Modellen vs waarnemingen: trends

Mijn lange uitgeschreven stuk voor het NNV-symposium heeft geleid tot waardering en kritiek. What’s new 🙂

Vooral op de blog van Bart Verheggen heerst (weer) veel verontwaardiging, met name over grafiek 5 uit mijn uitgeschreven presentatie. Ik heb Spencer en Christy een mail gestuurd met de kritiek en zal hier later over berichten. [Update: Spencer reageert op de kritiek in een blogbericht]

Een andere manier om modellen en waarnemingen te vergelijken is door te kijken naar trends. In het rapport A Sensitive Matter laten wij de volgende figuur zien afkomstig uit dit lezenswaardige blogbericht van McIntyre:

Welnu, speciaal voor Neven heb ik McIntyre gevraagd of hij deze figuur kan actualiseren. Hier is het resultaat. De actualisatie eindigt in september 2015 voor de waarnemingen, modellen tot eind 2015.

Als de twee extra jaren iets duidelijk maken, dan is het wel dat modeltrends en de waargenomen trend nog duidelijker niet met elkaar overeenkomen.

Hier is een andere figuur uit hetzelfde blogbericht van McIntyre. Deze is heel interessant omdat de recente waarnemingen richting de rode lijn (het modelgemiddelde) kruipt, door de huidige krachtige El Niño. Hieruit zou je kunnen concluderen dat modellen en waarnemingen ‘consistent’ zijn, zeker als je bedenkt dat rond het modelgemiddelde zich uiteraard een onzekerheidsrange bevindt. Als je echter trends vergelijkt dan valt de waarneming (ok zonder foutenrange) buiten vrijwel alle modeltrends inclusief onzekerheidsrange.

Hier is ook nog de geactualiseerde trend voor de troposfeer in de tropen. Zie voor verdere uitleg McIntyre’s blogbericht:



New Climate Dialogue about climate sensitivity

Today – after a long pause – a new Climate Dialogue has started about climate sensitivity and transient climate response. This of course is a highly relevant topic. Equilibrium climate sensitivity (ECS) and especially the transient climate response (TCR) largely determine how much warming we can expect this century.

Climate Dialogue is a platform for discussions between invited climate scientists on controversial climate topics. They represent a range of views. Discussions are strictly moderated and should be on topic. Last year we did four Climate Dialogues, about arctic sea ice, long-term persistence, regional climate models and the hot spot in the tropics.

We are very happy that a few key players in the debates surrounding climate sensitivity have agreed to participate in this Climate Dialogue. John Fasullo of NCAR is well-known for his publications with Kevin Trenberth about the role of the natural variability and the oceans in the recent hiatus. James Annan, who recently moved back to the UK after working for many years in Japan, has also published a lot about climate sensitivity and is also frequently blogging about it. Finally Nic Lewis is a relative newcomer in climate science. After a career in the financial sector he recently became a climate scientist, focusing on climate sensitivity. He published a few papers about climate sensitivity, one with a group of IPCC lead authors.

A Sensitive Matter
Some readers will remember that Nic Lewis and I published a GWPF report in March of this year with the title A Sensitive Matter: How the IPCC hid the good news on global warming. One of the main conclusions of our report was that observationally based estimates for ECS and TCR (based on the so-called instrumental period, say 1850-2014) are “superior” at the moment and are to be preferred over estimates from GCMs or paleorecords.

We claim that these “observational” estimates indicate best estimates for ECS that are close to the lower boundary of the likely range in several IPCC reports which is 1.5–4.5°C. We give an “observational” likely range of 1.25-3°C with a best estimate of 1.75°C. This is substantially lower than the average ECS value of the CMIP5 models which is more than 3°C.

IPCC gave a best estimate of 3°C in AR4 but none in AR5. This lack of a best estimate was only mentioned in a footnote in the SPM. Lewis and I wrote in our report that the discrepancy between the observationally based best estimate and the model based best estimate was likely the main reason why IPCC didn’t give a best estimate this time. So IPCC on the one hand says climate sensitivity will likely be anywhere between 1.5–4.5°C and no best value can be given. But when doing projecetions AR5 relies (also in the Working Group II and III reports) on climate models that have an average climate sensitivity of 3.2°C.

