This post addresses some questions I was asked on another thread ("CRU 'not especially honest' on MBH98": Nov 26, 2011 at 9:56 AM | sam) and it was suggested by matthu that I post as a discussion topic.

The responses that follow are my own personal interpretation and understanding of the evidence. Others may have different interpretations and understanding, and in many cases will know more than me. If anyone who is more expert than me in any of these topics wants to jump in and correct me, they will be very welcome!

In particular, none of this should be taken as an “official” view from either the Met Office or IPCC.

Question 1
The 2007 IPCC AR4 report says: "Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations."
(a) What value scientifically has this conclusion?
(b) Do you agree with the strength of certainty expressed in the conclusion ("very likely" means more than 90% confidence)? If you do not agree with the confidence level expressed above what quantitative value would you place on the certainty/uncertainty of the conclusion?
Please cite evidence in support of your opinion and explain breifly the uncertainties involved in deciding such a matter?

(a) The scientific value of this conclusion is that it is an explanation for changes we are seeing in the world – and hence it helps with our understanding of climate processes. It also helps with our ability to estimate future changes that may result from an ongoing increase in greenhouse gas concentrations – estimates which can be tested against real data in decades to come.

(b) Yes I do agree with the “very likely” judgement. (I use “judgement” because it is indeed an expert judgement – there is no other way of assigning a likelihood. There are 3 pieces of evidence to support the statement:
i) An increase in global average temperature similar to that which actually occurred was forecast in advance in the early 1970s, on the basis of the expected increase in atmospheric CO2

ii) Estimates of the various external forcings of the climate system (radiative forcing, ie: the perturbation to the Earth’s energy balance) suggest that the net anthropogenic forcing is extremely likely (95%) to be substantial and positive, and likely (66%) to be at least five times larger than the natural radiative forcing (solar). The evidence for this is presented in the IPCC AR4 Radiative Forcing chapter on which I was a lead author . Since then, further evidence has emerged than the solar forcing may actually be smaller than that used in AR4 – see the other Bishop Hill discussion thread “Richard Betts: 20 C Temperature Attribution20C temperature attribution”

iii) General circulation models of the climate (which I do consider to be useful even if far from perfect!) do not reproduce the observed warming when driven with natural forcings alone. However they do reproduce it when anthropogenic forcings are included. It is important that all anthropogenic forcings are included – aerosols and land use as well as GHGs – because GHGs alone give a warming that is larger than observed.

iv) Changes over the last century appear to be unusual in the context of the last millennium.

There are of course uncertainties in all of this. For the radiative forcing estimates, those for CO2 and other well-mixed GHGs are reasonably well-known, but the forcings due to aerosols are much more uncertain. The uncertainties in land use forcing (surface albedo) are also large relative to the central estimate, but the central estimate is still relatively small compared to GHGs and aerosols. I’ll deal with limitations of models and palaeoclimate reconstructions in response to the specific questions on these topics below.

Question 2
Are global temperatures today within or outwith the range of historical natural varianbility?
Please give a quantitative value to the level of certainty/uncertainty you assign to your answer. Also, please cite evidence to support your conclusion and briefly explain the uncertainties involved in reaching the conclusion.

Depends what timescale you are looking at. The last decade has been warmer than any other in the instrumental record (ie¨last 150 years or so, which is when actual measurements of temperature have been taken in enough places across the world to allow a global average to be estimated), and this is shown in 3 datasets, but going back millions of years then the fossil evidence suggests a much warmer world than now. A key issue of course is how recent decades compare to the last couple of thousand years. A difficulty there is estimating global temperatures prior to the instrumental record – while thermometer records extend further back than 150 years in a few places, they don’t extend further than about 500 years even in the oldest local records, so “proxy” records are used, which are evidence from the natural environment which (if analysed with care) can give an indication of temperatures relative to the present-day. It is difficult to give an estimate of global temperatures before about 150 years ago, but northern hemisphere temperature variability has been estimated / reconstructed a number of times. The IPCC AR4 conclusion based on a number of these studies was that “It is likely (66%) that [the second half of the 20th Century] was the warmest Northern Hemisphere period in the last 1,300 years”.

As for whether the NH temperatures of the last couple of decades were matched by similar warmth lasting a couple of decades at times in the last over the last millennium – well my understanding is that none of the palaeoclimate reconstructions show comparable warm periods over the last 1,300 years, but there are of course uncertainties in these especially for shorter time periods.

