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Climate change commitments

Filed under: — gavin @ 3 March 2010 - (Español)

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 Responses to “Climate change commitments”

  1. 101
    Completely Fed Up says:

    BPL: “How the hell did this denier meme get started?”

    The same way as the one about volcanoes produce more in one year than humans have done in their history.

    Someone lied to them and they unquestioningly accepted it.

  2. 102

    Phil Scadden #75: Jean is obviously an old-school social-ist, who believes everything of social value should be free.

    I admire the idealism, impractical though it is in the real world.

  3. 103
    Gilles says:

    “[Response: Gilles, posting under different names in the same thread is a strict no-no. Please do not do it again. – gavin]”
    Sorry Gavin, it was totally unwanted. I just posted that in a hurry before going to work, and I assume I misclicked somewhere and edited the field with my name without noticing that I types strange characters. I am not Ary, I’m Gilles, and I have no intention of hiding anything. BTW part of my post was messed up by a unidentified bug (actually I guess the misuse of “>” and “<" in the wrong order, confusing with HTML flags) , and is partly not understable . I meant that for t much smaller than tr, the evolution is quadratic in time (developing the exponential), but it grows then linearly with time when t larger than tr. Sorry for the inconvenience.

  4. 104
    Completely Fed Up says:

    Tim G says:
    3 March 2010 at 3:04 PM

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

    I’d have to see the methodology, but it could be that the period over which they consider a useful integral the pipeline empties quickly and any effervescing of CO2 from oceans countered by biological takeup.

    But even if it’s taking things far too optimistically, this is no different from those who look at the sensitivity ranges from the models and assume that 1.5-2C per doubling is right and therefore we have another hundred years to work on something else.

  5. 105
    Icarus says:

    I was a little surprised by this post too – my understanding was that, if humans suddenly disappeared from the planet and all our CO2-producing activities ceased, atmospheric CO2 would still only decline slowly as there is no great natural capacity for absorbing CO2 on short timescales over and above the annual ‘breathing’ of around 6ppm. This post suggests that atmospheric CO2 would almost instantly decline by tens of ppm so that the current radiative imbalance would disappear almost immediately, and global mean temperature would stabilise (all other natural factors being equal). Is that correct?

    I think the key to resolving my confusion, and perhaps that of others, would be if we could see how the CO2 levels are projected to change in this scenario, rather than just temperature. I can see that atmospheric CO2 would stop increasing straight away, but I’d like to see how quickly it *declined* to levels that would cancel out the current radiative imbalance. I think that would help people understand the argument put forward here. Is such a graph presented in the paper? Could Gavin or someone run one off, or would that involve a lot of work? I don’t understand how global temperature would stop rising unless and until the radiative imbalance disappeared.


  6. 106
    Completely Fed Up says:

    Gilles, I guess that since you made a mistake there, everything you’ve ever posted is wrong, as is all the stuff you’ve cited.

    Just like happened in “*gate”.

  7. 107
    Walt The Physicist says:

    #100 My estimates are little bit different from Mr. Gavin’s. Linear thermal expansion coefficient for water at 20 C is A=6.910^-5, 1/K (taken from Wikipedia, of course). Let’s assume that only L= 1 m of water is heated up, and the increase of temperature is DT = 10C. Then, linear thermal expansion DL = A*L *DT= 6.910^-5*1*10 = 6.910^-4, m. The center of gravity raises half of that and then the increase of the potential energy per unit area is DE_p=ro*L*g*DL/2 =ro*L^2*g*A*DT, where water density is ro=10^3 kg/m^3, and g=10m/s^2. Then for the case of 1 m thickness of the heated water layer and temperature increase of 10C the increase of potential energy per square meter is DE=3.4 W/m^2. This is 5 orders of magnitude higher that estimated by Mr. Gavin. However, it could be that he assumed that only top10 millimeters of water is heated and the average increase of temperature is only 1 degree C. Or may be, just may be he assumed that the increase of potential energy is DE=ro*DL*g*DL/2?

    [Response: I assumed a sea-level rise of about 0.5 mm/yr due to thermal expansion over the whole ocean. You have calculated the Joules/m2, not W/m2 since you do not have any time scale in your calculation. That might make a significant difference. – gavin]

  8. 108
    meteor says:

    Hi again Gavin

    In the graph you show, I don’t understand the blue curve who shows a constant temperature
    In the case of zero emissions the temperature must decrease, because the concentration and subsequent radiative forcing of CO2 decrease.
    It’s showed in the Bern 2.5CC curve.
    So what about the blue curve?

