Nic Lewis’s submission to the UK government

I was hesitating about writing this post because I’m going to find it hard to avoid some snark. Apologies in advance. A number of people seem to think that Nic Lewis’s submission to the UK government’s IPCC inquiry is very good. Judith Curry seems to think it’s a tour de force. Personally, it seems a little like someone trying to say: I wrote a paper. I’m proud of my paper. I think my paper is better than everyone else’s papers. Why didn’t the IPCC take more notice of my paper? Also, I’m only going to mention uncertainties when it suits me to do so.

I don’t have any particular issues with Nic Lewis’s work. I’ve worked through Otto et al. (2013) in quite a bit of detail. I haven’t quite managed to work out what he’s getting at in Lewis et al. (2013), but have no reason to think that it’s not a reasonable piece of work. It’s just that, in my view at least, if you’re interested in doing science, you immerse yourself in the subject, you build up a portfolio of work, and you gain credibility with your peers and with others. Getting your name on 2 or 3 papers doesn’t suddenly make you an expert and doesn’t, typically, give you the credentials to review the validity of other aspects of the same field. There’s nothing fundamentally wrong with this, it just seems an odd way to build a scientific career. Might make it seem that your desire to do science is driven more by the policy implications of what other work suggests, than by some deep desire to really understand something.

Anyway, Nic Lewis’s submission is quite long, so I thought I might highlight a few things and make a few comments. He discusses the Transient Climate Response (TCR) and the Equilibrium Climate Sensitivity (ECS), but – as far as I can tell – makes no mention of the Earth System Sensitivity (ESS). The ECS is the equilibrium temperature after a doubling of CO2, but is based only on fast feedbacks. It’s now accepted that there are likely slower feedbacks that on longer timescales will lead to a higher equilibrium temperature than ECS estimates would suggest. He goes on to say

The IPCC considers all observational ECS estimates in AR5 WG1. It concludes that estimates based on

  • paleoclimate data reflecting different past climate states
  • climate response to volcanic eruptions or solar changes
  • satellite measurements of short-term changes in heat radiation

are unreliable and/or unable to provide usefully well-constrained estimates. I agree with this conclusion. That leaves in essence only estimates based on observations of warming over multi-decadal periods. Useful surface temperature records extend back approximately 150 years (the ‘instrumental period’).

I’d love to know if this is correct. I can’t find anything in the IPCC document that seems consistent with this claim. Essentially he seems to be arguing that the only reliable estimates are his own.

He goes on to say,

However, as noted above, between AR4 and AR5 there has been a major reduction in the IPCC’s estimate of the cooling strength of aerosol pollution, which necessarily implies that estimates of climate sensitivity should be substantially lower than previous estimates. However, the current CMIP5 generation of GCMs still very largely reflects the earlier understanding of a stronger aerosol effect.

I’m not convinced this is true either. I believe the influence of anthropogenic aerosols is quite uncertain. The AR5 document suggests a likely value of around -0.5Wm-2, with a range from about -1.3Wm-2 to around -0.1Wm-2. However, there are some who think – I believe – that the actual aerosol forcing is quite likely more negative than the IPCC most likely estimate. If so, that would imply a higher ECS, not lower. Again, maybe I’m wrong and the GCMs are using aerosol forcings that are too large, but that was not my impression.

He continues with,

A particularly robust way of empirically estimating climate sensitivity is the so-called ‘energy-budget’ method, which is based on a fundamental physical law – the conservation of energy. Energy-budget best estimates of ECS fall in a range between 1.5°C and 2.0°C (1.25–1.4°C for TCR), depending on the exact periods chosen for analysis. Using the longest available periods that were free of major volcanism gives a ECS best estimate of approximately 1.7°C (1.3°C for TCR).

Particularly robust. Really? Where does that come from? Is that some kind of objective judgement? I notice that he doesn’t mention the ECS range from Otto et al. (2013). Most of the Otto et al. (2013) estimates were around 2oC for the ECS, with a range from around 1.3oC – 3.9oC. I appreciate that there are estimates with the ECS below 2o, but if one considers the recent Trenberth & Fasullo (2013) and Cowtan & Way (2013) papers, then even ‘energy-budget’ estimates give ECS likely values around 2.5oC. Again, there is a large range, but it’s still not clear that ‘energy-budget’ estimates are particularly inconsistent with other estimates.

He also adds

Note that the CMIP5 GCMs give an estimate for the warming over the next two decades as 0.48–1.15°C.21 In the AR5-WG1 final draft, however, that estimate was reduced by 40% to 0.3–0.7°C, apparently recognising that overall the models were warming unrealistically quickly. Inconsistently, no change was made to the longer term GCM projections.

Well, I believe that this is because we are aware that there is a mismatch between models and observations. There are various explanations for this. It could be internal variability, volcanoes, anthropogenic aerosols, or – possibly – something else altogether (maybe there are fundamental issues with the models). However, this mistmatch clearly exists and so will likely influence the warming over the next two decades. It, however, doesn’t immediately imply that the long-term trend is wrong. Hence, no change to the longer term projection is not necessarily inconsistent.

He finished his submission with

If TCR really is 1.35°C then under RCP8.5 – the worst-case, business-as-usual scenario – the end of the 21st century will be approximately 2°C warmer than today.

The meta-analysis in Tol (2009)22, of fourteen estimates from economists, suggests that a temperature of 2°C warmer than today is likely to have a negligible impact on welfare.

Indeed, if the TCR is 1.35oC, the end of the 21st century would be about 2oC warmer than today. However, that will make it higher than at any time in human history and means that we will have locked in at least a further 1oC of warming. I discussed Tol’s meta-analysis in an earlier post (although – as usual – the comments may be more informative than the post itself). I would argue that Nic Lewis’s statement is, even based on Tol (2009), incorrect. Tol (2009) suggest that 2oC warmer than today is when there will likely be no net benefit (roughtly 50% chance of benefit and 50% chance of damage). I wouldn’t say that a 50% chance of the impact being negative is consistent with likely negligible impact on welfare.

There is, however, also a typo in Tol (2009). The paper indicates that Hope (2005) was +0.9, rather than -0.9. When one corrects for this typo it not only reduces, slightly, the warming for which we will see benefits, but also makes it very clear that the possibility of a net benefit is based very strongly on a single piece of work (Tol 2002).

Additionally, many argue that acting against global warming will harm the poor who will lose access to cheap energy. What those who promote Tol’s (2009) meta-analysis fail to point out is that even this analysis acknowledges that- in a warmer world – most of the benefits will go to the developed world (who contributed most to global warming) while the poorer parts of the world will likely suffer. This seems like a moral issue that is at least worth considering, not something we should be ignoring altogether.

Anyway, that’s all I was going to say. There probably is more that could be said, but I’ll leave it at that. Apologies if the beginning seemed a bit snarky. Hard not to be when someone with the publication record of an average PhD student thinks that there are issues with the IPCC because they didn’t take his work more seriously (or, at least, that’s how it comes across). As usual, comments welcome, especially if they can clarify the bits about which I’m uncertain (most of it really).

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128 Responses to Nic Lewis’s submission to the UK government

  1. I dare you to review Scottish Climate & Energy Forum’s submission. Go on, you know you want to really ;-)

  2. I did consider it, but my ability to write satire is limited :-)

  3. guthrie says:

    Lewis’s paper seems to involve Bayesian statistics, surely james of Jules and James Blog fame would be the one to talk to? Only he’s moving to the UK at the moment.

  4. I think Lewis’s paper uses what are called objective priors. I think this means that the prior is unbiased, but given that I don’t quite understand how Bayesian statistics works with normal priors, I’m going to struggle to understand how objective priors makes things better :-)

  5. BBD says:

    What concerns me ;-) is that those who hold NL in high regard are perhaps insufficiently sceptical.

  6. John Mashey says:

    1) Well, Scottish Sceptic did offer a useful list of climate websites/blogs. He lists ATTP as a sceptic site… (which may be true in the hallowed meaning of sceptic, but probably not the way he means it :-))

    2) I see his post on citizen scientists., but I didn’t notice a link to his submission. where is that?

  7. Barry Woods says:

    I think nic lewis’ s papers and some others are just to long/technical to get much attention from the parlimentarians. Dr Ruth Dixon’s is interesting and written in the style more likely to be noted by that audience.

  8. John, it’s his 4th most recent post. His submission is formally from the Scottish Energy and Climate Forum which, I think, might be just him.

    Barry, I haven’t really read Ruth’s in detail.

  9. John Mashey says:

    Thanks, in any case, I found it at Curry’s, where SCEF was labeled a well-known sceptic organization. I see he referenced Salby a few times, and in case people are interested. I recently put up a review of Salby’s recent book.

  10. guthrie says:

    I don’t understand Bayesian stats either, except to say that I think it depends on your selection of priors as to what sort of results you get, which obviously leaves plenty of room for manouver.