Reconstructions of northern hemisphere temperatures over the last millennium (or starting earlier in some cases) are published in the following papers, which show varying levels of agreement or disagreement with each other for different times over the past few centuries:

Briffa, K.R., 2000: Annual climate variability in the Holocene: interpreting the message of ancient trees. Quat. Sci. Rev., 19(1–5), 87–105.

Briffa, K.R., T.J. Osborn, and F.H. Schweingruber, 2004: Large-scale temperature inferences from tree rings: a review. Global Planet. Change, 40(1–2), 11–26.

Cook, E.R., J. Esper, and R.D. D’Arrigo, 2004a: Extra-tropical Northern Hemisphere land temperature variability over the past 1000 years. Quat. Sci. Rev., 23(20–22), 2063–2074.

D’Arrigo, R., R. Wilson, and G. Jacoby, 2006: On the long-term context for late twentieth century warming. J. Geophys. Res., 111(D3), doi:10.1029/2005JD006352.

Esper, J., E.R. Cook, and F.H. Schweingruber, 2002: Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability. Science, 295(5563), 2250–2253.

Jones, P.D., K.R. Briffa, T.P. Barnett, and S.F.B. Tett, 1998: Highresolution palaeoclimatic records for the last millennium: interpretation, integration and comparison with General Circulation Model control-run temperatures. The Holocene, 8(4), 455–471.

Jones, P.D., T.J. Osborn, and K.R. Briffa, 2001: The evolution of climate over the last millennium. Science, 292(5517), 662–667.

Mann, M.E., R.S. Bradley, and M.K. Hughes, 1999: Northern hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations. Geophys. Res. Lett., 26(6), 759–762.

Mann, M.E., and P.D. Jones, 2003: Global surface temperatures over the past two millennia. Geophys. Res. Lett., 30(15), 1820, doi:10.1029/2003GL017814.

Moberg, A., et al., 2005: Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data. Nature, 433(7026), 613–617.

Hegerl, G.C., T.J. Crowley, W.T. Hyde, and D.J. Frame, 2006: Climate sensitivity constrained by temperature reconstructions over the past seven centuries. Nature, 440, 1029–1032.

Question 3
(1) How accurate is the measured temperature record
(a) on land?
(b) at the sea surface?
(c) by satellite?
"Accurate" means "showing a negligible or permissible deviation from a standard".

Accuracy varies according to where you are and how far back you are looking. In terms of the recent differences relative to the baseline (1961-1990 average) the annual global average air temperature over land is given to just under +-0.2 degrees C (95% confidence), and the sea surface temperature to about +-0.1 degrees C.

For recent decades, the difference in global average temperature for each year compared to the baseline (1961-1990) is given to within about 0.1 degree Celcius.
See and papers by Brohan et al, 2006, J. Geophys. Res, 111, D12106, doi:10.1029/2005JD006548 and Rayner et al, 2003 for further information.

Accuracy tends to decrease further back in time due to sparser data and difficulties with re-calibration on changes of instrument, siting of weather stations, etc

(I'm not sure of the numbers regarding satellite data at the moment – I’ll try to get back to you on that.)

(2) How reliable are paleoclimate reconstructions?
"Reliable" means "able to be trusted".

Well of course they are not as good as instrumental records by any means, but we don’t have any choice if we want to try to quantify and understand past climate variability. Each individual reconstruction has significant uncertainties, arising from issues such as the reliance on point data which is sometimes sparse (making it hard to estimate a large-scale average) and other effects on the proxy other than the one that it is being assumed to indicate (eg: potential effects of CO2 fertilization on tree rings being used as an indicator of temperature). As far as I can see, palaeoclimatologists go to great care to try to minimize the effect of these. The key thing is of course not to rely on any one individual reconstruction (just as one would not rely on any one individual model) and look at whether different reconstructions give similar results.

(3) How reliable are computer models, particularly your own?

Depends what you want to use them for. General circulation models have demonstrated a high level of success for weather forecasting on the timescale of a few days. OK they don’t always get it right, but they’re doing pretty well these days, especially when ensembles (several models) are used for a few days ahead and beyond, and especially with some expert human interpretation with knowledge of model biases and limitations (ie: don’t just treat them as a black box!)