    [Response: Different carbon cycle model. – gavin]

  9. 109
    Ray Ladbury says:

    Gavin’s inline to Jimbo: “Response: If you believe the New York Post over the IPCC report, you are far more foolish than you appear.”

    Based on Jimbo’s previous posts, can I register a dissenting opinion here?

  10. 110
    Walt The Physicist says:

    May be I assumed too fast heating rate. If the rate is a day it does give about 10^-5 W/m^2. However, you assumed the average motion of the center of gravity of the ocean. This assumes total depth involved. Let’s assume depth of 1000m and heating by 10C over period of 100 days. Then the formula DE_p/Time=ro*L*g*DL/2 =ro*L^2*g*A*DT/Time will again give about 1W/m^2. I think that in general, such oversimplified estimates never give accurate picture. The outcome depends on too many parameters that are not known with sufficient accuracy.

    [Response: Huh? 10C over 1000m in 100 days? What planet are you living on? Sea level rise is about 3 mm/yr – say half is due to thermal expansion (which is the only bit that counts for this calculation). Do the math and stop making excuses. – gavin]

  11. 111

    Philip (#102),
    You just wrote a pithy anti-freedom comment on a free CMS running on a free web server. How impractical is the free exchange of information again?

    The global public is already footing much of the bill for Nature through institutional subscribtions and such. I used to be able to check out this stuff through my U’s web proxy with my own student login. Now I need to use someone else’s login. What could this hurdle possibly achieve?

  12. 112
    Geoff Wexler says:

    Re: my#61

    I think that I have seen more than one contrarian argument which uses a non-stated assumption that the climate response to a change in greenhouse gases should be instantaneous. As I see it this was and still is an error.

    It is introduced whenever the effect is to favour the author’s goal of reducing the estimated warming. I have not got the details here, but Lindzen’s non peer reviewed letter to his mayor and Monckton’s pseudo-paper in the Sunday Telegraph
    come to mind, except that the latter contained additional errors. That is one reason why the implications of this paper need to be expressed very carefully.

  13. 113
    Walt The Physicist says:

    May be wea re talking about different things. Lets estimate the work per unit area done on the water column due to thermal expansion during seasonal temperature variations. The work is proportional to the second power of length of the water column, i.e. DE_p/Time= =ro*L^2*g*A*DT/Time. Thus the estimate depends strongly on the assumed depth of the column of water that expands. Assuming that the water column is 1m deep, the increase of temperature is 10C, and the time that of this temperature increase is about two months, the power density that is consumed for increase of potential energy of water column is ~10-6 W/m^2. If the length of the water column is assumed as 10 m. the power density consumed for expansion is 0.01 W/m^2. And if L is 100m the power density consumed for expansion is 1 W/m^2. And this is something that should be taken into account if one is trying to achieve accuracy of modeling ~ 0.1 C. I thought that this is what post#100 was asking for.

    [Response: But then the fluxes of heat on a seasonal time scales are much much larger. For your example, the heat flux for the 1m/10 C change is 4000*10*1000*1 = 4×10^7 J/m2, or 7 W/m2 (for two months), for 10m/10C, 70W/m2 and for 100m/10C, 700 W/2 – and so the heat fluxes are always almost three orders of magnitude larger. Potential energy changes are therefore negligible. – gavin]

  14. 114
    Sloop says:

    An FYI:

    To view an archived video of a March 2, 2010, lecture by Dr. Naomi Oreskes at the University of Rhode Island’s 2010 Vetlesen Lecture Series entitled: “Merchants of Doubt: How a Handful of Scientists Obscure the Truth about Climate Change,” please visit:

  15. 115
    Ron Taylor says:

    Jimbo (94), I gavee a quick read to your New York Post reference. It is a typical misuse of valid information to make a point. For example, Gore’s statement about additional moisture in the atmosphere contributing to more extreme precipitation events was countered with references to reductions in stratospheric water vapor. That is totally irrelevant, since weather events are generated in the troposphere, not the stratosphere. And as Gavin noted, there is definitely more water vapor in the troposphere. Also, as predicted by AGW, the stratosphere is cooling, which should lead to reduced water vapor there.

