Climate change commitments

There is an interesting letter in Nature Geoscience this month on what climate changes we have actually already committed ourselves to. The letter, by Mathews and Weaver (sub. reqd.), makes the valid point that there are both climatic and societal inertias to consider.

Their figure neatly demonstrates the different issues:

The upper line is often what is referred to as the ‘climate change commitment’ (for instance Wigley, 2005). This is the warming you get if we keep CO2 (and other GHG and pollutant levels) constant at today’s values. (Technically, the figure shows the case staying at year 2000 values). In such a scenario, the planet still has a radiative imbalance, and the warming will continue until the oceans have warmed sufficiently to equalise the situation – giving an additional 0.3 to 0.8ºC warming over the 21st Century. Thus the conclusion has been that because of climate inertia, further warming is inevitable.

However, constant concentrations of CO2 imply a change in emissions – specifically an immediate cut of around 60 to 70% globally and continued further cuts over time. Matthews and Weaver make the point that this is a little arbitrary and that the true impact of climate inertia would be seen only with emissions cut to zero. That is, if we define the commitment as the consequence only of past emissions, then you should set future emissions to zero before you calculate it. This is a valid point, and the consequence of that is seen in the lower lines in the figure.

CO2 concentrations would start to fall immediately since the ocean and terrestrial biosphere would continue to absorb more carbon than they release as long as the CO2 level in the atmosphere is higher than pre-industrial levels (approximately). And subsequent temperatures (depending slightly on the model you are using) would either be flat or slightly decreasing. With this definition then, there is no climate change commitment because of climate inertia. Instead, the reason for the likely continuation of the warming is that we can’t get to zero emissions any time soon because of societal, economic or technological inertia.

That is an interesting reframing of an issue that comes up all the time in discussions of adaptation and mitigation. This is because it demonstrates that adaptation (over and above what is necessary to reduce vulnerabilities to current climate conditions) is unnecessary if mitigation is dramatic enough.

However, the practical implication of this reframing is small. We are clearly not going to get to zero emissions any time soon, and even the 60-70% cuts required to stabilise concentrations initially seem a long way off. Thus as a practical matter, it doesn’t really matter whether the inertia is climatic or societal or technological or economic because the globe will continue to warm under all realistic scenarios (what we do have a possible control over is the magnitude of that warming). Thus further adaptation measures will still be needed.

212 comments on this post.
  1. CM:

    Solomon et al. (2009) did essentially the same, didn’t they? They ran various scenarios with abrupt transitions to zero emissions, albeit all peaking at at higher CO2 concentrations later in the 21st century.

    Their glass seemed to be half empty, and was widely misreported to say our goose was cooked no matter what we did to mitigate. Matthews and Weaver find the glass half full and use it to reframe the debate in favor of strong mitigation. Full marks to M&W for grasping the psychology of communicating climate change.

    But how much sea-level rise would we still be committed to if we quit carbon cold turkey now? That’s one adaptation cost they don’t seem to discuss.

    Zero emissions, now, is not realistic, of course. But just think where we could have been already if we hadn’t wasted two decades. Sigh. Better not waste any more.

    Wonder how the deniers are going to spin this graph. I mean, damn the context, they cannot not abuse graph that shows some temperatures going down while the IPCC says they’ll go up! All they need is a name for the IPCC’s latest “mistake” … hm … “Realismgate”?

    Solomon, Susan et al. (2009). “Irreversible climate change due to carbon dioxide emissions,” PNAS, online January 28, 2009, doi:10.1073/pnas.0812721106.

  2. wilt:

    I am very puzzled by the Figure that you provide with the text, because it suggests that the mean value for the IPCC models during the 21st century almost coincides with the “constant composition” scenario. It is stated that the latter scenario would yield a 0.3 to 0.8ºC warming over the 21st century. As far as I understand, the IPCC predictions have always been much higher. Can you perhaps explain this, before we get endless debates based on misunderstandings?

    [Response: The diagram is only for the constant-2000 concentrations. The business-as-usual scenarios that people talk about have steadily increasing concentrations. – gavin]

  3. Sean A:

    Angelo: Future warming is not necessarily inevitable, if we drastically cut emissions now. Since immediate and drastic cuts are not very likely, we will see further warming. Not due to climatic inertia, but to social inertia. Seems pretty simple to me. Or are you being deliberately obtuse?

  4. Tim G:

    I may be misreading the graph, but doesn’t it imply that there is no “warming in the pipeline”? I would consider that good news.


  5. cougar_w:

    I’ve always interpreted the “we will simply adapt” meme as an implied appeal to techno-triumphalism … the idea that technology will bail us out. The abstract idea then becomes the concrete excuse; we don’t have to do anything about this because “someone” will come up with an “idea” that will change everything. This for all values of “someone” not equal to me and all values of “idea” that don’t overlap with the set of solutions that entail life style changes.

    Technology is the final balm for the weak minded because it really is indistinguishable from magic. We will happily go into a dark place and then wait for someone to invent light.