  11. Steve Bloom says:

    The mid-Pliocene warm period is of most relevance to the longer-term trajectory of AGW, and indeed Lewis is correct to imply that no useful information can be extracted from the relevant proxies in terms of ECS. Even so, neglecting it and ESS generally is a transparent dodge.

    (Anders, not for the first time you’ve phrased a discussion of these issues to imply that slow feedbacks will somehow not kick in until after ECS has happened. To repeat myself, because slow feedbacks will become significant long before the fast feedbacks have run their course, and indeed some already are doing so, e.g. permafrost melt, ECS is properly seen as a notional quantity that will not be seen in the real climate. Please be careful with this.)

    Here’s the relevant AR5 WG1 passage:

    “5.3.1 High CO2 Worlds and Temperature

    “Cenozoic (last 65 Ma) geological archives provide examples of natural climate states globally warmer than the present, which are associated with atmospheric CO2 concentrations above pre-industrial levels. This relationship between global warmth and high CO2 is complicated by factors such as tectonics and the evolution of biological systems, which play an important role in the carbon cycle (e.g., Zachos et al., 2008). Although new reconstructions of deep-ocean temperatures have been compiled since AR4 (e.g., Cramer et al., 2011), low confidence remains in the precise relationship between CO2 and deep-ocean temperature (Beerling and Royer, 2011).

    “Since AR4 new proxy and model data have become available from three Cenozoic warm periods to enable an assessment of forcing, feedbacks and the surface-temperature response (e.g., Dowsett et al., 2012; Lunt et al., 2012; Haywood et al., 2013). These are the Paleocene-Eocene Thermal Maximum (PETM; Table 5.1), the Early Eocene Climatic Optimum (EECO; Table 5.1) and the mid-Pliocene Warm Period (MPWP; Table 5.1). Reconstructions of surface temperatures based on proxy data remain challenged by: (i) the limited number and uneven geographical distribution of sites, (ii) seasonal biases and (iii), the validity of assumptions required by each proxy method (assessed in Table 5.A.3). There is also a lack of consistency in the way uncertainties are reported for proxy climate estimates. In most cases error bars represent the analytical and calibration error. In some compilations qualitative confidence assessments are reported to account for the quality of the age control, number of samples, fossil preservation and abundance, performance of the proxy method utilized, and agreement of multiple proxy estimates (e.g., MARGO Project Members, 2009; Dowsett et al., 2012).

    “The PETM was marked by a massive carbon release and corresponding global ocean acidification (Zachos et al., 2005; Ridgwell and Schmidt, 2010) and, with low confidence, global warming of 4°C–7°C relative to pre-industrial (Sluijs et al., 2007; McInerney and Wing, 2011). The carbon release of 4500–6800 PgC over 5–20 kyr translates into a rate of emissions of ~0.5–1.0 PgC yr–1 (Panchuk et al., 2008; Zeebe et al., 2009). Greenhouse gas emissions from marine methane hydrate and terrestrial permafrost may have acted as positive feedbacks (DeConto et al., 2012).

    “The EECO represents the last time atmospheric CO2 concentrations may have reached a level of ~1000 ppm (Section 5.2.2.2). There were no substantial polar ice sheets, and oceanic and continental configurations, vegetation type and distribution were significantly different from today. Whereas simulated SAT are in reasonable agreement with reconstructions (Huber and Caballero, 2011; Lunt et al., 2012) (Box 5.1, Figure 1d), there are still significant discrepancies between simulated and reconstructed mean annual SST, which are reduced if seasonal biases in some of the marine proxies are considered for the high-latitude sites (Hollis et al., 2012; Lunt et al., 2012). Medium confidence is placed on the reconstructed global mean surface temperature anomaly estimate of 8°C–14°C.

    “The Pliocene is characterized by a long-term increase in global ice volume and decrease in temperature from ~3.3–2.6 Ma (Lisiecki and Raymo, 2005; Mudelsee and Raymo, 2005; Fedorov et al., 2013), which marks the onset of continental-scale glaciations in the NH. Superimposed on this trend, benthic 18O (Lisiecki and Raymo, 2005) and an ice proximal geological archive (Lisiecki and Raymo, 2005; Naish et al., 2009a) imply moderate fluctuations in global ice volume paced by the 41 kyr obliquity cycle. This orbital variability is also evident in far-field sea level reconstructions (Miller et al., 2012a), tropical Pacific SST (Herbert et al., 2010) and Southern Ocean MDA records (Martinez-Garcia et al., 2011), and indicate a close coupling between temperature, atmospheric circulation and ice volume/sea level (Figure 5.2). The MPWP and the following 300 kyr represent the last time atmospheric CO2 concentrations were in the range 350–450 ppm (Section 5.2.2.2, Figure 5.2). Model-data comparisons (Box 5.1, Figure 1) provide high confidence that mean surface temperature was warmer than pre-industrial for the average interglacial climate state during the MPWP (Dowsett et al., 2012; Haywood et al., 2013). Global mean SST is estimated at +1.7°C (without uncertainty) above the 1901–1920 mean based on large data syntheses (Lunt et al., 2010; Dowsett et al., 2012). General circulation model (GCM) results agree with this SST anomaly (to within ±0.5°C), and produce a range of global mean SAT of +1.9°C and +3.6°C relative to the 1901–1920 mean (Haywood et al., 2013). Weakened meridional temperature gradients are shown by all GCM simulations, and have significant implications for the stability of polar ice sheets and sea level (see Box 5.1 and Section 5.6). SST gradients and the Pacific Ocean thermocline gradient along the equator were greatly reduced compared to present (Fedorov et al., 2013) (Section 5.4). Vegetation reconstructions (Salzmann et al., 2008) imply that the global extent of arid deserts decreased and boreal forests replaced tundra, and GCMs predict an enhanced hydrological cycle, but with large inter-model spread (Haywood et al., 2013). The East Asian Summer Monsoon, as well as other monsoon systems, may have been enhanced at this time (e.g., Wan et al., 2010).

    “Climate reconstructions for the warm periods of the Cenozoic also provide an opportunity to assess Earthsystem and equilibrium climate sensitivities. Uncertainties on both global temperature and CO2 reconstructions preclude deriving robust quantitative estimates from the available PETM data. The limited number of models for MPWP, which take into account slow feedbacks such as ice sheets and the carbon cycle, imply with medium confidence Earth-system sensitivity may be up to 2 times the model equilibrium climate sensitivity (ECS) (Lunt et al., 2010; Pagani et al., 2010; Haywood et al., 2013). However, if the slow amplifying feedbacks associated with ice sheets and CO2 are considered as forcings rather than feedbacks, climate records of the past 65 Myr yield an estimate of 1.1°C–7°C (95% confidence interval) for ECS (PALAEOSENS Project Members, 2012) (see also Section 5.3.3.2).”

  12. BBD says:

    I’m going to go out on a limb here and agree with Steve’s argument that we are missing something in terms of modelled positive feedback. More at Science of Doom.

  13. BBD says:

    Paleoclimate variability is the reality, not the mad aunt in the attic.
    :-)

  14. Steve Bloom says:

    Note that Dixon’s submission fails to observe that all of the papers used in the WG1 report have already been peer-reviewed (with minor exceptions for gray lit). So she wants yet more peer review of a broad expert assessment of previously reviewed material? I’ll bet they don’t do that in her field.

  15. Steve,

    (Anders, not for the first time you’ve phrased a discussion of these issues to imply that slow feedbacks will somehow not kick in until after ECS has happened. To repeat myself, because slow feedbacks will become significant long before the fast feedbacks have run their course, and indeed some already are doing so, e.g. permafrost melt, ECS is properly seen as a notional quantity that will not be seen in the real climate. Please be careful with this.)

    In truth, I’m including a mention of the ESS because I’m aware that the ECS alone doesn’t tell the full story. I may well be phrasing it poorly, but that’s partly my own ignorance and partly because getting everything right in this debate is much harder than it might seem (although I suspect that you realise this yourself). I’ll do my best to be more careful in future :-)

  16. > Dr Ruth Dixon’s is interesting and written in the style more likely to be noted by that audience.

    I concur, and will add that it’s the best.

    As far as I can tell, Nic may have rinsed and repeated stuff from his correspondence with the MET Office:

    I am reminded of a famous line by Bertold Brecht to the effect of: “The people have failed the government. The government must elect the new people.” But the Met Office can no more replace the real climate system with one that agrees with the models than a communist government could replace the people with one that satisfied its ideology.

    http://judithcurry.com/2013/09/25/nic-lewis-vs-the-uk-met-office/

    There’s also a prequel to that harrangue.

  17. Steve, maybe you can clarify a few things for me. Your earlier comment, if I understand it properly, is that there are certain past climate periods that may be relevant but for which it’s difficult to extract ECS/ESS estimates. That sounds reasonable. Nic Lewis seems to have concluded from this that the only reliable estimates are multi-decadal ones which – if I understand what he’s saying – is basically suggesting that the only reasonable estimates are his own. That doesn’t seem like a reasonable conclusion to draw from what the IPCC has said. Have I interpreted this correctly, and do you agree?

