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Targeting GGE levels – the next 90 years

This paper by James Hansen and a cast of thousands  (HT John Quiggin)  takes a longer-term view of climate change targeting than is conventional – targets are set for 2100* – with arguments for a 350 ppm GGE target rather than the supposedly ambitious 450 ppm target favoured by many in the Green movement and the politically realist target of 550 ppm favoured by the Stern and Garnaut Reviews.  This would mean an eventual cut in CO2 emissions below current levels.

Abstract: Paleoclimate data show that climate sensitivity is ~3°C for doubled CO2, including only fast feedback processes. Equilibrium sensitivity, including slower surface albedo feedbacks, is ~6°C for doubled CO2 for the range of climate states between glacial conditions and ice-free Antarctica. Decreasing CO2 was the main cause of a cooling trend that began 50 million years ago, the planet being nearly ice-free until CO2 fell to 450 ± 100 ppm; barring prompt policy changes, that critical level will be passed, in the opposite direction, within decades. If humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted, paleoclimate evidence and ongoing climate change suggest that CO2 will need to be reduced from its current 385 ppm to at most 350 ppm, but likely less than that. The largest uncertainty in the target arises from possible changes of non-CO2 forcings. An initial 350 ppm CO2 target may be achievable by phasing out coal use except where CO2 is captured and adopting agricultural and forestry practices that sequester carbon. If the present overshoot of this target CO2 is not brief, there is a possibility of seeding irreversible catastrophic effects.

The paper is a compressed and difficult read although the policy discussion towards the conclusion is easy to assess.  The gist of the argument is that current levels of warming are already causing serious problems such as drought and having effects – such as the disappearance of ice sheets – that will compound warming though reduced albedo effects over the period up to 2100. These will bring about a long-term climate sensitivity that is eventually about double current estimates. Thus, accounting for these feedbacks, temperatures will eventually rise by 6 degrees C if GGE levels double.

I’ll scout around if I get a chance this week and provide any online feedback on this paper I can find and update the post below this line without further comment.

Update:  A good critical survey of these arguments (with background) is provided at RealClimate. The standard climate sensitivity definition (the Charney sensitivity), assumes land surface, ice sheets and atmospheric composition (chemistry and aerosols) stay the same. Hansen’s long term sensitivity (the Earth System sensitivity, ESS) allows these to vary and feed back on temperature. Different sensitivities can be defined by including more feedbacks.  The decision to include or exclude a feedback is usually based on timescales and complexity – slow feedbacks are excluded as are complex feedbacks  due to the change in ozone or aerosols.

The ESS can be deduced from paleo-climate records. What is required is a good enough estimate of the global temperature change and measures of the various forcings. But getting ‘good enough’ estimates for global temperatures changes is hard – while sufficient accuracy in the last few centuries is a couple of tenths of a degree, this is unobtainable for the last glacial maximum or the Pliocene (3 million years ago).  In addition, although many forcings can be derived from paleo-records (long-lived greenhouse gases from bubbles in the ice cores most notably) many cannot. Finally ESS is not stable over geologic time. It is clear that from the Pliocene to the Quaternary (the last ~2,5 million years of ice age cycles), the climate has become more sensitive to orbital forcing. It is conceivable that any sensitivity derived from paleo-climate will not apply to the future.

Finally here is a report (from Nature) on a seminar on related doomsday scenarios.

* Weitzman (2009) considers climate change catastrophes over a 200 year horizon.  This paper by Hansen et al. adds substance to the Weitzman concerns.

17 comments to Targeting GGE levels – the next 90 years

  • John Quiggin

    “Thus, accounting for these feedbacks, temperatures will rise by 60C by 2100 if GGE levels double”

    That wasn’t my reading, assuming you meant 6.0 degrees. I read them as saying that, if CGE levels double and remain at that level beyond 2100, temperatures will eventually rise by 6.0 degrees. There’s a big difference in terms of the time scale for a return to 350 ppm.