    See how perfectly valid scientific information can be misused to turn scientific logic on its head? Dunning-Kruger (or calculated dishonesty) strikes again.

  16. 116
    Rod B says:

    BPL (98), but shouldn’t the cooling from IR radiation be netted out with the 330 or so IR back radiation? (I don’t know if this would alter your main thought though.)

  17. 117
    Septic Matthew says:

    More about societal inertia: Barton Paul Levenson has generously supplied the following figures for the fraction of new electricity generation in the US from new wind installations:

    2004 4%
    2005 12%
    2006 19%
    2007 35%
    2008 42%

    I think that total figures for 2009 have not yet been compiled, but the absolute amount for 2009 was substantially more than in 2008. This is in a nation that is occasionally portrayed as one of the most societally intert in response to the AGW challenge. Figures like this for the US and EU are somewhat misleading because we have exported so much manufacturing capacity to China, which has increased its fossil-fuel burning capacity greatly. But now even China is expanding its non-fossil fuel energy supply faster than its fossil fuel energy supply (albeit from a small base), and building some of the largest CC&S plants in the world. China even has massive reforestation projects underway (can my favorites — the salt-tolerant mangroves — be far behind?) What is being called BAU is in fact a tremendous shift in investment toward renewables, mostly prompted by the limited supply of fossil fuels.

    This does not affect the science of AGW, but it ought to inform the prognostications and policy recommendations.

  18. 118
    Doug Bostrom says:

    Mark S says: 4 March 2010 at 7:23 AM

    (work done raising sea level)

    Negligible as Gavin said, but still a cool question.

  19. 119
    ICE says:

    I don’t know. Isn’t all this essentially a matter of semantics ?
    To me the notion of “unavoidable warming in the pipeline” or “inertia” clearly refers to the constant-forcing commitment.
    If you further cut emissions to zero, then CO2 begins to be withdrawn from the atmosphere (BTW it would be interesting to see the corresponding atmospheric CO2 concentrations on their figure, for the UVIC, HadCM3 and Bern models), so I guess a negative radiative forcing is applied, right ? so it is like releasing the accelerator pedal but also hitting the brakes (so you’re not truly measuring ‘inertia’). I guess that you are talking about something else, then (maybe, the fact that the combined carbon cycle/climate system has no inertia in terms of T° with respects to CO2 emissions).

  20. 120
    Walt The Physicist says:

    True, relatively to the absorbed sun irradiance and radiative heat loss the work spent for potential energy change of ocian water is small; however, how smal is small. If one tries to compute temeprature change due to very small optical absorption in atmosphere with accuracy much better than 0.1 degree (let’s say 0.01 degree) than such “cool question”, as Doug Boston said in #118, becomes important. Your resistance to even consider it as a posibility reinforces my feeling that simulation accuracy of 0.01 degree in temperature predictions wasn’t actually achieved.

    [Response: I have no idea to what you are referring. Someone asked me a question about potential energy and I did the math and showed it to be a negligible effect.. How does that get translated into a refusal to consider the possibility. And who has ever claimed an accuracy of 0.01 degree C in temperature predictions? Please stay focussed. – gavin]

  21. 121
    Septic Matthew says:

    further on the issue of “societal inertia”, here are two tables documenting the recent reductions in the use of coal and natural gas in the production of electricity in the US:

    Obviously, some of this reduction is caused by the financial panic and recession, but combined with the increased deployment of wind and solar generation the reduction will probably be sustained, and increased. Recently, with the discovery and extraction of more natural gas, these tables include conversion of some coal-fired plants to gas-fired. Decreasing the consumption of coal is costly, but not catastrophically so, if not done too rapidly.

    We don’t know the future, but I’d bet on a 75% reduction in coal use in the US in 2 decades before I’d bet on the devastation of US agriculture in 2 decades, just with programs already in place. Unless, of course, CC&S proves out. Capturing CO2 to grow algae looks like a good bet, but I don’t know how good.

  22. 122
    Walt The Physicist says:

    I’d like to ascertain your idea of requred accuracy of numerical model prediction of temperature increase due to CO2 concentration increase. If the temeprature raise measured is in the order of few tens of a degree, isn`t it reasonable to expect accuracy of 0.01 degree from modeling?

