Nature this week has an excellent summary of the state of the science with regards to possible changes in the ocean thermohaline (or meridional) circulation in the Atlantic and its impact on climate. Even though it quotes a couple of us, it’s still worth reading if you want to understand how results like the Bryden et al paper – that suggested that the Atlantic overturning had reduced by 30% in recent decades – are assimilated into the scientific picture.
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Archives for 2006
Atlantic circulation change summary
New look
Hopefully readers will appreciate the new look we have given the site (you may need to reload for it to work properly). We have added some new features attached to the buttons above – an index which may prove useful in navigating the site, a more prominent Search function (which searches posts and comments), a link to the archives etc. This has allowed us to reduce some of the clutter and hopefully make this site a little more user friendly. If there are any problems, wrinkles that need to be ironed out, or if you have suggestions for further improvement, let us know at contrib -at- realclimate -dot- org.
Was the record Amazon drought caused by warm seas?
On December 11, 2005, The New York Times ran a story on record drought conditions in the Amazonas region of Brasil, linking it to global warming, and specifically the warm ocean temperatures in the North Atlantic that have also been linked to the ferocity of the 2005 Atlantic hurricane season. This prompted a response from Chris Mooney, calling for a comment from RealClimate about whether such an assertion is valid, as we earlier made it very clear that it is impossible to say whether one single extreme event in a very noisy environment – such as Hurricane Katrina – is related to climate change. So we decided to take a look at this phenomena, and address why there might be a connection and what it takes to make an attribution. [Read more…] about Was the record Amazon drought caused by warm seas?
Scientists baffled! Une surprise pour les scientifiques !
Every so often a scientific paper comes out that truly surprises. The results of Keppler et al in Nature this week is clearly one of those. They showed that a heretofore unrecognised process causes living plant material to emit methane (CH4, the second most important trace greenhouse gas), in quantities that appear to be very significant globally. This is surprising in two ways – firstly, CH4 emission is normally associated with anaerobic (oxygen-limited) environments (like swamps or landfills) but chemistry in plants is generally thought of as ‘aerobic’ i.e. not oxygen-limited, and secondly, because although the total budget for methane has some significant uncertainty associated with it (see the IPCC assessment here), the initial estimates of this effect (between 62–236 Tg/yr out of a total source of 500+ Tg/yr!) give numbers that might be difficult to incorporate without some significant re-evaluations elsewhere.
Reactions so far have been guarded, and there will undoubtedly be a scramble to check and refine the estimates of this process’s importance. Once the dust settles though, the situation may not be so different to before – some emissions may turn out to have been mis-identified, this source may not be as large as these initial estimates (10-30% of total sources) suggest, or it might radically challenge our current understanding of methane’s sources and sinks. However, the process by which this is decided will demonstrate clearly that the scientific method is alive and well in the climate sciences. That is, as long as a work is careful and the conclusions sound, papers that upset the apple cart can appear in the major journals and have a good chance of ending up being accepted by the rest of the field (providing the conclusions hold up of course!).
Update 19 Jan: The authors of the study have released a clarification of their study to counter some of the misleading conclusions that had appeared in the press.
Les réactions jusqu’ici ont été réservées, et il y aura assurément un grand nombre d’études pour vérifier et raffiner les évaluations de l’importance de ce processus. Une fois que la poussière se sera redéposé, la situation pourrait ne pas être si différente que celle précédent cette étude – certaines émissions pouvant s’avérer avoir été mal interprétées, cette source pouvant ne pas être aussi importante que suggérée par ces évaluations initiales (10-30% de sources totales), ou au contraire elle pourrait radicalement défier notre compréhension actuelle des sources et puits du méthane. Cependant, le processus par lequel cette étude sera confirmée ou pas démontrera clairement que la méthode scientifique est belle-et-bien vivante dans les sciences de climat. C’est-à-dire, aussi longtemps qu’un travail est soigné et rigoureux, et que les conclusions sont justifiées, les papiers bousculant le courant de pensée dominant peuvent paraître dans les journaux les plus importants, et ont une bonne chance à la fin d’être accepté par le reste des scientifiques (si les conclusions tiennent la route bien sûr !).
Polar Amplification
Guest commentary by Cecilia Bitz, University of Washington
“Polar amplification” usually refers to greater climate change near the pole compared to the rest of the hemisphere or globe in response to a change in global climate forcing, such as the concentration of greenhouse gases (GHGs) or solar output (see e.g. Moritz et al 2002). Polar amplification is thought to result primarily from positive feedbacks from the retreat of ice and snow. There are a host of other lesser reasons that are associated with the atmospheric temperature profile at the poles, temperature dependence of global feedbacks, moisture transport, etc. Observations and models indicate that the equilibrium temperature change poleward of 70N or 70S can be a factor of two or more greater than the global average. [Read more…] about Polar Amplification