  • hc

    John, I am confident your interpretation is broadly correct since the slower feedbacks are related to surface ice melts. In fact Hansen et al say ‘This long term climate sensitivity is relevant to GHGs that remain airborne for centuries to millenia’. (p.5) However note that “One third of the response occurs in the first few years, in part because of the rapid response over land, one half in about 25 years , three quarters in 250 years, and nearly the full response in a millenium’ (p.6). So quite a bit of the response will occur in 90 years – my rough interpolation around 60%.

    Of course Hansen et al are not thinking about long-term policy responses. They favour cutting out all coal emissions by 2030 which is only 20 years away. Even this won’t be enough to keep GGEs below 350 ppm so that favour massive reafforestation and biochar programs that return CO2 levels to 350 ppm by the end of this century.

    But the point you make about the incidence of long-run temperature changes is correct. I altered the passage that you quote above to reflect it. Thanks.

  • The usual drivel from Hansen, Quiggin, and HC. When are you guys going to wake up to the fact that as much as 70-80% of gross emissions is taken up every year by the global biota? The EPA estimates human CO2 emissions at c 2 GtC p.a. growing at over 1% p.a., with livestock good for another 2 GtC growing at quite a bit more than 1% p.a. (FAO). With fossil fuel and LUC emissions of over 10 GtC in 2008, and with Mauna Loa recording only an extra 3.3-3.4 GtC since 2008, the biota is taking up about 7 GtC p.a., or 70% of gross incremental emissions.

    So dear Harry when you Hansen & Quiggin call for nil or even negative emissions what then will happen to the biotic uptakes, with all that entails for world food production?

    But clearly all 3 of you are unaware that there is ZILCH correlation at Mauna Loa between CO2 as measured there and temperatures also AS MEASURED THERE (from 1958 to 2009). Try Googling ML and temperature.

    Whatever happened to radiative forcing at Mauna Loa?

    Sadly, I admit that you lot would not know the difference between black and white swans.

  • Mike Hart

    Harry – A timely reminder of how time is running out for us. I recently read the work by Lean and Rind (Geophyscical Research Letters) and Anil Anamthaswamy (New Scientist) about temperature change scenarios and more importantly changes to global water distribution (ice to water – water to vapour) global dimming etc.

    While no climate expert I am sufficiently educated enough to appreciate the detail and the arguments (and the math). I think Hansen is correct thaqt 350 ppm is it and we have to get back there, if we can. However I am somewhat despondent this will be after looking at a graph about the contributors to sea level change. What was most striking was the information contained, not about rises in sea level but where the drivers were and how they were behaving, glacial and artic ice and land water sources all had curves that were not linear and increasing in steepness. Looking at the curves befor they went linear suggested dynamic stability than had now become dynamically unstable and increasing in the deviation from equilibrium, ergo – we have passed the tipping points.

    All my future life plans are now for acute risk management and climate adaption planning as the global system runs rapidly to a new and very hot (historical) equilibrim with less water and a lot of climate variability all over the globe. Sadly I will be long dead before the worst arrives but my children and especially my grandchildren are in for a very hard time indeed.

  • hc and jq: I will try again – your targets imply as you say “an eventual cut in CO2 emissions BELOW current levels.” As at least 60-70% of current levels are taken up by the golbal biota, especially, agriculture (including livestock), forestry, and fisheries, to the tune of at least 6-7 GtC p.a., what will happen to the output of those primary industries if your hopes are realised?

    You never answer either because you neither know nor care, or alternatively think there are too many people, especially non-whites, who as the Ehrlichs’ protege John Holdren hopes, would be the first to be eliminated by the global famine resulting from zero emissions.

  • conrad

    “You never answer either because you neither know nor care, or alternatively think there are too many people, especially non-whites”
    I’ve never met JQ or HC face-to-face. But, being non-white, in case I do, I’ll make sure I keep my guard up! I hadn’t even realized this was their grand plan. I’m so ignorant.