  6. Bob:

    I’d be very interested in seeing a projection that mirrors what is actually likely to happen. That is, an apathetic “show me the money” style public combined with “we like things as they are” power bases will combine to obstruct any mitigation whatsoever until perceptible climate changes are more apparent and so more difficult to refute. The two scenarios outlined here, both constant composition and zero emissions, are very, very unlikely to happen even within a decade.

    For example:

    Phase I, Apathy: Two more decades of warming and accompanying side effects (ice melt, etc.) equivalent to the 1990-2010 increase will probably be enough (necessary and sufficient?) to start to make people question their own hesitation to act.

    Phase II, Reluctant Concern: After that, mitigation efforts will be slow, taking another decade or so before people really get scared, and get serious.

    Phase III, Action-with-Friction: After that, it will take another decade (at least) for the politics, cold warfare, technology and other social aspects to catch up and start to make a truly noticeable dent in where CO2 goes (i.e. get it to start declining).

    Phase IV, Concerted Action: Finally, 40 years from now, things will be in place to begin to actually either level off or possibly reduce atmospheric CO2 levels.

    This is all a hypothetical, of course, with rule-of-thumb time periods thrown in. Other people could put other time frames on these four phases of climate change reaction (20 more years of apathy, 10 years of reluctant concern, 10 years of action-with-friction, an eventual future of concerted action). Sorry if my own time frames are depressingly pessimistic. It would actually make an interesting sociology study.

    But however this is framed… what do future temperatures look like if this pattern is followed?

  7. Dan Sinnett:

    Angelo –

    I had to re-read Gavin’s take a couple of times before I got the gist of it. I also had access to the article which helped.

    Matthews and Weaver were making the point that the issue of climate inertia has been overstated/conflated with a different issue. The climate inertia issue is whether the CO2 that we have already dumped into the atmosphere is going to keep the warming going even IF we ended all emissions. If there was a significant amount of climatic inertia, the Earth would continue to warm despite zero future emissions.

    Matthews and Weaver’s conclusion is that with a zero emission policy, global temperatures would remain constant or even begin to decrease (which makes some amount of sense – trees and other biota would start to remove the CO2 and store it). That means that there is no climatic inertia in the system.

    The constant CO2 scenario means that we have to continue emitting CO2, but at the same rate as the Earth can store it, which would require a 60-70% cut, as Gavin points out. Even in this scenario, the Earth would continue to warm.

    I think Matthews and Weaver were pointing out that continued warming with constant CO2 is associated with climate inertia, which is incorrect. It is the inertia in society, our dependence on fossil fuels for example, which will drive the continued warming – NOT the inertia in the climate system.

    So the short summary abstract from Matthews and Weaver, which you have access to, is true – that unavoidable warming due to climatic inertia is incorrect. From my read, Gavin agrees with this. However, Gavin very correctly points out that zero emissions is a bit of a pipe dream, and that 60-70% cuts are also unlikely. Therefore, even if the climatic inertia will have little to no effect on future warming, the significant societal inertia essentially guarantees it.

    From my viewpoint, Matthews and Weaver point out that we have much more control over our own climatic future than some people realize. Or, and to quote a favorite cartoon character from my youth (and now I’m dating myself and pointing out my geek-hood):

    “The Power is yours!”
    -Captain Planet (from Captain Planet and the Planeteers)

  8. Tony Lowes:

    Feddback indeed – how can you ‘set future emissions to zero’ with the forcing of natural emmissions of carbon dioxide and methane – surely this ensures ‘unavoidable warming owing to inertia in the climate system’?

  9. John Cook:

    I wonder if in calculating the zero emission scenario, they take into account the drop in aerosols that result from fossil fuel burning. As these have a cooling effect that cancels out much of greenhouse gas warming, the removal of the cooling effect would also have a warming impact.

  10. Dan Sinnett:

    P.S. To those lacking a subscription or university access, some (most?) public libraries have subscriptions to scientific magazines. If you really care enough about this subject, or truly want to be educated on it, take advantage of these resources. Further, there are motions towards making publicly funded research more available to the public after a period of time. Lastly, reports by the national academies and other government agencies are often freely available.

  11. Geoff Wexler:

    Interesting discussion, but perhaps we should now guess and adapt to the way this paper is likely to be misrepresented.

  12. Dr Nick Bone:

    It’s nice to see discussion of an actual science paper again, rather than yet more media analysis.

    The question about “what would happen with zero emissions” is an interesting one, albeit hypothetical. We could imagine it happening if a sudden plague wiped out our civilization, for instance.

    As far as I can understand it, reading across several papers (references below), there might well be a number of stages.

    Stage 1: CO2 levels in the atmosphere start declining straight away (while the oceans continue to acidify).

    The radiative imbalance due to CO2 forcing starts to fall, counteracting the “warming in the pipeline”.
    Global temperature stays approximately at today’s level or falls a little.

