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Archives for November 2005

Decrease in Atlantic circulation? Ralentissement de la circulation Atlantique?

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by Gavin Schmidt and Michael Mann

In a sure-to-be widely publicized paper in the Dec. 1 Nature, Bryden et al. present results from oceanographic cruises at 25°N across the Atlantic showing a ~30% decline in the ocean overturning circulation. These cruises have been repeated every few years since 1957, and the last two cruises (in 1998 and 2004) show notable changes in the structure of the deep return circulation. In particular, the very deepest part of the return flow (at around 3000 to 5000 m) has reduced and moved up in the water column compared to previous decades. How solid is this result and what might it imply for climate?par Gavin Schmidt et Michael Mann (traduit de l’anglais par T. de Garidel)

Dans un article largement commenté dans la presse (voir par exemple ici et la) dans le numéro du 1er déc. de Nature, Bryden et al. présentent des résultats de croisières océanographiques à 25°N à travers l’Océan Atlantique qui montrent un déclin d’environ 30% de la circulation océanique “générale”–dite circulation thermohaline-. Ces croisières ont été répétées régulièrement depuis 1957, et les deux dernières croisières (en 1998 et 2004) montrent des changements notables de la structure de la circulation de retour profonde. En particulier, le flux dans la partie la plus profonde du courant de retour (entre environ 3000 et 5000 m) a diminué et est remonté dans la colonne de l’eau par rapport aux décennies précédentes. Quelle est la robustesse de ces résultats et quelles en sont les implications potentielles pour le climat ?
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Greenhouse gases help seasonal predictions Gaz à effet de serre et prédictions saisonnières

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The conventional wisdom in meteorology has been that certain factors such as the complete oceanic state and the exact concentrations of greenhouse gases are of minor importance for a normal weather forecast. Moreover, whereas sea surface temperatures (SST) are important, the deep sea temperatures are believed to have little impact for predictions for the next few days. The reason is that the ocean reacts slowly to changes in the atmosphere (has much higher inertia and much higher heat capacity). Hence, the most important information needed for such a weather forecast is the atmospheric initial conditions, a description of what the atmosphere and the SST look like when the weather model starts computing the weather evolution.
Il est généralement admis en météorologie que certains facteurs, tels que l’état global des océans et la concentration exacte de gaz à effet de serre sont de faible importance pour une prévision météo normale. De plus, si les températures de surface des océans (TSO) sont importantes, les températures des eaux profondes semblent avoir peu d’influence sur les prévisions pour les prochains jours. La raison en est que les océans réagissent lentement aux changements atmosphériques (leur inertie et capacité thermique est beaucoup plus élevée). Dès lors, l’information la plus importante pour de telles prévisions météo est l’ensemble des conditions initiales de l’atmosphère, c’est-à-dire une description des caractéristiques de l’atmosphère et des TSO au moment où le modèle commence à calculer l’évolution du temps.
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650,000 years of greenhouse gas concentrations 650 000 années de concentrations de gaz à effet de serre

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The latest results from the EPICA core in Antarctica have just been published this week in Science (Siegenthaler et al. and Spahni et al.). This ice core extended the record of Antarctic climate back to maybe 800,000 years, and the first 650,000 years of ice have now been analysed for greenhouse gas concentrations saved in tiny bubbles. The records for CO2, CH4 and N2O both confirm the Vostok records that have been available for a few years now, and extend them over another 4 glacial-interglacial cycles. This is a landmark result and a strong testament to the almost heroic efforts in the field to bring back these samples from over 3km deep in the Antarctica ice. So what do these new data tell us, and where might they lead? Les derniers résultats du forage EPICA en Antarctique viennent juste d’être publiés dans le numéro de cette semaine de Science (Siegenthaler et al. et Spahni et al.). Cette carotte glaciaire a permis d’étendre l’enregistrement du climat Antarctique jusqu’à 800 000 ans, alors que les concentrations de gaz à effet de serre, piégées sous forme de minuscules bulles de gas, ont été analysées pour les 650 000 dernières années. Ces enregistrements de CO2, CH4 et N2O sont en accord avec ceux de Vostok (également en Antarctique) disponibles depuis quelques années, et permettent d’observer 4 cycles d’alternance glaciaire/interglaciaire supplémentaires. Ces travaux sont remarquables, et justifient des efforts gigantesques effectués sur le terrain pour ramener des échantillons enfouis jusqu’à 3km de profondeur dans la glace Antarctique. Que nous disent ces nouvelles données, et dans quelle direction peuvent elles nous mener ?
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Books books books

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Perhaps you’re interested in supplementing your tapas-style RealClimate reading with a full meal of a book to curl up with. Maybe you’d like to send such a book to your good-hearted but clueless Cousin Bob, to convince him not to buy an SUV next time. Here are some possibilities …. [Read more…] about Books books books

Busy Week for Water Vapor

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It’s been a busy week for water vapor, and I have two recent papers to discuss. The first is the paper "Anthropogenic greenhouse forcing and strong water vapor feedback increase temperature in Europe" by Rolf Philipona et al. (GRL, 2005, subscription required for full text), which has attracted a certain amount of media attention. The overall goal of the paper is to understand, from a physical standpoint, why European temperatures have been increasing three times faster than the Northern Hemisphere average. It focuses on the changes between 1995 and 2002, over which time good surface radiation budget observations are available. The paper reports some results on the role of large scale circulation changes (which they conclude are minor) but I’ll concentrate on the results relating to water vapor.