    [Response: What you expect has nothing to do without what is possible. But I have no idea what you are talking about – accuracy in what metric over what time based on what assumptions? Where did you see such a claim in the first place? – gavin]

  23. 123
    Len Ornstein says:


    With respect to your response to 71 (and 49?), I just don’t see how your answer is a response to my questions ;-)

    In Hansen et al (2005) you state:

    “The lag in the climate response to a forcing is a sensitive function of equilibrium climate
    sensitivity, varying approximately as the square of the sensitivity (1), AND IT DEPENDS ON THE RATE OF HEAT EXCHANGE BETWEEN THE OCEAN’S SURFACE MIXED LAYER AND THE DEEPER OCEAN (2–4).
    The lag could be as short as a decade, if climate sensitivity is as small as 0.25ºC per
    W/m2 of forcing, but it is a century or longer if climate sensitivity is 1ºC perW/m2 or larger
    (1, 3). Evidence from Earth’s history (3–6) and climate models (7) suggests that climate
    sensitivity is 0.75º ± 0.25ºC perW/m2, implying that 25 to 50 years are needed for Earth’s
    surface temperature to reach 60% of its equilibrium response (1).”

    So why isn’t THAT lag the same as the “inertia in the climate system” to which M & W are referring?

    Doesn’t M & W’s blue and grey lines in their figure ‘deny’ this lag/inertia?

    Isn’t their:

    “We argue that the notion of unavoidable warming owing to inertia in the climate system is based on an incorrect interpretation of climate science.”

    saying that the Hansen et al (2005) “additional global warming of 0.85×0.67 ~0.6ºC is ‘in the pipeline’ ” is “an incorrect interpretation”?

    [Response: No. But the translation of a radiative imbalance into a temperature rise implies the continuation of the that drivers of that imbalance. Thus it is equivalent to the constant-concentration commitment. – gavin]

  24. 124
    David B. Benson says:

    Lab Lemming (86) — There is certainly hysteresis in the climate system so return to the exact regional conditions of, say, the first quarter of the 20th century is not possible. On the other hand, there is always the necessity of continual adapation to the pink noise of climate.

  25. 125
    Doug Bostrom says:

    Walt The Physicist says: 4 March 2010 at 3:12 PM

    “I’d like to ascertain your idea of required accuracy of numerical model prediction of temperature increase due to CO2 concentration increase. ”

    Whats your notion of that, Walt? I may be wrong but I smell a rhetorical question. If I’m not wrong, why not say what’s on your mind?

  26. 126
    Jeffrey Davis says:

    The more I think about the issue and the discussion, the more I don’t understand the article or its implications at all.

    My primitive understanding of climate inertia is that it needs to be fairly sizable for the issue of AGW to matter at all. Otherwise, every night when the sun goes down the threat from AGW would go away.

  27. 127
    Len Ornstein says:


    With respect to your answer to 123, (and some further remarks about M & W – since I’ve now read the letter):

    In Hansen et al (2005) you state

    “Our climate model, driven mainly by increasing human-made greenhouse
    gases and aerosols, among other forcings, calculates that Earth is now absorbing
    0.85 ± 0.15 watts per square meter more energy from the Sun than it
    is emitting to space. This imbalance is confirmed by precise measurements of
    increasing ocean heat content over the past 10 years. Implications include (i) the
    expectation of additional global warming of about 0.6ºC without further change
    of atmospheric composition”.

    How can “without further change of atmospheric composition” mean anything other than essentially complete cessation of the burning of fossil fuels together with the end of deforestation?

    [Response: No. It means that atmospheric composition stays the same. Same CO2 concentration, same aerosol concentration, same ozone concentration. – gavin]

    So the 0.6ºC is a “temperature rise” WITHOUT “the continuation of the drivers of that imbalance”!

    This would be a ‘sort of’ “constant-concentration commitment” (leading SLOWLY to the probable ensuing oceanic and biospheric drawdown towards pre-industrial atmospheric ~280 ppm).

    M & W state:

    “Stable atmospheric concentrations of greenhouse gases would lead to continued warming, but if carbon
    dioxide emissions could be eliminated entirely, temperatures would quickly stabilize or even decrease
    over time.”

