future anthropogenic emissions would need to be eliminated in order to stabilize global-mean temperatures. As a consequence, any future anthropogenic emissions will commit the climate system to warming that is essentially irreversible on centennial timescales.

    Later on, the authors rather refer to “effectively irreversible on human timescales” instead of “essentially irreversible.” The authors don’t say anything about Dyson trees.

    As far as I am concerned, the whole analysis rests on a misreading of the word “irreversible.”

  90. anoilman says:

    Mark Bahner says: “Again, this is very straightforward. It demonstrates that, unless economic growth stops, there is virtually no chance that human beings will allow CO2 concentrations in the atmosphere to remain above 300-400 ppm for 1000+ years. So Anders whole analysis is predicated on a situation that is very unlikely to occur. ”

    Actually, you’ve made far far larger assumptions than Anders.

    Please prove with a decree of certainty that growth will continue. 2008 has proven beyond a shadow of a doubt that economists are incredibly bad at predicting the future.

    You hand wave and gesticulate the the effect that growth will continue unabated… and the entire foundation of even that claim is low energy prices… And we know energy prices will be going up.

    I’d say that you have yet to begin to make an argument to support your claims. Again, please prove with certainties and error margins what the growth for the next 100 years will be, or admit you’re wrong.

  91. izen says:

    If my very rough numbers are correct – they could be orders of magnitude out! – the extra 70kg of CO2 in the atmosphere per person that we have added would require about 1 megawatt of energy to convert back into a solid form of carbon if the conversion process was 100% efficient with no other energy losses.

    Given a population of 7 billion that would require around 7000 TeraWatts of power.
    Total human power generation at present is about 16 TeraWatts.

    So just removing the CO2 we have added would require generating at least twice as much power as we do at present for at least 70 years, Without generating any extra CO2.

    BUt unless my chem is totally flawed (!) if we remove all the CO2 added to the atmosphere, the half of total emissions that have been distributed into oceans, land and biota will re-establish the partition ration and become sources of carbon emissions until about half of that sequestered by the fast carbon cycle is back in the atmosphere.

  92. Tom Curtis says:

    izen, Watts are the wrong unit. You need Joules. Taking the cumulative emissions to 2010 from the SRES scenarios, and the energy of combustion for carbon to CO2 from the engineer’s toolbox, it would require 5.47*10^21 Joules to completely return CO2 to C and O2. Based on Flanner (2009), and using the estimate of industrial waste heat in 2005, that means it would take 12-13 years of total human energy production to sequester CO2 by conversion to Carbon, assuming no inefficiencies.

    As noted before, however, returning CO2 to its constituent parts is the least energy efficient proposed method of sequestering CO2. This calculation suggests an upper limit on energy cost, not a lower limit. To determine the true upper limit we would need to allow for inefficiencies and the the cost of burial of the carbon produced.

  93. Mark Bahner says:

    “With regard to Mark Bahner’s proposal for the reversibility of climate change, I will first note that his calculations assume not oceanic outgassing with the decline in CO2 concentration.”

    OK, so more CO2 needs to be removed than was depicted in my blog post calculations. Let’s call it roughly twice as much CO2 as in my blog post calculations. (I think that overestimates the amount, but 2 is a nice round number.)

    “Even allowing for that, however, his proposal is not altogether unrealistic as an abstract technical excercise.”

    Wow. Golly. Thanks! (It’s in fact much more realistic than the Mathews and Solomon paper in Science to which I was responding in my blog post. But I digress…)

    “A sequestration cost of @220 per tonne of Carbon has already been estimated for at least one current technology, so sequestration costs for a return to preindustrial concentrations over 100 years are unlikely to be more than 5% of GWP and may be as little as 0.5% of GWP.”

    OK, let’s get this straight. My calculations are somewhere up to a factor of ~2 too low on the amount of CO2 that needs to be removed. But you then criticize my calculations for assuming a cost of $1000 per tonne of CO2 ($3667 per tonne of carbon). You instead point to a value of $220 per tonne of carbon…approximately a factor of 17 lower than my value.(!)

    So you in fact conclude that my 10%-of-GWP value is much too high…and that the real value is “unlikely to be more than 5% of GWP and may be as little as 0.5% of GWP.”

    So, in your opinion, the problem is even more easily solvable than my calculations depicted. OK then.