    Stage 2: CO2 stops falling, because there is a portion (20-25%) of our emissions which is persistent for thousands of years. The airborne fraction of our emissions has been 40-50%, which means about half the extra CO2 in the atmosphere will stay there long-term i.e. CO2 bottoms out at around 335ppm. Temperature rises owing to fast-feedbacks (Charney sensitivity) for that level are around 0.75 degrees C above pre-industrial, roughly where we are today.

    Stage 3: However, this is high enough to cause melting on all our land ice-sheets, and so slow albedo feedbacks will kick in too (Earth System Sensitivity). A slow warming resumes, leading to an additional 0.75 degrees or so over the next few centuries. But at the same time, we see the full temperature-dependent CO2 response, with CO2 levels slowly rising again, likely about 16-20ppm per degree C judging by the change between LGM and Holocene. This increased CO2 causes a bit more warming, which causes a bit more CO2, and so on, but in a convergent series.

    Stage 4: CO2 levels converge back up to around today’s levels (370-400ppm), and the temperature to around
    2.5 to 3 degrees above pre-industrial levels. The Greenland and West Antarctic ice-sheets have gone. Part
    of the East Antarctic ice-sheet has gone too. Earth resembles the Pliocene.

    Stage 5: Our persistent CO2 finally drops out of the atmosphere after maybe 100,000 years. Milankovich cycles resume, and eventually there is a new stade allowing ice sheets to grow again. A climate like the
    Holocene is not restored until the next interglacial after that.

    That seems to be what we’re committed to: “Hell and high water” for thousands of years plus a probable mass extinction whose effects will last for millions of years. Given that (or even a fraction of that), it’s not enough to reduce emissions to zero: somehow we must make them NEGATIVE (i.e. suck CO2 out of the atmosphere again). It’s a long away from current policy discussions.

    References: Stage 1 is described in the above paper.

    For persistent fraction of CO2, see e.g. <a href="; Archer, <a href="; Montenegro et al,
    <a href="; Archer et al.

    For evidence on Charney sensitivity, see Annan and Hargreaves.

    On Earth System Sensitivity, see Hansen et al and the Pliocene papers below.

    For CO2 response to temperature, see Cox and Jones and the discussion of Frank et al here .

    A number of recent papers on the mid-Pliocene indicate that CO2 levels were similar to today’s
    including Pagani et al, Lunt et al and Schneider and Schneider . Whereas Tripati et al reconstruct them even lower than today.

    For a discussion why it takes 100,000 years or more to undo the damage, see How Long will global warming last?

  13. Hank Roberts:

    Just to track this question:

    5, 6, 9, 20 (implicitly), 22, and 59 mention the need to consider the result of aerosols (sulfates) falling rapidly once fossil fuel burning ceases. Gavin affirms that as a good question, inline in 20.

  14. Foobear:

    We can easily get to a 50% cut without changing peoples’ lives – replace coal power with nuclear.

  15. Nonlinear Guy:

    I’d like to give a second response in order to clarify the absurdity of the Figure
    above which “neatly demonstrates the different issues”. If you add a carbon cycle
    model to demonstrate that actually there is no future warming commitment, then
    you should also add ice-sheet responses, for which you don’t even need the fancy
    super computer GCMs. Paleo data (Hansen et al, 2008) provide sufficient information
    to see that the long-term equilibrium warming would amount to 2 x 1 = 2 degrees in
    the zero emissions case (based on the plm 1 degrees oceans-only induced equilibrium value presented in the figure).

  16. Ike Solem:

    Okay, we’ve been over the carbon cycle responses about a thousand times now – your shallow Arctic seabeds & permafrost regions, which are going to continue outgassing by all estimates, both modeled and real-time measurements.

    This was also a problem with a previous paper on this subject:

    Here’s the problematic statement:

    CO2 concentrations would start to fall immediately since the ocean and terrestrial biosphere would continue to absorb more carbon than they release as long as the CO2 level in the atmosphere is higher than pre-industrial levels (approximately).

    I’m sure gavin would admit that his expertise is not in the area of biogeochemical cycling – but aren’t there several huge questions here? What’s the basis of this argument when we know quite clearly that terrestrial environment is NOT absorbing more carbon than it is releasing?

    Look at the land use change estimates – deforestation has played a large role. Permafrost outgassing is similarly a major issue – and what about all the studies on the Southern Ocean sink saturation – they don’t matter either? Canadian pine forests – they were going to be a source of “carbon credits” for Canada to exchange for tar sand emissions, but they’ve lost so much mass that they now count as an emission debt, not a credit – which shows how unscientific the carbon trading schemes are, by the way.

    Consider the natural uptake of CO2 during the slow progression into a glacial maximum – what is the range? 280 ppm to 190 ppm – a 110 ppm drop over tens of thousands of years. Why on earth would you expect the atmospheric CO2 to start declining rapidly, even if we halted emissions?