    So by “Stable atmospheric concentrations of greenhouse gases” they mean holding the level constant by continuing to burn enough fossil fuel to stay near (for example) 390 ppm. By “if carbon dioxide emissions could be eliminated entirely” they PROBABLY mean my “essentially complete cessation of the burning of fossil fuels together with the end of deforestation”.

    Therefore, if Hansen et al (2005) is essentially ‘correct’, M & W are wrong on about “quickly stabilize” – so long as “quickly means more rapidly than ~80 years – as is certainly implied by there 2 lower plots!

    You really need to restate your interpretation of their letter to make clear what you mean visa vis Hansen et al (2005) and what you’ve said above that could easily be interpreted as a reversal of your 2005 position ;-)

  28. 128
    Walt The Physicist says:

    As I understood from your appearance on CNN, you know from computer simulations that the CO2 emission that started in 1800s with some estimated variable in time rate causes the observed increase of average temperature during past 200 years. This observed increase of temperature is several tenths of a degree C. Then, simulation accuracy higher than 0.1C is required to model such increase. Is such accuracy achievable and do you guys know all the heat sources and sinks with sufficient accuracy?

    [Response: For the long term global trends, the signal clearly comes out of the noise. – gavin]

  29. 129

    re. 126Jeffrey Davis says:

    “”””The more I think about the issue and the discussion, the more I don’t understand the article or its implications at all.

    My primitive understanding of climate inertia is that it needs to be fairly sizable for the issue of AGW to matter at all. Otherwise, every night when the sun goes down the threat from AGW would go away.”””

    Think of one watt per square meter extra energy not being allowed to escape back to space from the Sun. That is a lot of energy. It can warm up the land reasonably quickly…but the oceans are so huge that it takes about 30-50 years to warm them up. This slows up global warming for 30-50 years, but once the oceans have warmed up to a point (caught up), the extra 1 W/M2 can now show itself and warm up the land surface and create climate changes.

    IPCC- 2007, 2001, 1995, 1990.

  30. 130
    David B. Benson says:

    Walt The Physicist (122 & 128) — I have posted a simple conceptual model of climate which explains the instrumental record surprisingly well. You’ll find it in a recent comment of the Whatevergate thread.

  31. 131
    Hank Roberts says:

    Just to elaborate for anyone who doesn’t recognize the chart that Gavin points in 128 to Fig. 9-3 (IPCC AR4 WG1, Summary for Policymakers)

    It’s a two-part picture. The black line in both is the observed temperature change.

    The upper chart shows how models do match temperature when the models run include the forcings caused by human activity.

    The lower chart shows how models run without including human-caused CO2 etc. don’t match the temperature)

    If you need the caption and full discussion see the chapter:

    (I’m sure I posted a html link to the same information a few weeks ago when that same figure was posted — but darned if I can find it now).

  32. 132

    Anonymous Coward #111. Curious that you interpreted my comment as “anti-freedom”. I was merely commenting on the state of the world, and the demise of idealism.

    But your logic is interesting. Nature is a private enterprise as far as I know (if it’s not, pick another journal to correct the argument: there are many that are run for profit). By your logic, a privately-owned journal when selling subscriptions to a publicly funded institution must also be selling such a subscription to the general public. Take this a step further. If NASA or your publicly funded alma mater buys a car, does this mean every member of the public is entitled to drive that car?

    Don’t get me wrong. I would much prefer that all information was free and accessible. I just find it very odd that this argument is coming from a direction that is usually blindly pro-business.

  33. 133
    David Horton says:

    Gavin – I think, given the comments on this thread, which reflect my own confusion, that you need to have another go at summarising the implications of this research. If this is overturning the concept of “temperature rise already in the system” then it needs much more explanation. If it is saying that instantly turning off the CO2 tap leaves global temperatures constant, then it also needs explanation. If it is saying that turning the tap off gives an immediate rapid decline in temperatures, even more explanation is needed. Or am I being particularly stupid today?

