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Climate Change Commitment II

Filed under: — gavin @ 2 June 2010 - (Español)

A couple of months ago, we discussed a short paper by Matthews and Weaver on the ‘climate change commitment’ – how much change are we going to see purely because of previous emissions. In my write up, I contrasted the results in M&W (assuming zero CO2 emissions from now on) with a constant concentration scenario (roughly equivalent to an immediate cut of 70% in CO2 emissions), however, as a few people pointed out in the comments, this exclusive focus on CO2 is a little artificial.

I have elsewhere been a big advocate of paying attention to the multi-faceted nature of the anthropogenic emissions (including aerosols and radiatively and chemically active short-lived species), both because that gives a more useful assessment of what it is that we are doing that drives climate change, and also because it is vital information for judging the effectiveness of any proposed policy for a suite of public issues (climate, air pollution, public health etc.). Thus, I shouldn’t have neglected to include these other factors in discussions of the climate change commitment.

Luckily, some estimates do exist in the literature of what happens if we ceased all human emissions of climatically important factors. One such estimate is from Hare and Meinshausen (2006), whose results are illustrated here:

The curve (1) is the result for zero emissions of all of the anthropogenic inputs (in this case, CO2, CH4, N2O, CFCs, SO2, CO, VOCs and NOx). The conclusion is that, in the absence of any human emissions, the expectation would be for quite a sharp warming with elevated temperatures lasting almost until 2050. The reason is that the reflective aerosols (sulphates) decrease in abundance very quickly and so their cooling effect is removed faster than the warming impact of the well-mixed GHGs disappears.

This calculation is done with a somewhat simplified model, and so it might be a little different with a more state-of-the-art ESM (for instance, including more aerosol species like black carbon and a more complete interaction between the chemistry and aerosol species), but the basic result is likely to be robust.

Obviously, this is not a realistic scenario for anything that could really happen, but it does illustrate a couple of points that are relevant for policy. Firstly, the full emissions profile of any particular activity or sector needs to be considered – exclusively focusing on CO2 might give a misleading picture of the climate impact. Secondly, timescales are important. The shorter the time horizon, the larger the impact of short-lived species (aerosols, ozone, etc.). However, the short-lived species provide both warming and cooling effects and the balance between them will vary depending on the activity. Good initial targets for policy measures to reduce emissions might therefore be those where both the short and long-lived components increase warming.

727 Responses to “Climate Change Commitment II”

  1. 51
    Ray Ladbury says:

    Again, temperature and economic growth are negatively correlated. a 2 degree C rise in temperature results in GDP growth rate declining by 2.2 degrees per doubling. Moreover, the uneven distribution of temperature increase impacts rich industrial countries more, so the effect on global economic health is proportionately greater.

    Don’t confuse fetid with fertile. They aren’t the same thing.

  2. 52
    Geoff Wexler says:

    Re: #44

    This is balanced by some (weaker) negative feedbacks such as increased albedo due to more cloud cover due to greater humidity.

    I’m afraid that remark is over-simplified; also its conclusion is uncertain. As I see it…here is another version, also simplified, but a bit less:

    The sign of the feedback depends on altitude.High clouds tend to have positive feedback and low ones a negative feedback. The reason is that the former are dominated by their effect on the infra-red (greenhouse) whereas the latter are dominated by their effect on the visible radiation (albedo). The point is that the greenhouse effect arises from the reduction of temperature (and hence reduced infra-red radiation) of matter (gas, liquid or solid) at higher altitudes.

    This may all be buried in a computer simulation but no matter how it is done, two contributions of opposite sign tend to make the final output less accurate. For example the proportion of high clouds might vary between different models; thats a guess. Perhaps one of the modelers will correct me if I am wrong.

  3. 53
    Benjamin says:

    “Of course, it is possible that Lindzen is right and everyone else who has looked into the matter is just being stupid, or worse, lying for various nefarious reasons. But, seriously, how likely is that?”

    That’s typically anti-science reasoning.
    What Nature does is not linked to the number of people supporting a theory of what it should do.
    That’s Science 101.

    As Judith Curry recently said, uncertainties on various topics have been underestimated in IPCC AR4. A lot is still unknown or not well understood, climate science is a young science and a very complex one.