    The real question here is the extent to which we’ve enlarged the circulating carbon pools – and also changed the global ocean circulation. There are plenty of reasons to wonder about a slowed ocean circulation, and spreading hypoxia and anoxic conditions in deep waters, as well.

    Finally, it seems that Wigley did indeed fix conditions:

    The Climate Change Commitment
    T. M. L. Wigley

    Even if atmospheric composition were fixed today, global-mean temperature and sea level rise would continue due to oceanic thermal inertia.

    Wigley also neglects carbon cycle feedbacks, but step by step is the way science is done.

    So, are we saying that CO2 levels would start dropping by what, a ppm every few years? if we suddenly stopped burning fossil fuels?

    That seems highly unlikely – what if the permafrost starts outgassing at higher rates?

  17. Jacob Mack:

    Gavin well put. This is somewhat along the lines of what I have been saying, but better put in the terms of climate inertia. Of course we should do what we can to reduce future emissions, but we also have to accept a growing population will still need technology which emits GHG.

    Oh and on a side note I liked the recent commentary you wrote on Gilbert N. Plass on pp. 64-65 of the Jan-Feb 2010 issue of American Scientist.

    Plass was certainly very accurate considering the technology he had to work with… for those who have not done so, I suggest you grab that issue of AS.

  18. Witgren:

    “Dr Nick Bone says:
    3 March 2010 at 5:03 PM

    It’s nice to see discussion of an actual science paper again, rather than yet more media analysis.

    The question about “what would happen with zero emissions” is an interesting one, albeit hypothetical. We could imagine it happening if a sudden plague wiped out our civilization, for instance.”

    It’s an interesting thought experiment…I’m not a scientist, but I think in the absence of man Mother Nature might recover more quickly than we might think. For example, a lot of new vegetation would soon appear in areas man currently keeps in closely manicured lawns or even in roads and such. And sites subjected to heavy grazing by farm animals would start to recover as those farm animals died down to a more natural population. How much and how fast that would affect CO2 uptake, I couldn’t begin to guess, but I’d think it could be noticeable within a decade or two.

  19. SecularAnimist:

    From the abstract: “… mitigation efforts to minimize future greenhouse-gas emissions can successfully restrict future warming to a level that may avoid dangerous anthropogenic interference with the climate system.”

    But the warming that has already occurred from the excess GHGs that we have already emitted is already causing “dangerous anthropogenic interference with the climate system”.

  20. sidd:

    Dr. Bone: Thanx for a cogent analysis.

    But what if the trajectory you outline destabilizes a)the permafrost or b)mathane clathrates ?

  21. Len Ornstein:


    Hansen et al (2005) (Gavin is one of the “et al”)

    talks about “warming in the pipeline”.

    Isn’t that most of the ‘further’ warming (climatic inertia?) that would be realized if all burning of fossil fuel and all deforestation came suddenly to an end?

    Wouldn’t that warming continue for a number of years?

    Isn’t that mainly due to the time it takes for the heat, previously absorbed near the surface of the oceans, to mix to a steady-state distribution in the oceans and with the atmosphere?

    Please answer!

    [Response: No. The heat that goes into the ocean generally stays there. The upper ocean will only warm to the equilibrium level if it stops losing heat to the deep ocean. At equilibrium, the ocean will have a significantly larger heat content than originally (which is why there is sea level rise via thermal expansion). – gavin]

  22. Gail:

    “On the other hand this assumes no positive feedbacks are already in play, no?”

    No, just no runaway positive feedback – which we pretty clearly don’t have yet.

    Comment by NoPreview NoName — 3 March 2010 @ 12:48 PM

    Um…albedo effect? permafrost releasing methane? melting polar ice? forests turning from carbon sinks to carbon emitters? If those aren’t runaway positive feedbacks, what would be? Does anyone have any clue how to stop them?

    Thought not.

  23. Ron Taylor:

    I agree with Bob (56). His scenario strikes me as more realistic, if politically incorrect. Remember, even though it was killing tens of thousands each year, it took forty years to get something done about tobacco. Big money carries a big stick.

    If we started analyzing such scenarios, maybe it would help get the attention of the policy makers.

  24. David B. Benson:

    David (65) — On the Whatevergate thread I posted a prediction for GISTEMP global decadal averge for the 2010s; warmer. That used just the Arrhenius approximation for CO2. I’m working up a slighter better predictor program, a slightly more complex conceptual model of the global climate, so watch for it.

    But I don’t know how to make regional predictions although I have seen papers which attempt this. Generally drier and hotter in southern Europe over the rest of the century as I recall.

  25. Phil Scadden:

    Jean,Once again, the scientific study referenced, certainly paid by tax payers, is not available to the general public.

    I presume you mean that you have to pay Nature to read what they publish? I would like to know what you think would be both better and practical. Is the US taxpayer going to fund Nature? If all research is made available free, then journals disappear. How do you ensure archive, referencing, and more importantly manage the peer-review process? Do you as tax payer want to stump up for that? Are you going to increase research funding to cover that cost? At the moment, the system is “user-pays” which I understood to be the American way. (I am not a US citizen. I would be very happy for you, the tax payers of US, to pay for my journal subscriptions).