On climate timescales the models are generally looking reasonable for large-scale and multi-year averages, eg: reproducing decade-by-decade changes in response to external forcing (both anthropogenic and natural). Regional climate changes are much more uncertain, and models often disagree on things like regional rainfall changes – although in some regions there is higher agreement between different models. Part of the problem is that there has not yet been large enough systematic climate change in comparison with natural variability to be able to test the models. Forecasting of internal variability (the natural fluctuations in climate that emerge just through the oceans and atmosphere affecting each other, and not through external forcing) is much more challenging, but this is what we really need to achieve because the most important requirement is to be able to forecast regional variability at timescales of a season to a few years ahead (a high aspiration!)

Since you ask, the Met Office Hadley Centre models are generally regarded as among the better models.

There is an enormous amount of quantification of climate model performance compared to observations, too much to do justice here in a short blog post. Sorry if it's a bit of a cop-out but I really would recommend reading the relevant AR4 chapter which gives lots of figures and tables showing the strengths and weaknesses of the models used at the time of that report (analysis of the latest models for AR5 has not been published yet).

Interestingly, I think palaeoclimate reconstructions and climate models have opposite problems. The former use point data and the uncertainty is in reconstructing the large-scale signal, whereas the latter are more skilful at large-scale changes and less reliable at individual points.

Question 4
In providing information to scientists/ policy makers/ journalists/ people do you normally provide a quantitative value to the level of certainty/ uncertainty to any conclusions you have reached?

Yes – see for example the UKCP09 projections, where we estimated the uncertainty in projected climate changes for the UK. Care is needed in interpretation of these – the UKCP09 documentation explains this in some detail for technical users, and when we provide information based on this to policymakers etc we do make clear the levels of certainty/uncertainty.

Of course it is not always possible to be quantitative in this (ie: some things are so uncertain you can’t put error bars on them, such as the IPCC AR4 estimates of the contribution of changes in ice dynamics to sea level rise. In these cases you just have to be clear that you don’t know enough to put numbers on it.)

Hope this helps. Scientific discussion on the evidence I have presented is welcome!

Sorry to be picky, Richard, but since you mentioned the "20 C Temperature Attribution" thread in your answer (b)(ii) above:-

1/ The recent evidence (TSI reconstructions) suggests that solar forcing in the first half of the 20th century was significantly smaller than that used in AR4.
2/ Since GCM reproductions of changes across the first half of the 20th century depend on an old solar reconstruction, they are presumably unable to now reproduce those changes.

Oh dear, I should have said "solar forcing changes in the first half of the 20th century".

As you yourself suggested in an earlier comment, the AR4 story behind the 20th C global temperature changes was as follows:-

1/ The rise 1910-40 corresponds to the rise in TSI minima seen in earlier TSI reconstructions.
2/ The decrease during 1940-70 corresponds to an increase in sulphate emissions.
3/ The rise 1970-00 corresponds to the observed increase in atmospheric CO2 levels.

Both #1 and #2 are in doubt; therefore mainstream climate science has NO realistic explanation available for 20th C temperature changes up until the satellite era. In particular, there is now no reasonable basis for your claim that GCMs are able to reproduce these changes. You don't need to look far for reasonable explanations of why this should be the case:-

A/ It is not possible to accurately initialize models for such runs because there are variations on all climate relevant time scales.
B/ Parameterizations used for cloud cover and other small scale phenomena are order of magnitude approximations; hence long time-scale results from GCMs are also only order of magnitude.

I found a talk by David Deutsch the other day that summarizes a lot of what I feel about this. As he says, "the rational thing for a layman to do is to take seriously the prevailing scientific theory", and of course I completely agree with him. The problem is that when that theory is constantly undermined by the advocacy, misrepresentation and frankly revolting behaviour of many of its supporters, the layman is left unsure what is or is not trustworthy.

I find it difficult to understand why people in your position would keep on pushing the kind of fairy story I mentioned above with such conviction. Why keep on doing this, when there are already strong and uncontested reasons for concern over increasing greenhouse gasses? The result of this kind of argument, constantly repeated, is to convince people - even including people like myself - that climate science is incompetent and untrustworthy. Society needs science to be in good working order, if the problems that lie ahead are to be solved successfully.

Richard has emphasised that "none of this should be taken as an “official” view from either the Met Office or IPCC."

Perhaps it would help if he were to clarify where his view differs from either the Met Office, the IPCC or the consensus view? In fact it would be fascinating to hear where he feels these three views no longer coincide.