  4. 54
    Edward Greisch says:

    45 vote no to kyoto: If you don’t like winter, move south. Why did you move north and then want a southern climate? You knew you didn’t like winter in the first place. The warming we have already had is Negatively affecting agriculture Now. We are having both droughts and flooded out crops in different places in this country and around the world. Why do I have to reprint the following so often? [Please read the books listed below before commenting again.]

    Global Warming can make the human race EXTINCT. The #1 kill mechanism is famine. See “The Long Summer” by Brian Fagan and “Collapse” by Jared Diamond.
    6 degrees C is the for-sure extinction point for Homo Sapiens as reported in a bunch of reports and books.
    The book “Six Degrees” by Mark Lynas says: “If the global warming is 6 degrees centigrade, we humans go extinct.” See:
    Lynas lists several kill mechanisms, the most important being famine and methane fuel-air explosions. Other mechanisms include fire storms.

    The following sources say H2S bubbling out of hot oceans is the final blow at 6 degrees C warming:
    “Under a Green Sky” by Peter D. Ward, Ph.D., 2007. is a NASA web zine. See:

    “Climate Code Red” by David Spratt and Philip Sutton says the following:
    Long term warming, counting feedbacks, is at least twice the short term warming. 560 ppm CO2 gets us 6 degrees C or 10.8 degrees F. We will hit 560 ppm before mid century.

    Per “Climate Code Red”, we need ZERO “Kyoto gas” emissions RIGHT NOW and we also need geo-engineering because we have already gone way beyond the safe CO2 level of 300 to 325 ppm. We are already at 455 ppm equivalent and we have tripped some very big tipping points. We aren’t dead yet, but the planet needs critical intensive care if we humans are to have a chance of survival.

    “Storms of My Grandchildren” by James Hansen, chief of NASA-GISS paints the bleakest picture: Earth goes Venus, becoming a completely dead hot rock at 800 degrees and our Mars colonies cannot survive because Mars is a dead planet.

    “The Vanishing Face of Gaia” by James Lovelock has identified a 9 degree lurch in the temperature that happens at 450 ppm equivalent.
    Looks like we are not going to make it. We HUMANS could be EXTINCT by 2050 because politicians are not considering sufficiently strong action.

  5. 55
    Jim Eager says:

    voteno writes @45: I know there will be some losers but there will be more winners than losers.

    And you “know” this how? Or, are you just posing as being clairvoyant?

    Do you also “know” that a 2C increase will not disrupt the timing or distribution of the south Asian monsoon?

    Do you know that in some parts of south Asia overnight temperatures are already at the upper limit for rice germination and that yields are already beginning to slip?

    Do you know how much rice is produced in the Ganges, Irrawaddy and Mekong deltas, all of which will be threatened by sea level rise that will result from an increase of 2C?

    Perhaps you don’t eat much rice, but do you know what portion of the human population depends on rice for the bulk of it’s calories?

    Or perhaps you do know and you’re not worried since most of that population lives in Asia and Africa and you’re not too troubled by consigning them to the “loser” column.

    The fact of the matter is we do not know exactly what the consequences of a 2C rise in global mean temperature will be since human civilization has never experienced it before, but we do know what has happened when regional temperatures have increased by similar levels and precipitation patterns have shifted. Think collapse of the Akkadian Empire 4000 years ago, or the Mayan collapse 1200-1100 years ago, which coincided with the start of the Medieval warm period that allowed European civilization to bloom.

    Yes, there will be winners and losers. That someone would take comfort in that is repugnant.

  6. 56
    J. Bob says:

    #52, Geoff, you might want to look at the effects of particulates, as they also have an effect.

  7. 57
    Gilles says:

    RL#51 : “Again, temperature and economic growth are negatively correlated.”
    That’s very weird, since they both increased throughout the XXth century. That’s a very strange mathematical curiosity : two growing quantities that are negatively correlated ?

    ” a 2 degree C rise in temperature results in GDP growth rate declining by 2.2 degrees per doubling. ”
    uuuh? what is a GDP growth rate declining by 2.2 degrees (of what) per doubling (of what ?)

  8. 58
    Frank Giger says:

    “The following sources say H2S bubbling out of hot oceans is the final blow at 6 degrees C warming”

    No, they don’t. Not a single one of them say “at 6 degrees warming the oceans will produce a massive outpouring of H2S and kill us all.”