  26. Hank Roberts:

    For those like me who don’t have a subscription and haven’t gotten out of the house and down to the library yet, abstracts of a few possibly related articles can be found. Looks like there’s a lot of teaching possible here, if the paywall can be gotten around somehow.

    Too bad there’s no millionaires’ tip jar for scientists wondering about buying out the publisher so their work could be made available right away.

    Nature. 2009 Jun 11;459(7248):829-32.
    The proportionality of global warming to cumulative carbon emissions.

    Matthews HD, Gillett NP, Stott PA, Zickfeld K.

    Department of Geography, Planning and Environment, Concordia University, 1455 de Maisonneuve Blvd W., Montreal, Quebec, H3G 1M8, Canada.

    The global temperature response to increasing atmospheric CO(2) is often quantified by metrics such as equilibrium climate sensitivity and transient climate response. These approaches, however, do not account for carbon cycle feedbacks and therefore do not fully represent the net response of the Earth system to anthropogenic CO(2) emissions. ….

    Proc Natl Acad Sci U S A. 2007 Jun 12;104(24):9949-54. Epub 2007 Jun 4.
    Transient climate-carbon simulations of planetary geoengineering.
    Matthews HD, Caldeira K.
    Comment in:
    * Proc Natl Acad Sci U S A. 2007 Jun 12;104(24):9915-6.
    Geoengineering … there may be little cost to delaying the deployment of geoengineering strategies until such a time as “dangerous” climate change is imminent.

    Proc Natl Acad Sci U S A. 2009 Sep 22;106(38):16129-34. Epub 2009 Aug 17.
    Setting cumulative emissions targets to reduce the risk of dangerous climate change.
    Zickfeld K, Eby M, Matthews HD, Weaver AJ.
    Comment in:
    * Proc Natl Acad Sci U S A. 2009 Sep 29;106(39):16539-40.

  27. Richard Ordway:

    re 30 Jean says:

    “”Once again, the scientific study referenced, certainly paid by tax payers, is not available to the general public.

    If I cannot have access to the information, I cannot communicate around me, because I don’t know.

    We therefore cannot assess the claims and should not expect the general public to be well informed and make rational voting decisions.

    When will they get it?”””

    Jean, one study does not the body make since 1824…and it sure did not when I was at the place I was for 11 years. The synthesis of published climate science since 1824 is the IPCC 2007 AR4 which is freely available.

    That is why political people say, “OMFG!!! this one study that just came out disproves human caused global warming.”…again. again. again and yet again (absolutely none of which stands up over time. This is deceiptful to say this. It is really a body of evidence of thousands of studies since 1824 that you need to concern yourself with…not just one study.Only politicans say this.

    Remember, this study is available at most libraries if you are so desperate to make a voting policy decision based on only one study out of thousands that have the same general conclusions.

    A small sample of freely available (downloadable to the public) studies stating that anthropogenic climate change is happening.

    Remember, to use only the latest studies from reputable scientific journals that have been vetted over about two years because science moves on too.

    One magazine for instance, Energy and Environment is not a scientific journal and prints at best pseudo science that does not stand up over time and sometimes seems to act like a scientific journal. Any real scientist whose climate science work holds up over time would know this…not the public or the pseudo scientists. This is the way it has been done since the 1600s.

    TC Johns et al., Climate Dynamics, 2003

    Oreskes, 2004, Science

    Nature, CD Thomas, 2004

    JT Houghton, Intergovernmental Panel on Climate Change, 2001

    JT Houghton, Intergovernmental Panel on Climate Change, 1995

    Karl, Trenberth, Science, 2003

  28. Ray Ladbury:

    Look into how much it costs to publish an article in a journal like Nature. Now, look at your contribution to this study (about $0.05). Do you see why you have to pay for the subscription now?

  29. Anonymous Coward:

    Hank (#63),
    I’m 6. I did not mention that. Read my post again. What I mentionned is the need to consider not only the cooling commitment from the mitigation which ain’t happening but also the cooling commitment from geoengineering which ain’t happening as well. Surely all counterfactuals deserve equal consideration.

    Alert readers might have picked up the modest proposal between the lines. Recall that the only reliable way to neutralize “social inertia” would also stop emissions and send a whole lot of aerosols up there in one fell swoop. Let it not be said there are no alternatives to adaptation!

  30. Don Condliffe:

    The comment here by Bart Verheggen using work by Ramanathan and Feng, coupled with the comment by Elmar Veerman about the greenhouse gases remaining long after shorter lived masking aerosols are removed, identify a flaw in the argument and they seem to effectively rebut the argument that ending carbon dioxide emissions would lead quickly to global temperature stabilizing.