    Since you seem to be the ESS expert, there is something that’s confused me. I was reading Hansen (2011). Figure 4 shows that past 800000 years and includes the variations in forcings and the resulting temperature anomalies. In the text he discusses how this is all consistent with 0.75Wm-2 per degree or 3oC per doubling of CO2 and associates this with fast feedbacks. Why, for such long timescales, are we not seeing evidence for a higher ESS, or am I missing something obvious here?

  18. Rachel says:

    I have a dumb question. What’s the difference between ECS and ESS?

  19. Rachel, as I understand it, the ECS is associated largely with fast feedbacks (increased water vapour for example). The ESS is associated with slower feedbacks (reduction in ice/snow coverage, change in vegetation). So, normally, the ECS estimates don’t really take into account the slower feedbacks and so one would expect the actual rise in temperature to be higher than ECS estimates would suggest.

  20. ECS ignores slow feedbacks like permafrost, oceans, methane hydrates, ice sheets, vegetation, etc. ESS is the real Earth System Sensitivity; it includes those.

  21. Steve,

    Note that Dixon’s submission fails to observe that all of the papers used in the WG1 report have already been peer-reviewed (with minor exceptions for gray lit). So she wants yet more peer review of a broad expert assessment of previously reviewed material? I’ll bet they don’t do that in her field.

    I haven’t read Ruth Dixon’s in detail, but I did wonder the same. Not only is most of it already peer-reviewed, but who would do the extra peer-reviewing if it were instituted.

  22. More later, but ponder the last sentence in Steve’s quote: if the slow amplifying feedbacks associated with ice sheets and CO2 are considered as forcings rather than feedbacks, climate records of the past 65 Myr yield an estimate of 1.1°C–7°C (95% confidence interval) for ECS (PALAEOSENS Project Members, 2012) (see also Section 5.3.3.2).”

    They basically removed slow feedbacks, so it’s consistent with a higher ESS.

  23. Tom Curtis says:

    Rachel, on Equilibrium Climate Sensitivity (ECS, also called the Charney Climate Sensitivity) and the Earth System Sensitivity (ESS), Gavin writes at Real Climate:

    “However, depending on what the boundary conditions include, you can get very different numbers. The standard definition (sometimes called the Charney sensitivity), assumes the land surface, ice sheets and atmospheric composition (chemistry and aerosols) stay the same. Hansen’s long term sensitivity (which might be better described as the Earth System sensitivity) allows all of these to vary and feed back on the temperature response. Indeed, one can imagine a whole range of different sensitivities that could be clearly defined by successively including additional feedbacks. The reason why the Earth System sensitivity might be more appropriate is because that determines the eventual consequences of any particular CO2 stabilization scenario.”

    That is not a simple fast feed back/ slow feed back split. For example, changes in albedo due to the retreat of glaciers and ice sheets does fall under ESS, but changes in albedo due to retreating sea ice and reduces snow coverage fall under the ECS. Changes in natural methane emissions due to metling permafrost, however, even though not significantly slower than changes in snow or sea ice cover, do not fall under ECS.

    IMO, this is one of the problems of relying too heavily on the remaining energy imbalance with a given temperature and forcing increase to determine ECS. Some of the climate feedbacks involved in the ECS are quite slow, and made slower by thermal inertia from the ocean. In contrast, other feedbacks are quite fast, reaching quasi-equilibrium in days or weeks. The result is that mix of contributions to the ECS changes with time from the initial forcing. It follows that the estimated ECS will also change with time. Consequently, the method used by Nic Lewis and Otto et al is likely to underestimate the ECS; and the more rapid the change in forcing, the more likely it is to do so. Only with constant change in forcing over time sustained over many decades, is it going to be very accurate given sufficiently accurate data.

  24. Tom,

    Consequently, the method used by Nic Lewis and Otto et al is likely to underestimate the ECS; and the more rapid the change in forcing, the more likely it is to do so. Only with constant change in forcing over time sustained over many decades, is it going to be very accurate given sufficiently accurate data.

    Thanks. I was going to comment on this in my post, but both forgot and it was getting a little long anyway. Nic Lewis seemed to completely ignore any issues (such as you describe) with his method. It’s clear that these empirical estimates fail to capture the non-linearities that are likely to exist.

  25. BBD says:

    Which is why NL is not advancing anything of merit. And why his supporters are not granted the kudos they seem to believe they deserve. Insufficient scepticism and too much bias.

    The discussion of fast and slow feedbacks is in Hansen & Sato (2012) section 3.5.

  26. BBD, you’ve just made me realise that the comment I posed for Steve was actually based on Hansen & Sato (2012) not Hansen 2011. Anyway, maybe you solve my issue (I think I may have some idea, but getting someone else to confirm it – or not – would be good). In Fig 2 of Hansen & Sato, it shows the variation in forcings and the change in temperature. The paper then uses this to determine an ECS of 3 degree per doubling (or 0.75 Wm-2 per degree). Why is it 3 rather than something higher (if slow feedbacks are operating)?

  27. BBD says:

    Because of orbital dynamics – it gets cooold again and feedbacks work both ways.

  28. BBD says:

    This sounds more flippant than intended and H&S 3.5 is too long and self-referential to quote in chunks but perhaps will reward a second reading.

  29. BBD, yes I realise that. My question was subtler I think. If you consider Fig. 2, and consider the third panel from the bottom, it shows the change in forcing due to CO2 and albedo. By eye, it appears that the total change (if you sum the two) is around 5 Wm-2. If you consider the temperature (lower to figures), this produces a change in temperature of around 4oC and, hence, a sensitivity of around 0.8Wm-2 per K (or about 3 degrees per doubling of CO2).

    My question relates to why, if the ESS suggests a greater temperature changes than the ECS, is the temperature change bigger?

    The answer I’ve come up with is that by including the albedo forcing, we’re treating a feedback as a forcing. If we considered CO2 only, then it would be around 6 degrees per doubljng. The only issue I have with this is that this would imply that the change in albedo is a feedback response to changes in CO2 forcing only, when it would seem that some of this must be due to changes on solar forcing. Hence, is treating the change in albedo forcing as a feedback correct or not (or is it a combination of a feedback response to changes in CO2 forcing and a response to changes in solar forcing).

    Also, does my question make any sense at all? :-)

  30. Frank says:

    Figure 7.19 of AR5 summarizes AR4 and AR5 estimates for forcing from aerosols. The central estimate by AR5 is at the weaker end of the 25-75% box of the box-and-whiskers plot for AR4. The central estimate for AR4 is at the stronger end of the box for the AR5 plot. So the central estimate of aerosol forcing has weakened by more than one standard deviation. (Aerosol forcing determined from climate models is even weaker.) This is why Nic Lewis asserts that “between AR4 and AR5 there has been a major reduction in the IPCC’s estimate of the cooling strength of aerosol pollution”. (You might want to do a little research before assuming Nic is wrong.)

    Nic discusses comments he submitted to the IPCC after seeing the aerosols section of Second Order draft of AR5 at http://bishophill.squarespace.com/blog/2012/12/19/why-doesnt-the-ar5-sods-climate-sensitivity-range-reflect-it.html

    If we continue on the RCP8.5 scenario until the end of the century and it only warms 2 degC, you believe that another 1 degC of warming will follow. That seems realistic. What doesn’t seem realistic is continuing business-as-usual for the whole century: The supply of fossil fuels still in the ground is massive, but the cost of obtaining them certainly could rise as the most accessible supplies get used up. The cost of non-fossil fuel energy is likely to come down in the next half-century. At some point, business-as-usual should stop because it will be cheaper to stop. The real question is whether we should ignore the marketplace and force a switch to non-fossil fuel energy sources while they are still more costly. If Nic Lewis and RIchard Tol are correct, we can probably afford to wait.

  31. BBD says:

    ATTP

    I have a problem – I am trying to build a Mars rover out of lego with my son as we speak, and this is… constraining my ability to respond sensibly. Dare I proffer a link to discussion at SkS?

    Apologies. More later.

  32. BBD says:

    If Nic Lewis and RIchard Tol are correct, we can probably afford to wait.

    Since both are partisan, this is an unacceptable risk. The board rejects.
    ;-)

  33. BBD says:

    Hence, is treating the change in albedo forcing as a feedback correct or not (or is it a combination of a feedback response to changes in CO2 forcing and a response to changes in solar forcing).

    My understanding is that albedo is a feedback, always. Feedback to solar (Milankovitch) *and* to GHG change which is also a feedback to orbital forcing.

    From H&S12:

    Now let us turn to a more general discussion of climate feedbacks, which determine climate sensitivity. Feedbacks do not come into play coincident with a forcing. Instead they occur in response to climate change. It is assumed that, to a useful approximation, feedbacks affecting the global mean response are a function of global temperature change.
    ‘Fast feedbacks’ appear almost immediately in response to global temperature change. For example, as Earth becomes warmer the atmosphere holds more water vapor. Water vapor is an amplifying fast feedback, because water vapor is a powerful greenhouse gas. Other fast feedbacks include clouds, natural aerosols, snow cover and sea ice.