  94. Mark Bahner says:

    “For a scientifically literate but mathematically challenged layperson like myself (and other laypeople), it seems to me a very strong argument can be made on the difficulties of carbon sequestration and storage just from the sheer quantities involved.”

    The U.S. Geological Service (USGS) has studied this question. Per their study results, the world emitted approximately 32 metric gigatons of carbon in the form of carbon dioxide in 2011.

    The median USGS estimate of geological carbon sequestration potential for the U.S. (alone) is approximately 3000 metric gigatons of carbon in the form of carbon dioxide. Therefore, the U.S. alone can geologically store roughly 100 years of the entire world’s CO2 emissions at the rate of global CO2 emissions in 2011.

    “The gigaton question”

  95. Mark,

    Therefore, the U.S. alone can geologically store roughly 100 years of the entire world’s CO2 emissions at the rate of global CO2 emissions in 2011.

    Sure, but we’ve already emitted around 2000 GtCO2.

  96. Tom Curtis says:

    I have made an error in my various calculations of sequestration costs above. Specifically, I used the figure for cumulative emissions from the SRES A2 scenario, but it turns out that those are just the cumulative emissions since 1990. I have now corrected my spreadsheets using the data for cumulative emissions from the CDIAC global carbon budget project so that they now represent the cumulative emissions from 1750-2010, and where relevant, plus the SRES A2 AIM emissions through to 2100.

    The table in my response to Mark Bahner on Oct 22nd now reads:

    A2 AIM
    Target Year 2300 2250 2200 2250
    Gigatonnes/$Trillion GWP 0.1402343 0.1525671 0.1790882 0.2656708
    $/tonne % GWP
    30 0.42% 0.46% 0.54% 0.80%
    60 0.84% 0.92% 1.07% 1.59%
    100 1.40% 1.53% 1.79% 2.66%
    200 2.80% 3.05% 3.58% 5.31%
    220 3.09% 3.36% 3.94% 5.84%
    500 7.01% 7.63% 8.95% 13.28%
    1000 14.02% 15.26% 17.91% 26.57%

    The difference is not substantial relative to my comments. The benchmark values for a sequestration cost of $220 per tonne of Carbon rises from 3.03% to 3.09% of projected GWP for a reduction over two hundred years, and from 5.39% to 5.84% of projected GWP for a reduction over 50 years.

    The values in my response to izen should by adjusted from 5.47 * 10^21 Joules to 1.7 * 10^22 Joules for the total energy to decompose the CO2 of anthropogenic emissions to 2010 back to Carbon O2, and 12-13 to 37-40 years of total human energy production at 2008 levels to decompose the CO2. That lifts the time estimate from approx 18% to approx 55% of izen’s estimate.

  97. Tom Curtis says:

    Anders, I think you have missed Mark Bahner’s point. He is responding to verytallguy’s claim that there is not unlimited dumping grounds for waste (CO2). The US represents just 6.6% of total global land area. If suitable reservoirs scale on that basis, there are sufficient reservoirs for over a thousand years of CO2 emissions at 2010 rates to be sequestered by underground storage, and over three hundred years at 2100 emission rates under the A2 AIM scenario. Those are not unlimited “dumping grounds”, but they are sufficient for any practical estimate of carbon sequestration needs.

    The more serious problem for geological sequestration is cost, which assuming all sequestration can be done at the base cost, amounts to 7% of GWP in 2010 and 3% of GWP in 2100 to sequester 100% of respective annual emissions. Cost to sequester the cumulative emissions to their respective dates fall from 360% to 210% of GWP for their respective product. These costs are likely significant underestimates given that the technology is costed for capturing standing power emissions only, and allows 10% fugitive emissions. Emissions from other sources and the fugitive emissions will need to be scavenged by some additional process at increased expense. Whether 7 or 3%, the cost is likely to be greater than that of mitigation by reduction of emissions for the vast majority of emissions.

    A further problem is that there will be leakage from reservoirs. Not all reservoirs, and not necessarily at catastrophic rates, but there will inevitably be some fail rate on seals, or geophysical disturbances. How much of a problem this would be, I am insufficiently informed to say.

  98. Tom,

    I think you have missed Mark Bahner’s point. He is responding to verytallguy’s claim that there is not unlimited dumping grounds for waste (CO2). The US represents just 6.6% of total global land area.

    Ahh, okay, fair enough. Thanks.

  99. > It’s in fact much more realistic than the Mathews and Solomon paper in Science to which I was responding in my blog post.