    On the question of positive feedbacks I am reminded of the study “Abrupt Climate Change: Inevitable Surprises” (2002) National Academy of Sciences, which identified potential positive feedback loops that could result in rapid and harmful climate shifts. Now recent work shows carbon dioxide and methane feedback loops are initiating [1-4]. The question is as a practical matter can we do anything effective to limit greenhouse emissions before we pass critical tipping points? Tipping points after which mitigation will not work because release of carbon stores now sequestered due to being frozen in permafrost takes over the system. It seems clear we do not have sufficient understanding and data to say where the tipping points may be, nor even to know if we have already passed a point of no return.

    Meanwhile reading the US Energy Information Agency global forecasts for coal mining and petroleum production makes it quite clear that Business As Usual is the global reality. As Copenhagen clearly showed there is no political will to force massive economic changes and there will not be, not until there are immense and clear cut catastrophic changes that obviously are the result of global warming. I think that is almost certain to be too late. We are committed to the Hot World and adaptation is the way of the future for my children and grandchildren, much as I wish it were not so.

    1. Ping, C.-L., et al., High stocks of soil organic carbon in the North American Arctic region. Nature Geosci, 2008. 1(9): p. 615-619.
    2. Lawrence, D.M., et al., Accelerated Arctic land warming and permafrost degradation during rapid sea ice loss. Geophys. Res. Lett., 2008. 35.
    3. Walter, K.M., L.C. Smith, and F.S. Chapin, 3rd, Methane bubbling from northern lakes: present and future contributions to the global methane budget. Philos Transact A Math Phys Eng Sci, 2007. 365(1856): p. 1657-76.
    4. Walter, K.M., et al., Methane bubbling from Siberian thaw lakes as a positive feedback to climate warming. Nature, 2006. 443(7107): p. 71-75.

  31. Septic Matthew:

    How would you assess the state of “societal inertia” right now?

    Even without ratifying the Kyoto treaty the US embarked under Bush on a faster development of non-hydro renewables and CC&S, increased the investment still more, and yet again still more under Obama. The UN, EU, and China have massive reforestation projects, and nearly every industrial nation is expanding its non-hydro renewable energy supplies and nuclear power generation.

    The strongest motivator (except for CC&S) is the worry over declining or unreliable oil supplies, but the impact on AGW is substantial.

  32. flxible:

    Jean@30 says:
    Once again, the scientific study referenced, certainly paid by tax payers, is not available to the general public.
    If I cannot have access to the information, I cannot communicate around me, because I don’t know.
    We therefore cannot assess the claims and should not expect the general public to be well informed and make rational voting decisions.

    When will they get it?

    Jean – For starters, it’s not a “scientific study”, it’s a letter to the editor of a scientific journal, definitely available to the public, with payment of the magazine cost, same as anything else on your news stand – Gavin choosing to discuss it here makes it available to the public.

    Next off, it’s likely the authors were not paid with any tax money for thinking about climate inertia vs social inertia and writing a letter to an editor about it, and if they were, it would only be your tax money if you are Canadian, in which case you might try emailing either author, both professors at Canadian Universities and both amenable to public outreach, and largely paid by their respective provinces and student fees. You might even be able to audit a course with one of them, but of course that would cost you!
    As for assessing “the claims”, Gavin gave us a good leg up on that, although many of the “general public” might not be interested in thinking about what he had to say, prefering to immediateely decide it’s easier to claim something is being hidden, which just goes to show Gavin got it right. :)

  33. Dave E:

    re: Steve A Morris (#14)
    “The Earth is only heated via Radiation, and cools via Radiation, Convection, and Evaporation in order of increasing magnitude.”
    In fact, I believe that the Earth is only cooled by radiation. Convection and Evaporation will move energy between the Earth Surface and the atmosphere but the energy still remains in the Earth system, only when this results in increased radiation from the Earth will the Earth system cool–but of course, this is exactly what the climate models are modelling.

  34. Steve Fish:

    RE: Steve A Morris — 3 March 2010 @ 10:32 AM and Frank — 3 March 2010 @ 12:41 PM:

    Evaporation and convection move heat about, but it can only be transferred to the vacuum “thermos bottle” of space via radiation.


  35. Brian Dodge:

    At the current setting of the climate “thermostat”, the Greenland Ice sheet is melting and losing mass by calving icebergs faster than snow is accumulating at high elevations. The rate of loss is accelerating, partly because we keep turning up the thermostat with more CO2, and partly because the lost mass moves more surface into the melt zone and out of the accumulation zone. It’s obvious to me that unless we turn down the thermostat (eliminate CO2 emissions, maybe act to restore some of the natural sinks we’ve upset), Greenland will continue to melt. Only the Bern2.5CC model scenario shows declining Temperatures, but I don’t know when Greenland will stop melting even under that (unlikely) trajectory. I wonder how much sea level rise we have in the pipeline.

  36. Lab Lemming:

    Does a return to pre-industrial mean global temperature necessarily mean no adaptation? Or could you get the same mean with large regional differences?