    Indeed, every single one of them speaks of the possibility and uncertainty of the hypothesis that it caused the Permian extinction event.

    How the hell did you extrapolate such a claim from your sources?

  9. 59
    Completely Fed Up says:

    “How do you know that there will be more winners than losers. Also, how do you know that the net gain to the winners will offset the loss to the losers.”

    Or, in other words, “A rising tide sinks all ships”.


    Well, it’s true if you subsitute “coastal cities” (which is most of the big ones) for “ships”.

    I wonder how Vote is going to handle that…

  10. 60
    SecularAnimist says:

    Benjamin wrote: “A lot is still unknown or not well understood …”

    Your comments give no indication that you know or understand what is and what is not known and understood by climate scientists.

    In fact, what IS known and IS well understood is far more than sufficient to justify urgent action to phase out all fossil fuel use as rapidly as possible. Which is why every major scientific organization in the world that has anything to do with climate science has officially called for such urgent action.

    Benjamin wrote: “… climate science is a young science …”

    That is a false statement. Climate science is not a “young” science. And the basic mechanisms underlying anthropogenic global warming have been well understood for over a century.

  11. 61
    Ray Ladbury says:

    Benjamin, While you are correct that scientific truth is not determined by a vote, that is a straw man. What matters is what the evidence will support, and Lindzen’s position is utterly devoid of evidence.

    Unfortunately, Dr. Curry’s credibility has taken 3 direct hits midship. It’s pretty clear from her blog on the Heartland Conference that she doesn’t know what she is talking about.

    As to underestimates of uncertainty–actually most of the errors in the IPCC represent under-estimates of the threat rather than exaggerations (e.g. ice melt and sea-levelrise).

    Climate science young? Please. We’ve known CO2 was a greenhouse gas for ~160 years. Anthropogenic warming was predicted in 1894–106 years ago. And the science has been pretty mature for 30-40 years. You sound like a man who could benefit from the tutelage of the good Dr. Weart:

  12. 62
    Ray Ladbury says:

    Gilles, the relationship is roughly 1.1% decrease in GDP per degree of warming.

  13. 63

    52 (Geoff Wexler),

    I’m afraid that remark is over-simplified; also its conclusion is uncertain.

    Unquestionably, yes. I was trying not to get carried away with the whole explanation, but simply wanted to give a nod to the fact that there are negative as well as positive feedbacks, and it is the sum of all (interacting) effects that lead to an understanding of the mechanisms behind climate sensitivity.

    But yes, clouds are complicated, and may provide both positive and negative feedbacks. Perhaps I should have said “Increased albedo from a potential increase in certain clouds is an example of a negative feedback.”

  14. 64
    Hank Roberts says:

    Well, yeah. When you hear marine biologists talking about invertebrate mortality, don’t think it’s unrelated to what we’re doing.

    From one of those links:

    “… the study finds that organisms in the deep ocean started dying first, followed by those on ocean shelves and reefs, and finally those living near shore.

    “Something has to be coming from the deep ocean,” [USC doctoral student Catherine] Powers said. “Something has to be coming up the water column and killing these organisms.”

    That something probably was hydrogen sulfide, according to Powers, who cited studies from the University of Washington, Pennsylvania State University, the University of Arizona and the Bottjer laboratory at USC.

    Those studies, combined with the new data from Powers and Bottjer, support a model that attributes the extinction to enormous volcanic eruptions that released carbon dioxide and methane, triggering rapid global warming.

    The warmer ocean water would have lost some of its ability to retain oxygen, allowing water rich in hydrogen sulfide to well up from the deep (the gas comes from anaerobic bacteria at the bottom of the ocean).

    If large amounts of hydrogen sulfide escaped into the atmosphere, the gas would have killed most forms of life ….”

    I doubt any of this makes it into the climate models yet, although the change in dissolved oxygen, like the change in dissolved CO2, is chemistry.

  15. 65
    Hank Roberts says:

    Frank, look beyond Ed Grielsch’s words.

    He’s given the citations, good ones worth reading (and applaud him for citing sources so people can look — that’s good behavior).