    ‘Slow feedbacks’ may lag global temperature change by decades, centuries, millennia, or longer time scales. Principal slow feedbacks are surface albedo and long-lived GHGs. It thus turns out that slow feedbacks on millennial time scales are predominately amplifying feedbacks. As a result, the feedbacks cause huge climate oscillations in response to minor perturbations of Earth’s orbit that alter the geographical and seasonal distribution of sunlight on Earth.

    Surface albedo refers to continental reflectivity. Changes of ice sheet area, continental area, or vegetation cover affect surface albedo and temperature. Hydrologic effects associated with vegetation change also can affect global temperature. Numerical experiments (Hansen et al., 1984) indicate that ice sheet area is the dominant surface feedback in glacial to interglacial climate change, so ice sheet area is a useful proxy for the entire slow surface feedback in Pleistocene climate variations. Surface albedo is an amplifying feedback, because the amount of solar energy absorbed by Earth increases when ice and snow area decreases.

    If this Mars rover fails to deploy because of design flaws, it’s on your head.

  34. Tom Curtis says:

    Frank, regardless of my disagreements with Richard Tol, he does take the very sensible attitude that the climate scientists know climate science better than he does; and accepts IPCC estimates of climate sensitivity. Based on that, he recommends a carbon tax set at between 50 and 150 US dollars per ton of carbon. Do you accept that as an appropriate policy given our current state of knowledge? Or do you base your policy that any high side uncertainties are certain not to happen?

  35. Given the success of the UK’s previous attempt at a Mars rover (Beagle 2) I’m unwilling to accept any liability :-)

    I’m on my phone so will respond to your longer comment later.

  36. Tom Curtis says:

    BBD, in the glacial/interglacial cycle, both CO2 and ice albedo are feedbacks on each other.

  37. BBD says:

    Yes, Tom, I do grasp that.
    ;-)

  38. Tom Curtis says:

    BBD, I don’t doubt it. I just thought it needed stating explicitly.

  39. Frank,

    Thanks for the clarification.

    This is why Nic Lewis asserts that “between AR4 and AR5 there has been a major reduction in the IPCC’s estimate of the cooling strength of aerosol pollution”. (You might want to do a little research before assuming Nic is wrong.)

    You might want to consider that when I say maybe I’m wrong, I actually mean it. I have no problem with being corrected. Ideally without the accompanied snark, but – to be fair – given the snark in my post, maybe a little snark in return is to be expected :-)

    The point I was trying to make relates partly to this comment (for example). It’s my understanding that there is still some evidence that the aerosol forcing is greater than the current IPCC estimates. Also Hansen et al. (2011) says (pg 13421)

    Our derived aerosol forcing does exceed aerosol forcings
    employed in most climate simulations carried out for IPCC
    (2001, 2007). For example, an ensemble of models from sev-
    eral groups (Fig. 9 of Stott and Forest, 2007) had aerosol
    forcings in the range −0.4 to −1.1 Wm−2. Our interpreta-
    tion of why these models produced agreement with observed
    temperature change over the past century is that the ocean
    models have a slow response function, slower than the real
    world, mixing heat too efficiently into the deep ocean, and we
    have cited several ocean model/data comparisons that pro-
    vide some support for this interpretation

    Hence, it doesn’t appear that Nic Lewis’s claim the aerosol forcings in the models are too high is necessarily correct.

    Even if he does have a point, we would also expect the aerosol forcing to reduce (both in relative and absolute terms) as we clean up our future emissions. Hence the ECS estimated from through ‘energy-balance’ today will likely produce a value below what will likely occur. This, to me, is an illustration of what Tom was pointing out above. The empirical estimates are unable to capture future changes such as non-linearities in the feedbacks and likely reductions in aerosol forcing.

  40. Rachel says:

    Tom, thanks. And DumbSci, too.

  41. Frank,

    The supply of fossil fuels still in the ground is massive, but the cost of obtaining them certainly could rise as the most accessible supplies get used up. The cost of non-fossil fuel energy is likely to come down in the next half-century.

    I agree. Why, then, do we continually see commenters on the other side of the debate suggesting that anything other than fossil fuels will increase poverty and destroy our economies. Even in the absence of a risk from climate change it would seem sensible to start investing in alternatives, both so as to have a mature technology ready for the future and so as to benefit from the likely spin-offs that will result.

  42. Tom,

    BBD, in the glacial/interglacial cycle, both CO2 and ice albedo are feedbacks on each other.

    Thanks, I think I’m starting to get this. Let me potentially embarrass myself by elaborating on how I now understand it :-)

    The interglacials are driven by variations in solar forcing and variations in CO2 forcings. Hence identifying forcings and feedbacks is difficult given that changes in albedo and changes in CO2 can, as you say, be both forcings and feedbacks.

    In Hansen & Sato (2012) they seem to combine both the CO2 and albedo forcings so as to get a total change in forcing which (if I understand this properly) then reflects the total change in external forcing. Comparing this with the change in temperature can then give a climate sensitivity. However, since the change in albedo (a slow feedback presumably) is included in the forcing, this means that the climate sensitivity derived this way is the response to fast feedbacks only, and hence is more like an ECS than an ESS.

  43. Tom Curtis says:

    Anders, yes! The only quibble is that the glacial cycle is triggered by regional variations in insolation, and driven by both albedo and CO2/CH4 feedbacks; of which the albedo response to increasing or decreasing ice sheet size is slightly more important than the greenhouse response.

  44. Tom, thanks. Yes, I do realise that the trigger is variations in insolation, but didn’t make that clear in my elaboration :-)

  45. John Mashey says:

    ” regional variations in insolation”
    Yes, or in more detail, what seems to matter is NH summer insolation, typically at 60-65 degrees North. See Ruddiman, Kutzbach, Vavrus(2011):
    Fig 1: Caloric summer season insolation departures at 65°N from the present-day value for the Holocene (in red) and for equivalent intervals in previous interglaciations …
    Fig 2.Dome C concentrations of (A) CH4 and (B) CO2 for the Holocene and seven previous interglaciations

    Although the paper is about the differences between the Holocene and earlier interglacials, the graphs and surrounding discussion are good explanations of interglacial dynamics.
    Note of course, that we live in a peculiar time in Earth’s history, that allows for cyclic glaciation/deglaciation patterns:
    1) If CO2 at bottom were, say 100ppm, we’d have permanent glaciers over Canada, if were 280ppm at bottom, we’d have no ice ages (until the CO2 weathered out. ) As it stands (as per David Archer’s The Long Thaw), we’re unlikely to have another ice age for a very long time.
    2) the continents need to have appropriate configurations.

  46. BBD says:

    Yes, thanks Tom. Interesting discussion. Who’s going to invoice Steve Bloom?
    ;-)

  47. Ian Forrester says:

    John, or anyone else who can help me, is it possible to convert cal/cm2/day into watts/m2? or am I wrong in thinking they are convertible?

  48. Ian, 1 calorie is 4.184 Joules, cm2 to m2 is 1cm-2 is 0.0001m2, 1 day is 86400s. So, it would seem that to convert cal/cm2/day into watts/m2 is multiply by 4.184, then by 10000, then divide by 86400, which I get to be 0.048 (i.e., to convert from cal/cm2/day to watts/m2 multiply by 0.048). I could be wrong though :-)

  49. tlitb1 says:

    @Anders

    Regarding one of your quoted parts of Lewis’s submission: (which I hope will look similar quoted below)

    The IPCC considers all observational ECS estimates in AR5 WG1. It concludes that estimates based on

    * paleoclimate data reflecting different past climate states
    * climate response to volcanic eruptions or solar changes
    * satellite measurements of short-term changes in heat radiation

    are unreliable and/or unable to provide usefully well-constrained estimates. I agree with this conclusion. That leaves in essence only estimates based on observations of warming over multi-decadal periods. Useful surface temperature records extend back approximately 150 years (the ‘instrumental period’).

    You say:

    I’d love to know if this is correct. I can’t find anything in the IPCC document that seems consistent with this claim. Essentially he seems to be arguing that the only reliable estimates are his own.

    Do you think this following passage from Wg1 Ar5 12.5.3 Forcing and Response, Timescales of Feedbacks, would cover, if not all, most of that and help answer your question regarding your own interpretation about what he is arguing there?:

    Equilibrium climate sensitivity undoubtedly remains a key quantity, useful to relate a change in greenhouse gases or other forcings to a global temperature change. But the above caveats imply that estimates based on past climate states very different from today, estimates based on timescales different than those relevant for climate stabilization (e.g., estimates based on climate response to volcanic eruptions), or based on forcings other than greenhouses gases (e.g., spatially non-uniform land cover changes, volcanic eruptions or solar forcing) may differ from the climate sensitivity measuring the climate feedbacks of the Earth system today, and this measure, in turn, may be slightly different from the sensitivity of the Earth in a much warmer state on timescales of millennia

  50. tlitb1, yes, I think that probably does cover what I was asking. What I’m still uncertain about is what Nic Lewis appears to be concluding from that. It appears that he’s suggesting that these caveats imply that the only reliable estimates are his own (or, at least, those that use the same method that he uses). Have I interpreted what he concludes from this correctly, or not?