  37. Thomas:

    I really question whether the (zero emissions) scenario really makes sense. Without resorting to GCMs, we can probably answer some questions. The most salient issues I think would be:
    (1) Rapid reversal of the aerosol effect (or should we assume deliberate “geoengineering” to counteract it).
    (2) The evolution of CO2 level with time.
    (3) Thermal inertia of the climate system.
    (4) Vegetation and ice feedbacks that over time change the albedo as a function of temperature.
    Factor 2, clearly is a cooling effect. Last time I had seen results for CO2 retention the results were expressed as a prony series (a weighted sum of decaying exponentials). IIRC the first couple of terms had pretty low time constants, so the concentration decay forcing might give a significant cooling effect in early years. The first factor is likely pretty substantial. The third one is what roughly twenty years for near surface ocean heating? The fourth could be important over decadal and longer time scales.

    I’m guessing W&W essentially did 2, and 3, and they had them roughly cancelling out. But aren’t (1) and (4) both warming effects? (1) should be pretty fast acting, and probably not that hard to estimate. (4) Contains both short (vegetation, sea ice) and long (ice sheets) time scales.

  38. GFW:

    Despite several people mentioning it, and Hank R doing a round-up of who has mentioned it, I’m not sure most of the commentariat have understood the crucial importance of Bart V’s critique right there at comment #4. The idea of testing zero CO2 emission with constant (current) sulfate emission is unphysical (unless we’re geoengineering the sulfates). So anyone who thinks this paper means there’s no warming in the pipeline is wrong. I would suggest to Gavin that he amend the original post to reflect what Bart said.

    On an entirely separate, and off topic issue, can anyone tell me what the typical spatial and temporal resolution of a full-scale GCM run is? For example, how about the GISS-E runs in the IPCC AR4. Thanks in advance.

  39. ary:

    I tried a simple modeling of the temperature curve by assuming a (linear) relaxation equation towards the equilibrium temperature Teq with a time constant tr (representing the climatic inertia) : dT/dt = – (T-Teq)/tr . With an increasing forcing F(t), Teq is itself a function of time , which can be in the same spirit approximated by a linear relationship Teq(t) = To + A F(t) where A is the sensitivity to forcing.
    F(t) can be further approximated. If we take a logarithmic sensitivity to GHG concentration, and an exponential growth of this concentration, it is something like ln(1+Aexp(kt)) which is close to 0 as long as exp(kt) << 1/A and then grows asymptotically linearly with time. So it seems a good approximation to take a linear forcing after some date Tbeg (around 1970 in the models) F = F0.t

    finally we get dT/dt =- (T-T0-A.F0.t)/tr after Tbeg, and 0 before.
    this is a very simple linear differential equation whose solution is analytic and reads
    T(t) = T0 + (t/tr-(1-exp(-t/tr))

    This has the right behaviour : for small times t<>tr it grows linearly with the forcing but with some shift due to the accumulated delay (and the shift is necessary for the small imbalance to produce the warming). I think that most of the climate solutions can be reproduced by this two-parameters (forcing+relaxation time) solutions.
    Problem : with a linearly increasing forcing, the slope should also increase linearly because of the quadratic behavior as long as t<<tr. If the warming trend has increased indeed since 1970, it doesn't seem to be true anymore since 2000. If it were the saturation of relaxation time, it would indicate a small time (30 years) and a small sensitivity. Or the curve is messed up by natural fluctuations but it means than the 1970-2000 warming was also partly due to fluctuations. In any case, the absence of acceleration of the trend points towards a low climate sensitivity.
    T(t) =

    [Response: Gilles, posting under different names in the same thread is a strict no-no. Please do not do it again. – gavin]

  40. meteor:

    Hi Gavin

    In the constant CO2 scenario (about 370ppm) how are accounted, if they are, the others radiative species : aerosols, GES (other than CO2,…?

    [Response: Not included at all. – gavin]

  41. Martin Vermeer:

    CM #51

    But how much sea-level rise would we still be committed to if we quit carbon cold turkey now?

    Our a href=””>PNAS formula says

    dH/dt = a T + b dT/dt.

    Believing that, with dT/dt = 0, T = 1 degree constant (assumed from the graph to be over pre-industrial?) and a = 0.56 cm/degree/year, we get a total sea level rise 2010-2100 of 50 cm. And going on at 56 cm/century after that.

  42. Dr Nick Bone:

    Wow! I composed my 5-stage scenario when there were only 2 comments, and we’re already up to 70. (My own came in at comment 62.) Quite a lot of other posters have also mentioned positive feedbacks, including albedo and carbon feedbacks.

    On aerosols (comments 5,6,9,20,22,59,63); so it looks like “Stage 1” would be a bit of a bumpy ride after all. Total human pollution consists of CO2 (+ve forcing), other GHGs (+ve forcing), areosols (-ve forcing) and a few others, netting out to roughly the same effect as CO2. See Section 2.9.2 of AR4 WG1 report. If human civilization stopped suddenly, then the aerosols would flush out fastest, so radiative imbalance increases. But most of the other GHGs start going down pretty fast too (< century), and CO2 starts going down straight away too, especially given regrowth in cities, agricultural land etc. (See comment 68). So we probably get a sudden bump up in temperature, followed by a decline to the "Stage 2" temperature and CO2 level (with other forcings back to pre-industrial).