Very briefly, Richard, since I haven't dug into the details yet and i have other commitments just now, but:
1. Thanks again for your input into the debate;
2. I am with Philip on the doubts arising about the reliability of the evidence for earlier warming/cooling in the 20th century and, until I read your post here, I hadn't realised just how much seeing the names Briffa, Mann, Jones, Bradley, Hughes, Hegerl, et al quoted as reliable sources for anything to do with climate makes the heart sink. It's probably the spillover from Climategate 1.0 and 2.0 but it does pose the question how, if we cannot trust these people in the small things, how can we possibly be expected to trust them in the big things?

Would Philip be prepared to provide the calculated results from the Met Office GCMs based on the two possible extremes of data input i.e. from the 'sceptic' and the 'alarmist' points of view?
This would show how far apart the two 'camps' really are.

Richard

How can any scientist or group of scientists claim to realistically assign % certainties to currently understood factors influencing our climate? AR4 dismisses known factors we do not fully understand, ignores the obvious fact that there are many factors we do not even know exist and then settles on CO2 as the cause of warming.
Our knowledge of all sciences is fledgling knowledge, the things we do not know dwarf the few things that we do know.
What the IPCC has done can be likened to a man who has one piece of a 10,000 piece jigsaw who then claims to deduce the whole picture from that single piece.
What do we really know about CO2? Everything we think we know about climate history says that CO2 is not the cause of recent warming. The only source of "evidence" supporting CO2 (as the culprit) is the study of radiative forcings and feedbacks. Scientists involved in these studies can not even agree on whether water vapour has a warming or cooling effect? The models simply assume CO2 has a warming effect and should be ignored.

No person involved in the climate debate argues against the statement that CO2 causes some warming, however it then gets very confused.
AR3 stated that the relationship between atmospheric CO2 and temperature was logarithmic but did not put any firm numbers into the equation. At what level does CO2 cease to warm the planet? This question is not really discussed anywhere but what we think we know about climate history says that we have already passed the point at which CO2 continues to warm the planet.
In all the previous interglacials in our current ice age, levels of CO2 were rising at the point where temperatures began to fall as we returned to the ice age. On some ocassions CO2 rose for 2000 years after the high point of the interglacial was reached.

Thanks everyone for your responses.

Philip, I do understand your point, but I hoped this specific issue was included in my acknowledgement of uncertainties. I don't think the possibility of a smaller solar forcing necessarily blows the climate models out of the water, the ability to reproduce the early 20th Century solely with natural forcing isn't a major part of validating the models, as there was some anthropogenic forcing then already anyway, and with the anthropogenic forcing also being made of different and opposing components (some of which are also poorly-constrained, like land use), the early 20th Century unfortunately does not give us a nice neat way of validating/invalidating the models. However I do completely agree that it is something we need to look at more closely.

matthu, I didn't mean to imply that my view is different to any "official" view, just that there isn't really an "official" view. I have quoted evidence from AR4 but AR5 is being prepared as we speak, and the issues I discussed are being looked at by people other than myself, so the AR5 conclusions may (or may not) be different to what I wrote. Thanks for the opportunity to clarify myself though - sorry it wasn't clear to start with!

Mike, you're welcome, and thanks for your comment, but please note that I cited other authors too. It is important to look at the bigger picture and see what the whole set of evidence is suggesting. If there are other papers which give alternative reconstructions that disagree with the above then I'd be genuinely interested to see. I am aware of the papers which discuss the difficulties in palaeoclimate reconstructions and criticise some of the papers I cited above, but that's a different issue to actually providing alternatives (again please note that I have acknowledged uncertainties!). Please note that I don't have any particular axe to grind here, as I don't do palaeoclimate reconstructions myself - the closest I've ever got was being involved in Simon Tett's paper on simulating the climate of the last 500 years with our model - you can easily read some of our emails on this if you are interested... :-)

Dung, you are not the only person to question our ability to assign % confidence limits. For example, Lenny Smith and Dave Stainforth at LSE are both prominent critics of this kind of thing. All I can say is that these confidence / uncertainty estimates are based on current understanding and are themselves uncertain, and this is made clear when we communicate them (see the UKCP09 links in my original post).

Cheers

Richard

Richard

Thank you very much for the replies to my questions. Some of them are a bit above my head but your answers have prompted other questions which i hope you will be good enough to address for me.

I'll go back to question 1. Here it is

Question 1

The 2007 IPCC AR4 report says: "Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations."
(a) What value scientifically has this conclusion?
(b) Do you agree with the strength of certainty expressed in the conclusion ("very likely" means more than 90% confidence)? If you do not agree with the confidence level expressed above what quantitative value would you place on the certainty/uncertainty of the conclusion?
Please cite evidence in support of your opinion and explain breifly the uncertainties involved in deciding such a matter?