  51. Ian Forrester says:

    Thanks Anders.

  52. BBD says:

    As I read it, 12.5.3 cautions that ECS is neither the only nor necessarily the best way of quantifying climate change on all time-scales. It points out that attempts to quantify the full effects of forced change may be underestimates – ECS rather than ESS.

    While the conclusion is that TCR is more useful for establishing near-term policy response, the IPCC does not appear to conclude that NL is the only reliable source of information on the topic. This is unsurprising since nobody expects NL’s work or indeed any single study to be the last word on this.

  53. tlitb1 says:

    @Anders

    You said (my emphasis in quoted stuff below):

    It appears that he’s suggesting that these caveats imply that the only reliable estimates are his own (or, at least, those that use the same method that he uses).

    In that case I think this part of the Lewis submission is relevant and might be illuminating to you:

    Since AR4 a series of papers have derived estimates of ECS and TCR from observational data. Although not done in AR5, if those estimates:
    * using methods considered in AR5 to provide unreliable or ill-constrained estimates;
    * involving poor experimental design or unsuitable data; and/or
    * that were significantly affected by use of subjective priors (uniform or ‘expert’)

    are eliminated from the assessment, the average ECS for those that remain [Ref 19] is, at 1.8°C, considerably lower than the GCM average of 3.2°C, but close to the energy-budget best estimate of 1.7°C that was outlined in the last paragraph

    I think the reference he used in the above is the most illuminating part of it:

    [Ref 19] Aldrin et al. (2012) (the estimate of which was, exceptionally, not significantly affected by the subjective Bayesian method used);

    If Lewis says that“those that remain” that give lower ECS includes Aldrin, and Lewis says differs from his method – using subjective Bayesian method – it seem here that Lewis is not making a case for his own works preeminence.

    Do you think Lewis has some latent issues with hubris? From my subjective opinion of what I have read of his, in various places, I have only picked up quite the opposite demeanor. I certainly can’t see it in this submission.

    What am I missing?

  54. BBD says:

    What am I missing?

    Perhaps this?

    Because of the time dependence of effective climate sensitivity, fitting simple models
    to AOGCMs over the first few centuries may lead to errors when inferring the response on multi-century timescales. In the HadCM3 case the long term warming would be underestimated by 30% if extrapolated from the first century (Gregory et al., 2004), in other models the warming of the slab and coupled model is almost identical (Danabasoglu and Gent, 2009). The assumption that the response to different forcings is approximately additive appears to be justified for large scale temperature changes but limited for other climate variables (Boer and Yu, 2003; Sexton et al., 2003; Gillett et al., 2004; Meehl et al., 2004; Jones et al., 2007). A more complete discussion of the concept of ECS and the limitations is given in Knutti and Hegerl (2008).

    And the general assumption that you can calculate ECS from “observational” data is questionable. These are subject to uncertainty, to natural variability and exclude the future effects of non-linear feedbacks.

  55. BBD says:

    What NL is doing is over-reaching himself. He is arguing that the various attempts to calculate TCR from “observational” data are both far more robust and informative than they actually are and capable of forcing a re-evaluation of a large body of other work informing the estimates of ECS.

  56. tlitb1,

    are eliminated from the assessment, the average ECS for those that remain [Ref 19] is, at 1.8°C, considerably lower than the GCM average of 3.2°C, but close to the energy-budget best estimate of 1.7°C that was outlined in the last paragraph

    Yes, I noticed that too and it seemed to be roughly consistent with what I was suggesting. The average for the GCM estimates is – I think – 3.2oC. The typical value from paleo-climatology studies is around 3oC. So, it seems that he has eliminated almost all other estimates. It may well be that he hasn’t eliminated all, but mostly all. I would argue, that finding some studies that are not the same as his but that aren’t eliminated doesn’t negate the point I’m making.

    I’ve no idea whether or not Lewis suffers from Hubris. I do think, however, that his behaviour is not entirely consistent with someone who is genuinely interested in the science associated with climate sensitivity. I do find it odd that a group who seem to think that scientists who advocate policy lose credibility, have no issue with a businessman – who decides to become a climate scientist – suddenly getting one of the lowest ECS estimates, but who also decides to submit evidence to the parliamentary inquiry that is highly criticial of a large fraction of the other methods. That doesn’t mean he’s wrong, but I would guess that the same people who think Nic Lewis’s submission is fantastic would have been highly critical of James Hansen had he submitted something with the same general tone.

  57. tlitb1 says:

    @BBD

    Thanks for that quote from Ar5 Wg1 12.5.3 Forcing and Response, Timescales of Feedbacks

  58. tlitb1 says:

    @Anders

    I do think, however, that his behaviour is not entirely consistent with someone who is genuinely interested in the science associated with climate sensitivity.

    I think this is a very interesting concept. An implied latent correct behaviour to be seen by scientists in certain subjects?

    And is correctly detectable in some way?

    This is quite a step out of the fundamentals of ECS, TCR or even ESS don’t you think?

    I do find it odd that a group who seem to think that scientists who advocate policy lose credibility, have no issue with a businessman – who decides to become a climate scientist – suddenly getting one of the lowest ECS estimates, but who also decides to submit evidence to the parliamentary inquiry that is highly criticial of a large fraction of the other methods.

    I see a proposition here:

    I.e. That there are a couple of groups:

    Group who seem to think that scientists who advocate policy lose credibility

    Group who hate businessmen who decide to become climate scientists

    However, is it valid that either of these groups could do the next?

    Decides to submit evidence to the parliamentary inquiry that is highly criticial of a large fraction of the other methods.

    Or even more likely members of both groups could more prosaically decide to submit evidence to the parliamentary inquiry because they think they have something they feel strongly about and have worked on without even considering they are in a group let alone antagonism to another group in their procedure.

    Which of the above propositions is the more likely?

  59. tlitb1 says:

    Or there aren’t just two “groups” ;)

  60. tlitb1, I’m not quite following your comment. To be clear, I have no issue with scientists advocating policy and I have no issue with businessmen becoming scientists. I also have no issue with Nic Lewis’s published work. My only real issue is with what he seems to be suggesting in his submission to the UK government. I think someone serious about doing science would be working with other scientists, not submitting comments to the government criticising their work. My previous comment was reflecting on why some who seem critical of scientists advocating policy seem to think what Nic Lewis’s has submitted is fantastic despite it appearing to have quite a strong policy steer.

    Now that I’ve clarified my position, maybe you could clarify what you were suggesting in your previous comment?

  61. tlitb1

    Or there aren’t just two “groups” ;)

    Indeed, but you probably know what I meant even if it wasn’t quite the best way to describe it :-)

  62. Nic Lewis has made claims like this before: “Most observationally-constrained studies use instrumental data, for good reason. Reliance cannot be placed on paleoclimate proxy-based estimates of ECS – the AR4 WG1 report concluded (Box 10.2) that uncertainties in Last Glacial Maximum studies are just too great, and the only probability density function (PDF) for ECS it gave from a last millennium proxy-based study contained little information.”

    Does anyone have a link to the IPCC AR4 WG1 box 10.2? I’m skeptical of Nic Lewis’s interpretation of that box, mainly because Figure 3a in both the PALAEOSENS paper and Knutti and Hegerl 2008 summarize dozens of sensitivity studies. If box 10.2 really does dispute these results, it would help to see the IPCC’s exact wording.

  63. tlitb1 says:

    @Anders

    My only real issue is with what he seems to be suggesting in his submission to the UK government. I think someone serious about doing science would be working with other scientists, not submitting comments to the government criticising their work.

    Don’t you think the Government understand the weight these submissions have?

    If not then it does seem you are unduly worried here about the power Lewis’s submission could have upon the Government.

  64. tlitb1, ahh, I see. No, I’m not worried. I’m simply exercising my right to comment on what is now a publicly available submission to the UK government. I’m in no way suggesting that Nic Lewis shouldn’t have submitted what he did, nor am I suggesting that those involved aren’t capable of judging these submissions suitably.

    Having said that, if you – or anyone else – thinks any of my criticisms are unfounded, I’m happy for anyone to comment and suggest (convince me) that what I’ve said is wrong. Part of the reason for writing these posts is to learn from what others say in the comments and – typically – I learn quite a lot.

  65. > This is quite a step out of the fundamentals of ECS, TCR or even ESS don’t you think?

    Having some engineering-level formal steps from the fundamentals of ECS, TCR or even ESS to Nic’s conclusions in his comment might be nice.

  66. Thanks BBD. It’s unclear how Lewis drew such a strange conclusion about paleoclimate estimates in general after referring to Box 10.2 discussing the Last Glacial Maximum (LGM). Just to be clear, the LGM did not last 420 million years. Many proxies recorded the climate during periods other than the LGM.