    On comment 70, I hadn't considered a sudden "belch" of methane from clathrates and permafrost: I didn't think the temperature would get hot enough, fast enough in the zero-emissions scenario. (Though it might do if we continue emitting through the 21st century.) The effect of "slow leak" methane could be added: roughly the same effect as the CO2 response to temperature, but amplifying it somewhat. (Hansen et al's paleo data suggest the amplification is by about 25% when CH4 and N2O move in synch with CO2). The point is that CH4 is oxidized over ~decade timescales, so the "slow leak" is balanced at a new methane equilibrium. Maybe it adds another half degree at Stage 4, but it's swamped by the error margins of the CO2 response anyway.

    The real issue is that residual ~20% of industrial CO2. It is like a stubborn stain which just won't go away and eventually causes most of the long-term damage (Stages 3 and 4). Even when the carbon cycle is in our favour, draw-down gets buffered by the oceans putting CO2 back again. I'm mostly interested in feasible suggestions for how to get rid of that residual stain, and estimates of how long they'd take.

  43. CM:

    Ike Solem (#66) said:

    we know quite clearly that terrestrial environment is NOT absorbing more carbon than it is releasing

    Huh? Despite deforestation dominating over regrowth, there’s been a net carbon uptake by the terrestrial biosphere over the past decades (AR4 carbon budget: fig. 7.3, table 7.1, discussion). What we don’t clearly know is where, or why, or for how long.

  44. Jimbo:

    2001-2010 was the Snowiest Decade on Record

    I know it’s just weather not climate.

    As for Al Gore my question is he right about moisture in the atmosphere? Do I believe the scientists or Al Gore? The choice is yours!

    [Response: If you believe the New York Post over the IPCC report, you are far more foolish than you appear. There is more moisture in the air and that does lead to observed and predicted increases in precipitation intensity (section in AR4 WG1). – gavin]

  45. Tim Curtin:

    What are the implications for world food production of reducing CO2 emissions below the current annual incremental 57% uptake thereof by the world’s biota (ie from c.57% of 10 GtC in 2009 to c57% of 2 GtC as proposed by Hansen and at Copenhagen)?

  46. Barton Paul Levenson:

    Steve A. Morris (14),

    You have the order wrong. The Earth cools by 389 watts per square meter by radiation, 80 by evapotranspiration and 17 by conduction and convection. And evaporation, while cooling the surface, also puts more water vapor in the air, and water vapor is a greenhouse gas.

    What makes you think climate models ignore surface cooling other than radiative? Manabe and Strickler introduced a convective adjustment into their RCM in 1964.

  47. Barton Paul Levenson:

    Richard C (28): There is nothing magical about pre-industrial CO2 levels.

    BPL: They’re the levels our entire civilization developed in.

  48. Barton Paul Levenson:

    Frank (38): isn’t it true that most energy is removed from the earth’s surface by convection and evaporation, not radiation

    BPL: NO. It is not even remotely true. Surface cooling is as follows:

    Radiation: 389 W m^-2
    Latent heat*: 80 W m^-2
    Sensible heat**: 17 W m^-2

    **Conduction and convection

    How the hell did this denier meme get started? I think I saw it advanced first by a crackpot on a blog, possibly the engineer who signs himself Ali Tekhassi. But it is measurably, verifiably WRONG. And misleading. Which I suppose is the idea.

  49. Timothy:

    @cervantes [1]
    “On the other hand this assumes no positive feedbacks are already in play, no?”

    Note that one of the models on the figure is HadCM3LC. I *think* the “LC” stands for “Land Carbon”, in which case there has been an attempt to use a model that would include some of the possible carbon-cycle positive feedbacks.

    As I understand it, the contributions for carbon-cycle feedbacks aren’t expected to kick in until later in the century, depending on the scenario, so this isn’t too surprising.

    I think the paper makes a very good point – which is that, essentially, how much the climate warms is up to us. Whilst a certain amount of economic inertia is inevitable [eg think of the carbon emissions necessary to manufacture wind turbines, until there are enough wind turbines to power their own manufacture] we still have the discretion to choose a rapid or slow transition.

  50. Mark S:

    Some of the energy going into the oceans gets converted to potential energy due to the higher surface level, i.e. “work” is being done to push up the surface against gravity. Does anybody have a sense of how much this reduces the surface temperature?

    [Response: Completely negligible. Work out the average movement up of the centre of mass of the ocean due to thermal expansion- maybe 0.5/mm per year. Calculate the increase in potential energy m*g*delta h per m2, and you get roughly 6×10^-5 W/m2. Roughly 4 orders of magnitude smaller than the heating rate. – gavin]