    As I said twice already, Mark, your post does not “respond” to Mathews & Solomon. The TL;DR is that their concept of irreversibility is unaffected by your napkin exercise, and is quite compatible with it. You’re just in violent agreement with their claim “that future anthropogenic emissions would need to be eliminated in order to stabilize global-mean temperatures,” that’s all.

  100. You’re just in violent agreement with their claim “that future anthropogenic emissions would need to be eliminated in order to stabilize global-mean temperatures,” that’s all.

    Essentially, yes. With the caveat, I guess, that Mark seems to think that it is a trivial and obvious consequence of continued economic growth. I haven’t yet established if Mark thinks that continued economic growth is itself trivial and obvious?

  101. Sources tell me this may be of interest to those who study Grrrowth and the BAU scenario:

    Failure to tackle climate change will impact GDP

    For all the sophistication of many climate models, most are not designed with feedback effects on GDP built in. GDP is treated as an exogenous factor, that is an isolated input to the model, rather than one which iterates in relation to the scenario that develops. This means that in a 4°C or 6°C warming scenario, there is no in-built mechanism to reflect the impacts of the associated increased extreme weather events, disruption to economic activity, migration, conflict, etc. on economic growth. Even where some impacts are integrated, they may not be a complete set due to modelling limitations.

    http://www.carbontracker.org/wp-content/uploads/2015/10/Lost-in-transition_Full_Final1.pdf

  102. Tom Curtis says:

    Anders:

    “I haven’t yet established if Mark thinks that continued economic growth is itself trivial and obvious”

    You probably missed this link about economic growth then. He proposes that growth rates are a product of “Human brains (or their equivalents)”, and argues that massive future growth will occur as a consequence of the computer revolution. In doing so he conveniently refutes economic theory off screen by an aside.

  103. Mark Bahner says:

    “As I said twice already, Mark, your post does not “respond” to Mathews & Solomon. The TL;DR is that their concept of irreversibility is unaffected by your napkin exercise, and is quite compatible with it.”

    You can say the same nonsense two thousand times, but that doesn’t make it any less false.

    My post *does* respond to Mathews & Solomon. Mathews & Solomon say that global warming is “irreversible”. That’s nonsense. As my calculations demonstrate, under IPCC scenarios A1FI, A1B, B1, and B2, assuming 10% of GDP is spent every year beginning in 2100, the global atmospheric concentration of CO2 can be brought down to 300 ppm before 2200.

    Some people have objected to my not accounting for ocean outgassing. But if the ocean outgassing doubled the amount of CO2 that needed to be removed, the curves would look *exactly the same* if one assumed $500 per ton of CO2 removed ($1833 per ton of carbon) rather than the $1000 per ton of CO2 removed ($3667 per ton of carbon removed) that I assumed.

    “You’re just in violent agreement with their claim “that future anthropogenic emissions would need to be eliminated in order to stabilize global-mean temperatures,” that’s all.”

    No, I’m not in agreement with that claim, because it’s patently false.

  104. Mark,
    You clearly don’t understand what is being said to you. Mathews & Solomon are pointing out that on the basis of natural sinks only, climate change is essentially irreversible. Your napkin exercise does not change that.

    But if the ocean outgassing doubled the amount of CO2 that needed to be removed, the curves would look *exactly the same* if one assumed $500 per ton of CO2 removed ($1833 per ton of carbon) rather than the $1000 per ton of CO2 removed ($3667 per ton of carbon removed) that I assumed.

    Sure, if you halved the cost. However, if only 20% of our emissions remain in the atmosphere, if we wanted to get back to around 300ppm, we would need to remove an amount roughly 5 times greater than the atmospheric enhancement, not simply double.

    No, I’m not in agreement with that claim, because it’s patently false.

    You either don’t understand what is meant by the term “emissions” or you’re heading into denial territory.

  105. > No, I’m not in agreement with that claim [that future anthropogenic emissions would need to be eliminated in order to stabilize global-mean temperatures], because it’s patently false.

    The Dyson CO2-suckers emerging from your Simon-Kurzweil theorem about the infinite Grrrrowth (because, mind) are relevant because of two assumptions you made earlier:

    [Bad] Excess CO2 (above say, 300-400 ppm) is bad.

    [Breaking Bad] Therefore, people will eventually want to get the concentration down to 300-400 ppm.