    If he quoted directly what the scientists say, it would be far scarier, because harder to dismiss as opinion.

  16. 66
    Benjamin says:

    “Your comments give no indication that you know or understand what is and what is not known and understood by climate scientists.”

    Judith Curry :
    “To keep this short, I will only itemize some topics where I think the confidence levels in the IPCC are too high and uncertainties have been inadequately characterized: much of what is in the IPCC WG2 report (impacts), the 20th century external climate forcings, the historical surface temperature record prior to 1960, attribution of the 20th century climate variations (including the role of the multidecadal ocean oscillations), the impacts of land use change, sea level rise, paleoclimate reconstructions, uncertainties of climate models and lack of metrics for evaluating climate model performance.”

    [Response: Such statements are one person’s opinion, without the support of backing evidence. You will find many who disagree with it, based on evidence.–Jim]

  17. 67
    Daniel Goodwin says:

    #53, Benjamin:

    As Judith Curry recently said, uncertainties on various topics have been underestimated in IPCC AR4.

    If Curry is right, there still exists a more significant problem with the error-bars in IPCC reports. Using standard statistical techniques, uncertainties are quantified as equally likely on the high and low sides. This has proven ill-advised time and time again. As we watch further data emerge, the uncertainties consistently break out on the high side of consensus scientific estimates.
    Additionally, what we know about the physical situation gives much more confidence to the pessimistic edge of the error-bar. Numerous uncertainties (such as the behavior of marine clathrates) can only make matters worse, not better.

  18. 68

    Re #57:

    “uuuh? what is a GDP growth rate declining by 2.2 degrees (of what) per doubling (of what ?)”

    Come on, Gilles, you know perfectly well what was meant. You’re not a fool, and your English is pretty good.

    Degrees C (global mean anomaly), and doubling of CO2e. (That’s a pretty safe presumption, and I didn’t even read the original post.)

    Re #53 et seq:

    As for the “young science” of climatology, here’s the state of play in 1938:

    (A supplement to Weart for folks interested as much in the people who did the science as the science itself.)

    On another note, we currently have record or near-record tropospheric temps as measured by AMSU, and the lowest sea-ice extent ever recorded for this date (per IJIS.) Can we at least agree that there is a present dearth of evidence that “warming has stopped,” or “sea-ice recovered?”

    (Yeah, I know we’re coming out of an El Nino, but that was true back in 1998, too. “Apples to apples!”)

  19. 69

    OT, but worth noting:

    Of course, this has predictably drawn much negative comment from conservative/libertarian quarters. (Can you “ad-hom” an organization? If so, they did.)

    The salient points about diet/ag and consumerism have been made here repeatedly, to be sure.

  20. 70

    Arctic sea ice, almost normal in April, rapidly melting (red line in graph). Now lowest extent ever this time of year:

  21. 71
    Rod B says:

    Ray, your climate vs GDP alignment sounds a little like using your thumb and forefinger to visually the cut on the tree 200 yards away, then making the cut with a laser beam. Exactness does not equal accuracy. Exactness in economic predictions doesn’t equal much of anything.

  22. 72
    Foobear says:

    If the problem is with aerosols vanishing too quickly, perhaps we should look at ways of putting more aerosols into the atmosphere to counter the heat inertia we have built up.

    Oh, wait, that’s called geoengineering and “real” climate change people don’t believe in it. :p

  23. 73
    Ray Ladbury says:

    Rod B, all I have done is call attention to a well known and irrefutable inverse correlation between higher temperature and wealth and economic growth. This is hardly controversial, and it holds quite broadly. I will leave it for the economists to posit why–and many have. I would also note that tropical agriculture yields fewer calories per hectare than agriculture in temperate climates.

    My point is that the data do not support the rosy scenarios posited by denialists in a warmer world. If anything, the trend is in the opposite direction–a worrying possibility with the population growing to 9-10 billion by mid-century.

  24. 74
    Doug Bostrom says:

    Foobear says: 3 June 2010 at 4:56 PM

    Oh, wait, that’s called geoengineering and “real” climate change people don’t believe in it. :p

    How very vapid. Foobear, do you -know- your remark is laughable in a way you don’t intend?

