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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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Michael Crichton’s State of Confusion II: Return of the Science

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Our first post on Crichton’s new novel “State of Fear” hits most of the key points, though there are a few more errors in the book that we hope to expand upon in future posts.

But for those of you uninterested in buying and reading the book, you can actually find a similar-minded opinion piece by Crichton criticizing climate science (and everything from SETI and the “Drake Equation” to Carl Sagan in the process) here in the public domain.

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Michael Crichton’s State of Confusion L’état de confusion de Michael Crichton

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In a departure from normal practice on this site, this post is a commentary on a piece of out-and-out fiction (unlike most of the other posts which deal with a more subtle kind). Michael Crichton’s new novel “State of Fear” is about a self-important NGO hyping the science of the global warming to further the ends of evil eco-terrorists. The inevitable conclusion of the book is that global warming is a non-problem. A lesson for our times maybe? Unfortunately, I think not.

par Gavin Schmidt (traduit par Alain Henry)

Ce message s’écarte des pratiques habituelles de ce site pour commenter une pièce de pure fiction (au contraire des autres messages qui abordent le sujet sous un angle plus subtil). Le nouveau roman de Michael Crichton, « Etat d’urgence » raconte comment une ONG encourage la recherche scientifique sur le réchauffement global pour servir les objectifs de méchants éco-terroristes. Le roman nous amène inévitablement à la conclusion que le réchauffement global est un faux problème. Une leçon pour notre époque? Malheureusement, je ne le pense pas.
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Climate Change Disinformation

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by Michael Mann and Gavin Schmidt
As highlighted in the introduction to the site, we seek to clarify the findings of scientists who study the earth’s climate, and have an informed view on the science of climate change. Additionally we will speak out where we feel that the public discourse surrounding the science is being detrimentally impacted by the shrill voices and disinformation campaigns of the “partisan think-tanks or other interested parties”.

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Welcome to RealClimate Bienvenue à RealClimate

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Climate science is one of those fields where anyone, regardless of their lack of expertise or understanding, feels qualified to comment on new papers and ongoing controversies. This can be frustrating for scientists like ourselves who see agenda-driven ‘commentary’ on the Internet and in the opinion columns of newspapers crowding out careful analysis.
Les sciences du climat forment une discipline dans laquelle qui que ce soit, indépendamment de son expertise ou de sa compréhension, se sent qualifiée pour présenter ses observations sur de nouveaux articles et polémiques en cours. Ceci peut se révéler frustrant pour les scientifiques, comme nous-mêmes, qui lisont des ‘commentaires’ sur le web dictés par des préjugés politiques qui ne tiennent compte de la rigueur des observations scientifiques.

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Comment policy

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revised 01/06/11

Weren’t temperatures warmer than today during the “Medieval Warm Period”? Ne faisait-il pas plus chaud au Moyen-Age, pendant “l’Optimum climatique”, que maintenant?

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This is one of a number of popular myths regarding temperature variations in past centuries. At hemispheric or global scales, surface temperatures are believed to have followed the “Hockey Stick” pattern, characterized by a long-term cooling trend from the so-called “Medieval Warm Period” (broadly speaking, the 10th-mid 14th centuries) through the “Little Ice Age” (broadly speaking, the mid 15th-19th centuries), followed by a rapid warming during the 20th century that culminates in anomalous late 20th century warmth. The late 20th century warmth, at hemispheric or global scales, appears, from a number of recent peer-reviewed studies, to exceed the peak warmth of the “Medieval Warm Period”. Claims that global average temperatures during Medieval times were warmer than present-day are based on a number of false premises that a) confuse past evidence of drought/precipitation with temperature evidence, b) fail to disinguish regional from global-scale temperature variations, and c) use the entire “20th century” to describe “modern” conditions , fail to differentiate between relatively cool early 20th century conditions and the anomalously warm late 20th century conditions.

par Michael Mann (traduit par Thibault de Garidel)
C’est un des nombreux mythes populaires concernant les variations de température sur les siècles passés. A l’échelle globale ou hémispherique, il est admis que les températures de surface ont suivi une évolution en forme de “crosse de hockey” – (“hockey stick”), caractérisée par une longue tendance au refroidissement depuis “l’Optimum Climatique Médiéval” (grosso modo, du Xie au milieu du XIVie siècle) jusqu’au “Petit Age Glaciaire” (grosso modo du milieu du XVie au XIXie siècle), suivie d’un réchauffement rapide au XXie siècle qui culmine par les températures anormalement élevées de la fin du XXie siècle. Ces températures élevées de la fin du XXie siècle, aux échelles hémisphérique ou globale, apparaissent, d’après de nombreux travaux récents évalués par des pairs, supérieures à celles maximales de l’Optimum Médiéval.
Les assertions de températures moyennes globales plus élevées au Moyen Age que maintenant sont fondées sur un certain nombre de prémisses fausses qui (a) confondent les indicateurs de sécheresse/précipitation avec ceux de température, (b) ne font pas la différence entre des variations globales et régionales de température, et (c) utilisent tout le 20ie siecle pour définir les conditions ‘modernes’, ce qui empêche de différencier les conditions relativement fraiches du début du 20ie et celles anormalement chaudes de la fin du 20ie.