    These two assumptions seem consistent with the claim that future anthropogenic emissions would need to be eliminated in order to stabilize global-mean temperatures. Do you dispute your own assumptions?

  106. Mark Bahner says:

    “Excess CO2 (above say, 300-400 ppm) is bad. Therefore, people will eventually want to get the concentration down to 300-400 ppm.”

    “These two assumptions seem consistent with the claim that future anthropogenic emissions would need to be eliminated in order to stabilize global-mean temperatures.

    If those statements “seem consistent with the claim that future anthropogenic emissions would need to be eliminated in order to stabilize global-mean temperatures,” then either 1) you don’t understand the term “emissions” as it is commonly applied regarding climate change, or 2) you don’t understand that human emissions can be balanced with human removal of atmospheric emissions, or 3) you have some other misunderstanding.

    Once again, the claim that “future anthropogenic emissions would need to be eliminated in order to stabilize global-mean temperatures” is patently false.

  107. Once again, the claim that “future anthropogenic emissions would need to be eliminated in order to stabilize global-mean temperatures” is patently false.

    No it’s not. Do you care to explain why you think it’s patently false, or are you simply going to keep simply stating this as true? I’ll also give you a slight hint. When people say “anthropogenic emissions” they mean net emissions.

  108. Willard says:

    > either 1) you don’t understand the term “emissions” as it is commonly applied regarding climate change, or 2) you don’t understand that human emissions can be balanced with human removal of atmospheric emissions, or 3) you have some other misunderstanding.

    Another possibility is that I have read the first paragraph [of Matthews & Caldeira 2008]:

    Avoiding dangerous anthropogenic interference in the climate system has been a key international policy goal since the publication of the United Nations Framework Convention on Climate Change in 1992 [United Nations, 1992]. Since that time, scientific and policy literature concerning climate change mitigation has been centered around stabilizing concentrations of greenhouse gases in the atmosphere [Wigley, 2005; Stern, 2006; Meehl et al., 2005]. However, stable greenhouse gas concentrations do not equate to a stable global climate. Model simulations have demonstrated that global temperatures continue to increase for many centuries beyond the point of CO2 stabilization [e.g., Matthews, 2006]. As such, we are committed to future warming, even with stable greenhouse gas concentrations [Hansen et al., 1985; Wigley, 2005; Meehl et al., 2005]. This implies that stabilizing global climate within the next several centuries would require decreasing, rather than stabilized, greenhouse gas levels. In this paper, we demonstrate that to achieve atmospheric carbon dioxide levels that lead to climate stabilization, the net addition of CO2 to the atmosphere from human activities must be decreased to nearly zero.

    Have you?

  109. Mark Bahner says:

    I wrote, “Once again, the claim that ‘future anthropogenic emissions would need to be eliminated in order to stabilize global-mean temperatures’ is patently false.”

    Anders responds, “No it’s not.”

    Yes, it is. It’s patently false. And no matter how many times you and Willard and any of your friends say the statement is true, it will remain patently false here on planet Earth.

    Just like no matter how many times you or anyone else on this blog claim that this statement is true: “Of the 4,014 abstracts that expressed a position on the issue of human-induced climate change, Cook et al. (2013) found that over 97% endorsed the view that the Earth is warming up and human emissions of greenhouse gases are the main cause”…it will still be as false as the golden threads of the “Emperor’s New Clothes.”

    Anders continues, “I’ll also give you a slight hint. When people say ‘anthropogenic emissions’ they mean net emissions.”

    No, Anders, when knowledgeable people say “anthropogenic emissions” they mean “anthropogenic emissions.” When they mean “net emissions” they say “net emissions.” That’s how we avoid misunderstandings. (Here on Earth, anyway. I don’t know about your planet.)

    That’s why here on Earth we have a U.S. EPA document of the ““U.S. Inventory of Greenhouse Gas Emissions and Sinks. If your statement was true, there would be no such document.

    And that’s why page 1-1 of the Introduction to that document, in discussing the UN Framework on Climate Change (UNFCC), contains the statement, “Parties to the Convention, by ratifying, ‘shall develop, periodically update, publish and make available…national inventories of anthropogenic emissions by sources and removals by sinks of all greenhouse gases not controlled by the Montreal Protocol, using comparable methodologies…’”

    If your statement was true—which it most emphatically is not—then the phrase “national inventories of anthropogenic emissions by sources” would include “removals by sinks” because “anthropogenic emissions” would mean “anthropogenic net emissions.” But it does not…here on Earth, anyway.

