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Scientists baffled! Une surprise pour les scientifiques !

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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.

De temps en temps, un papier scientifique crée de véritables surprises. Les résultats de Keppler et al. publiés cette semaine dans la revue Nature est clairement un de ceux-çi. Ces auteurs ont prouvé qu’un processus jusqu’ici non reconnu fait que les plantes vivantes émettent du méthane (CH4, le deuxième gaz à effet de serre après le CO2), dans des quantités qui semblent être très significatives globalement. Ceci étonne de deux manières – premièrement, l’émission de CH4est normalement associée aux environnements anaérobies (c’est-à-dire pauvres en oxygène) comme les marais ou décharges, alors que la chimie dans les plantes est généralement considérée comme étant ‘aérobie ‘ c.-à-d. non limitée en oxygène, et deuxièmement, parce que les évaluations initiales de cet effet (entre 62-236 Tg/an sur une source totale de 500+ Tg/an!) donne des valeurs qu’il sera difficile d’incorporer dans le budget total du méthane sans des ré-évaluations majeures (et ce malgré les incertitudes liées au budget total – voir l’évaluation de celui-ci par le GIEC).

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

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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

One year on…

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RealClimate has been online for just over a year, and so this is probably a good time to review the stories we’ve covered and assess how well the whole project is working out.

Over the last 12 months, we’ve tackled a 100+ scientific topics that range from water vapour feedbacks, the carbon cycle, climate sensitivity, satellite/surface temperature records, glacier retreat, climate modelling to hurricanes. We’ve had guest postings that span questions of Martian climate change to Arctic ozone depletion and solar forcing. We’ve crossed virtual swords with Michael Crichton, the Wall Street Journal’s editorial board, George Will, Nigel Lawson, Fox News and assorted documentary makers (though only one person ever threatened to sue us). Hopefully our contributions have interested, intrigued and occasionally amused (at least a few of you…). [Read more…] about One year on…

How to be a real sceptic

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Scepticism is often discussed in connection with climate change, although the concept is often abused. I therefore thought it might be interesting to go back and see what the epitome of 20th Century sceptics, Bertrand Russell, had to say on the subject. This is extracted from the Introduction to his ‘Sceptical Essays’ (1928):
[Read more…] about How to be a real sceptic

Naturally trendy?

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From time to time, there is discussion about whether the recent warming trend is due just to chance. We have heard arguments that so-called ‘random walk‘ can produce similar hikes in temperature (any reason why the global mean temperature should behave like the displacement of a molecule in Brownian motion?). The latest in this category of discussions was provided by Cohn and Lins (2005), who in essence pitch statistics against physics. They observe that tests for trends are sensitive to the expectations, or the choice of the null-hypothesis .

[Read more…] about Naturally trendy?

2005 temperatures Températures 2005

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Due to a historical quirk (of unknown origin), the World Meterological Organisation releases its summary for each year based on the Dec to Nov ‘meteorlogical year’ means (rather than the more usual calendar year). Anyway, the WMO summary is now available, as is the NASA GISS analysis and the CRU summary. The point upon which all the analyses agree is that 2005 was exceptionally warm and that it continues the long term mean warming trend. All show record warmth in the Northern Hemisphere since 1860, while GISS gives 2005 as the warmest year globally as well (CRU/WMO have it second after 1998). As the summaries indicate, the differences in ranking are on the order of a few hundredths of a degree (smaller than the accuracy of the analysis) and so a definitive ranking is not possible. Differences in how the separate analyses deal with missing data are responsible for most of the apparent variations. Note too that the convention for the base periods for the anomalies differ between the analyses (1961-1990 for CRU/WMO, 1951-1980 for GISS), but this does not affect the rankings.

Update 7pm: The GISS analysis curiously appears to have gone off line….
Update 8am 16 Dec: The GISS summation is still not back up, but the raw data and new figures do seem to be available http://data.giss.nasa.gov/gistemp . Note that as pointed in comment #5, the WMO/CRU/Hadley Centre analysis is for Jan-Nov, and not for the met. year as stated above (though the GISS analysis is). Don’t ask us why!
Final Update 11pm 16 Dec: The GISS analysis is back!