I was made curious by this statement from the IPCC by the Interacademy Council report on the IPCC. The Conclusions section of the IAC report dealt with the IPCC reporting of uncertainties. It said this.

“ IPCC’s guidance for addressing uncertainties in the Fourth Assessment Report urges authors to consider the amount of evidence and level of agreement about all conclusions and to apply subjective probabilities of confidence to conclusions when there was “high agreement, much evidence.” However, such guidance was not always followed, as exemplified by the many statements in the Working Group II Summary for Policymakers that are assigned high confidence but are based on little evidence. Moreover, the apparent need to include statements of “high confidence” (i.e. an 8 out of 10 chance of being correct) in the Summary for Policymakers led authors to make many vaguely defined statements that are difficult to refute, therefore making them of “high confidence”. Such statements have little value.”

The IAC also said: “In the Committee’s view, assigning probabilities to imprecise statements is not an appropriate way to characterize uncertainty.”

I regard the use of the word "most" as imprecise and its inclusion in the IPCC statement beginning, "Most of the observed increase in gloabal average temperatures..." leads to a "vaguely defined statement." On the strength of that i would say that the IPCC statement has "little value".

Given my lack of a scientific background i find it difficult to comment much on the evidence you adduce in support of your opinion of the IPCC claim. You do not mentiion the difficulty of teasing out internal variability over the long term such as AMO and PDO (magnitude and timing) from any man-made warming there may be. This makes detection of any man-made "signal" uncertain. Also, you do not mention that the computer models all need "fixes" in the form of adjustment (bodges) to the degree by which aerosols are deemed to affect the simulated temperature in order to be able to track the measured temperature. Even a non-scientist can see there must be a fair degree of uncertainty attached to the output from any computer model for this reason alone. Then there is the fact that all the models use different inputs about different warming components. Which is correct? Does it matter? If not, why?

As an aside, the BBC Trust, Chair of Editorial Standards, Alison Hastings used the IPCC conclusion to support the move away by the BBC from reporting climate science impartially. She misquoted. Under the title " Trusting what you see and hear: the media's role in covering science accurately" she said; " Climate change is 90 per cent likely to have been caused by humans. That is the conclusion of the influential Intergovernmental Panel on Climate Change in 2007." Anyone can make a mistake. This seems dreadfully ill-informed.Richard, do you think the BBC should try to report climate science impartially?

On to question 2 which I'll put up below again.

Are global temperatures today within or outwith the range of historical natural varianbility?
Please give a quantitative value to the level of certainty/uncertainty you assign to your answer. Also, please cite evidence to support your conclusion and briefly explain the uncertainties involved in reaching the conclusion.

Why do you not include history as evidence? I read that there was farming done in Greenland and grapes grown in Northern England. Is this not evidence of a warmer MWP than today's temperatures? And what, if any, evidence is there that the MWP was limited in geographical extent? Also, what weight should be given to historical evidence compared with paleo reconstructions?

The studies you have cited appear to have provoked dread in Mike Jackson. Did you know that you have cited the "hockey stick" reprise - MBH 1999? I am sure that His Grace will have something to say about it. As I am sure you know, one of the criticisms of Mann's work was that the "hockey stick" shape depended on the inclusion of bristlecone pine tree ring data. Without bristlecones, no "hockey stick". A question for you. Why would a reputable scientist include in the data something known in the literature not to be a reliable proxy for temperature? Idso and Graybill 1993 confirmed an earlier study concluding that the growth pulse of bristlecones could not be accounted for by temperature. Following a Congressional hearing the National Academy of Sciences stated that bristlecones should not be used in paleo reconstructions. In those circumstances would not a reputable scientist re-run the reconstruction without the inclusion of bristlecones as data or withdraw the paper? What is the IPCC doing citing such unreliable evidence?

I have listed the evidence you cite below

Briffa, K.R., 2000: Annual climate variability in the Holocene: interpreting the message of ancient trees. Quat. Sci. Rev., 19(1–5), 87–105.

Briffa, K.R., T.J. Osborn, and F.H. Schweingruber, 2004: Large-scale temperature inferences from tree rings: a review. Global Planet. Change, 40(1–2), 11–26.

Cook, E.R., J. Esper, and R.D. D’Arrigo, 2004a: Extra-tropical Northern Hemisphere land temperature variability over the past 1000 years. Quat. Sci. Rev., 23(20–22), 2063–2074.

