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Moberg et al: Highly variable Northern Hemisphere temperatures?

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by William Connolley and Eric Steig

The 10th Feb edition of Nature has a nice paper “Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data” by Anders Moberg, DM. Sonechkin, K Holmgren, NM Datsenko, & W Karlin (doi:10.1038/nature03265). This paper takes a novel approach to the problem of reconstructing past temperatures from paleoclimate proxy data. A key result is a reconstruction showing more century-scale variability in mean Northern Hemisphere temperatures than is shown in previous reconstructions. This result will undoubtedly lead to much discussion and further debate over the validity of previous work. The result, though, does not fundamentally change one of the most discussed aspects of that previous work: temperatures since 1990 still appear to be the warmest in the last 2000 years.

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A disclaimer

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Readers of the Feb. 14th, 2005 Wall Street Journal may have gotten the impression that RealClimate is in some way affiliated with an environmental organisation. We wish to stress that although our domain is being hosted by Environmental Media Services, and our initial press release was organised for us by Fenton Communications, neither organization was in any way involved in the initial planning for RealClimate, and have never had any editorial or other control over content. Neither Fenton nor EMS has ever paid any contributor to RealClimate.org any money for any purpose at any time. Neither do they pay us expenses, buy our lunch or contract us to do research. All of these facts have always been made clear to everyone who asked (see for instance: http://www.sciencemag.org/content/vol306/issue5705/netwatch.shtml).

Strange Bedfellows

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Here’s a curious observation. Some commentators who for years have been vocally decrying the IPCC consensus are lining up to support the ‘Ruddiman’ hypothesis. A respected paleoceanographer, Bill Ruddiman has recently argued that humans have been altering the level of important greenhouse gases since the dawn of agriculture (5 to 8000 years ago), and in so doing have prevented a new ice age from establishing itself. This intriguing idea is laid out in a couple of recent papers (Ruddiman, 2003; Ruddiman et al, 2005) and has received a fair degree of media attention (e.g. here, and here).

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Exeter conference: Avoiding Dangerous Climate Change

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The conference last week in Exeter on “Avoiding Dangerous Climate Change” grew out of a speech by UK Prime Minister Tony Blair. He asked “What level of greenhouse gases in the atmosphere is self-evidently too much?” and “What options do we have to avoid such levels?”. The first question is very interesting, but also very difficult. As Roger Pielke has noted the conference organisers actually choose three “key questions”:

  1. For different levels of climate change what are the key impacts, for different regions and sectors, and for the world as a whole?
  2. What would such levels of climate change imply in terms of greenhouse gas stabilisation concentrations and emission pathways required to achieve such levels?
  3. What technological options are there for achieving stabilisation of greenhouse gases at different stabilisation concentrations in the atmosphere, taking into account costs and uncertainties?

It is worth thinking about the difference between the initial aim and the “key questions” chosen. Question 1 is essentially IPCC WGII impacts); question 2 is firmly WGI (how-much-climate-change); question 3 is fairly WG III (mitigation, including technical options). I guess they switched questions 1 and 2 round to avoid making the identification too obvious. The conference steering committee report makes it very clear that they are building on the IPCC TAR foundation.

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11ºC warming, climate crisis in 10 years?

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by Gavin Schmidt and Stefan Rahmstorf

Two stories this week, a paper in Nature (Stainforth et al, 2005) describing preliminary results of the climateprediction.net experiments, and the Meeting the Climate Challenge report from a high level political group have lead to dramatic headlines. On the Nature paper, BBC online reported that “temperatures around the world could rise by as much as 11ºC “; on the latter report it headlined: “Climate crisis near ‘in 10 years’”. Does this mean there is new evidence that climate change is more serious than previously thought? We think not.

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What If … the “Hockey Stick” Were Wrong?

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The “hockey stick” reconstruction of temperatures of the past millennium has attracted much attention – partly as it was high-lighted in the 2001 IPCC report as one of the important new results since the previous IPCC report of 1995, and partly as it has become the focus of a number of challenges. Discussion about the “hockey stick” is conducted with considerable fervor in the public media, where this curve is often presented as if it were a proof, or even the most important proof, of anthropogenic influence on climate.

As someone who has not worked on the past millennium, I do not want to discuss the merits of the often rather technical challenges (which have been dealt with elsewhere on this site). Rather, I want to discuss the “what if…” question: what if really some serious flaw was discovered in the “hockey stick” curve? What would that mean?

La reconstruction “crosse de hockey” des températures du dernier millénaire a beaucoup attiré l’attention – en partie car elle a été mise en avant dans le rapport IPCC 2001 comme l’un des nouveaux résultats importants depuis le précédent rapport IPCC de 1995, et en partie car elle est devenue le point de mire d’un certain nombre de défis. La discussion sur la “crosse de hockey” est transmise avec une ferveur considérable dans les médias, où cette courbe est souvent présentée comme une preuve ou même la preuve la plus importante de l’influence anthropogénique sur le climat.