    P.S. Anders, it doesn’t bother me when you and Willard don’t know what you’re talking about. But I do find it very insulting when you both insist in a rude and mocking manner that I don’t know what I’m talking about. If you’re going to give me “hints” about matters related to what I do for a living, you should be sure you’re right.

  110. Mark Bahner says:

    Tom Curtis writes, regarding me, “He proposes that growth rates are a product of ‘Human brains (or their equivalents)’, and argues that massive future growth will occur as a consequence of the computer revolution. In doing so he conveniently refutes economic theory off screen by an aside.”

    Three questions:

    1) Where is it that you think I “conveniently refute economic theory”?

    2) In my initial survey of leading thinkers regarding economic growth in the 21st century, one of the three people who responded was Arnold Kling. Dr. Kling has a PhD in Economics from MIT, was an economist at the Federal Reserve and Freddie Mac, and taught economics at George Mason University. His predictions for annual growth rate in per-capita GWP were: 4.5% for 2010-2020, 6.0% for 2020-2030, 10% for 2030-2040…and continuing rising after that. Do you think Dr. Kling does not know economic theory, or is “refuting” it?

    3) Robin Hanson, in a paper titled, “Economic Growth Given Machine Intelligence,” states, “At first, complementary effects dominate, and human wages rise with computer productivity. But eventually substitution can dominate, making wages fall as fast as computer prices now do. An intelligence population explosion makes per-intelligence consumption fall this fast, while economic growth rates rise by an order of magnitude or more.” Do you think Dr. Hanson is “conveniently refuting economic theory”? (That would be very surprising, since Dr. Hanson explicitly uses “a standard neo-classical (Solow-Swan) growth model with diminishing returns, and modif(ies) it minimally to include ordinary computers and machine intelligence”…see page 4 of the paper.)

  111. Mark,

    P.S. Anders, it doesn’t bother me when you and Willard don’t know what you’re talking about. But I do find it very insulting when you both insist in a rude and mocking manner that I don’t know what I’m talking about. If you’re going to give me “hints” about matters related to what I do for a living, you should be sure you’re right.

    If you want to whine, go somewhere else. It’s tedious.

    To stablise temperatures would require that the amount of CO2 we add to the atmosphere be close to zero. Whether we achieve that through not using fossil fuels, using fossil fuels and capturing the CO2 before it reaches the atmosphere, or emitting the CO2 into the atmosphere but removing an equivalent amount from the atmosphere, doesn’t really matter – the point is we need to be essentially adding/emitting almost no CO2 to the atmosphere in order for temperatures to stabilise.

    If you want to actually have an interesting discussion about this, we could possibly do so. If you want to simply whine and state things as true without explaining why, go somewhere else. If you appeal to your supposed authority one more time, I might make the decision for you. I don’t hugely care, but I do have much better things to do than deal with someone who thinks they know better than others, but seems completely incapable of actually thinking about what others are saying, or really explaining themselves clearly in the first place.

  112. Mark,
    A simple question. Are you simply arguing about whether or not “emissions” means net, or are you really suggesting that stablising temperature would not require that the amount of CO2 we add to the atmosphere be close zero? The reason I ask is because this doesn’t make any sense to me

    If your statement was true—which it most emphatically is not—then the phrase “national inventories of anthropogenic emissions by sources” would include “removals by sinks” because “anthropogenic emissions” would mean “anthropogenic net emissions.” But it does not…here on Earth, anyway.

    Anthropogenic net emissions means the net amount we emit. The removal of some from the atmosphere by the natural sinks does not reduce our net emissions.

  113. verytallguy says:

    Some interesting questions.

    Rather than what % of a putatively hugely increased global gdp this scheme requires, what % of total future world energy supply does it need?

    What would the impact of raising energy production to these levels in advance of bringing it online be on carbon emissions?

    What quantity of raw materials would it need? In absolute terms and proportionately?

    Is the proposal in fact compatible with the vision of future growth being driven by intellectual and computational progress rather than physical activity advocated by Mark?

    And finally, what would Charles Ponzi make of it?

  114. Willard says:

    > [W]hen knowledgeable people say “anthropogenic emissions” they mean “anthropogenic emissions.” When they mean “net emissions” they say “net emissions.” That’s how we avoid misunderstandings. (Here on Earth, anyway. I don’t know about your planet.)