    [Response: The point Matthews and Weaver are making is partly a matter of semantics, but I think it’s an improved way of thinking about warming commitment. There is absolutely nothing incorrect about the old notion of warming that remains “in the pipeline” if you hold the atmospheric CO2 concentration fixed. What Matthews and Weaver are pointing out is that using fixed CO2 concentration as your standard is kind of ridiculous. To maintain the concentration fixed, you would need to have continuing emissions, in small but ever decreasing amounts. If you could reduce the emissions that much and calibrate them so closely, why not just reduce them to zero? If you do reduce them to zero, then CO2 goes down very slowly, and that’s enough to cancel out the warming that was “in the pipeline” leading to a flat temperature (or perhaps a declining temperature, depending on how rapidly the carbon cycle model makes things go down. So, properly viewed, the “commitment” to future warming in the old way of thinking is just a commitment because you’ve made a commitment to continue emitting. It’s your choice, not wired into the climate system. Now, the sad fact of the matter is that even if emissions go all the way down to 1 Gt carbon per year, that still isn’t enough to keep CO2 from growing; it does slow things down considerably, but that last gigatonne still gives you a gradually rising (rather than stabilized) CO2 concentration. This is probably the most realistic optimistic scenario that is likely to occur, unless air capture methods come along that can take care of that last gigatonne. So, I agree with Gavin that Matthews and Weaver are right, but the point is probably moot. –raypierre]

  34. 134
    Hank Roberts says:

    For the chart Gavin links to above as
    the signal clearly comes out of the noise
    –> the final figures and captions are also available separately in this PowerPoint:

    IPCC Working Group I Technical Summary FINAL FIGURES
    To view the caption, select “Notes Page” from the “View” Menu….

    For Walt, below is a brief excerpt from the full caption; you can look it up
    (I admit it’s hard to find!)

    “Figure 9.5. Comparison between global mean surface temperature anomalies (°C) from observations (black) and AOGCM simulations forced with (a) both anthropogenic and natural forcings and (b) natural forcings only. …

    … in (a) as obtained from 58 simulations produced by 14 models with both anthropogenic and natural forcings. The multi-model ensemble mean is shown as a thick red curve and individual simulations are shown as thin yellow curves. Vertical grey lines indicate the timing of major volcanic events….

    … The simulated global mean temperature anomalies in (b) are from 19 simulations produced by five models with natural forcings only….

    Further details of the models included and the methodology for producing this figure are given in the Supplementary Material, Appendix 9.C. After Stott et al. (2006b).”

  35. 135

    What would help to reduce a lot of the confusion would be if the graph included lines indicating the projected CO_2 level, not just the projected temperature.

    If we could literally turn off the taps today (including stopping land clearing etc.) the CO_2 level would drop reasonably fast by about 50% of recent emissions that had not yet had time to be absorbed by natural processes. However the increase that’s there from the longer term has already had the opportunity to be absorbed and hasn’t, and so will be there longer-term.

    Also, it’s not clear to me that the various carbon cycle models that quantify the fast, medium and slow absorption processes will still work the same way if the increase stops. Increased ocean solubility of CO_2 with increasing atmospheric partial pressure for example would stop fairly quickly if you stop adding CO_2 to the atmosphere (much of the 50% “fast” absorption), and we would switch over to the competing effect of warming oceans having lower CO_2 solubility (Henry’s law) being the major effect on the oceans.

    On the other hand, temperature change for constant CO_2 takes time to bed down because of slow feedbacks. The confusion here looks to me to be over the extent to which these two effects (slow down of absorption, longer-term feedbacks) interact.

  36. 136

    Philip (#132),
    Idealism isn’t dead. One of the places where it lives today is in the software you’re using right now. You may be surprised but idealism has become a big business. Red Hat’s market cap is quite practical at over 5 billion dollars for instance but its main product is free software. You can basically download it, use it, modify it and resell it as your own without owing them a penny.

    As a practical matter, people don’t need subscriptions to share the contents of Nature. So I would hope that Nature will wake up to the 21st century and make its content freely available to the public. It’s in their interest not to wait too long.

    The ennemies of the free exchange of ideas have long stretched analogies between information and physical objects beyond any usefulness. I’m not interested in going over this argument again, least of all here.

  37. 137
    calyptorhynchus says:

    Bob #56 I think this is a realistic time-frame. At the same time the phrase “We’re utterly r@@ted” keeps on drifting through my mind when I think about that scenario.

  38. 138
    Brian Dodge says:

    “What would help to reduce a lot of the confusion would be if the graph included lines indicating the projected CO_2 level, not just the projected temperature.”
    The Solomon et al PNAS paper assumed different scenario – growth of emissions @2% to various levels, then immediate transition to zero emmissions, but it is a similar set of curves – decreasing CO2 & temperatures with multiple time constant long tails. see
    “Eyeball extrapolation” to a peak of 400ppm followed by zero emissions would lead one to the conclusion that temperature would stay above preindustrial for at least the next thousand years, although there would be a short term decline; CO2 shows a larger drop, but still remains above preindustrial levels for millenia.