En raison d’une incongruité historique (d’origine inconnue), l’Organisation Météorologique Mondiale publie son compte-rendu annuel basé sur les moyennes d’une “année météorologique” allant de décembre à novembre (plutôt qu’une année civile normale). Ce compte-rendu de l’OMM est désormais disponible, ainsi que l’analyse du GISS-NASA et celle du CRU. Le point sur lequel toutes ces analyses convergent est que l’année 2005 était exceptionnellement chaude et qu’elle poursuit la tendance à long terme d’un réchauffement moyen global. Toutes ces analyses montrent que 2005 correspond à une température record dans l’hémisphère nord depuis 1860, alors que le GISS donne 2005 comme l’année la plus chaude globalement (le CRU l’indique comme la seconde la plus chaude juste après 1998). Comme ces analyses l’indiquent, les différences dans ces classements sont dues à des différences de quelques centièmes de degré (inférieures à la justesse de l’analyse). Les variations apparentes entre ces différentes analyses résultent principalement de la manière par laquelle chaque analyse traite des données manquantes. Un dernier point, la convention qui définit la période de référence pour la détermination des anomalies de température diffère pour chaque analyse (1961-1990 pour le CRU, 1951-1980 pour le GISS), mais ceci n’affecte pas le classement.

(traduit par T. de Garidel)

Natural Variability and Climate Sensitivity

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One of the central tasks of climate science is to predict the sensitivity of climate to changes in carbon dioxide concentration. The answer determines in large measure how serious the consequences of global warming will be. One common measure of climate sensitivity is the amount by which global mean surface temperature would change once the system has settled into a new equilibrium following a doubling of the pre-industrial CO2 concentration. A vast array of thought has been brought to bear on this problem, beginning with Arrhenius’ simple energy balance calculation, continuing through Manabe’s one-dimensional radiative-convective models in the 1960’s, and culminating in today’s comprehensive atmosphere-ocean general circulation models. The current crop of models studied by the IPCC range from an equilibrium sensitivity of about 1.5°C at the low end to about 5°C at the high end. Differences in cloud feedbacks remain the principal source of uncertainty. There is no guarantee that the high end represents the worst case, or that the low end represents the most optimistic case. While there is at present no compelling reason to doubt the models’ handling of water vapor feedback, it is not out of the question that some unanticipated behavior of the hydrological cycle could make the warming somewhat milder — or on the other hand, much, much worse. Thus, the question naturally arises as to whether one can use information from past climates to check which models have the most correct climate sensitivity.

[Read more…] about Natural Variability and Climate Sensitivity

Methane hydrates and global warming

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There is an enormous amount of methane (CH4) on earth frozen into a type of ice called methane hydrate. Hydrates can form with almost any gas and consist of a ‘cage’ of water molecules surrounding the gas. (The term ‘clathrate’ more generally describes solids consisting of gases are trapped within any kind of cage while hydrate is the specific term for when the cage is made of water molecules). There are CO2 hydrates on Mars, while on Earth most of the hydrates are filled with methane. Most of these are in sediments of the ocean, but some are associated with permafrost soils.

Methane hydrates would seem intuitively to be the most precarious of things. Methane hydrate melts if it gets too warm, and it floats in water. Methane is a powerful greenhouse gas, and it degrades to CO2, another greenhouse gas which accumulates in the atmosphere just as fossil fuel CO2 does. And there is a lot of it, possibly more than the traditional fossil fuel deposits. Conceivably, climate changes could affect these deposits. So what do we know of the disaster-movie potential of the methane hydrates?

[Read more…] about Methane hydrates and global warming

Climate meeting blogging

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Two climate-related meetings are being covered quite extensively this week, the American Geophsyical Union meeting in San Francisco is being blogged for Woods Hole Oceanographic Institution, and the COP/MOP meeting in Montreal is being podcasted by the New York Times and blogged by other attendees. Hopefully this is a sign that scientists are starting to use these tools more effectively than they have so far.

Debate over the Early Anthropogenic Hypothesis

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There have been a few mentions of the ‘early anthropocene’ hypothesis recently (cf. the EPICA CO2 results, and Strange Bedfellows). We therefore welcome Bill Ruddiman to RealClimate to present his viewpoint and hopefully stimulate further discussion – gavin.

[Addendum: For a non-technical backgrounder on the ‘early anthropocene’ hypothesis and its significance in the context of anthropogenic climate change, see Bill Ruddiman’s article “How Did Humans First Alter Global Climate?” from the March 2005 issue of “Scientific American” (first two paragraphs available for free; full article must be purchased). -mike]

Guest posting from Bill Ruddiman, University of Virginia

The hypothesis (Ruddiman, 2003) that early agriculture caused large enough emissions of greenhouse gases millennia ago to offset a natural climatic cooling remains controversial. The centerpiece of the hypothesis was a comparison of the increases of CO2 and CH4 values in Vostok ice during the current (Holocene) interglaciation versus the (natural) drops during similar portions of the three previous interglaciations. [Read more…] about Debate over the Early Anthropogenic Hypothesis