    How about in the paper you criticize, Mark? Start with the first paragraph, right where they say “net emissions.”

    You seem to be switching to “they’re wrong” to “were they writing like human beings, they’d be wrong” defense.

    ***

    Since you may not have read it, here’s the second paragraph:

    Recent research has highlighted the very long lifetime of anthropogenic carbon in the atmosphere; while approximately half of the carbon emitted is removed by the natural carbon cycle within a century, a substantial fraction of anthropogenic CO2 will persist in the atmosphere for several millennia [Archer, 2005]. A recent analysis by Montenegro et al. [2007] found that 25% of emitted CO2 will have an atmospheric lifetime of more than 5000 years. Studies of the climate response to declining CO2 concentrations have generally assumed that global temperatures will decrease in response to decreases in atmospheric CO2 [Friedlingstein and Solomon, 2005]. However, as we demonstrate here, because of the high heat capacity of the ocean, global temperatures may not parallel decreases in atmospheric concentrations of greenhouse gases, but rather will increase and remain elevated for at least several centuries. Thus, fossil fuel CO2 emissions may produce climate change that is effectively irreversible on human timescales.

    Interestingly, your napkin calculation does seem to assume that assumption they criticize.

    Perhaps you can tell us what “lifetime of anthropogenic carbon in the atmosphere” means on Earth.

  115. Mark Bahner says:

    “A simple question. Are you simply arguing about whether or not “emissions” means net, or are you really suggesting that stablising temperature would not require that the amount of CO2 we add to the atmosphere be close zero?”

    I am really suggesting that stabilizing temperature would not require that the amount of CO2 we add to the atmosphere be close to zero.

    In order to stabilize temperature, the amount of NET CO2 added to the atmosphere would need to be close to zero. (And this could be done by any number of ways, including completely artificial removal of CO2 from the atmosphere and storage underground, boosts in CO2 sinks such as using ocean iron fertilzation to promote CO2 removal and transport to the deep ocean, etc.)

    That’s why the statement (made by Willard on October 23rd at 9:33 PM, and asserted by you to be true) “that future anthropogenic emissions would need to be eliminated in order to stabilize global-mean temperatures”…is patently false. As I’ve repeatedly written.

    That is also why the actual statement made in the Mathews and Solomon paper is correct: “In this paper, we demonstrate that to achieve atmospheric carbon dioxide levels that lead to climate stabilization, the net addition of CO2 to the atmosphere from human activities must be decreased to nearly zero.”

    Do we finally agree on this? Or do you still maintain that Willard’s statement “that future anthropogenic emissions would need to be eliminated in order to stabilize global-mean temperatures” is true?

  116. Mark,

    In order to stabilize temperature, the amount of NET CO2 added to the atmosphere would need to be close to zero.

    Which is the question I asked you, in which case the answer you could have given would be “yes”.

    (And this could be done by any number of ways, including completely artificial removal of CO2 from the atmosphere and storage underground, boosts in CO2 sinks such as using ocean iron fertilzation to promote CO2 removal and transport to the deep ocean, etc.)

    Well, unless we find a way to transport it to the deep ocean, you don’t understand this very well and should stop appealling to your authority (you don’t have any).

    Do we finally agree on this? Or do you still maintain that Willard’s statement “that future anthropogenic emissions would need to be eliminated in order to stabilize global-mean temperatures” is true?

    Willard is right. Either you agree with him, or you’re wrong.

  117. Mark Bahner says:

    I asked, “Do we finally agree on this? Or do you still maintain that Willard’s statement ‘that future anthropogenic emissions would need to be eliminated in order to stabilize global-mean temperatures’ is true?”

    Anders replied, “Willard is right. Either you agree with him, or you’re wrong.”

    So David Keith, and Greg Lau, and Klaus Lackner, and probably thousands of others, are wrong, and Willard and you are right?

  118. Mark,
    Firstly, this is not complicated. Also, this is not Willard and me, this is most of the climate science research community. Read this post, look at the figure, read the links in the post.

    To summarise: to stabilise temperatures will require that anthropogenic emissions are close to zero. This means that either we use something other than fossil fuels, or we capture the CO2 and store it before it reaches the atmosphere, or we somehow remove as much CO2 from the atmosphere, and sequester it somewhere, as we’re emitting into the atmosphere. If you disagree with this, provide some actual evidence. If you post another comment with some rhetorical question, or simply a claim that you’re right without any evidence, I will simply delete it.