  • hc: it was actually begun by me on an earlier thread at Jen’s (27 August). I see you still have no alternative explanation of the lack of correlation between [CO2] and temperature at Mauna Loa, where if ever there ought to be one, it is at that pristine site from which we all including IPCC derive our [CO2] data. Actually it is worse than that for you and your co-religionists, as there is equally minimal relation between changes in [CO2] and changes in in situ temperatures at both the other main [CO2] sites, Cape Grim (Tasmania) and Pt Barrow (Alaska) – both at about sea-level unlike ML, but both also distant from anthropogenic warming due to energy usage.

    The truth is that [CO2] has nothing to do with AGW, except as a very poor proxy for energy utilisation. Consider France, with now 88% nuclear energy sourcing of its total electricity demand, and the same “warming” as its immediate neighbours, which all have similar energy utilisation levels but much less reliance on nuclear. Replacing all fossil fuel sources of power by wind & solar & nuclear will do nothing at all to reduce “warming”, as it is Energy that powers the Work that produces the Heat (not just waste heat) which generates Warming.

    You probably have never heard of Eric D Beinhocker’s The Origin of Wealth (2006, 2007, Hravard Business School Press, Boston, Mass.). He has little or nothing to say about climate change, but he does explain how the 1st & 2nd Laws of Thermodynamics eventually found their way, tortuously, into Economics, along with the role of entropy (via Georgescu-Roegen and Paltridge & Farquhar inter alia). You are repesentative of the Australian economics profession’s failure in the context of CC to grasp the endgame for the Greens (for whom G-R is a main guru) of zero CO2 and better, zero energy usage, and thereby total entropy, i.e. return to a primeval world empty of all wicked humans (white or non-white) but rampant bio-diversity apart from us, have you heard of their showpiece communes in Queensland working on this as I write?

    Finally, I repeat that the “warming potential” of CO2 is ludicrously less than that of global energy production. But to grasp that is I fear a step too far for the Editor of Economic Papers, witness his refusal to accept the zero correlation between [CO2] and temperature in the places where both are measured.

  • hc: for the record, here is the opening of the Marohasy thread which cites me:

    Let’s Stop Averaging Global Temperatures (Part 1)
    Posted by jennifer, August 27th, 2009 – under Opinion.
    Tags: Climate & Climate Change
    Comments: 215

    FEAR of global warming is a preoccupation of western societies at the beginning of this 21st century. This fear is usually explained in terms of changes in the surface temperature of the earth as averaged from varying numbers of thermometers from around but the world. But given the many disputes concerning how this data is collected, compiled, adjusted and averaged (see notes and links below), it would perhaps be better if there was some agreement to focus on the temperature as measured from one or just a few sites.

    Tim Curtin has suggested that as carbon dioxide concentrations are reported for Mauna Loa, Hawaii, why not also focus primarily on this site when discussing global warming?

    Later in the thread there are references by E.M. Smith to my earlier postings on the same subject, e.g. Comment from: E.M.Smith August 28th, 2009 at 7:12 pm

    Comment from: sod August 28th, 2009 at 4:34 am
    “Tim Curtin has suggested that as carbon dioxide concentrations are reported for Mauna Loa, Hawaii, why not also focus primarily on this site when discussing global warming?

    this is a completely insane idea. there are so many things wrong about it, that it is hard to figure out where to start”.

    You seem to have a lot of difficulty figuring out where to start. I’ll help. Start with a very long temperature series taken at a place that had changed very little and by the same staff that record the CO2. That is it up on a mountain ought not to matter at all (you said so earlier – it ought to just have an anomaly like all the others…). It is a site located thousands of miles from most major land sources of temperature influence, so there is plenty of time for the air to stabilize before it gets to the mountain, and the same effect that makes the CO2 desirable to measure (well mixed air away from people) ought to make the temperature more representative of an untainted record too.