    Anyone who’s interested in what the IPCC really says might want to read BBD’s link. But here’s a teaser:

    “Two recent studies use a modelled relation between climate sensitivity and tropical SSTs in the Last Glacial Maximum (LGM) and proxy records of the latter to estimate ranges of climate sensitivity (Annan et al., 2005b; Schneider von Deimling et al., 2006; see Section 9.6). While both of these estimates overlap with results from the instrumental period and results from other AOGCMS, the results differ substantially due to different forcings and the different relationships between LGM SSTs and sensitivity in the models used. Therefore, LGM proxy data provide support for the range of climate sensitivity based on other lines of evidence. Studies comparing the observed transient response of surface temperature after large volcanic eruptions with results obtained from models with different climate sensitivities (see Section. 9.6) do not provide PDFs, but find best agreement with sensitivities around 3°C, and reasonable agreement within the 1.5°C to 4.5°C range (Wigley et al., 2005). They are not able to exclude sensitivities above 4.5°C.”

  67. tlitb1 says:

    @Anders

    Having said that, if you – or anyone else – thinks any of my criticisms are unfounded, I’m happy for anyone to comment and suggest (convince me) that what I’ve said is wrong

    I do think you are wrong when you diverge from the IPCC latest AR5 in the following quote of yours, and, unless you substantiate it, you are wrong, or at least contradict the AR5 which is the subject of the Parliamentary IPCC 5th Assessment Review submission process :

    You said (my highlight) in your criticism of Lewis not using Earth system sensitivity (ESS):

    It’s now accepted that there are likely slower feedbacks that on longer timescales will lead to a higher equilibrium temperature than ECS estimates would suggest.

    However the nearest direct quote in the IPCC Ar5 I could find seems to contradict this:

    Earth system sensitivity over millennia timescales including longterm feedbacks not typically included in models could be significantly higher than ECS.

    The IPCC AR5 “could be” is not equivalent your “are likely” is it?

  68. BBD says:

    AR5 WG1 12.5.3:

    A number of recent studies suggest that equilibrium climate sensitivities determined from AOGCMs andrecent warming trends may significantly underestimate the true Earth System Sensitivity (see Glossary) which is realized when equilibration is reached on millennial timescales (Hansen et al., 2008; Rohling et al., 2009; Lunt et al., 2010; Pagani et al., 2010; Rohling and Members, 2012). The argument is that slow feedbacks associated with vegetation changes and i
    ce sheets have their own intrinsic long timescales and are not represented in most models (Jones et al., 2009).

  69. tlitb1, I’ve discussed the long-term feedbacks which distinguish ECS from ESS. In fact, my day job is using GRACE satellite data to watch the “long-term” ice sheet feedback kick in faster than models like ISSM are currently able to explain.

    I’ve also repeatedly pointed out that to make an apples-to-apples comparison, the PALAEOSENS paper had to remove feedbacks that were present in the paleodata but weren’t being simulated by climate models, which implies that ESS > ECS for the past 65 million years.

    So in my opinion Anders’ “likely” is more accurate than the IPCC’s “could be”.

    Congratulations. You just discovered a probable inaccuracy in the latest IPCC report. Do you want to tell Anthony Watts so he can post this discovery on the world’s best science blog? (He banned me, so I can’t let him know this good news.)

  70. Scratch that. The IPCC referred to “significantly” higher, which is entirely consistent with Anders’ “likely” higher.

  71. tlitb1 says:

    @BBD

    Er, Ok, judging by the context, thanks for yet another quote from Ar5 Wg1 12.5.3 Forcing and Response, Timescales of Feedbacks

    This time without the slightest attendant wordage that could help illustrate or support any meaning or show if even you have a stance.

    So, in that case, I am left with sad conclusion that you think the word “suggest” is equivalent to our hosts “there are likely”

  72. tlitb1, I wasn’t quoting the IPCC specifically, and never said I was. The IPCC reports are assessment reports, not gospel. As @DumbSci has already illustrated, there is plenty of scientific literature suggesting that the ESS is likely higher than the ECS.

  73. BBD says:

    And we are drifting away from the issue of NL having a sound basis for suggesting that ECS is lower than generally supposed.

  74. tlitb1 – I’m really not interested in a debate about semantics. All I really mean is that it appears that there is evidence to suggest that there are slow feedbacks that typically are not captured by estimates of the ECS. Whether the correct term is likely, or could be, or suggests isn’t really the point. Interpret it any way you like, but that doesn’t change that evidence exists for an ESS that is higher than the ECS.

  75. BBD says:

    tlitb1

    This time without the slightest attendant wordage that could help illustrate or support any meaning or show if even you have a stance.

    Well, I did say this, earlier.

  76. tlitb1 says:

    @Dumb Scientist

    So in my opinion Anders’ “likely” is more accurate than the IPCC’s “could be”.

    Which is fair enough in itself, however, in that case this only helps to highlight the fact the critique by Anders here of a named expert reviewer of AR5 – Nic Lewis- to a specific Parliamentary committee with a specific purpose i.e. the “IPCC 5th Assessment Review”, is less valid because it is relying on extraneous results to AR5; which neither Lewis or the Government are supposed to depend upon!

  77. tlitb1 – oh please. Firstly, I’ve never said what I write has any validity whatsoever. You, and everyone else, gets to judge it based on what I say and how it gets corrected (or not) in the comments. Secondly, appeal to authority? I’ll let others comment on the significance of being a named expert reviewer (Christopher Monckton anyone?).

  78. tlitb1 – plus this

    is less valid because it is relying on extraneous results to AR5; which neither Lewis or the Government are supposed to depend upon!

    is neither here nor there. The IPCC reports may well provide easy access to information for policy makers. That does not mean that other information (the actual scientific literature) is no longer relevant. Furthermore, to suggest that Lewis (an actual climate scientist) can now ignore the actual scientific literature and can focus only on the IPCC reports is completely absurd. It’s a synthesis report, not the gospel (I may have already said that, but you appear not to have noticed).

  79. Tom Curtis says:

    AR5 Chapter 12, page 75:

    “On timescales of many centuries, additional feedbacks with their own intrinsic timescales (e.g., vegetation, ice sheets; see Section 5.3.3, 12.5.3) (Jones et al., 2009; Goelzer et al., 2011) may become important but are not usually modelled. The resulting Earth System Sensitivity (ESS) is less well constrained but likely to be larger than ECS (Hansen et al., 2008; Rohling et al., 2009; Lunt et al., 2010; Pagani et al., 2010; Rohling and Members, 2012), implying that lower atmospheric CO2 concentrations are needed to meet a given temperature target on multi-century timescales. A number of caveats, however, apply to those studies (see Section 12.5.3.1). Those long-term feedbacks have their own intrinsic timescales, and are less likely to be proportional to global mean temperature change.

    (My emphasis)

    Turns out that the IPCC goes with likely in just the way that Anders does. Specifically, it is likely that the ESS will be higher than the ECS, and it could be significantly higher.

  80. Tom Curtis says:

    tlitb1 quotes a passage of AR5 above which he suggests shows caution about methods other than those based on a similar times scale to those by Nic Lewis. In fact the passage in question is not about methods, but a caution about the size of the response to temperature, which may vary on different time scales. In box 12.2, when methods are specifically discussed, the IPCC mentions caveates about several different methods. They all, afterall, have their pit falls. In particular, the IPCC makes the following caveat:

    “Analyses of observations and simulations of the instrumental period are estimating the effective climate sensitivity (a measure of the strengths of the climate feedbacks today, see glossary), rather than ECS directly. In some climate models ECS tends to be higher than the effective climate sensitivity (see Section 12.5.3), because the feedbacks that are represented in the models (water vapour, lapse rate, albedo and clouds) vary with the climate state.

    So, not only does the IPCC have caveats for other methods, but they explicitly include a caveat for methods using the instrumental (and ergo including those used by Nic Lewis), with the further information that there is reason to suspect they low ball the ECS.

    Faced with multiple methods, each with their own pitfalls, a sensible approach is to use studies using all methods. and that is what the IPCC does:

    “Based on the combined evidence from observed climate change including the observed 20th century warming, climate models, feedback analysis and paleoclimate, equilibrium climate sensitivity (ECS) is likely in the range 1.5°C–4.5°C with high confidence. ECS is positive, extremely unlikely less than 1°C (high confidence), and very unlikely greater than 6°C (medium confidence).

    I think it is clear Nic Lewis has misrepresented the IPCC. In particular, an organization that uses particular methods does not think that they ” …are unreliable and/or unable to provide usefully well-constrained estimates”. In fact, that they used the methods to constrain the ECS shows directly that they thought the methods could “usefully constrain” the ECS.

    Further, Nic Lewis misrepresented the IPCC not only by overstating the caveats regarding other methods, but failing to mention their caveats regarding methods using the instrumental record, and therefore his own methods. Given that their caveat suggested that such methods would low ball ECS, and that he was arguing for a low ECS, the caveat was certainly germane, and he had no justification for not mentioning it.