En tant que personne n’ayant pas travaillé sur le dernier millénaire, je ne veux pas discuter des mérites des défis techniques (qui sont discutés dans une autre section du site). Je veux plutôt discuter de la question “et si…” : et si de sérieux défauts étaient trouvés dans la courbe “crosse de hockey” ? Qu’est ce que cela signifierait ?

(suite…)

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Peer Review: A Necessary But Not Sufficient Condition II

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by Michael Mann and Gavin Schmidt

In a previous post, we discussed a number of examples where the “Peer Review” process has failed, and poor papers have been published in the ostensibly peer-reviewed literature. In this context, we revisit our previous discussions of the flawed work of McIntyre and McKitrick (henceforth “MM”). MM published a paper, in the controversial journal Energy and Environment, claiming to “correct” the proxy-based reconstruction of Northern Hemisphere temperatures published by Mann et al (1998–henceforth “MBH98”). Following the all-too-familiar pattern, this deeply flawed paper was heavily promoted by special interests as somehow challenging the scientific consensus that humans are altering the climate (an excellent account is provided by science journalist Dan Vergano of USA Today here). As detailed already on the pages of RealClimate, this so-called ‘correction’ was nothing more than a botched application of the MBH98 procedure, where the authors (MM) removed 80% of the proxy data actually used by MBH98 during the 15th century period (failing in the process to produce a reconstruction that passes standard “verification” procedures–an error that is oddly similar to that noted by Benestad (2004) with regard to another recent McKitrick paper). Indeed, the bizarre resulting claim by MM of anomalous 15th century warmth (which falls within the heart of the “Little Ice Age”) is at odds with not only the MBH98 reconstruction, but, in fact the roughly dozen other estimates now published that agree with MBH98 within estimated uncertainties.

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Anomalous Recent Warmth in Europe

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Guest Contribution by Juerg Luterbacher, University of Bern, Switzerland

While the anomalous nature of recent trends in global average temperature is often highlighted in discussions of climate change, changes at regional scales have potentially greater societal significance. Of particular interest, for example, is the possible relationship between climate change and the incidence of summer heat waves [Meehl, G.A. and C. Tebaldi, Science, 305, 994-997 , 2004] such as those observed in Europe during summer 2003 [see Schaer et al, Nature 427, 332-336 2004; Stott et al, Nature, 432, 610-614­, 2004]. Preliminary analyses of the annual mean surface air temperatures for Europe for 2004 show it be among the few warmest (though not as warm as 1989, 1990, and 1999-2003) since widespread instrumental records have been kept (roughly the past 150 years). 2004 exceeded the reference period (1961-1990) mean temperature by more than 0.8°C. The largest deviations were found over Northern and Eastern Europe. Every single month of 2004 contributed to the overall warmth; February-April, August, October and December were all more than 1°C warmer than the 1961-1990 period. Annual mean European surface air temperatures have increased by around 0.85°C over the last 100 years. The upward trend has accelerated in recent decades, with about 1.2°C of warming taking place over the past 30 years (1975 to 2004). Indeed, the last thirty years likely represent the warmest multidecadal period for Europe in at least the past half millennium [ Luterbacher, J., Dietrich, D., Xoplaki, E., Grosjean, M. and H. Wanner, Science, 303, 1499-1503, 2004], while the last decade (1995-2004) is likely the warmest decade, and summer 2003 the warmest summer. These conclusions are similar to those reached for the entire Northern Hemisphere on the whole.

Peer Review: A Necessary But Not Sufficient Condition

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by Michael Mann and Gavin Schmidt

On this site we emphasize conclusions that are supported by “peer-reviewed” climate research. That is, research that has been published by one or more scientists in a scholarly scientific journal after review by one or more experts in the scientists’ same field (‘peers’) for accuracy and validity. What is so important about “Peer Review”? As Chris Mooney has lucidly put it:

[Peer Review] is an undisputed cornerstone of modern science. Central to the competitive clash of ideas that moves knowledge forward, peer review enjoys so much renown in the scientific community that studies lacking its imprimatur meet with automatic skepticism. Academic reputations hinge on an ability to get work through peer review and into leading journals; university presses employ peer review to decide which books they’re willing to publish; and federal agencies like the National Institutes of Health use peer review to weigh the merits of applications for federal research grants.

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Global Dimming II

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Guest commentary on BBC documentary on “Global Dimming” aired on January 13th 2005 by Beate Liepert, LDEO, Columbia University

I haven’t yet seen the documentary. I have only read the transcript and hence was spared the pictures of the potential apocalypse and the invocation of biblical-scale famines. However, as one of the lead scientists on the topic [and who was interviewed by the BBC for the Horizon documentary (transcript, previous post)], I feel I should explain a few things about it without using religious analogies and stoking unnecessary fear.

First though, this is a nice example of the power of words: Gerry Stanhill coined the observed reduction in solar energy reaching the ground “global dimming”. He called it “global” dimming because the technical term for the radiative energy is called “global solar radiation” and it contrasts nicely with the more common “global warming”.

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