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An icy retreat

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Translations: (Deutsch) (Español)

Guest Commentary by Dirk Notz, MPI Hamburg

It’s almost routine by now: Every summer, many of those interested in climate change check again and again the latest data on sea-ice evolution in the Arctic. Such data are for example available on a daily basis from the US National Snow and Ice Data Center. And again and again in early summer the question arises whether the most recent trend in sea-ice extent might lead to a new record minimum, with a sea-ice cover that will be smaller than that in the record summer of 2007.

However, before looking at the possible future evolution of Arctic sea ice in more detail, it might be a good idea to briefly re-capitulate some events of the previous winter, because some of those are quite relevant for the current state of the sea-ice cover. The winter 2009/2010 will be remembered by many people in Europe (and not only there) as particularly cold, with lots of snow and ice. Not least because of the sustained cold, some began to wonder if global warming indeed was real.

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The Montford Delusion

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Guest commentary by Tamino

Update: Another review of the book has been published by Alistair McIntosh in the Scottish Review of Books (scroll down about 25% through the page to find McIintosh’s review)

Update #2 (8/19/10): The Guardian has now weighed in as well.

If you don’t know much about climate science, or about the details of the controversy over the “hockey stick,” then A. W. Montford’s book The Hockey Stick Illusion: Climategate and the Corruption of Science might persuade you that not only the hockey stick, but all of modern climate science, is a fraud perpetrated by a massive conspiracy of climate scientists and politicians, in order to guarantee an unending supply of research funding and political power. That idea gets planted early, in the 6th paragraph of chapter 1.

The chief focus is the original hockey stick, a reconstruction of past temperature for the northern hemisphere covering the last 600 years by Mike Mann, Ray Bradley, and Malcolm Hughes (1998, Nature, 392, 779, doi:10.1038/33859, available here), hereafter called “MBH98” (the reconstruction was later extended back to a thousand years by Mann et al, 1999, or “MBH99” ). The reconstruction was based on proxy data, most of which are not direct temperature measurements but may be indicative of temperature. To piece together past temperature, MBH98 estimated the relationships between the proxies and observed temperatures in the 20th century, checked the validity of the relationships using observed temperatures in the latter half of the 19th century, then used the relationships to estimate temperatures as far back as 1400. The reconstruction all the way back to the year 1400 used 22 proxy data series, although some of the 22 were combinations of larger numbers of proxy series by a method known as “principal components analysis” (hereafter called “PCA”–see here). For later centuries, even more proxy series were used. The result was that temperatures had risen rapidly in the 20th century compared to the preceding 5 centuries. The sharp “blade” of 20th-century rise compared to the flat “handle” of the 15-19th centuries was reminiscent of a “hockey stick” — giving rise to the name describing temperature history.
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Revisiting the Younger Dryas

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Guest Commentary by Chris Colose

One of the most intriguing and well-studied climatic events in the past is the Younger Dryas (YD), a rather abrupt climate change between ~12.9 and 11.6 thousand years ago. As the world was slowly warming and ice was retreating from the last glaciation, the YD effectively halted the transition to today’s relatively warm, interglacial conditions in many parts of the world. This event is associated with cold and dry conditions increasing with latitude in the North, temperature and precipitation influences on tropical and boreal wetlands, Siberian-like winters in much of the North Atlantic, weakening of monsoon intensity, and southward displacement of tropical rainfall patterns. RealClimate has previously discussed the YD (here and here) however there have been a number of developments in recent years which deserve further attention, particularly with respect to the spatial characteristics and causes of the YD.
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The Muir Russell report

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by Gavin and Mike

The long-awaited and surprisingly thorough Muir Russell report (readable online version) was released this morning. We’ve had a brief read through of the report, but a thorough analysis of this and the supplemental information on the web site will have to wait for a day or so.

