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Raymond T. Pierrehumbert

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Pierrehumbert Portrait
Raymond Pierrehumbert is the Louis Block Professor in Geophysical Sciences at the University of Chicago, having earlier served on the atmospheric science faculties of MIT and Princeton. He is principally interested in the formulation of idealized models which can be brought to bear on fundamental phenomena governing present and past climates of the Earth and other planets. His recent research interests have included water vapor feedback, baroclinic instability, the Neoproterozoic Snowball Earth, the climate of Early Mars, and methane hydrological cycles on Titan. He has been director of the Climate Systems Center, a US National Science Foundation Information Technology Research project aimed at bringing modern software design techniques to the problem of climate simulation. He has also collaborated with David Archer on the University of Chicago’s global warming curriculum.

He received an A.B. degree in Physics from Harvard, was then a Knox Fellow in the Department of Applied Mathematics and Theoretical Physics at Cambridge University, and completed his PhD on hydrodynamic stability theory at MIT, in the Department of Aeronautics and Astronautics. He was a lead author of the IPCC Third Assessment Report, and a co-author of the National Research Council study on abrupt climate change. He is a Fellow of the American Geophysical Union.

Pierrehumbert is the author of the textbook Principles of Planetary Climate, available from Cambridge University Press.

More information about his research, including a complete publication list, can be found here.

The Arctic Climate Impact Assessment

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In early November 2004 the results of the Arctic Climate Impact Assessment (ACIA) were published, a uniquely detailed regional study compiled by 300 scientists over 3 years. The study describes the ongoing climate change in the Arctic and its consequences: rising temperatures, loss of sea ice, unprecedented melting of the Greenland ice sheet, and many impacts on ecosystems, animals and people. The ACIA is the first comprehensively researched, fully referenced, and independently reviewed evaluation of arctic climate change and its impacts for the region and for the world.

Sadly, in recent years we have become accustomed to a ritual in which the publication of each new result on anthropogenic climate change is greeted by a flurry of activity from industry-funded lobby groups, think tanks and PR professionals, who try to discredit the science and confuse the public about global warming.

[Read more…] about The Arctic Climate Impact Assessment

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

Temperature Variations in Past Centuries and the so-called "Hockey Stick" Variations de température sur les derniers siècles et la "crosse de hockey"

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Instrumental data describing large-scale surface temperature changes are only available for roughly the past 150 years. Estimates of surface temperature changes further back in time must therefore make use of the few long available instrumental records or historical documents and natural archives or ‘climate proxy’ indicators, such as tree rings, corals, ice cores and lake sediments, and historical documents to reconstruct patterns of past surface temperature change. Due to the paucity of data in the Southern Hemisphere, recent studies have emphasized the reconstruction of Northern Hemisphere (NH) mean, rather than global mean temperatures over roughly the past 1000 years.


par Mike Mann (traduit par Gilles Delaygue)
Les données intrumentales décrivant les changements à grande échelle de la température de surface ne sont disponibles que pour les derniers 150 ans environ. Pour estimer des changements de température de surface antérieurs, il faut ainsi utiliser les quelques longs enregistrements disponibles, ou des documents historiques, ainsi que des archives naturelles ou proxies climatiques, comme les cernes d’arbres, coraux, carottes de glace et sédiments lacustres, pour reconstruire les changements de température dans le passé. En raison de la rareté des données dans l’hémisphère sud, les études récentes ont été focalisées sur les reconstructions de moyennes pour l’hémisphère nord, plutôt que globales, sur les derniers 1000 ans environ.

[Read more…] about Temperature Variations in Past Centuries and the so-called "Hockey Stick" Variations de température sur les derniers siècles et la "crosse de hockey"

False Claims by McIntyre and McKitrick regarding the Mann et al. (1998) reconstruction

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A number of spurious criticisms regarding the Mann et al (1998) proxy-based temperature reconstruction have been made by two individuals McIntyre and McKitrick ( McIntyre works in the mining industry, while McKitrick is an economist). These criticisms are contained in two manuscripts (McIntyre and McKitrick 2003 and 2004–the latter manuscript was rejected by Nature; both are collectively henceforth referred to as “MM”). MM claim that the main features of the Mann et al (1998–henceforth MBH98) reconstruction, including the “hockey stick” shape of the reconstruction, are artifacts of a) the centering convention used by MBH98 in their Principal Components Analysis (PCA) of the North American International Tree Ring Data Bank (‘ITRDB’) data, b) the use of 4 infilled missing annual values (AD 1400-1403) in one tree-ring series (the ‘St. Anne’ Northern Treeline series), and c) the infilling of missing values in some proxy data between 1972 and 1980. Each of these claims are demonstrated to be false below. [Read more…] about False Claims by McIntyre and McKitrick regarding the Mann et al. (1998) reconstruction

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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What does the lag of CO2 behind temperature in ice cores tell us about global warming? Quelle information sur le réchauffement climatique nous apportent les études qui concluent à un retard du CO2 sur la température, réalisées à partir des carottes de glace?

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This is an issue that is often misunderstood in the public sphere and media, so it is worth spending some time to explain it and clarify it. At least three careful ice core studies have shown that CO2 starts to rise about 800 years (600-1000 years) after Antarctic temperature during glacial terminations. These terminations are pronounced warming periods that mark the ends of the ice ages that happen every 100,000 years or so.

Does this prove that CO2 doesn’t cause global warming? The answer is no.
Par Jeff Severinghaus (traduit par Nicolas Caillon)

Les résultats de ces études ne sont pas toujours bien compris par le public, souvent mal restitués par les médias, et méritent donc davantage d’explications. Au moins 3 études détaillées réalisées à partir de carottes de glace montrent que le CO2 commence à augmenter autour de 800 ans (entre 600 à 1000 ans) après le démarrage de l’augmentation de température lors des terminaisons glaciaires. Ces terminaisons sont les périodes de réchauffement qui marquent la fin des périodes glaciaires et qui se produisent tous les 100 000 ans.
[Read more…] about What does the lag of CO2 behind temperature in ice cores tell us about global warming? Quelle information sur le réchauffement climatique nous apportent les études qui concluent à un retard du CO2 sur la température, réalisées à partir des carottes de glace?

Michaels misquotes Hansen

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Pat Michaels (under the guise of the Greening Earth society) is particularly fond of misquoting Jim Hansen, director of the NASA GISS laboratory (and in the interests of full disclosure, GS’s boss).

Recently he claimed that Dr. Hansen has now come around to the ‘skeptics’ (i.e. Pat Michaels) way of thinking and suggests that they agree on the (small) amount of warming to be expected in the future. Michaels quotes Hansen from a 2001 PNAS paper:

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