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about Gavin Schmidt

Gavin Schmidt is a climate modeler, working for NASA and with Columbia University.

Global Dimming? Assombrissement global?

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It just so happens that most of the posts on this site have tried to counteract arguments from those who would sow fake “uncertainty” in the climate debate. But lest our readers feel that we are unjustifiably certain about our knowledge, let us look at a recent example of the opposite tendency: too much certainty.

A recent BBC Horizon documentary (transcript) raised the issue of ‘global dimming’ and argued that this ‘killer’ phenomena’s newly-recognised existence would lead to huge re-assessments of future global warming. As part of the hyperbole, the process of global dimming was linked very clearly to the famines in Ethiopia in the 1980s and the implication was left that worse was to come. Media reports with headlines like “Fossil Fuel Curbs May Speed Global Warming” swiftly followed. So what’s the real story?
par Gavin Schmidt (traduit par Pierre Allemand)
Il est un fait que la plupart des interventions sur ce site ont essayé de contrer les arguments de ceux qui voudraient semer une “incertitude” trompeuse dans le débat sur le climat. Mais, de peur que nos lecteurs pensent que nous sommes abusivement certains de nos connaissances, examinons un exemple récent de la tendance inverse : trop de certitude.

Un récent documentaire de la série “Horizon” de la BBC (transcription) a soulevé la question d’un “assombrissement global” et a indiqué que l’existence récemment reconnue d’un tel phénomène « tueur » pourrait amener à reconsidérer très fortement l’hypothèse d’un futur réchauffement global. Cet audacieux raisonnement faisait un lien très clair entre l’assombrissement global et les famines en Ethiopie durant les années 1980, le plus grave restant encore à venir. Des dépêches de presse avec des titres du genre « Le coup de frein sur les énergies fossiles pourrait accélérer le réchauffement global » suivaient dans la foulée. Mais, qu’en est-il exactement ?
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Is Climate Modelling Science? La modélisation climatique est-elle de la science?

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At first glance this seems like a strange question. Isn’t science precisely the quantification of observations into a theory or model and then using that to make predictions? Yes. And are those predictions in different cases then tested against observations again and again to either validate those models or generate ideas for potential improvements? Yes, again. So the fact that climate modelling was recently singled out as being somehow non-scientific seems absurd.
par Gavin Schmidt (traduit par Gilles Delaygue)

A première vue, cela semble une question étrange. Est-ce-que la science n’est pas précisément la quantification d’observations dans une théorie ou un modèle, et ensuite son utilisation pour faire des prédictions ? Oui. Et est-ce-que ces prédictions de différents cas sont ensuite confrontées, maintes fois, aux observations, afin soit de valider ces modèles ou bien de faire émerger des idées d’amélioration ? Oui, encore une fois. Ainsi la mise à l’index récente de la modélisation climatique comme quelque chose de non scientifique semble absurde.

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Imprecision of the Phrase “Global Warming”

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Guest Contribution by Michael Tobis, University of Chicago

Consider the possibility that the expression “global warming” has become a problematic one, and that it might be best to avoid it.

A big part of the public confusion about climate change comes from sloppy language. The naysayers prey on this confusion, very much as their peers prey on the phrase “evolutionary theory” to suggest that “evolution, well, it’s just a theory”.

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A Welcoming Nature

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Getting a serious paper into Nature or Science is deservedly hard. Getting a mention for your climate blog is apparently a little easier!

We are of course collectively very pleased that Nature has welcomed the RealClimate.org effort so forthrightly. We only hope that we will be able to match up to their expectations. As with anything new, done by inexperienced first-timers who really should be concentrating on their actual jobs, there are bound to be teething problems. One, alluded to in the editorial and accompanying news story, is who gets to decide what’s posted, and getting the balance right between inclusiveness and clarity.

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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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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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Gavin A. Schmidt

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Gavin Schmidt is a climate modeller at the NASA Goddard Institute for Space Studies and Earth Institute at Columbia University in New York and is interested in modeling past, present and future climate. He works on developing and improving coupled climate models and, in particular, is interested in how their results can be compared to paleoclimatic proxy data. He has worked on assessing the climate response to multiple forcings, including solar irradiance, atmospheric chemistry, aerosols, and greenhouse gases.

He received a BA (Hons) in Mathematics from Oxford University, a PhD in Applied Mathematics from University College London and was a NOAA Postdoctoral Fellow in Climate and Global Change Research. He was cited by Scientific American as one of the 50 Research Leaders of 2004, and has worked on Education and Outreach with the American Museum of Natural History, the College de France and the New York Academy of Sciences. He has over 100 peer-reviewed publications and is the co-author with Josh Wolfe of “Climate Change: Picturing the Science” (W. W. Norton, 2009), a collaboration between climate scientists and photographers. He was awarded the inaugural AGU Climate Communications Prize and was the EarthSky Science communicator of the year in 2011. He tweets at @ClimateOfGavin.

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

All posts by gavin.

The Arctic Climate Impact Assessment III

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Does the ACIA overstate the problem of ozone depletion? The overview report states that the “stratospheric ozone layer over the Arctic is not expected to improve significantly for at least a few decades”. This is partly because CFC concentrations (that enhance stratospheric ozone destruction) are only expected to decrease slowly as a function of restrictions imposed by the Montreal Protocol and subsequent amendments. Another factor is the fact that stratospheric temperatures are generally cooling as greenhouse gases increase (see MSU Temperature Record, also Why does the stratosphere cool when the troposphere warms?). Due to the temperature dependence on the rates of chemical reactions involving ozone, cooler temperatures also lead to more ozone destruction. Stratospheric temperatures, particularly near the pole are also significantly influenced by dynamical changes, and in particular, the strength of the [Read more…] about The Arctic Climate Impact Assessment III

Antarctic cooling, global warming? Refroidissement de l’Antarctique, réchauffement global ?

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by Eric Steig and Gavin Schmidt
Long term temperature data from the Southern Hemisphere are hard to find, and by the time you get to the Antarctic continent, the data are extremely sparse. Nonetheless, some patterns do emerge from the limited data available. The Antarctic Peninsula, site of the now-defunct Larsen-B ice shelf, has warmed substantially. On the other hand, the few stations on the continent and in the interior appear to have cooled slightly (Doran et al, 2002; GISTEMP). At first glance this seems to contradict the idea of “global” warming, but one needs to be careful before jumping to this conclusion.

par Eric Steig et Gavin Schmidt (traduit par Claire Rollion-Bard)

Les données de température à long terme de l’hémisphère sud sont difficiles à trouver, et au moment où vous accédez au continent Antarctique, les données sont extrêmement éparses. Néanmoins quelques tendances émergent des quelques données disponibles. La Péninsule Antarctique, lieu de la barrière de glace Larsen-B, maintenant disparue, s’est réchauffée substantiellement. D’un autre côté, les quelques stations sur le continent et à l’intérieur semblent s’être légèrement refroidies. (Doran et al., 2002 ; GISTEMP). Au premier coup d’œil, cela semble contradictoire avec l’idée de réchauffement “global”, mais on a besoin d’être prudent avant de sauter sur cette conclusion.
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