D’Arrigo, R., R. Wilson, and G. Jacoby, 2006: On the long-term context for late twentieth century warming. J. Geophys. Res., 111(D3), doi:10.1029/2005JD006352.

Esper, J., E.R. Cook, and F.H. Schweingruber, 2002: Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability. Science, 295(5563), 2250–2253.

Jones, P.D., K.R. Briffa, T.P. Barnett, and S.F.B. Tett, 1998: Highresolution palaeoclimatic records for the last millennium: interpretation, integration and comparison with General Circulation Model control-run temperatures. The Holocene, 8(4), 455–471.

Jones, P.D., T.J. Osborn, and K.R. Briffa, 2001: The evolution of climate over the last millennium. Science, 292(5517), 662–667.

Mann, M.E., R.S. Bradley, and M.K. Hughes, 1999: Northern hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations. Geophys. Res. Lett., 26(6), 759–762.

Mann, M.E., and P.D. Jones, 2003: Global surface temperatures over the past two millennia. Geophys. Res. Lett., 30(15), 1820, doi:10.1029/2003GL017814.

Moberg, A., et al., 2005: Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data. Nature, 433(7026), 613–617.

Hegerl, G.C., T.J. Crowley, W.T. Hyde, and D.J. Frame, 2006: Climate sensitivity constrained by temperature reconstructions over the past seven centuries. Nature, 440, 1029–1032.

Moberg et al 2005 contains three sets of bristlecones. Hegerl et al 2006 has Mann's PC1 and foxtails. Foxtails are poor proxies, having no significant relationship to temperature. Mann and Jones 2003 contains Mann's PC1. Esper et al 2002 has two foxtail series.

I have not time to look at the others. Nor have I performed any grreat research. Richard and others, you can find much more detailed and learned criticism of the studies cited here at climateaudit: IPCC AR4 and the return of Chucky -He's baaack! Wonderful title.

I would not trust any science done by Mann, Jones, Bradley, Hughes, Briffa, Hegerl, Osborn and others I won't mention. In the face of the criticisms of McIntyre supported by expert comment why would one? That's a question for you Richard. At the heart of it lies questions of scientific competence,honesty and integrity. Would you, Richard, criticise the "hide the decline" involvement of Briffa, Jones and Mann who were directly involved in these shady enterprises? How do you regard it? Others, Folland perhaps might be one, must have known what was going on. One day soon, someone should trawl through the work of McIntyre and make a list of all the authors and co-authors who are incompetent, dishonest or both. These names should be prominently placed on His Grace's blog.

Why do you trust the studies you have cited? Did you cite them without knowledge of what was in them? Do you believe that your willingness to cite such work may affect how others see your credibility ( not just on this blog) and, indeed, your integrity?

I can't finish this now, I'll come back to it. Thanks again, Richard. Will you re-consider your answers to questions 1 and 2?

I am sorry Dr. Betts, but I just do not buy this. These subjects have been discussed in detail here at BH, and in other places, but although you have previously debated the pros and cons of the science and the evidence, your article seems to take no account of this.

For example, I am dismayed by the statement "It is likely (66%) that [the second half of the 20th Century] was the warmest Northern Hemisphere period in the last 1,300 years”. This flies in the face of historical evidence for the MWP, as pointed out above. The Met Office computer models can not be verified or validated and your references to Jones, Mann and the other Climategate scoundrels, in my opinion, discredits any arguments that you make.

I do believe that the AGW hypothesis deserves serious academic study, but I, and many other scientists, can see no reason to implement national or international policies to mitigate against an unproven and probably non-existant problem, that incur catastrophic consequences to our economy and suffering to our people.

Richard, you say;

matthu, I didn't mean to imply that my view is different to any "official" view, just that there isn't really an "official" view.

Really?
The Met office has no official view any more?
There is no longer an established consensus?

Dec 1, 2011 at 1:58 PM | sam

Hi sam

Thanks for the detailed comments.

What about Cook et al and D'Arrigo et al? Do you have issues with those authors?

And do you (or any CA readers) know of alternative reconstructions other than those I cited? Like I said, I'm aware of the criticisms (and also of the uncertainties given by the authors of the original studies and acknowledged in AR4), so the thing I am really interested in is whether there is any work suggesting significantly different climate histories to the (sometimes large) range of possibilities given by the papers I listed, as opposed to questioning the reliability of those studies?

Thanks!

Dec 1, 2011 at 4:31 PM | matthu

I think the "consensus" has always been somewhat loosely defined!

