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Worldwide glacier retreat Recul mondial des glaciers

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One of the most visually compelling examples of recent climate change is the retreat of glaciers in mountain regions. In the U.S. this is perhaps most famously observed in Glacier National Park, where the terminus of glaciers have retreated by several kilometers in the past century, and could be gone before the next century (see e.g. the USGS web site, here, and here). In Europe, where there is abundant historical information (in the form of paintings, photographs, as well as more formal record-keeping), retreat has been virtually monotonic since the mid 19th century (see e.g. images of the glaciers at Chamonix). These changes are extremely well documented, and no serious person questions that they demonstrate long term warming of climate in these regions. New work published in Science (“Extracting a Climate Signal from 169 Glacier Records”) highlights these results, and uses them to make a new estimate of global temperature history since about 1600 A.D., which agrees rather well with previous, independent temperature reconstructions.

Par Eric Steig (traduit par Claire Rollion-Bard)

Un des exemples les plus irrésistibles visuellement du récent changement climatique est le recul des glaciers dans les régions montagneuses. Aux Etats-Unis, c’est peut-être ce qui est le plus fameusement observé au Glacier National Park où les terminus des glaciers se sont retirés de quelques kilomètres au cours du dernier siècle (voir e.g. le site web de USGS, ici, and ici)ici et ici). En Europe, où il y a des informations historiques importantes (sous la forme de peintures, photographies, aussi bien que sous forme d’enregistrements plus formels), le recul a été virtuellement monotone depuis le milieu du 19ème siècle (voir e.g. images de glaciers à Chamonix). Ces changements sont extrêmement bien documentés si bien qu’aucune personne sérieuse ne doute que cela démontre le réchauffement à long terme du climat dans ces régions. Un travail récent publié dans Science (“Extracting a Climate Signal from 169 Glacier Records”) souligne ces résultats et les utilise pour faire une nouvelle estimation de l’histoire globale des températures depuis environ 1600 A.D., et qui est en assez bon accord avec les précédentes reconstructions indépendantes de la température.
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A disclaimer Mise au point

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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).
par Eric Steig

Les lecteurs du Wall Street Journal du 14 fév. 2005 ont pu avoir l’impression que RealClimate pourrait être associé à une organisation environnementale. Nous souhaitons préciser que bien que notre domaine soit hébergé par “Environmental Media Services”, et le communiqué de presse initial a été organisé par “Fenton Communications”, aucune de ces deux organisations n’était de quelque façon impliquée dans la planification initiale du site RealClimate, et n’a jamais eu quelque contrôle éditorial ou tout autre. Ni Fenton, ni EMS n’ont jamais payé aux auteurs de RealClimate.org quoique ce soit. Ni l’un ni l’autre ne nous ont rémunérés ou financent notre recherche. Tous ces faits toujours ont été clairement communiqué à quiconque le demandait (voyez par exemple: http://www.sciencemag.org/content/vol306/issue5705/netwatch.shtml ).

Will-full ignorance

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It is not worthwhile for RealClimate to post a response to each misinformed newspaper commentary on climate change that we come across. However, George Will’s recent article in the Washington post (in which he praises Michael Crichton’s State of Fear) perhaps deserves special attention because Will is so widely read and respected. We find it disappointing that Will appears not to have bothered looking up the most basic facts before writing his article. See also our earlier post on the George Will article.

We have already posted detailed responses to State of Fear. Here, we respond briefly to the points Will tries to make. The italics are direct quotes from his article.

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How do we know that recent CO2 increases are due to human activities? Comment savons-nous que l’augmentation récente du CO2 est due aux activités humaines ? (mise-à-jour)

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Note:This is an update to an earlier post, which many found to be too technical. The original, and a series of comments on it, can be found here. See also a more recent post here for an even less technical discussion.

Over the last 150 years, carbon dioxide (CO2) concentrations have risen from 280 to nearly 380 parts per million (ppm). The fact that this is due virtually entirely to human activities is so well established that one rarely sees it questioned. Yet it is quite reasonable to ask how we know this.

Det finns en svensk översättning tillgänglig här
Una traducción en español está disponible aquí.

par Eric Steig (traduit par Gilles Delaygue)

Note :Ceci est une mise-à-jour d’un article précédent, que beaucoup ont trouvé trop technique. L’original, ainsi qu’une série de commentaires, se trouvent ici.

Pendant les 150 dernières années, la concentration en dioxyde de carbone (CO2) a augmenté de 280 à 380 parties par million (ppm). Le fait que cette augmentation soit due pratiquement entièrement aux activités humaines est si bien établi qu’on le voit rarement remis en question. Pourtant, il est tout à fait raisonnable de se demander comment nous le savons.