    Imagine how silly you’d feel if you could see a film of yourself dialing a phone number at random and then mouthing off some infantile remark to the party answering. YouTube is full of snippets like that, filmed by giggling children who don’t realize where the real joke lies. Now why would you choose to humiliate yourself here, in the same way?

    Why not instead dream up or cite a means of geoengineering you believe has promise and ask the denizens here whether they think it worthwhile? Are you able to support a discussion of that kind?

  25. 75
    Hank Roberts says:

    > If the problem is with aerosols vanishing too quickly
    There are several CO2-related problems; that’s a symptom of one of them.
    Ocean pH change is the fastest problem; geoengineering that would be smart.

  26. 76
    Mark A. York says:

    Yeah, that underwater geoengineering is going well, eh?

  27. 77
    Gilles says:

    RL :#62 : the observed correlation is between temperature increase and increase of GDP rate of ppor countries
    “In poor countries, we estimate that a 1ºC temperature increase in a given year reduced economic growth in that year by about 1.1 percentage points. In rich countries, changes in temperature had no discernable effect on growth”

    I have a few comments :

    a) taking this seriously, it would mean that diminishing temperature would cause a strong growth in these countries. I doubt very much that this is realistic.
    b) this is obviously du to the fact that “poor” countries GDP are dominated by agriculture , in hot conditions, so probably “the agriculture of hot countries is sensitive to temperature ” . But the difference between poor and rich country is due and this is due to the large difference between their FF consumption – the correlation is much more prominent than that with temperature. So reducing FF consumption would first raise the number of poor countries, and thus increase the average sensitivity to temperature – at least in warm parts of the world.

  28. 78
    Gilles says:

    and last : if your goal is to optimize the RATE of GDP growth (= exponential growth), then it is the best way to insure the total exhaustion of all resources. The only sustainable growth rate is ZERO. Meaning that if your “law” is true, we NEED a temperature increase to make the growth rate vanish.

  29. 79
    Leonard Evens says:

    “If the problem is with aerosols vanishing too quickly, perhaps we should look at ways of putting more aerosols into the atmosphere to counter the heat inertia we have built up.”

    There are several problems with this. First, it would be major intervention in the climate system. One would certainly want a lot of confidence that it would work and that there wouldn’t be horrible unintended consequences. How would you obtain such confidence? Computer models?

    Secondly, if we didn’t limit greenhouse gas emissions, we would have to continually increase the amount of aerosols to compensate. If we ever stopped, the cooling effect of the aerosols would disappear in a few years, leaving very high load of greenhouse gas concentration with the consequent rapid warming.

    Thirdly, would we attempt to do this through international agreement? If no t, how would we deal with violent objections from other countries which felt they would lose out in the process? If we can’t today get agreement on limiting greenhouse gas emissions, it seems unlikely we could get agreement on the injection ofaerosols in the atmosphere.

    It is possible that at some point in the future, a desperate humanity might consider radical geoengineering solutions of this nature, but doesn’t it make sense to try to avoid such difficult choices by limiting greenhouse gas emissions starting today?

  30. 80
    Wayne says:

    Global warming has had and will have a destablizing effect on our weather patterns. Floods in one place, droughts in another. Extremely hot weather in summer seasons mirrored by extremely record cold temperatures edging into new areas. Our weather patterns could be best described by a gallon of milk, left at room temperature which eventually seperates into liquids and solids. Our global weather system seems pretty stable most of the time, however it’s fragility is constantly being measured by means of new record weather extremes.
    This will continue to increase in severity until we see possibly 30 to 40 below zero temperatures in populated areas, which we will have no power to anticipate. Also common will be high temperature extremes which will likely exceed 120 degrees in populated areas. this highlights the immense damage man has done to the earth.
    And yet no one corporation or entity can be blamed for the problem. It has a unique global fingerprint. Uncommon to other disasters. Billions of people operating gas powered machinery, planes, tractors, lawn equipment, trucks, cars, and the list goes on. Factories which belch out pollution into our atmosphere all to satisfy our insatiable desire to seperate ourselves from nature. The modern industrial age, which began in the early 20th century and even before.
    What can be done? get a lawn chair and a radio. That’s about it. I can’t say it will be a fun show. We will all be involved.