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Climate Basics

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Recently, Oxford University launched a new initiative called Climate.Basics. This Internet site provides a nice explanation and simple illustrations on what is meant by ‘climate’ and how the climate system works. The Climate.Basics site is a collaboration with the climateprediction.net project, which is the world’s largest climate prediction experiment. We think this is quite good, but as always, let us know if you think something could be explained better

The False Objectivity of “Balance”

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We here at RC continue to be disappointed with the tendency for some journalistic outlets to favor so-called “balance” over accuracy in their treatment of politically-controversial scientific issues such as global climate change. While giving equal coverage to two opposing sides may seem appropriate in political discourse, it is manifestly inappropriate in discussions of science, where objective truths exist. In the case of climate change, a clear consensus exists among mainstream researchers that human influences on climate are already detectable, and that potentially far more substantial changes are likely to take place in the future if we continue to burn fossil fuels at current rates. There are only a handful of “contrarian” climate scientists who continue to dispute that consensus. To give these contrarians equal time or space in public discourse on climate change out of a sense of need for journalistic “balance” is as indefensible as, say, granting the Flat Earth Society an equal say with NASA in the design of a new space satellite. It’s plainly inappropriate. But it stubbornly persists nonetheless. [Read more…] about The False Objectivity of “Balance”

More satellite stuff

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The November 17th issue of Science has an interesting exchange of letters between Christy and Spencer; Mears and Wentz; and Sherwood and Lanzante (ref here; subs required for substance). The context of this discussion is the tropospheric temperature record; see Et tu LT and The tropical lapse rate quandary for two RC posts that discuss the issue, and in particular three papers in the August 11th issue of Science.

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Framing of climate science

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There is an interesting article in this month’s Global Environmental Change journal. The paper, Climate of scepticism: US newspaper coverage of the science of climate change (subscription only at the moment) by L. Antilla, documents the way in which the mainstream media (at least in the U.S.) tends to present climate science as more controversial than it actually is. A major focus of the paper is an analysis of the way in which climate science is “framed” (in the journalistics sense of “highlighting certain aspects of a story so as promote a particular interpretation”). In a recent Scientific American article (here), a similar argument is made with respect to the health industry; in this case the writer, David Michaels, is quite blunt that the “framing” is the purposeful fomenting of doubt by powerful industry lobbyists, rather than innocent errors by naive journalists. Antilla doesn’t go so far, but she does give some striking examples, such as an Associated Press piece about the impact of soot on the albedo of snow, which AP titled “Scientists blame soot for global warming”. As if the title weren’t misleading enough, the article goes on to say that “Many scientists believe the burning of fossil fuels is causing an increase in atmospheric carbon dioxide, triggering … the greenhouse effect.” Whether purposeful, or merely due to careless writing, this kind of statement casts the science (and the opinion of scientists) as far more uncertain that it is in reality — in this case implying that there is doubt that CO2 levels are increasing, something which actually has zero uncertainty. [Read more…] about Framing of climate science

Update on 2005 temperatures Mise à Jour sur les températures 2005

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Further to our post about whether 2005 will be a year of record warmth, Jim Hansen has put out a brief discussion on the Washington Post report and some of the subsequent discussion. One minor clarification to his statements is that the reporter involved (Juliet Eilperin) did in fact leave messages for the relevant people at GISS (including me) prior to publication, but sometimes people can just be difficult to track down. Oh….and for those who are counting, with the preliminary October data in, 2005 has pulled ahead of 1998 in both the GISS land based met. station index (0.76 to 0.73°C) and the GISS land-ocean index (0.59 to 0.58°C). All previous caveats still apply….

En complément du message sur le record de température possible de l’année 2005, Jim Hansen a écrit une courte discussion (en anglais) sur l’article du Washington Post report et des discussions sur cet article. Et pour le record, avec les données disponibles d’octobre, 2005 est passé devant 1998 dans les deux types de données du GISS, l’index “GISS land” sur des stations météo terrestres (0.76 comparé a 0.73°C) ainsi que pour l’index “GISS land-ocean” (0.59 to 0.58°C). Les mises en garde précédentes sont toujours valables…