@ Richard

We touched on the issue in another thread but I wanted to return to the matter of predictions 100 years into the future. I know they're termed "scenarios" or "projections" rather than "predictions", but this distinction seems to me to be sophistry in most cases, in that if these "projections" were not intended to be taken as having some predictive power, nobody would be paying attention to them.

It is, I hope, common ground that we cannot predict energy price, population or technology change 100 years into the future. The evidence for this is partly the total failure of anyone at any time in the past to predict anything 100 years in their future (well, a caveman of 50,000 years could probably have confidently predicted that all three would be about the same, and he would have been right, but that's not massively relevant). Mainly, though, it's the fact that there is no industry that lives by predicting these things accurately, which argues strongly that it's not possible.

This being so, estimates of future temperature are surely just variants of the Drake Equation: T = C x E x P x Te x ....etc.

Why should anyone rationally base any economic decision today on a formula in which every single term, including all that bear on emission levels, is wholly unknown and in fact unknowable? The price of energy in 2100 could be anything from $1 per unit to $1,000. Nobody knows. What use is a formula in which several terms could vary by a couple of orders of magnitude?

The analogy I like is the newsagent who sells 2 copies of the Radio Times one week, 4 the next and 8 the next. He does the math and concludes that in 4 weeks' time he'll be selling 4 billion copies a week and thus should invest now in a bigger shop.

His maths are fine, but if he asked around he'd find there are only 300 homes in the village, the print run is only 100,000 copies, there aren't enough delivery vans to deliver 4 billion magazines, and so on, and so on. That is, this is not just a mathematical problem, and what's more, there are no experts and no consensus in the key input areas. So what's the point? Isn't the whole thing basically frivolous?

For example, here's a chart of oil prices since 1860:
http://www.evsroll.com/images/Historic-Oil-Price-Graph.gif

Based on that, what would an observer in say 1930 have considered a low oil price? A high oil price? Where might they have predicted the price to be in 50 years? How about 1980, same question? How about now?

Furthermore, when in that graph is the arrival of nuclear power? When was Chernobyl? Where's shale gas? Where's the Clean Air Act? The fact is that there has been one 100-year period in which the oil price was in real terms stable, but it ended 30 years ago.

I don't see how anyone can look at that chart, say "making forecasts is hard, especially about the future," then shrug and say "but we're going to do so anyway, here's a bill for £17 billion a year and old people will die in their thousands of the cold in consequence". Can you explain this, or has anyone else attempted to? I'm aware this might be someone else's job, but if that's the answer, how are you different from my newsagent above?

Richard Betts

[I was writing this while you posted your recent comment, but I will put it up anyway as it may help focus on what is - and is not - broadly defined as the scientific consensus on CC]

Before you answer matthu, it will be helpful for the thread if you clarify with him exactly what his views are.

His position (at least as I understand it) is that CO2 has been displaced from its role as the primary anthropogenic forcing agent. Instead, we now have a scientific consensus that holds that climate change is the imperfectly understood result of natural influences (he favours GCRs and possibly ocean oscillations), land use change (a la Pielke Snr, I think) and some GHG forcing.

He argues that all is uncertain, and nothing more so than the ever-diminishing role of CO2. This is explored in some detail on the IEA Strategy thread, but this comment at Nov 12, 2011 at 4:25 PM (p. 7) conveys the flavour:

I have simply been exploring why you continue to cling to an outdated consensus that no longer applies, opinion having moved on, uncertainties being greater than previously acknowledged and many more factors playing a part than were properly considered in 2007.

A substantial body of scientists today acknowledge that there is a significant risk of material cooling over the next 20-30 years. That by itself is enough to undermine the previous consensus of ever-increasing temperatures unless we bring CO2 under control.

I bring this up as matthu believes (or at least did a week ago) that you endorse his views:

This is my understanding of the consensus as I outlined to Richard Betts (who agreed with it)
1) global warming is real (whatever that means)
2) man is having an impact
3) at least some of the impact is likely caused by CO2 emissions

And:

"Most of the impact is likely caused by CO2 emissions, and the effect will steadily intensify over time"

BBD - this is your belief - but certainly not the scientific consensus. And I gave Richard every opportunity to correct me here.

You also omit the effects of deforestation, cosmic rays. oceanic oscellations. Plus numerous other unlisted effects. And the fact that the effect of CO2 emissions are logarithmic and hence not intensifying over time unless you assume all sorts of other unproven side-effects.