  119. Mark Bahner says:

    “Firstly, this is not complicated.”

    I agree, it’s not complicated.

    “To summarise: to stabilise temperatures will require that anthropogenic emissions are close to zero.”

    First of all, you’re changing the wording from “would need to be eliminated” to that the emissions must be “close to zero.” But even your statement that anthropogenic emissions must be “close to zero” is false, by your own words, in your very next sentence.

    Here is your very next sentence, with emphasis added:

    “This means that either we use something other than fossil fuels, or we capture the CO2 and store it before it reaches the atmosphere, or we somehow remove as much CO2 from the atmosphere, and sequester it somewhere, as we’re emitting into the atmosphere..”

    The last part of the sentence, “or we somehow remove as much CO2 from the atmosphere, and sequester it somewhere, as we’re emitting into the atmosphere” proves that the emissions do not need to be “close to zero”…let alone “eliminated” which is what you insisted was a true statement.

    Suppose there was a global warming test for undergraduate students that asked, “Which of the following statements must be true, in order for global temperatures to be stabilized:

    1) Anthropogenic emissions must be eliminated.
    2) If anthropogenic emissions are not eliminated, then we must somehow remove as much CO2 from the atmosphere, and sequester it somewhere, as we’re emitting into the atmosphere.
    3) Both of the above.”

    …what do you think the correct answer would be?

  120. Mark,
    Jeepers, this is tiresome. If we remove CO2 from the atmosphere, it is called an emission – a negative one. I’ll repeat the point, which is what virtually everyone here has been trying to say to you for a day or so: to stabilise temperatures there must be virtually no net addition of anthropogenic CO2 to the atmosphere (whether we do that via not actually adding it to the atmosphere, or do it via adding it to the atmosphere and removing an equivalent amount). If you want to simply have a pedantic argument about terminology, please go and do it somewhere else. I have little interest in this and, so far, your contribution to this discussion has been a negative – like what we’d call an emission in which we remove CO2 from the atmosphere.

    Also, there is nothing wrong with this sentence

    “This means that either we use something other than fossil fuels, or we capture the CO2 and store it before it reaches the atmosphere, or we somehow remove as much CO2 from the atmosphere, and sequester it somewhere, as we’re emitting into the atmosphere..”

    It is exactly the point; if we want to stablise temperatures. If you want to simply troll, go somewhere else. I don’t need a lesson from someone who clearly understands this topic far less well than they seem to think they do. If you want to have an actual discussion, try one more time. I’ll happily delete it if it is simply more of the same. It’s no skin of my nose; deleting comments is easy.

  121. And if you don’t believe me about negative emissions, try reading this.

  122. Willard says:

    > Or do you still maintain that Willard’s statement […]

    Correction: it’s not my statement, but a statement from the abstract of Matthews & Caldeira 2008. That statement follows quite directly from your own “excess CO2 (above say, 300-400 ppm) is bad.”

  123. Mark Bahner says:

    “If we remove CO2 from the atmosphere, it is called an emission – a negative one.”

    If removing CO2 from the atmosphere “is called an emission – a negative one,” then the claim that “future anthropogenic emissions would need to be eliminated in order to stabilize global-mean temperatures” is clearly false. It is clearly false because it’s saying all emissions, both the positive ones and the “negative ones,” need to be eliminated.

    So I’m very curious about what you think is the correct answer to the hypothetical multiple choice question. Do you think, like I do, that the correct answer is #2?

  124. Willard says:

    Also note the third paragraph of Matthews & Caldeira 2008:

    In this paper, we present a series of idealized climate simulations to assess the centennial-scale climate response to anthropogenic CO2 emissions, and conversely, to quantify the emissions requirements for climate stabilization. We have used the University of Victoria Earth System Climate Model (UVic ESCM), an intermediate complexity global climate model which includes an interactive global carbon cycle. We present first a series of 500-year simulations forced by CO2 emissions, in which a specified amount of carbon was added to the atmosphere either instantaneously, or following a business-as-usual emissions scenario. The model was then run for up to 500 years without additional carbon emissions to determine the persistence of climate warming resulting from past emissions. Second, we specified hypothetical future temperature trajectories for the UVic ESCM, and controlled emissions such that the specified future temperature changes were achieved. We used this method to estimate the CO2 emissions requirements for climate stabilization at levels between 1 and 4 degrees above pre-industrial temperatures.

    http://onlinelibrary.wiley.com/doi/10.1029/2007GL032388/full

    The emphasized bit shows that Matthews & Caldeira 2008 has very little to say about Dyson trees scenarios.