So it is really important to find out where the discrepancy between the observationally based and model based estimates comes from. This will certainly be a crucial question in this Climate Dialogue.

Lewis in his guest blog repeated his likely range for ECS being lower than that of AR5:

The soundest observational evidence seems to point to a best estimate for ECS of about 1.7°C, with a ‘likely’ (17-83%) range of circa 1.2–3.0°C.

Annan agrees that the observational record points towards lower values for ECS and TCR. But nevertheless he comes up with slightly larger value for the best estimate than Lewis:

The recent transient warming (combined with ocean heat uptake and our knowledge of climate forcings) points towards a “moderate” value for the equilibrium sensitivity, and this is consistent with what we know from other analyses. Overall, I would find it hard to put a best estimate outside the range of 2-3°C.

Fasullo did not yet give his preferred likely range but he emphasized in his guest blog that lowering the lower boundary of the likely range in AR5 to 1.5°C (was 2°C in AR4) maybe was justified at the time but not any longer:

In short, I argue that although IPCC’s conservative and inclusive nature may have justified such a reduction at the time of their report, the evidence accumulated in recent years argues increasingly against such a change. Lees verder…


Submission to AR5 inquiry

The UK Energy and Climate Change Committee invited anyone with interest in the AR5 report to submit answers on a long list of questions. The deadline has now passed and several people have already made their contribution public (Richard Tol, Paul Matthews, Mike Haseler). As sooner or later all the submissions will be public anyway I have decided to do the same. My submission follows below and can also be downloaded as a pdf here.

Energy and Climate Change Committee inquiry into AR5
Written submission by Marcel Crok

Credentials and statement of interests

I am a Dutch freelance science writer based in Amsterdam. Since 2005 I specialised in the global warming debate. In 2005 as an editor of the Dutch monthly popular science magazine Natuurwetenschap & Techniek (recently this has become the Dutch edition of New Scientist) I published a long and critical article about the infamous hockey stick graph featuring the criticism of Stephen McIntyre and Ross McKitrick. Many of the issues described in that article came back in the Climategate emails.
I published a critical book in 2010 that focused on the third and fourth assessment reports of the IPCC (TAR and AR4). The Dutch Ministry of Infrastructure and the Environment then gave me funding to critically review AR5 as an expert reviewer.
Since Climategate I am in favour of a more constructive interaction between climate scientists with opposing views. Late 2012 the Ministry of Infrastructure and the Environment funded an international discussion platform,, that organises constructive dialogues between climate scientists with opposing views. This has been set up by the leading Dutch climate related institutes KNMI and PBL and myself. [1] We cover controversial topics and invite scientists with a range of views.
In 2013 I was co-author of my first peer reviewed paper (describing a European temperature shift in 1988).

How robust are the conclusions in the AR5 Physical Science Basis report?
To answer this question is beyond the scope of this inquiry I would say. However your own introduction provides a good start to deal with it. You wrote: “The report concluded that, ‘it is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.’ But it reduced the lower bound for likely climate sensitivity and for the first time did not publish a best estimate of it because of lack of agreement.”
It’s good that you picked up this apparent paradox. AR5 itself focused on the 95% certainty that humans are the cause of most (>50%) of the warming since 1950. Most media outlets brought this as the major news of AR5 writing things like ‘how much more certainty do you want (before you act)?’.
However this interpretation of the 95% claim is misleading. In a sense the 95% claim of AR5 (itself a result of expert judgment and not some sort of mathematical calculation) is a no-brainer.
To understand this we focus on this other important parameter, climate sensitivity (the rise in global temperature after a doubling of the CO2 concentration). Recently several papers have been published estimating climate sensitivity from observational data since 1850. These studies assume that almost all of the warming since 1850 is due to greenhouse gases. These papers then come up with best estimates for climate sensitivity in the range of 1.5 to 2.0°C, considerably lower than the best estimate of 3.0°C that IPCC has presented in all their assessment reports so far.
So claiming that at least 50% of the warming since 1950 is due to humans is meaningless. The much more important question is whether the contribution of greenhouse gases to warming is big or small. AR5 has all the ingredients to conclude that the contribution is much smaller than we have thought for the last three decades. But by not giving a best estimate for climate sensitivity it failed to communicate this important message. So IPCC failed to give policy makers its most important conclusion. And IPCC only dealt with this important decision in a footnote in the Summary for Policymakers (SPM).
The 95% claim also tells you nothing about the seriousness of the climate issue. The 95% can be completely in accordance with there being no climate problem at all. IPCC failed to explain this clearly and journalists didn’t pick it up.
To conclude: the 95% claim of AR5 has been misinterpreted by most people, including policy makers and the media as the final proof that we have a huge anthropogenic climate problem. The claim itself proves no such thing and is in fact pretty meaningless.
Although it seems contradictory, there is in itself no conflict between the increasing certainty (the 95% attribution claim) and not giving a best estimate for climate sensitivity (less certainty). The 95% claim is just very conservative and tells you little about the seriousness of the climate issue. Lees verder…