OK, But we do know it was warmer than present 6000 years ago, don’t we? Sommes nous sûrs qu’il faisait plus chaud il y a 6000 ans ?

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This is yet another oft-repeated but problematic assertion based in this case on the mis-characterization of the so-called Mid-Holocene Climatic Optimum” or “Mid-Holocene Warm Period”. Paleoclimate experts now know that the mid-Holocene warmth centered roughly 8000 to 6000 years ago was probably restricted to high latitudes and certain seasons (summer in the Northern Hemisphere and winter in the southern hemisphere). Because much of the early paleoclimate evidence that was available (for example, fossil pollen assemblages) came from the Northern Hemisphere extratropics, and is largely reflective of summer conditions, decades ago some scientists believed that this was a time of globally warmer conditions. More abundant evidence now demonstrates, for example, that the tropical regions were cooler over much of the year.

par Michael Mann (traduit par Thibault de Garidel)

Cette assertion est très souvent répétée mais reste problématique en raison de la mauvaise caractérisation de cette période appelée ““Optimum climatique de l’Holocène moyen” ou “période chaude de l’Holocène moyen”. Les experts des paléoclimats, savent maintenant que cette phase chaude à l’Holocène (il y a approximativement 8000 à 6000 ans) était probablement limitée aux hautes latitudes et à certaines saisons (été dans l’hémisphère nord et hiver dans l’hémisphère sud). Comme la majorité des indicateurs du climat passé disponibles (comme par exemple, assemblages de pollens fossiles) provenaient des latitudes moyennes à hautes de l’hémisphère Nord, et étaient diagnostiques des condition climatiques d’été, certains scientifiques ont cru que cette période de temps était plus chaude globalement. Cependant, désormais, de nombreuses études montrent que les régions tropicales étaient plus fraîches pendant la plus grande partie de l’année.
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Are Temperature Trends affected by Economic Activity?

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In a recent paper, McKitrick and Michaels (2004, or “MM04”) argue that non-climatic factors such as economic activity may contaminate climate station data, and thus, may render invalid any estimates of surface tem­perature trends derived from these data. They propose that surface temperature trends may be linked to various local economic factors, such as national coal consumption, income per capita, GPD growth rate, literacy rates, and whether or not temperature stations were located within the former Soviet Union. If their conclusions were correct, this would hold implications for the reliability of the modern surface temperature record, an important piece of evidence indicating 20th century surface warming. However, numerous flaws with their analysis, some of them absolutely fundamental, render their conclusions invalid.

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Why does the stratosphere cool when the troposphere warms? Pourquoi la stratosphère refroidit alors que la troposphère se réchauffe ?

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This post is obsolete and wrong in many respects. Please see this more recent post for links to the answer.

14/Jan/05: This post was updated in the light of my further education in radiation physics.
25/Feb/05: Groan…and again.

Recent discussions of climate change (MSU Temperature Record, ACIA) have highlighted the fact that the stratosphere is cooling while the lower atmosphere (troposphere) and surface appear to be warming. The stratosphere lies roughly 12 to 50 km above the surface and is marked by a temperature profile that increases with height. This is due to the absorbtion by ozone of the sun’s UV radiation and is in sharp contrast to the lower atmosphere. There it generally gets colder as you go higher due to the expansion of gases as the pressure decreases. Technically, the stratosphere has a negative ‘lapse rate’ (temperature increases with height), while the lower atmosphere’s lapse rate is positive.
Par Gavin Schmidt (traduit de l’anglais par Vincent Noël)
Des études récentes du changement climatique (MSU température Record, ACIA) ont mis en évidence un refroidissement de la stratosphère, en parallèle a un apparent réchauffement de la surface et la basse atmosphère (troposphère). La stratosphère se situe entre 12 et 50 km d’altitude environ. Elle se caractérise par un profil de température qui augmente avec l’altitude, en raison de l’absorption des radiations solaires ultraviolettes par l’ozone stratosphérique. Les choses sont très différentes dans la troposphère (de 0 a 12 km d’altitude environ), ou, en général, la température baisse lorsque l’altitude augmente, en raison de l’expansion des gaz alors que la pression atmosphérique diminue. En d’autres termes, la stratosphère a un gradient de température négatif, alors que la troposphère a un gradient positif.
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