    ***

    Matthews & Caldeira 2008 matters because it’s the citation Matthews & Solomon offers for their claim that Further misunderstanding may stem from recent studies showing that the warming that has already occurred as a result of past anthropogenic carbon dioxide increases is irreversible on a time scale of at least 1000 years (5, 6). It’s citation number 6.

    Therefore you seem to be arguing that Matthews & Solomon 2013 is right and Matthews & Caldeira 2008 is wrong, when the only sentence you picked in Matthews & Solomon 2013 (in the very first paragraph) is based on Matthews & Caldeira 2008.

  125. Mark,

    If removing CO2 from the atmosphere “is called an emission – a negative one,” then the claim that “future anthropogenic emissions would need to be eliminated in order to stabilize global-mean temperatures” is clearly false. It is clearly false because it’s saying all emissions, both the positive ones and the “negative ones,” need to be eliminated.

    Good grief. No, what it means (or what it was intended to mean, which I thought was bleeding obvious) is that the overall anthropogenic emissions have to be close to zero. In other words, the sum of the positive and negative ones have to almost cancel. Given that CO2 is well mixed, and on quite short timescales, not emitting any CO2 (i.e., no positive or negative emissions) is going to be roughly equivalent to having positive and negative emissions that cancel.

  126. Willard says:

    > If removing CO2 from the atmosphere “is called an emission – a negative one,” then the claim that “future anthropogenic emissions would need to be eliminated in order to stabilize global-mean temperatures” is clearly false.

    This reading presumes that to speak of “removing a negative emission” would make sense. Double negatives are notoriously hard to sell to Earthlings.

    That semantic point is of little relevance for the sentence MarkB rejects, which comes from Matthews & Caldeira 2008. Here’s again the relevant part of the abstract:

    In this paper, we assess the CO2 emissions requirements for global temperature stabilization within the next several centuries, using an Earth system model of intermediate complexity. We show first that a single pulse of carbon released into the atmosphere increases globally averaged surface temperature by an amount that remains approximately constant for several centuries, even in the absence of additional emissions. We then show that to hold climate constant at a given global temperature requires near-zero future carbon emissions. Our results suggest that future anthropogenic emissions would need to be eliminated in order to stabilize global-mean temperatures. As a consequence, any future anthropogenic emissions will commit the climate system to warming that is essentially irreversible on centennial timescales.

    When Matthews & Solomon refer to “further misunderstanding,” they don’t imply that Matthews & Caldeira 2008 is wrong.

  127. Mark Bahner says:

    “In other words, the sum of the positive and negative ones have to almost cancel.”

    So the correct answer to this multiple choice question:

    Which of the following statements must be true, in order for global temperatures to be stabilized:

    1) Anthropogenic emissions must be eliminated.
    2) If anthropogenic emissions are not eliminated, then we must somehow remove as much CO2 from the atmosphere, and sequester it somewhere, as we’re emitting into the atmosphere.
    3) Both of the above.

    …is #2, right?

  128. Mark,
    I’ve given you a reasonable answer to the question numerous times. To stablise temperatures would require net emissions be close to zero.

    If you post your MCQ again, I will delete it.

  129. Willard says:

    The paper Mark criticizes is called Irreversible Does Not Mean Unavoidable. That claim is repeated at the end of the first paragraph: irreversibility of past changes does not mean that further warming is unavoidable. It does seem that MarkB’s reading of “irreversible” means it’s unavoidable.

    The second paragraph reads:

    The climate responds to increases in atmospheric CO2 concentrations by warming, but this warming is slowed by the long time scale of heat storage in the ocean, which represents the physical climate inertia. There would indeed be unrealized warming associated with current CO2 concentrations, but only if they were held fixed at current levels (1). If emissions decrease enough, the CO2 level in the atmosphere can also decrease. This potential for atmospheric CO2 to decrease over time results from inertia in the carbon cycle associated with the slow uptake of anthropogenic CO2 by the ocean. This carbon cycle inertia affects temperature in the opposite direction from the physical climate inertia and is of approximately the same magnitude (2, 6).

    http://www.sciencemag.org/content/340/6131/438.full

    Please recall that reference #6 is Matthews & Caldeira, 2008.

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