The main issue is that they conclude that the rigour and honesty of the CRU scientists is not in doubt. For anyone who knows Phil Jones and his colleagues this comes as no surprise, and we are very pleased to have this proclaimed so vigorously. Secondly, they conclude that none of the emails cast doubt on the integrity and conclusions of the IPCC, again, something we have been saying since the beginning. They also conclude as we did that there was no ‘corruption’ of the peer-review process. Interestingly, they independently analysed the public domain temperature data themselves to ascertain whether the could validate the CRU record. They managed this in two days, somewhat undermining claims that the CRU temperature data was somehow manipulated inappropriately. (Note that this exercise has been undertaken by a number of people since November – all of which show that the CRU results are robust).

All in all, none of the various accusations and insinuations that have been floating around the blogosphere have been sustained. (See some of the early media coverage of the report).

However, there are two issues that have come up that deserve some comment. The first are the evolving practices of data presentation and access, and the second is the issue of how to handle Freedom of Information (FOI) requests.

As climate science has moved away from single researcher/single study/single site analyses towards synthesis across multiple studies, across the globe and involving more and more researchers, practices that were appropriate at one time don’t necessarily scale up to the new environment. Data requests dealt with on an ad-hoc and informal basis work fine if only a couple of people are interested, but more formal and automated procedures are needed when the data sets grow and many more people are involved (see the PCMDI/CMIP3 archive of model results for instance). Given too, the obsession in certain quarters with irrelevant details of smoothing techniques and end-point padding in decade-old papers, it is clear that the more information that is put out as supplementary material to the creation of high-profile figures, the better off we will be. Examples of this for figures in IPCC AR4 already exist, but it will be helpful for IPCC to adopt this practice more generally. Historically, this hasn’t been done – mainly because no-one thought it particularly interesting (most smoothing methods produce very similar results for instance), particularly for figures that weren’t for publication in the technical literature.

One example of this was the cover art on a WMO 1999 report which, until last November, was completely obscure (we are not aware of any mention of this report or this figure before November in any blogospheric discussion, ever). Nonetheless, in the way of these things, this figure is now described as ‘an icon’ in the Muir Russell report (one of their very few mistakes, how can something be an icon if no-one has ever seen it?). In retrospect (and as we stated last year) we agree with the Muir Russell report that the caption and description of the figure could indeed have been clearer, particularly with regard to the way proxy and instrumental data sources were spliced into a single curve, without indicating which was which. The WMO cover figure appears (at least to our knowledge) to be the only instance where that was done. Moving forward, nonetheless, it is advisable that scientists be as clear as possible about what sorts of procedures have gone into the preparation of a figure. But retrospective applications of evolving standards are neither fair nor useful.

With respect to the continuing barrage of FOI requests (which are predominantly for personal communications rather than for data), we can attest from personal experience how disconcerting these can be at first. Since there are no limits on what can be asked for (though there are many limits on what will be delivered), scientists presented with these requests often find them personally invasive and inappropriate. Institutions that do not have much experience with these kinds of requests, and who are not aware of what their employees do that is, and is not, covered by the legislation, are often not much help in sorting out how to respond. This can certainly be improved, as can the awareness of the community of what is recoverable using these procedures. While it is not relevant to the legislation, nor to what can be released, the obvious bad faith of many of the requesters indicates that actual information about the functioning of public bodies is not the primary goal in making these requests. However, it would be a terrible mistake for scientists to retreat from the public discussion on climate science because of these attempts at intimidation.

We will post on more specific aspects of the report, and perhaps the legacy of the whole affair over the next few days…

Penn State reports

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The last part of the Penn State inquiry has now reported unanimously that Mike Mann did not engage in any activity that violated scientific norms. Quoting from the report conclusions,

Conclusion of the Investigatory Committee as to whether research misconduct occurred:

The Investigatory Committee, after careful review of all available evidence, determined that there is no substance to the allegation against Dr. Michael E. Mann, Professor, Department of Meteorology, The Pennsylvania State University.

More specifically, the Investigatory Committee determined that Dr. Michael E. Mann did not engage in, nor did he participate in, directly or indirectly, any actions that seriously deviated from accepted practices within the academic community for proposing, conducting, or reporting research, or other scholarly activities.

The decision of the Investigatory Committee was unanimous.

What we said last time….