  81. tlitb1 says:

    @Tom Curtis :

    Well thanks, I didn’t know that, I stopped at the first statement on ESS.

    So now we know that the IPCC report includes both these statements about ESS (my eye drawing emphasis in both :) ):

    Earth system sensitivity over millennia timescales including longterm feedbacks not typically included in models could be significantly higher than ECS

    The resulting Earth System Sensitivity (ESS) is less well constrained but likely to be larger than ECS..

    Now all is left is for both Dumb Science and our host to say they both firmly had your latter found in mind … ;)

    Me? Well it is near Christmas and I want to read something authoritative about spirituality; so I will be juggling whether I want Jesus to be born in a manger or a house .. so it will a toss up between reading Luke or Matthew depending how I feel :)

  82. BBD says:

    Headpiece filled with straw. Alas!

  83. Again, they’re both consistent because of the word “significantly.”

  84. Frank says:

    Tom: The most visible recommendation in Richard Tol’s latest paper (May, 2013, at the beginning of the conclusions) calls for a carbon tax $25/tonC, increasing at a rate of 2.3% per year and intended to stabilize CO2 at 625 ppm. This numbers seem very different from what you report. There are a lot of caveats, but he doesn’t discuss alternative estimates of ECS or TCR – or even specific what ECS/TCR was used in his analysis. Therefore, I presume, but do not know, that he is relying on the IPCC’s projections when calculation an optimum carbon tax. As best I can tell, if he were confident that the newer and lower figures from Otto, Lewis and others were correct, he might recommend a lower tax or none at all. The paper can be downloaded here: https://www.sussex.ac.uk/webteam/gateway/file.php?name=wps37-2012-tol.pdf&site=24

    FWIW, I am attracted to McKitrick’s suggestion for a carbon tax that rises with temperature (and possibly sea level). Like Hansen, I would rebate the proceeds of the tax to every individual (and to businesses competing overseas where there is no tax or effective regulation. I like Richard Tol because he doesn’t seem to be owned by any side in the debate

  85. Frank,

    And then there’s physics. We’re rapidly using up our carbon budget, so we can’t use time-delayed metrics like sea level or global surface temperature. (Or temperature subsets like some unintentional cherry pickers have proposed.)

    I left a few comments on this CCL article trying to explain that the rebates should all go to citizens, with border tariffs to protect businesses competing with imports produced in countries without effective regulation. I can’t include many links in each comment, but just look at all the countries moving towards acknowledging that we shouldn’t treat the atmosphere like a free sewer. This isn’t likely to be a problem for very long, as more people accept the physics of our situation.

  86. > Well it is near Christmas and I want to read something authoritative about spirituality

    Biblical, biblical,
    I wanna get biblical:

    http://neverendingaudit.tumblr.com/tagged/GettingBiblical

    Let me hear your Spirit talk.
    Your Spirit talk.

    Luke 6:37, everyone.

  87. Tom Curtis says:

    Frank, Tol writes:

    “Nonetheless, decisions should be made with the best available knowledge – even if the
    best available knowledge is not very good. The main advice to policy is given in Table 2.
    A government that plays a cooperative game on climate policy, and uses the same
    discount rate for climate change as for other decisions, should levy a carbon tax of $26/tC
    (mode) to $50/tC (mean). A higher tax can be justified by an appeal to risk (Weitzman,
    forthcoming), but not necessarily by an appeal for a lower discount rate (Nordhaus, 2008,
    Ch 9) or international equity (Schelling, 2000).”

    Table 2 is, of course, where I drew my figures from, and, apparently, he is basing his recommendations on a discount rate of 3% per annum, but leaving it open to policy makers to decide on a lower discount rate. I am puzzled by his ambiguity be using the mode or the mean. Rational policy would be based on the expected value of the policy, which will track the mean rather than the mode if costs are equal across the probability density function. In fact his formula for costs shows a sharply rising cost with higher values, so that the most rational policy would be based on a social cost of carbon significantly higher than the mean given by his PDF (between the 67th and 90th percentile). (I may be confused on this point in that that may already be factored in to his social costs, but that just means the mean is the relevant value.)

    Even that represents a low value for (as Tol acknowledges), the economic analyses he performed an relied on fail to capture many known and unknown costs of global warming, and he is not entitled to think that they are balanced by the few known or unknown benefits it also fails to capture.

    I note, in passing, that his preferred policy as noted by you, is entirely consistent with even a $150 dollar carbon tax because it increases every year. That reflects the simple fact that the least disruption (ie, avoidable economic losses) will be achieved by starting the carbon tax low and increasing it gradually with time. That allows for low initial impacts, and planning certainty. It gives people (and business) time to adjust to the higher rates that will follow.

    That last is a very important point. That is why I will accept any carbon tax now, so long as it increases with time in a reasonably predictable way. It starts a response. It will thereby allow the transition to higher carbon taxes that I think essential to be less economically damaging; and at least limits the long term harm if our species remains bent on long term disaster. Thus I would happily support McKitrick’s tax as an interim measure. I would prefer the tax to rise with the 5 year average of global temperatures to make decision making for business easier. I would also prefer the tax to rise at the percentage increase in the GMST anomaly relative to 1961-1990 (or 1951-1980), and to start with at least Tol’s 25$/TC.

    The only problem I have with multiple carbon price proposals is that they will fracture political support for any one price. I suspect that is McKitrick’s intent.

    Finally, I do not think somebody closely associated with the GWPF can claim to not be owned by either side of the debate. I like Tol for the most part because, for the most part, at least, he seaks to maintain his intellectual integrity/reputation.

  88. tlitb1,

    Now all is left is for both Dumb Science and our host to say they both firmly had your latter found in mind …

    Well, I didn’t. All I had in mind was our current scientific understanding of the ESS and ECS. Turns it, it seems, that my understanding was roughly correct.

  89. Frank says:

    Our host replied: “You might want to consider that when I say maybe I’m wrong, I actually mean it. I have no problem with being corrected.”

    Tom Curtis made a statement about Richard Tol that I believed was unlikely to be correct – or at least not relevant to Tol’s current views. I really wanted to question the validity of Tom’s statement, but a reference was far more valuable. If you had consulted AR5, you would have known why Nic made the statement he did about consensus estimates of aerosol forcing. If I had looked more closely before commenting on unforced variability, I wouldn’t have made the mistake of using the term confusing term “natural variability” and I might have found the reference at SkS that one of your other readers provided saying that an unforced variability of 0.3 degC has been observed (so unforced variability cam be at least this large.) We all need more up-to-date facts and fewer opinions.

  90. Frank says:

    Tom: I’m glad you are no longer saying that Tol supports up to $150/tC carbon tax (at least for not for six decades). If lower climate sensitivity becomes the consensus, the modest tax he currently supports could become smaller or vanish.

    I’d base my carbon tax on the temperature over the past 30 years; then all changes will be slow and reasonably predictable. Or I might base it on the rate of temperature rise over the past 30 years and how fast we are currently approaching a temperature change representing “catastrophe”. How many years of safety margin do we have left at the current rate of warming? The 2 degC rise that Tol thinks would bring us to net neutral wouldn’t be a catastrophe. If we arbitrarily chose 3 degC and current warming were about 0.15 degC/decade, we have a “safety margin” of 200 years, not enough to require a high carbon tax. If we were already at Tol’s breakeven point (+2 degC) and less than 50 years away from “catastrophe”, a tax high enough to eliminate the use of fossil fuels for generating electricity and non-airplane transportation might be appropriate.

  91. OPatrick says:

    I like Richard Tol because he doesn’t seem to be owned by any side in the debate

    Do the GWPF only rent him?

  92. Frank,

    I’m not quite sure what you’re implying by this

    We all need more up-to-date facts and fewer opinions.

    If I had an infinite amount of time, maybe I could read everything and make fewer mistakes. I don’t. Hence I write the way I do – allowing for the possibility that I’m wrong. It’s a blog, not a peer-reviewed publication. Personally, I think what we need are more people willing to acknowledge their errors and fewer people who think that nit-picking is the way to have a scientific discussion.

    So, yes I accept – happily – your correction that what Nic Lewis said about the change from AR4 to AR5 was correct. However, I was trying to make a broader point than simply that. In my previous comment I linked to a comment about how aerosol forcing could be higher than the IPCC estimates (which are uncertain anyway). There is a relevant paper, that I can’t quite find at the moment. I also included a paragraph from a paper that seemed too indicate that GCMs are not really using aerosol forcings that are outside the AR5 range. Also, even if they are, we would expect aerosol forcings to reduce (by in absolute and relative terms) in the future. So, that is something that energy budget estimates are unlikely to capture.

    So, my issue was more with that Nic Lewis was concluding from the change from AR4 to AR5 than with his statement about that change. He seems to be concluding that his low estimate is more robust than others, without acknowledging that future changes in aerosol forcing will likely result in a higher ECS than his estimate suggests, and he seems to be making claims about aerosol forcings in GCMs that are not obviously correct.