Nic Lewis’ response will hit the Met Office like a boomerang

Nic Lewis has published a lengthy and quite technical response on a recent Met Office report, see the posts at Bishop Hill and Judith Curry. His response will hit the Met Office like a boomerang.

Why like a boomerang? In July the Met Office published three reports about the ‘pause’. In the third and I would say most important one they looked at the implications of the pause for estimates of climate sensitivity and projections of future warming. Their key conclusions were (see their concluding remarks):

Despite the fact that the first decade of the 21st century has been a period during which there was very little global mean surface temperature rise, the range of TCR [Transient Climate Response, MC] estimates from the CMIP5 models lies within the TCR derived from observations, including this period.

When projections from the newer CMIP5 models are combined with observations, and specifically including the surface temperatures from the last 10 years, the upper bound of projections of warming are slightly reduced, but the lower bound is largely unchanged. More importantly, the most likely warming is reduced by only 10%, indicating that the warming that we might previously have expected by 2050 would be delayed by only a few years.

In simpler words, Met Office claims the recent pause in global warming has had little impact on estimates of climate sensitivity and future warming and models and observations largely agree with eachother. Met Office backed this up with several figures. Below I show their figure 5, showing estimates for Equilibrium Climate Sensitivity (ECS), which is the warming due to a doubling of the CO2 concentration, after the system has reached a new equilibrium.

Met Office figure 5

Otto et al is a recently published study that estimated climate sensitivity from observations. Visually the message is clear: there is a huge overlap between Otto et al (observations), CMIP3 and CMIP5 (the models) and palaeo estimates. Models therefore are ‘consistent with’ the observations, which is important to have faith in their projections of future climate. Nic Lewis was a coauthor of the Otto et al paper together with a large group of lead authors of the upcoming AR5 report. Lewis wrote the response in a personal capacity.

Now to make a long introduction short, here is Lewis’ adjusted version of the Met Office figure 5:

Lewis added other recent estimates of ECS based on observations (Aldrin, Lewis, Masters), he removed the palaeo estimates (as these are far too uncertain and contain “little information”) and he used flasks to show the 5-95% range of the distribution. The black bars are Lewis’ best estimates (medians). The white bars are the Met Office best estimates, for CMIP3 and 5 Met Office used the means instead of the medians.

The “boomerang” is the red bar on top of the CMIP5 distribution. This is the ECS of Met Office’s own flagship HadGEM2-ES model. As one can clearly see Met Office’s own model is not only far more sensitive than the observations suggest but even more sensitive than all other models. As Lewis put it:

And HadGEM2-ES has an ECS that exceeds not only the 95% bound from Otto et al but also that from two other recent observationally-based studies. Moreover, both the TCR and the ECS of HadGEM2-ES exceed the 95% bounds derived not only from CMIP3 models but also from CMIP5 models other than HadGEM2-ES.

So the Met Office model’s best estimate lies outside the range of both the observations and all the other models. It is a clear outlier. Met Office failed to disclose this in their own report, only showing the range of all the models in their figure 5 (and in other figures).