Atlantic Tropical Cyclone Records – Trends and Ephemerality

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Guest Commentary from Urs Neu

To understand the influence of climate change on tropical cyclone and hurricane activity, it is crucial to know how this activity has varied in the past. There have been a number of interesting new studies of Atlantic tropical cyclones (TCs) and hurricanes (tropical cyclones with maximum sustained winds exceeding 74 miles per hour) since my review of the topic a couple years ago (see here and here). These newer studies underscore that, while our knowledge continues to improve in this area, key uncertainties persist. In particular, it remains very difficult to confidently estimate trends in the past.

In assessing past trends, one must distinguish between two distinct time intervals: 1) the period of historical observations (mainly after 1850), and 2) the earlier period for which TC activity can only be reconstructed using proxy data. Furthermore, we have to distinguish between trends in tropical cyclone (TC) number and TC intensity–the latter measure is particularly important from the standpoint of impacts. There is no a priori reason to expect these quantities to vary in concert, either in the past, or in the future. Unfortunately, uncertainties are much greater for intensity than for counts.

In this article, I will review our current understanding of Atlantic TC and hurricane trends with respect to: A) the historical record of basin-wide TC numbers; B) the historical record of hurricanes and TC intensity; C) distant past proxy estimates of TC (primarily, hurricane only) counts; and D) distant past proxy measures of TC/hurricane intensity. I will conclude with a discussion of current methods for forecasting Atlantic hurricane activity.

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Recent trends in CO2 emissions

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Guest commentary by Corinne Le Quéré, Michael R. Raupach, and Joseph G. Canadell

There is a letter in Nature Geoscience this month by Manning et al (sub. reqd.) “Misrepresentation of the IPCC CO2 emission scenarios” discussing some recent statements about the growth rates of CO2 emissions compared to the IPCC scenarios that informed the climate modeling in the last IPCC report. In it they refer to results published by us and colleagues in a couple of recent papers (Raupach et al. 2007; Le Quéré et al. 2009), and to statements made by others on the basis of our results (Ganguly et al. 2009; Anderson et al. 2008; Reichstein 2010). Specifically, Manning et al object to the claim that “current CO2 emissions from fossil fuel burning were higher than the values used in climate projections by the IPCC”.

We agree with the Manning et al’s main point, and appreciate the chance to provide some clarification on the graph in question and subsequent use of our result. To be specific, recent emissions were not higher than each and every one of the climate projections by the IPCC, as has been claimed by some other studies citing our work, although they were near the top end of the range.

So what is the claim of ‘misrepresentation’ based on?
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Claude Allègre: The Climate Imposter

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Guest Commentary by Georg Hoffmann

In mathematical proofs, it’s a well-known fact that if at some point you divide by zero accidentally or on purpose, then you end up being able to prove absolutely anything you want – for instance, that 2+2=5 or that 1+1=0. The same phenomena appears to govern any number of publications that conclude that climate science is all a fraud – at some point, an impossible calculation is performed and from then on, anything (and everything) can be proven. Critical thinking appears to vanish.

The latest example is that of Claude Allègre – whose recent book “The climate imposture” would have you believe at least six impossible things before breakfast and a great many more before dinner. This is notable because Allègre is one of the most eminent figures in science communication in France, Academie de Sciences member, Crafoord prize winner, former minister of education and research and a fixture on the late night talk shows in France (including a topical satirical version of the ‘muppets’). One might expect a certain degree of rigour from an author with such a pedigree, but on the contrary, nearly every explanation, graphic, or citation in this book is misleading or just plain wrong. If Allègre was not such a high profile figure in France, this nonsense would have been dismissed and ignored, instead, it is regular fodder for the late night talk shows. In my entire career I have never seen so many factual errors in a single publication. It is truly a remarkable work!
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Science Story: the Making of a Sea Level Study

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Guest commentary by Martin Vermeer

On December 7, 2009 the embargo expired, and my and Stefan’s joint paper ‘Global sea level linked to global temperature’ appeared in the Proceedings of the U.S. National Academy of Sciences. It had been a long time coming! But this post is not so much about the science as about the process, and about how a geodesist from Helsinki and an oceanographer from Potsdam, who to this day have never even met, came to write, to the surprise of both of us, a joint paper on sea level rise.
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