    And then…
    Comment from: Louis Hissink August 30th, 2009 at 10:40 am

    “Tim Curtin,

    Well spotted – and I wonder how the AGW mob are going to explain this inconvenient fact away, as they will. My guess is Pious Silence hoping it will go away.”

    Comment from: Louis Hissink August 30th, 2009 at 10:58 am

    “Tim Curtin,

    Your observation is correct – the temperatures have not been increasing in line with the hypothesis. I’ve plotted the January and July temperatures – and it’s clear the AGW hypothesis has been falsified.

    Well done!”

    Many thanks from me to EM Smith and Louis Hissink. The latter is right about “Pious Silence” – and worse, both outright suppressio veri and shooting the messenger, as I know already to my personal cost.

  • hc

    Sounds to me like a totally crazy correlation to investigate. Medium term climate trends at a particular location are dominated by slowly changing ocean temperature changes that compound El Nino and other events. What does a correlation between a local temperature reading subject to these effects and that location’s globally dissipated level of CO2 emissions show?

  • hc: I thought you could do better than that. Here’s E.M. Smith again on why Mauna Loa is exactly as much the right spot for measuring temperature trends as it is for [CO2]:

    “It is a site located thousands of miles from most major land sources of temperature influence, so there is plenty of time for the air to stabilize before it gets to the mountain, and the same effect that makes the CO2 desirable to measure (well mixed air away from people) ought to make the temperature more representative of an untainted record too”.

    Why is ML more subject to El Nino than say Brisbane or New York? why is ML’s [CO2] temperature reading more relevant for those places than at ML itself?

    Curiously two recent papers in GRL

    1. Decadal to multidecadal variability and the climate
    change background
    David Parker,1 Chris Folland,1 Adam Scaife,1 Jeff Knight,1 Andrew Colman,1
    Peter Baines,2,3 and Buwen Dong4,5

    2. Secular temperature changes in Hawai‘i. GRL 2008
    Thomas W. Giambelluca,Henry F. Diaz and Mark S. A. Luke

    These papers completely confirm my thesis, since neither mentions [CO2] at Mauna Loa or anywhere else, still less as it having ANY impact on temperature trends at Hawaii or elsewhere in the South Pacific.

    What have you got say now other than armwaving? Perhaps you could pen a response to GRL pointing out what you must believe is a major omission in their papers.

    The point about [CO2] as measured at ML is that its trend and level within a few ppm have been amply confirmed at Pt Barrow and Cape Grim. Where would you nominate as a more pristine location for representing impact of [CO2] on global temperature? That means [CO2] is essentially the same everywhere, so for a clean bivariate regression analysis temps and [CO2] using both as at ML is just fine. For multivariate, then regress dTemps/dT against BOTH d[CO2]/dT AND the dE/dT for IEA Energy Consumption at any of your preferred locations.

    That was a step too far for David Karoly and his mates at IPCC AR4 WG1 chap.9 (Climate Change Attribution, sic!), which failed to mention let alone use any energy data.

    Do read EM Smith’s very detailed analysis of global temperature measurements at that 27 August thread at Jennifer’s, not to mention of course the audits by Steve McIntyre ( and Anthony Watts ( Watt’s latest will point you to the NOAA’s own rating of 1200 met stations in mainland USA, showing the majority (69%) to have errors of more than 2 oC, no doubt you will pick one of these!

  • Oh dear, the denier talking points are getting sillier and sillier…

  • Peter Wood: what a profound contribution! As you would not know a Prisoner’s Dilemma even if you were one – yours is the worst presentation I have ever attended at ANU, with its complete failure to get beyond the textbook account to explain why China and Australia are anyone’s prisoners – what exactly is “silly” about saying that if temperatures at Mauna Loa do not show any response to [CO2] at Mauna Loa, the whole theory of “radiative forcing” is bogus. You like hc can earn fame with a paper in GRL to explain why Parker et al and Giambelluca are wrong not to mention [CO2]. But alas, like hc, you have no statistics capability, so that is not on.

