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
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Temperature Variations in Past Centuries and the so-called "Hockey Stick" Variations de température sur les derniers siècles et la "crosse de hockey"
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temperature changes further back in time must therefore make use of the few long available instrumental records or historical documents and natural archives or ‘climate proxy’ indicators, such as tree rings, corals, ice cores and lake sediments, and historical documents to reconstruct patterns of past surface temperature change.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.
Myth vs. Fact Regarding the "Hockey Stick"
Numerous myths regarding the so-called "hockey stick" reconstruction of past temperatures, can be found on various non-peer reviewed websites, internet newsgroups and other non-scientific venues. The most widespread of these myths are debunked below:
[Read more…] about Myth vs. Fact Regarding the "Hockey Stick"
False Claims by McIntyre and McKitrick regarding the Mann et al. (1998) reconstruction
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 ?
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.
[Read more…] about Antarctic cooling, global warming?
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?
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.
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?
Michaels misquotes Hansen
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:
Climate model scenarios Les scénarios des modèles climatiques
A couple of commentators (Pat Michaels, Roy Spencer) recently raised an issue about the standard scenarios used to compare climate models, in this case related to a study on the potential increase in hurricane activity.
The biggest uncertainty in what will happen to climate in the future (say 30 years or more) is the course that the global economy will take and the changes in technology that may accompany that. Since climate scientists certainly don’t have a crystal ball, we generally take a range of scenarios or projections of future emissions of CO2 and other important forcings such as methane and aerosols.
La plus grande incertitude dans ce qui va se passer pour le climat du futur (dans 30 ans ou plus) est le cours que va suivre l’économie globale et les changements technologiques qui peuvent l’accompagner. Puisque les climatologues n’ont certainement pas une boule de cristal, nous considérons généralement une gamme de scénarios ou de projections des émissions futures de CO 2 et d’autres forçages importants comme le méthane et les aérosols.
[Read more…] about Climate model scenarios
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