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How do we know that recent CO2 increases are due to human activities?

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An updated version of this post is now available.

The fact that CO2 increases in the past 150 years are due virtually entirely to human activities is so well established that one rarely sees it questioned. Yet is is quite reasonable to ask how we know this.

There are actually multiple, largely independent lines of reasoning, discussed in some detail in the IPCC TAR report, Chapter 3. One of the best illustrations of this point, however, is not given in IPCC. Indeed, it seems not all that well appreciated in the scientific community, and is worth making more widely known.

Carbon is composed of three different isotopes 14C, 13C and 12C of which 12C is the most common and 14C (used for dating purposes) is only about 1 in 1 trillion atoms. 13C is about 1% of the total.

Over the last few decades, isotope geochemists have worked together with tree rings experts to construct a time series of atmospheric 14C variations over the last 10,000 years. This work is motivated by a variety of questions, most having to do with increasing the accuracy of the radiocarbon dating method. A byproduct of this work is that we also have a very nice record of atmospheric 13C variations through time, and what we find is that at no time in the last 10,000 years are the 13C/12C ratios in the atmosphere as low as they are today. Furthermore, the 13C/12C ratios begin to decline dramatically just as the CO2 starts to increase — around 1850 AD. This is no surprise because fossil fuels have lower 13C/12C ratios than the atmosphere.

The total change is about 0.15%, which sounds very small but is actually very large relative to natural variability. Although it has proved quite challenging to do the analyses, there are a limited number of measurements of the 13C/12C ratio in ice cores. The results show that the full glacial-to-interglacial change in 13C/12C of the atmosphere — which took many thousand years — was about 0.03% 00 or about 5 times less than that observed in the last 150 years. The ice core data also agree quite well with the tree ring data where these data sets overlap.

I will put a couple of plots up when I get a chance. For those who are interested, some relevant references are: Stuiver, M., Burk, R. L. and Quay, P. D. 1984. 13C/12C ratios and the transfer of biospheric carbon to the atmosphere. J. Geophys. Res. 89, 1731�1748. for tree rings, and
Francey, R.J., Allison, C.E., Etheridge, D.M., Trudinger, C.M., Enting, I.G., Leuenberger, M., Langenfelds, R.L., Michel, E., Steele, L.P., 1999. A 1000-year high precision record of d 13Cin atmospheric CO. Tellus 51B, 170�193.

Statistical analysis of consensus Analyse statistique du consensus

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Is there really “consensus” in the scientific community on the reality of anthropogenic climate change? As N. Oreskes points out in a recent article in Science, that is itself a question that can be addressed scientificially. Oreskes took a sampling of 928 articles on climate change, selected objectively (using the key phrase “global climate change”) from the published peer-reviewed scientific literature. Oreskes concluded that of those articles (about 75% of them) that deal with the question at all, 100% (all of them) support the consensus view that a significant fraction of recent climate change is due to human activities. Of course, there are undoubtedly some articles that have been published in the peer-reviewed literature that disagree with this position and that Oreskes’s survey missed, but the fact that her sample didn’t
Par Eric Steig (traduit par Pierre Allemand)

Y a-t-il réellement “consensus” dans la communauté scientifique sur la réalité du changement climatique anthropogénique ? Comme N. Oreskes le fait remarquer dans un récent article de Science, c’est une question qui peut être elle-même traitée scientifiquement. Oreskes a pris un échantillon de 928 articles sur le changement climatique , objectivement choisis (utilisation de la phrase clé “changement climatique”) dans la littérature scientifique relue par des pairs. Oreskes en a conclu que parmi les articles (environ 75 % du total) qui traitent de la question 100 % (tous) partagent la vue consensuelle selon laquelle une part significative du changement climatique récent est due à l’activité humaine.

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Eric Steig

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Eric Steig is an isotope geochemist at the University of Washington in Seattle. His primary research interest is use of ice core records to document climate variability in the past. He also works on the geological history of ice sheets, on ice sheet dynamics, on statistical climate analysis, and on atmospheric chemistry.

He received a BA from Hampshire College at Amherst, MA, and M.S. and PhDs in Geological Sciences at the University of Washington, and was a DOE Global Change Graduate fellow. He was on the research faculty at the University of Colorado and taught at the University of Pennsylvania prior to returning to the University of Washington 2001. He has served on the national steering committees for the Ice Core Working Group, the Paleoenvironmental Arctic Sciences initiative, and the West Antarctic Ice Sheet Initiative, all sponsored by the US National Science Foundation. He was a senior editor of the journal Quaternary Research, and director of the Quaternary Research Center. He has published more than 100 peer-reviewed articles in international journals.

More information about his research and publication record can be found here.

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