  31. 81
    Leonard Evens says:

    Benjamin takes me to task for saying

    “Of course, it is possible that Lindzen is right and everyone else who has looked into the matter is just being stupid, or worse, lying for various nefarious reasons. But, seriously, how likely is that?”

    And then he goes on to say

    “That’s typically anti-science reasoning.
    What Nature does is not linked to the number of people supporting a theory of what it should do.
    That’s Science 101.”

    He left out my previous statement that the evidence so far did not support Lindzen’s Iris Effect. Of course, nature is not interested in what human being think is going on. But, as human beings we have to make choices based on science.

    Let me look at an analogous situation. Peter Dusenberg has questioned the general consensus that Aids is cased by a virus. He has an alternate explanation. It is possible that the consensus is based on stupidy of a whole bunch of medical scientists or that they are engaged in a conspiracy for some nefarious purpose. But that doesn’t seem very likely. Hence, anyone who is unfortunate enough to contract Aids would be foolish to rely on Dusenberg’s being right and the rest of the community being wrong. Dio you disagree with that?

    the point is that we accept consensus science all the time. Doi8ng otherwise would be foolish. The fact that on occasiion, we may be wrong to do so is an unavoidable hazard of being human.

    How, for example, do the rest of us know that Wegener was right about continental drift and the rest of the geological community at the time was wrong? The answer is that it is now the consensus of the scientific community of geologists that such is the case. They base this on evidence that has been elucidated since Wegener’s time. Although nature doesn’t care what we think about it, there is no magic way to know what nature is doing except though human communication. If we decided things in all matters by trying to find some dissenter to the consensus and doing what he suggests, we would be in real trouble. I assume you are no different from the rest of us in ignoring those lone dissenters the great bulk of the time. So why do you find the dissenters so convincing in this particular matter?

  32. 82
    Edward Greisch says:

    79 Leonard Evens: Putting poison gas in the stratosphere is not the right kind of geo-engineering. If you must do geo-engineering, put something at the Earth-Sun L1 point to reflect sunlight. A harder problem: How would we terraform Venus?
    The only thing that makes sense is to quit burning coal now and outlaw oil shale and tar sands now and for ever.

  33. 83
    John Peter says:

    I scanned this thread for “oceans” for “memory” and for “balance” and got no meaningful hits. Please help me get straightened out.

    Hansen et al (Earth’s Energy Imbalance: Confirmation and Implications, Science 308 1431-1435 2005; you’re part of the et al) looked at some forcings, some feedbacks, and some heat storage and concluded that the energy had been out of balance for a decade or so. It seemed most likely that this excess energy has been stored in the ocean. Doesn’t this stored heat need to be included in addition to atmospheric GHG lifetimes when trying to assess what might happen should we cease AGW emissions? Or is it somehow included in M&W-like work in some other manner?

    For a couple of decades at least, surface temperature and radiation include oceans as well as land. With oceans providing about two thirds of the Earth’s surface and absorbing about half of the heat, I would expect to see more references to them in discussions and papers. For example, why do we say that GW occurs as predicted – just because, say, Nova Scotia is colder, there other regions that are warmer without mentioning oceans to a skeptic?

    Am I correct in assuming that “GW surface temperatures” (unqualified) should include both land and ocean surfaces?

    [Response: Yes. Global temperatures include both land and ocean. -gavin]

    Am I correct in assuming that “GW heat storage” (unqualified) should include land and ocean as well as atmosphere?

    [Response: Sure, but the heat conductivity over land is much smaller, and so the amount of heat being stored is overwelmingly in the ocean (80% or more). -gavin]

    BTW, I have been trying to understand some radiation balance/imbalance papers. I agree with you that the extra tracking measurements they need may not be forthcoming, but the calculations are useful to me because they can be done for some restrictive cases without requiring an ocean-atomosphere climate model. I agree that they might also be useful for addressing various regional mitigation proposals.

    I have looked at a lot of Trenberth, Schwartz and Liu. Any references to further energy imbalance work that seems promising to you would be appreciated. For example, I’m unable to find any follow-up to your Hansen et al 2005.

    [Response: the followup papers will start to come along with the new IPCC runs being done now. Patience. -gavin]

  34. 84
    Ray Ladbury says:

    Gilles says, “The only sustainable growth rate is ZERO.”