  39. 139
    Russell says:

    Gavin, why is there never any mention of what I consider to be the most realistic scenario where pretty much immediately after mankind goes CO2 neutral, it goes CO2 negative, and possibly aggressively so?

    Given that to become CO2 neutral there will have been massive exponential increases in non-fossil fuel energy (as is already happening with wind as has been pointed out earlier) it seems completely realistic to expect this not to just stop the exact instant there is enough energy to supply our needs, but to continue and produce energy that exceeds our needs. The extra energy could obviously then be used to suck the CO2 out of the air. There are already prototype machines that do this, of course in 50 years time they will be much better, and probably used to get CO2 as feedstock to make liquid fuels also.

    Is this not talked about because it is considered “moral hazard”?

    Honesty isn’t the most likely scenario the one where we “red line” the CO2 level, then try to fix it up, rather than just let CO2 stabilize, and do nothing about the fact that it will cause sea level rises large enough to flood many cities etc in the following hundred years.

  40. 140
    Tim Jones says:

    I’m not convinced that warming could stop as major emissions
    cease. Climate inertia is one aspect, but there are others to

    Assuming emissions means primarily emissions from coal
    fired power plants and transportation, wouldn’t the sudden
    loss of the reflective contribution of atmospheric aerosols
    allow slowly dissipating concentrations of ghgs to trap more
    IR radiation? As long as even the slight warming we have
    persists there will also be natural emissions we can’t stop.

    I’d suggest a graph that included warming as CO2 emissions
    stopped but taking into consideration that aerosols also
    stopped combined with potential natural outgassing of ghgs
    from permafrost and subsea formations. Do we have any
    idea of what that is?

    For insight see:

    “Methane Releases from Arctic Shelf May Be Much Larger
    and Faster Than Anticipated”
    Mar. 5, 2010
    “A section of the Arctic Ocean seafloor that holds vast stores
    of frozen methane is showing signs of instability and
    widespread venting of the powerful greenhouse gas, according
    to the findings of an international research team led by
    University of Alaska Fairbanks scientists Natalia Shakhova
    and Igor Semiletov.

    The research results, published in the March 5 edition of the
    journal Science, show that the permafrost under the East
    Siberian Arctic Shelf, long thought to be an impermeable
    barrier sealing in methane, is perforated and is leaking
    large amounts of methane into the atmosphere. Release
    of even a fraction of the methane stored in the shelf
    could trigger abrupt climate warming.

    “The amount of methane currently coming out of the East Siberian Arctic Shelf is comparable to the amount coming out of the entire world’s oceans,” said Shakhova, a researcher at UAF’s International Arctic Research Center. “Subsea permafrost is losing its ability to be an impermeable cap.”


  41. 141
    Gilles says:

    Using my (“Ary” ‘s one indeed :) ) simple linear approximation, the evolution of temperature would be given by

    dT/dt = – (T-To-A.F(t))/tr

    where A is the sensitivity to the forcing F(t) and To the preindustrial temperature

    The old “commitment” corresponds to a constant concentration, so a constant forcing Fc after some time, giving a simple exponential terminal rise towards the equilibrium temperature To+A.Fc

    The new “commitment” corresponds to the complete cut off of any emission, giving a gradual decrease of F(t). The general solution of the equation for any F(t) is reads:

    T = To + A.\int^t_to F(t) exp[(t-t’)/tr]dt’ (sorry for the latex style, int means integral)

    so you can play with any forcing you want. However, my equation can not describe a constant solution since it would mean that dT /dt = 0 so A.F(t) = T-To, which is contradictory if T is constant and F(t) varies. A constant temperature is ONLY possible for the exact solution T=Teq with a constant forcing, which is NEVER reached (mathematically) if there has been any variation in the past (which is obvious in the general exact solution above). This is NOT a feature of carbon cycle absorption model but a feature of the linear relaxation model of the temperature, what ever the forcing is and so whatever the carbon cycle used. So i understand the “Bern model” curve, describing a decreasing F(t) and and a decreasing temperature , but I’m surprised by the “constant temperature ” curve which is possible only if the linear relaxation towards equilibrium temperature is plainly wrong. But why is it wrong ?