Sorry, BBD. You assume much more consensus support than is actually the case.

In fact my current views are quite well matched by the following paper by Fang et al. 2011:

Based on an extensive literature review, we suggest that (1) climate warming occurs with great uncertainty in the magnitude of the temperature increase; (2) both human activities and natural forces contribute to climate change, but their relative contributions are difficult to quantify; and (3) the dominant role of the increase in the atmospheric concentration of greenhouse gases (including CO2) in the global warming claimed by the Intergovernmental Panel on Climate Change (IPCC) is questioned by the scientific communities because of large uncertainties in the mechanisms of natural factors and anthropogenic activities and in the sources of the increased atmospheric CO2 concentration. More efforts should be made in order to clarify these uncertainties.

FANG JingYun1,2*, ZHU JiangLing1,2, WANG ShaoPeng1, YUE Chao1 & SHEN HaiHua1

A propos of which, I have never seen a chart which correlated CO2 emissions with atmospheric CO2 with global average temperature. Does this exist covering the last 30 years, say? AIUI, the linkage between the first two is the difficult one, and hence the link between the first two and the third looks awfully like conjecture. Or a a leap of faith, depending on where you're at.

Sorry, I meant "human CO2 emissions with total atmospheric CO2", to be clear. AIUI the human contribution is within the bounds of estimation error, so if it reduced to zero, it wouldn't show up in the overall data. Happy to be corrected on this if this is not right.

Richard Betts asks
"What about Cook et al and D'Arrigo et al? Do you have issues with those authors?"
The abstract of D'Arrigo Wilson and Jacoby ends with
"presently available paleoclimatic reconstructions are inadequate for making specific inferences, at hemispheric scales, about MWP warmth relative to the present anthropogenic period."
which I think most sceptics would agree with.
Both of these find a MWP and a LIA, so are consistent with historical aevidence as pointed out by Sam.

Wilson of course is one of the 'goodies', in view of his emails
1527.txt: " There has been criticism by Macintyre of Mann's sole reliance on RE, and I am now starting to believe the accusations. "

4241.txt: " The whole Macintyre issue got me thinking...I first generated 1000 random time-series in Excel ... The reconstructions clearly show a 'hockey-stick' trend. I guess this is precisely the phenomenon that Macintyre has been going on about. "

Richard also asks if there are other reconstructions - well there is the one by Craig Loehle which you can easily find on the web. There is also of course the one by McShane and Wyner. Is Richard really not aware of these?

Dear Richard,
There is a serious flaw in your argument.

It refers to this portion:

General circulation models of the climate (which I do consider to be useful even if far from perfect!) do not reproduce the observed warming when driven with natural forcings alone. However they do reproduce it when anthropogenic forcings are included.

In the most general of terms, you do not validate or make inferences from a model output, by comparing it to outputs from the same model run under different conditions. You compare a model's output with the very system it is designed to emulate.

If you say [a] that a model is valid because it emulates reality well, and then turn around to say [b]: 'this is what would have happened, had condition x been different', what you actually doing is forgetting that [a], is an artificial construct.

Modeling exercises based on summative variables such as the global anomaly -cannot- validate the individual subcomponents and assumptions fed into the model.

Richard Betts

Matthu has been waving Fang et al. around since the GWPF flagged it up a couple of weeks ago. It's a bit jaw-dropping, really.

Nobody else I have talked to has come across this paper. Given Fang's involvement in the IAC's review of the IPCC, I would be most interested in your views on this.

Paul and Richard,

I've seen Ljundqvist recently cited in a couple of places. Is this also an independent reconstruction that should be considered?

Glad to hear of the impact Fang et al. has apparently been having, though I am at a bit of a loss to understand why exactly.

What they have done is simply to undertake an extensive literature review, including many well-recognised climate scientists (maybe all well-recognised) and try to represent the current state of the consensus. Which isn't terribly far removed from the consensus that I put to Richard a few weeks ago, so to say that the summary is "jaw-dropping" I think says more about one's own view of the science than anything it says about the consensus.

I nevertheless love to hear the sound of jaws hitting the table.

This very interesting thread could be ruined by the appearance of BBD.

Richard

M&M produced a paleo climate reconstruction which showed the LIA and the MWP, they did this by removing the tree rings from MBH's hockey stick.

750,000 years of ice core records show that atmospheric CO2 rises about 800 years after temperarture rises. The current rising trend in atmospheric CO2 began almost exactly 800 years after the MWP.