    This is simply, completely, 100% flat-assed WRONG! Sustainability has been achieved by several societies, and their society progresses. In a sustainable society, the growth rate is limited by the rate of technological advance rather than inceased exploitation. Dude, do you ever get tired of being so ignorant?

  35. 85
    Benjamin says:

    #62 Ray Ladbury + Kevin McKinney
    “Gilles, the relationship is roughly 1.1% decrease in GDP per degree of warming. ”

    Thanks for this rough estimate of how much GDP decreases per degree of warming.

    In SRES scenarios however, +6°C goes along well with a x24 GDP.
    Same kind of thing for all the other scenarios (x15 GDP on average)
    This information can be easily found on SRES website :

    If what you say is correct, then we agree that ALL SRES scenarios are wrong, right ?
    I mean you can’t have at the same time a GDP decrease with temperature, and a GDP increase with temperature.
    Do we agree on that ?

  36. 86

    Ben 53: climate science is a young science

    BPL: Look again.

    c. 300 BC Aristotle divides the world into torrid, temperate, and frigid zones.
    1610 Galileo invents the thermometer.
    1640 Torricelli invents the barometer. Shortly afterward, he shows air pressure declines with altitude.
    1740 Hadley works out the basic scheme of the general circulation of the atmosphere.
    1783 Ben Franklin suggests that aerosols from volcanic eruptions may temporarily cool the Earth.
    1824 Fourier discovers the greenhouse effect.
    1837 Agassiz demonstrates that there was at least one ice age which caused monster glaciers to cover much of Europe.
    1859 Tyndall determines that the major greenhouse gases in Earth’s atmosphere are water vapor and carbon dioxide, and elucidates exactly how the greenhouse effect works.
    1870 Croll suggests that astronomical cycles may infuence ice ages.
    1896 Arrhenius proposes the theory of anthropogenic global warming (AGW).

    So in short, climatology was a mature science years before special relativity or quantum mechanics were even proposed. Think those branches of science are poorly known?

  37. 87

    Gilles 57: That’s a very strange mathematical curiosity : two growing quantities that are negatively correlated ?

    BPL: Ever hear of “detrending?”

  38. 88
    Anonymous Coward says:

    Gavin penned a good post which ends on a hint of an argument for geoengineering. This evidently makes people uncomfortable. After some childish ad homs and other diversions, the ideological objections to geoengineering are coming out of the woodwork.

    So, Leonard (#79),
    -yes, models by all means but high confidence is not required if there’s no confidence inaction is safe to begin with
    -aerosols wouldn’t “vanish too quickly” without emission cuts in the first place
    -no international agreement has ever been required for emissions, whether the point is gross waste of natural resources or geoengineering
    -drastic GHGs emission cuts without geoengineering would be reckless, though admittedly less reckless than BAU

    Please come up with better arguments. You’ve got thirty years of inactivism to draw on. How about “more research is required” as a first line of defence? Then you can claim the people paid to research geoengineering are lying to the public in a conspiracy to obtain research grants…

    Would you rather preserve pollution that happens to have, among a number of nasty effects, a short-time cooling effect instead of having the cooling pollutants delivered in smaller amounts where they’re actually needed? And for what? Get rid of this ideological clutch!

  39. 89
    Sekerob says:

    BPL, what happened to Buys Ballot?

  40. 90
    Completely Fed Up says:

    And why must sustainability require growth?

    Back in the 70’s, the idea was that automation would free up so much laborious work that we’d only have to work 10 hours a week, and that there would be a problem in what to do with all our free time.

    That would have been a reduction rather than growth.

    But a very warranted outcome.

    After all, it’s not that money is worth anything. It’s only worth what you can do with it and if you’re dead, there’s not a lot you can do with it any more.

    People retire early if they can afford it.

    People work part time if they can afford it.

    People move to a rural life and “get out of the rat race” if they can afford it.

    All of these are reductions rather than growth.

    Hands up anyone who thinks they are bad goals?

  41. 91
    Bill says:

    Re #82: references please ?

  42. 92
    Richard Steckis says:

    Ray Ladbury says:
    3 June 2010 at 6:14 PM

    “I would also note that tropical agriculture yields fewer calories per hectare than agriculture in temperate climates. ”

    You are quite correct except for the wrong reasons. Tropical environments (including marine and terrestrial) are notoriously devoid of nutrients. Whilst there is a very high diversity of life, this is at the expense of productivity. This has more to do with ecology and climate interacting than just temperature (and probably more due to high rainfall leaching nutrients).