Relevance for the upcoming AR5 report
Although Lewis’ response is directed at the Met Office report, his piece is also highly relevant for the upcoming AR5 report. In an article today in the Wall Street Journal Matt Ridley quotes from the leaked SPM of AR5 (my bold):

Specifically, the draft report says that “equilibrium climate sensitivity” (ECS)—eventual warming induced by a doubling of carbon dioxide in the atmosphere, which takes hundreds of years to occur—is “extremely likely” to be above 1 degree Celsius (1.8 degrees Fahrenheit), “likely” to be above 1.5 degrees Celsius (2.4 degrees Fahrenheit) and “very likely” to be below 6 degrees Celsius (10.8 Fahrenheit). In 2007, the IPPC said it was “likely” to be above 2 degrees Celsius and “very likely” to be above 1.5 degrees, with no upper limit. Since “extremely” and “very” have specific and different statistical meanings here, comparison is difficult.

Still, the downward movement since 2007 is clear, especially at the bottom of the “likely” range. The most probable value (3 degrees Celsius last time) is for some reason not stated this time.

Apparently IPCC is planning (countries will negotiate about the final text in Stockholm later this month) to lower its likely lower bound for ECS from 2.0 in AR4 to 1.5 in AR5. By doing this the median estimates based on observations shown in the Lewis’ figure above fall into the likely range. So this rightly reflects the recent literature.

However, less assuring is that Ridley reports that in the draft SPM “The most probable value (3 degrees Celsius last time) is for some reason not stated this time”. As can be seen clearly in the Lewis’ figure, all the recent most probable values based on observations lie between 1.5 and 2. The central estimate of the models is 3. Or as Lewis put it into his conclusions:

Observationally-based median estimates for TCR and ECS are often comparable to the bottom of model-based uncertainty ranges.

This means that only the least sensitive models come close to the observations. Now this generates a big dilemma for the IPCC authors which could explain why so far – in their draft SPM – they failed to mention a best estimate for ECS. Recently there has been is a growing discrepancy between observationally based estimates and model based estimates for ECS. Should IPCC give equal weight to both methods? Should IPCC average the central estimates of both methods (leading to a reduced new estimate of let’s say 2.5)? Or should they put most weight onto the observations? In the last case they should lower their best estimate to at least 2. That would be a spectacular result as the best estimates for ECS hardly changed at all since the 1979 Charney report.

I hope many countries (including my own) will urge the IPCC to publish a best estimate for ECS (like they did in AR4) or – in case not – to clearly explain why they decided not to mention it this time. I see this as one of the most if not the most important decision for the four day meeting in Stockholm. On 27 September we will know the answer.


Klotzbach revisited, a reply by John Christy

Recently Jos Hagelaars published a very extensive blog post (on the blog of Bart Verheggen) about a widely discussed paper of Klotzbach et al 2009. The title of the blog post – Klotzbach revisited – is in English, however, the post itself was written in Dutch. As a fellow Dutchman I understand that writing in Dutch is easier than writing in English. However, in this case, the blog post is focussed so much on one single paper, that Jos Hagelaars, in my opinion, should have chosen for an English version, in order to give the authors of the Klotzbach papers the chance to give a reaction. I translated the article with google translator and did some minor editing. I then shared the article with a few of the coauthors. John Christy looked at some of the issues raised by Hagelaars and wrote the following reaction which I publish here as a guest blog.

Guest blog by John Christy

In a blog post entitled “Klotzbach Revisited” Jos Hagelaars updated the results of Klotzbach et al. 2009, 2010, suggesting that the main point of Klotzbach was no longer substantiated. Klotzbach et al.’s main point was that a direct comparison of the relationship of the magnitude of surface temperature trends vs. temperature trends of the troposphere revealed an inconsistency with model projections of the same quantities.  Klotzbach et al. offered suggestions for this result which included the notion that near-surface air temperatures are easily affected by factors unrelated to greenhouse gas increases, which then implies they may be poor proxies for detecting the magnitude of the greenhouse effect which has its main impact in the deep atmosphere.

It appears Hagelaars’ key point is that when the data from Klotzbach et al. are extended beyond 2008 to include data through 2012, the discrepancies, i.e. the observed difference between surface and tropospheric trends relative to what models project, are reduced somewhat.

Lees verder…




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