  • Tim, let me spell it out for you. Firstly, increased greenhouse gases are predicted to lead to increases in average global temperatures, while Mauna Loa is just one data point. Secondly, the data for Mauna Loa suggests that there is a warming trend. Just to make this more clear, let me quote the Giambelluca paper: “Despite its tropical oceanic location, Hawai‘i has experienced rapid warming, especially since the mid-1970s…. Temperature variation in Hawai‘i appears to have been tightly coupled to the PDO, perhaps through regional SST variation. However, in recent decades Hawai‘i’s air temperature trend has diverged from PDO and local SST trends, perhaps signaling increasing influence of global warming.”

  • Peter: let me spell it out for you, there is no doubt that there is warming especially at a multitude of urban, peri-urban, and airport locations which when added up appear to produce for those locations an increase in the mean warming of all locations including those without any warming. The issue is what causes this. The Giambelucca paper does NOT attribute this to increased [CO2] as measured at Mauna Loa. In fact, its data for 21 stations include 5 which are heavily urbanising while ML is one of only 4 stations above 800 metres and is in effect excluded because its annual records only extend from 1955 to 1992. It appears Al Gore may well have encouraged less assiduous temperature recording there after 1992, at any rate the staff there ceased a daily record for all too many months after 1992, excluding very cold days, as in January 2008 and 2009, when they ventured out only on the 18-19 warmer days respectively, thereby biasing the records for the month upwards. I’ll send you my NOAA data file showing this. All the same the annualised record for ML temperature still shows no stat. sig. upward trend, and absolutely zero correlation between the changes in temp. there and changes in [CO2] there between 1959-60 and either 1992 or 2008. This confirms that other influences must be at work in Hawaii, chiefly urbanisation and the PDO.

    Unlike you, I have compared the temperature data for Honolulu Observatory (at about sea-level) and Honolulu Airport, the latter shows a major upward trend after 1960, consistent with the expansion of air travel after the introduction of 707s in 1960, while the former like ML shows no trend. If eleven batsmen average 20 over 10 innings each, and Bradman does 100, the mean for them all is 27, although only one exceeded 20. That is the case in Hawaii. Five stations show some warming, the majority do not; the mean is not representative. The same applies to so-called “global warming”.

    For every location in the Gistemp set showing warming subject to the latest NOAA quality test indicating most do not, I will cite another with a flat or negative trend. When do you want to start this game? And while you are at it, please show me the results of your own multivariate regression of changes in GMT and changes in PDO or ENSO, [CO2] and Energy Consumption, with a separate run showing changes in PDO as a function of changes in [CO2] and Energy Consumption. It will be interesting to compare results, name the day and I will shout lunch!

    Finally, I repeat, bring your evidence for the theory of “radiative forcing” due to rising [CO2], at Mauna Loa or anywhere else where energy consumption is absent.

  • Mike Hart

    Focusing on temperature alone is like driving your car looking at the speedo and not considering the other variables; road surface, precipitation, road gradient, engine power, etc etc. AS the planet is some 80% water then what water is doing is the key, temperature is but a small part.

  • Mike Hart: Agreed – but tell that to the IPCC, with their devotion to a single cause – [CO2] – explanation. Garth Paltridge et al* have recently exploded the IPCC assumption that all feedbacks from humidity changes are positive (which they need to make temp changes from CO2 alone more scary). My own multivariate regression work brings in not just [CO2] but energy usage and the PDO just for starters. But the necessary first step is to show that there is no correlation between changes in [CO2] and temperature at places where there is little or no energy usage, as is the case at Cape Grim, Cape Otway, and Mauna Loa, all have flat or downward temp trends despite the same [CO2] at each.

    *Trends in middle- and upper-level tropospheric humidity; Journal of Theoretical Applied Climatology 2009
    from NCEP reanalysis data
    Garth Paltridge & Albert Arking & Michael Pook

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