  93. Frank,

    This is actually the comment I was thinking of when I mentioned some estimates still suggest aerosol forcing is larger than the IPCC estimate (although still within their range).

  94. Winding down:

    https://twitter.com/TLITB1/status/414742946496274432

    Seeking consistency can take many channels.

  95. Tom Curtis says:

    Frank, you would have to give me a reference for Tol recommending less a carbon tax of less than 150 $/TC. My understanding is that his policy is to show the desired carbon tax under a variety of policy objectives and assumptions and that therefore reducing that range of recommendations to a single figure does not reflect his thought. That he explicitly mentions the tax that would be ideal given:
    1) the use of the same discount for inter-generational as for intra-generational decisions;
    2) the assumption that the value of a life is given by the value of a persons income; and
    3) no consideration of large but uncertain risks
    based on the fact that that is how government policies are currently evaluated does not mean he agrees with those assumptions himself. Consequently, I believe the original range of values that I gave still reflects Tol’s thought on the issue, or at least what he is prepared to commit himself to in peer reviewed publication, better than a single value.

    Tol, I think, significantly underestimates the social cost of carbon by not doing enough to take factors 1-3 into account, and by precluding a priori the possibility that the effects of climate change could be sufficient to reverse global economic growth. Never-the-less his output is intellectually defensible because he takes pains to recognized the effects of at least some of those assumptions on his estimates, and allowing policy setters to take a different approach. I have no desire to reduce is position to a dogmatic and indefensible position by insisting that his recommendations should be interpreted in which arbitrarily excludes his caveats as you are doing.

    On another issue, setting a carbon tax to rise with the 30 year mean anomaly will place too much inertia in the system if temperatures quickly rise to catastrophic levels. By the time the rapid rise is fully recognized in the rate of increase in the carbon tax, we would already have passed dangerous thresholds of greenhouse concentration. Put simply, the virtue of McKitrick’s tax proposal is that it can remain neutral about IPCC projections. However, if IPCC projections are correct, CO2e levels can rise to dangerous levels in less than 30 years. Therefore a tax that makes minimal assumptions about the accuracy of the IPCC must be able to rise rapidly in less than that period. That limits the length of the mean anomaly that can be used setting the tax rate while still maintaining relative neutrality to IPCC projections.

  96. Tom Curtis says:

    Willard, what a bizarre conversation. I must wonder why an intelligent man(?) feels in necessary to defend himself against a transparent fool. I guess that is the magic of twitter.

  97. Tom,

    Is the question mark for man or intelligent? :-)

    Twitter has it’s magic, but is not a great medium for discussing a complex topic. I keep falling into the trap of thinking that what seems like a reasonable response to me will be seen as a reasonable response by the other party. I think my Twitter learning curve is a bit like temperature anomaly data – a long-term trend towards recognising that it’s usless for discussing a complex topic, but with a lot of noise :-)

  98. Tom Curtis says:

    Anders, I doubt your manhood, and reserve judgement on your intelligence :P

    I do not see how pointing out that:
    P(A>>B)>0 is not inconsistent with P(A>B)=>=66% is complex.

    Nor do I see the complexity in pointing out that saying that mentioning ESS would have been better (the strongest interpretation that can be placed on your mentioning that Lewid does not mention ESS) does not entail that mentioning ESS is mandatory (ie, he ought to have mentioned ESS).

    I am puzzled, however, that a presumably intelligent person by normal measures cannot see, or accept first without difficulty, or the second at all.

    I better not mention that 2+2=4, or he’ll be after me about my inconsistency as well.

  99. > [W]hat a bizarre conversation.

    Conversation? What conversation, Tom? After meditating either on Luke or Mark, our Leopard celebrated his own goal over Twitter. Not sure in which verse he found that “is likely” and “could” are contradictory, though.

    My favorite tweet is this one:

    This might come handy.

  100. Willard,

    I missed that tweet from Shub. The reason for that was simply because I decided ages ago that the most sensible way to engage with Shub was to block him/her.

  101. BBD says:

    One of the most insightful remarks I think I’ve heard from the Goat, who is not noted for wisdom.

  102. BBD, indeed – quite “familiar with”, but not necessarily typical “practice” for academics :-)

  103. BBD says:

    I think I should have made that point clear ;-) Familiar with because routinely used by “sceptics”.

  104. Shub seems not to appreciate having retweeted is tweet:

    The discussion that follows seems to have dissipated the #YesButModeration a bit.

    Shub’s tweet got some reshares, among them by Leo and of course Barry, who has a knack for smarm.

  105. Eli Rabett says:

    Eli seems to remember that Tol(2002) was incredibly (as in don’t believe that crap) optimistic on ag production as a function of CO2 and T. Frank Ackerman has more on that.

    Be that as it may, his submission to the panel was incredibly toned down.

  106. Willard,

    Just to be clear, I’ve only blocked Shub on Twitter. He/she is certainly not prevented from commenting here. He/she may choose not to respond, but is not prevented from doing so.

    Eli, Thanks. I haven’t read much of what Frank Ackerman has to say. Tol’s submission is certainly more measured than I might have expected.

  107. BBD says:

    “The BBD blog”?

    The Goat seems even more confused than usual.

    Perhaps if certain people spent less time on Twitter behaving like bitchy schoolgirls behind the bike sheds they’d have less to worry about by way of leakage.

  108. andrew adams says:

    My favourite tweet from the above exchanges was the one comparing Rachel to a jackbooted Rosa Klebb.

  109. I missed that one. Did Rachel enjoy that? Maybe I shouldn’t have blocked everyone on Twitter. Then I’d know what was going on :-)

  110. Rachel says:

    I missed that too! Can you post the tweet here, Andrew? I think that’s very funny.

  111. Someone somewhere does not follow my tweets:

    Grrr.

  112. I see, it’s not that I’m not following you, I blocked Foxgoose too. That’s why I missed that :-)

  113. Rachel says:

    Did you retweet that, Willard? I follow your tweets but some of them I miss. Mea culpa, mea culpa. There are so many things to read! But how funny is that tweet?!

  114. BBD says:

    I’ve had another look at this Twitter thing and it is a shocking mess. There’s somebody pretending to be God and somebody pretending to be Gavin Schmidt (very plausibly, but I have no doubt that he’s far too sensible to get sucked into anything like this), and worse besides. I won’t go into it now.

    * * *

    That is a squirrel, as I have pointed out before. What is wrong with these people? Heaven knows what happens when they get hold of a graph.

  115. Rachel says:

    Has Foxgoose’s tweet changed? Didn’t it say jackbooted before? Now it says steel tipped boots.

  116. andrew adams says:

    “Jackboots” might have been my faulty memory. “Steel tipped” would be more accurate if my memories of James Bond are correct. Which is not to suggest that you would wear such things Rachel (I obviously wouldn’t dare offend you!)

    I don’t know if Willard RT’d that particular tweet, It might have just been part of a conversation I saw from following one of his RTs.

  117. > That is a squirrel, as I have pointed out before. What is wrong with these people?

    Squirrels are everywhere:

    Personally, I do like the tweeter.

  118. Since it’s a thread about Nic Lewis’ submission, it might be appropriate to link to a prequel with a sneak preview:

    Nic, you are still confusing the issue with interpretations of probability.

    A prior is a prior probability distribution, because this is what Bayes’ Theorem and the axioms of probability require. How you interpret this probability is up to you, but the fact that it is probability is not up for debate. None of your references provide any support for you to dispute that a prior is a prior probability distribution.

    http://julesandjames.blogspot.ca/2013/02/yet-more-on-uniform-priors-and.html?showComment=1362089229021#c5787516431754745694

    Nic Lewis has yet to reply to that March 2013 comment.

  119. A related post at Eli’s:

    http://rabett.blogspot.ca/2013/02/on-priors-bayesians-and-frequentists.html

    I might not have an objective prior to link to that piece.

  120. Rachel says:

    “Jackboots” might have been my faulty memory.

    No, I could have sworn it read “jackbooted” before.

    In any case, BBD is exactly right. I am a squirrel and squirrels do not wear boots.

  121. Willard,

    Thanks for the links. Again I’m not an expert on Bayesian statistics but it is surprising that Lewis get a best estimate (median I think) of 1.7oC. The obvious question is why does this appear to be much lower than other estimates, including ‘energy budget’ estimates? From reading your links, there is a suggestion that a problem can be that if your prior distribution is poorly constrained, you can get a result that technically is what your Bayesian analysis would suggest is correct but that violates (or is inconsistent with) what you would get using a more physically motivated method. Is that a reasonable analysis? Apologies if the terminology isn’t quite appropriate.

  122. Joshua says:

    Shorter Nic = my priors are objectively derived, and anyone who disagrees is being subjective.

  123. BBD says:

    NL is an example of prior commitment.
    ;-)

  124. Pingback: Expertise | And Then There's Physics

  125. Pingback: Select committee report | And Then There's Physics

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