Greenhouse gases

by Rasmus Benestad and Ray Pierrehumbert

A special report in The Observer on Sunday (April 9) titled ‘Venus – The Hot Spot’, provides a well-written account on a mission called the Venus Express. The Venus express is an European Space Agency (ESA) mission to probe the the atmosphere of Venus and address questions regarding the differences between the climates on Venus and Earth. According to the plans, the probe will enter the final orbit around Venus in May 2006, i.e. within about a month.

What relevance does a mission to Venus have for a blog like RealClimate? Primarily, Venus offers scientists the chance to see how the same basic physics used to study Earth’s climate operates under a very different set of circumstances. In one sense, Venus is rather similar to Earth: it has nearly the same mass as Earth, and while its orbit is somewhat closer to the Sun, that effect is more than made up for by the sunlight reflected from Venus’ thick cloud cover. Because of the cloud cover, the surface temperature of Venus would be a chilly -42C if were not for the greenhouse effect of its atmosphere. In reality, the surface of Venus, at 740K (467C) is even hotter than the surface of Mercury, which is a (relatively!) pleasant 440K. Per unit of surface area, the atmosphere of Venus has as much mass as about 100 Earth atmospheres, and it is almost pure CO₂. This accounts for its very strong greenhouse effect. In contrast, the CO₂ in the Earth’s atmosphere accounts for a mere .00056 of the full mass of one Earth atmosphere.
[Read more…] about Lessons from Venus

James Lovelock, renegade Earth scientist and creator of the Gaia hypothesis, has written a gloomy new book called “Revenge of Gaia”, in which he argues that we should be stashing survival manuals, printed on good old-fashioned paper, in the Arctic where the last few breeding pairs of humans will likely be found after a coming climate catastrophe. The book is not published in the U.S. yet, but it is available from amazon.co.uk. Lovelock has never been one to shrink from a bold vision. What is it he sees now?

[Read more…] about James Lovelock’s Gloomy Vision

Guest comment by Malte Meinshausen, Reto Knutti and Dave Frame

Yesterday’s BBC article on the “Avoiding Dangerous Climate Change” report of the Exeter meeting last year, carried two messages that have left some a little confused. On the one hand, it said that a stabilization of greenhouse gases at 400-450 ppm CO₂-equivalent concentrations is required to keep global mean warming below 2°C, which in turn is assumed to be necessary to avoid ‘dangerous’ climate change. On the other hand, people are cited saying that “We’re going to be at 400 ppm in 10 years’ time”.

So given that we will exceed 400 ppm CO₂ in the near future, is a target of 2°C feasible? To make a long story short: the answer is yes. Commentaire par Malte Meinshausen, Reto Knutti and Dave Frame (traduit par Alain Henry)
Hier, un article de la BBC sur le rapport ” Eviter les changements climatiques dangereux” de la conférence d’Exeter de l’an dernier comportait deux messages qui pourraient entretenir une certaine confusion. D’une part, il mentionne qu’une stabilisation des gaz à effet de serre (GES) à 400-450 ppm de CO₂ équivalent est nécessaire pour garder le réchauffement global en dessous de 2°C, qui à son tour est supposé nécessaire pour éviter les changements climatiques ‘dangereux’. D’autre part, plusieurs personnes sont citées en disant « Nous atteindrons 400 ppm dans 10 ans ».

Donc, étant donné que nous allons dépasser les 400 ppm de CO₂ dans un futur proche, est-ce que la cible de 2°C est-elle faisable? En un mot, la réponse est oui.

(suite…)


[Read more…] about Can 2°C warming be avoided? Un réchauffement de 2°C peut-il être évité?

In another forum (on a planet far, far away), the following quote recently came up:

….the combined effect of these greenhouse gases is to warm Earth’s atmosphere by about 33 ºC, from a chilly -18 ºC in their absence to a pleasant +15 ºC in their presence. 95% (31.35 ºC) of this warming is produced by water vapour, which is far and away the most important greenhouse gas. The other trace gases contribute 5% (1.65 ºC) of the greenhouse warming, amongst which carbon dioxide corresponds to 3.65% (1.19 ºC). The human-caused contribution corresponds to about 3% of the total carbon dioxide in the present atmosphere, the great majority of which is derived from natural sources. Therefore, the probable effect of human-injected carbon dioxide is a miniscule 0.12% of the greenhouse warming, that is a temperature rise of 0.036 ºC. Put another way, 99.88% of the greenhouse effect has nothing to do with carbon dioxide emissions from human activity⁸.

We’ve discussed the magnitude of the greenhouse effect before, but it might be helpful to step through this ‘back-of-the-agenda’ calculation and see what the numbers really give. (Deltoid has also had a go at some of these mis-statements). [Read more…] about Calculating the greenhouse effect

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 !).