  42. 142
    anony says:

    So this chart says if we are able to cut emissions by 2/3rds the CO2 concentration will remain constant at ~400 ppm and global average temperatures will rise to an asymptote of 1.3 degC above 1800, only 0.3 degC higher than today.

    The chart suggests that 66% cuts will really stop GW for all practical purposes.

    Is the intent to this defuse the argument that we are already too late to stop catatrophic global warming? What about

  43. 143
    Geoff Wexler says:

    Future International Court Fantasy.

    Class action of victims of global warming vs UK government and Nigel Lawson’s Instititute.

    Nigel Lawson’s Institute.
    Yes we admit that we closed down the UEA , and the IPCC and blocked all action to reduce CO2 emissions after the year 2011, but that does not mean that we were responsible for such a high proportion of the damage. You should be looking at the UK government’s responsibility. How about the National Coal Board and the state controlled British Petroleum? and what about the actions of the owners of the coal mines before 1945?

    UK government.
    No ; these industries were recently privatised so it is the Lawson Institute which is more to blame ; we refer the jury to Mathews and Weaver. You are using the wrong definition of committed warming. If we had not followed the Lawson Institute’s advice we might have been able to reduce CO2 emissions to zero in 2011 and follow the horizontal line in the MW graph. The Lawson Institute should pay a higher proportion of the total damages.

  44. 144

    Tim Curtin (95),

    None whatsoever. My time series analysis of cereal production against CO2, fertilizer consumption, and dT for 1961-2002 indicate that the correlation with CO2 is spurious and that fertilizer consumption has been the only relevant factor.

  45. 145

    Rod B (116),

    No. If you want to net out ALL the cooling with ALL the warming, you get rough stability. But there is no reason to “net out” just the radiative cooling.

    Sunlight and atmospheric back-radiation HEAT the Earth.
    Longwave radiation, latent heat, and sensible heat COOL the Earth.
    Most of the cooling is radiative. Period.

  46. 146
    Mike Ern says:

    Any comments on the new Science study? Is any of this new information on methane release incorporated into the current models? I’m unsettled.

  47. 147
    Ron Taylor says:

    Raypierre, thanks for your clear explanation, but like some others here, I still do not understand why positive feedbacks like methane release, continued loss of sea ice albedo, and ocean saturation would not contribute additional warming for at least decades, independently of the direct CO2 effect. Perhaps that energy is taken up in the continuing warming of the ocean?

  48. 148
    Ron Taylor says:

    According to quotes from the lead scientist on the Science Magazine report, atmospheric methane levels in the Arctic are about 1.85 ppm, which is roughly three times the worldwide level.

    [Response: That’s not right. There is a north-south gradient, but it is small – mean CH4 levels globally are around 1800 ppb (=1.8 ppm). – gavin]

    I calculate that as roughly an additional 30ppm CO2 equivalent over the Arctic. That would seem to make a significant difference in the greenhouse effect there, and not good news, since there is reason to expect that the difference will continue to increase. It is a local positive feedback with global consequences.

  49. 149
    Ron Taylor says:

    Oops! Thanks Gavin, lesson learned. Check quotes like this, even if they come from a good scientist. I had your number right at my fingertips, but did not check.

  50. 150
    John E. Pearson says:

    123 Len Ornstein wrote:

    “So why isn’t THAT lag the same as the “inertia in the climate system” to which M & W are referring?”

    Len, here’s a naive calculation that I went through recently. Assume that a change in forcing results in a change in the equilibrium temperature. As a base line you can assume that a 1W/m^2 change in forcing results in a change of 1K. Ask yourself how long that will take if the forcing first heats the atmosphere plus the top couple meters of ocean, then next the top 200 meters of ocean, then next the rest of the ocean. In other words, ignore transport issues which can only slow things down in any event. The answers are: yearish for the atmosphere, 3 decades for the top 200 meters of ocean, and 500 years for the rest of the ocean. I haven’t read Hansen 2005 but elementary physics says there is no possible way for there to be no lag at all. The reason that the paper that started this thread says “there is no warming in the pipeline” is because they are considering a substantially different forcing scenario than the one that results from constant CO2.