    You should note that the current “temperate zone” agriculture is in regions that can also experience high temperature levels (e.g. Western Australia).

  43. 93
    Richard Steckis says:

    In tropical oceans there is a lack of upwellings that bring nutrients close to the continental margins and the ocean surface.

  44. 94
    Ray Ladbury says:

    Steckis, the increased precipitation also leaches nutrients from soils. I’m quite familiar with laterite. I did not say that the cause of the lower yield was temperature based.

    However, there are some rice varieties that are quite temperature sensitive–not to mention winter wheat.

  45. 95
    Ray Ladbury says:

    Benjamin@84, Huh? What are you talking about? I’m not seeing anything in that reference that could even be misinterpreted as supporting your point.

  46. 96

    83 (Benjamin),

    Obviously, temperature change is not the only factor that affects GDP. Temperature can go up, with a negative impact on GDP, while population also goes up, along with other factors, exerting a strong influence on GDP that overwhelms the “temperature signal.” The SRES scenarios are in no way inconsistent with a detrimental economic impact of climate change. A 1C temperature increase reduces GDP by 1.1% of what it would have been without the temperature increase.

    Beyond that, the SRES scenarios clearly to not include the negative impacts of climate change in the GDP projections themselves. It is being used to estimate long term fossil fuel usage (population growth and continued development implies GDP growth implies increased FF usage, implies emissions) with the intent of predicting actual future CO2 levels and therefore the extent of climate change. They could not and did not perform the recursive task of then shrinking GDP as an effect of the instigated, projected climate change.

    I’d also suggest that the impacts of climate change are very likely to be non-linear… a 1C temperature increase may equate to a 1.1% GDP decrease, but a 6C temperature increase will cause much more than a 6.6% GDP decrease.

    So you are right, we won’t see a 24x increase in GDP by 2100, because if we proceed at that rate based on a purely fossil fuel economy, we’re going to hit a precipice and topple over it. War, famine, and economic and social upheaval will prevent us from ever getting close to 24x, and that doesn’t even count the fact that there simply isn’t that much fossil fuel to burn, so the supply will be cut off long before we wean ourselves of the addiction.

  47. 97

    84 (Benjamin),

    And just to clarify, you are quoting a 24x figure which is based on where we’ll be by 2100, using an annual growth rate somewhere around 2.2% to 3%, so climate change is potentially going to cut growth, annually, by one third to one half (until the wheels come off).

  48. 98
    Richard Steckis says:

    Ray Ladbury says:
    4 June 2010 at 8:07 AM

    “Steckis, the increased precipitation also leaches nutrients from soils. I’m quite familiar with laterite. I did not say that the cause of the lower yield was temperature based.”

    Then why did you make the statement at all?

    Your original ststement was: “I would also note that tropical agriculture yields fewer calories per hectare than agriculture in temperate climates. ”

    You must have noted it for some reason and I think that reason is to link it to temperature of the tropics (which has a narrower range of temperature variation, compare Kuala Lumpur to Merredin Western Australia). Merredin is in the center of our wheatbelt.

    Otherwise there is no point in noting the ag yeilds for the tropics.

  49. 99

    When the effects of centuries of European colonialism are reversed, then I’ll believe that temperature =actually= impacts GDP.

    Has anyone noticed where Europe is, and where the the parts of the planet Europeans colonialized are?

  50. 100
    Thomas says:

    Leonard @79. If I understood the original comment corectly, the expressed concerned was the transient temperature spike that would be caused by a sudden cessation of polution. In that case continuing the aerosol emissions for some period of time would be the more conservative thing to do climate-wise. Of course his objection is purely academic,the only plausible scenarios for sudden cessation of GHG emissions are some sort of global catastrophy. If that happened we wouldn’t be embarking on geo-engineering. But I don’t think it was suggested here to simply mask warming via increasing aerosol emissions. I admit that the big danger with proposing geo-engineering solutions at this time is the temptation to, “why not continue business as usual, geo-engineering can save us from the consequences”.