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Greenhouse gases

Beck to the future

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Guest commentary from Georg Hoffmann

Our understanding of the natural carbon cycle has greatly improved since the times of Svante Arrhenius (1859-1927) and Guy Stewart Callendar (1898-1964). We know what the atmospheric background value of CO2 currently is (it passed 380ppm last year, about 100ppm over the pre-industrial level), we know the seasonal/diurnal cycle in different environments, we have been able to put reasonable constraints on terrestrial and marine sources and sinks, and finally we know the impact of fuel combustion both globally and locally in heavily polluted areas.
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The lag between temperature and CO2. (Gore’s got it right.)

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Translations: (Italian) (Español) (English)

When I give talks about climate change, the question that comes up most frequently is this: “Doesn’t the relationship between CO2 and temperature in the ice core record show that temperature drives CO2, not the other way round?”

On the face of it, it sounds like a reasonable question. It is no surprise that it comes up because it is one of the most popular claims made by the global warming deniers. It got a particularly high profile airing a couple of weeks ago, when congressman Joe Barton brought it up to try to discredit Al Gore’s congressional testimony. Barton said:

    In your movie, you display a timeline of temperature and compared to CO2 levels over a 600,000-year period as reconstructed from ice core samples. You indicate that this is conclusive proof of the link of increased CO2 emissions and global warming. A closer examination of these facts reveals something entirely different. I have an article from Science magazine which I will put into the record at the appropriate time that explains that historically, a rise in CO2 concentrations did not precede a rise in temperatures, but actually lagged temperature by 200 to 1,000 years. CO2 levels went up after the temperature rose. The temperature appears to drive CO2, not vice versa. On this point, Mr. Vice President, you’re not just off a little. You’re totally wrong.

Of course, those who’ve been paying attention will recognize that Gore is not wrong at all. This subject has been very well addressed in numerous places. Indeed, guest contributor Jeff Severinghaus addressed this in one of our very first RealClimate posts, way back in 2004. Still, the question does keep coming up, and Jeff recently received a letter asking about this. His exchange with the letter writer is reproduced in full at the end of this post. Below is my own take on the subject.

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Learning from a simple model

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A lot of what gets discussed here in relation to the greenhouse effect is relatively simple, and yet can be confusing to the lay reader. A useful way of demonstrating that simplicity is to use a stripped down mathematical model that is complex enough to include some interesting physics, but simple enough so that you can just write down the answer. This is the staple of most textbooks on the subject, but there are questions that arise in discussions here that don’t ever get addressed in most textbooks. Yet simple models can be useful there too.

I’ll try and cover a few ‘greenhouse’ issues that come up in multiple contexts in the climate debate. Why does ‘radiative forcing’ work as method for comparing different physical impacts on the climate, and why you can’t calculate climate sensitivity just by looking at the surface energy budget. There will be mathematics, but hopefully it won’t be too painful.
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Sauvez la planète ! Gagnez 25 millions de dollars !

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Translations: (Português) (Türkçe) (English)

Juliane Fry, UC Berkeley, Traduit par Etienne Pesnelle

Le 9 février dernier, Richard Branson, président du groupe Virgin, a annoncé qu’il offrait 25 millions de dollars à quiconque pourra présenter « une invention commercialement viable qui permette de retirer de l’atmosphère les gaz à effet de serre d’origine anthropique, de façon à contribuer sensiblement à la stabilisation du climat de la Terre ». A la conférence de presse où il annonçait son « « Défi Virgin pour la Terre » », Branson a été rejoint par Al Gore, et le comité des juges de ce concours comprend d’autres célébrités du réchauffement climatique : James Hansen, James Lovelock, Tim Flannery, et Sir Crispin Tickell.

L’objectif du concours est de trouver une méthode qui pourra retirer de l’atmosphère au moins un milliard de tonnes de carbone par an. Il va être très intéressant de voir quelles idées de nettoyage de l’atmosphère vont émerger. 25 millions de dollars devraient encourager la créativité ! (et bien sûr, quand ça fonctionnera, ça devrait rapporter une somme significative en crédits de compensations d’émissions de carbone). Il y eut du grabuge l’année dernière, quand le débat à propos de l’injection de SO2 dans la stratosphère, visant à produire des sulfates en aérosol réfléchissant la lumière solaire qui contreraient le réchauffement climatique, a donné l’impression aux scientifiques qu’ils avaient besoin d’exposer leur position sur cette proposition mal comprise et controversée.

Durant ce débat, un article de fond du *New York Times* (décrit ici) a commenté les différentes options de « géo-ingénierie » ayant un effet refroidisseur contrant le réchauffement climatique. Au moins cette fois-ci, on ne cherche pas à ajouter quelque chose de nouveau et d’incertain à l’atmosphère, mais bien à en retirer ce qu’on y a ajouté.

Le ciel nous tombe vraiment sur la tête

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Translations: (English)

Traduit par Etienne Pesnelle
Dans le numéro de cette semaine de Science, un article opportun de mise en perspective traite des problèmes du changement de l’atmosphère supérieure. Ladite atmosphère “supérieure” consiste en la stratosphère jusqu’à l’ionosphère (~20 à 300 km). Laštovicka et al soulignent que la tendance au refroidissement est exactement telle que prédite par la tendance à la hausse des gaz à effet de serre, et que l’accroissement de densité que cela implique est en train de provoquer la “chute” de différentes couches de la ionosphère. Cela a été mis en exergue il y a quelques années par Jarvis et al. (1998) et dans New Scientist en 1999 (et je m’excuse de leur avoir volé le titre de leur article!).

Les changements dans le graphique sont liés au refroidissement constaté dans les enregistrements MSU-4 de la basse stratosphère (que ce soit ceux provenant des bases de données UAH ou RSS), mais les changements à ces altitudes (~ 15-20 km) sont principalement dûs à la raréfaction de l’ozone. Plus on monte, plus le refroidissement dû au CO2 est important. Il est intéressant de noter qu’un forçage solaire significatif aurait exactement l’effet inverse (il provoquerait un réchauffement) – encore une autre raison de douter que le forçage solaire est un facteur significatif [du réchauffement climatique] des dernières décennies.

Mise à jour : la meilleure explication des tendances au refroidissement peut être trouvée sur ESPERE, en particulier la figure 3.

Avery and Singer: Unstoppable hot air

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Last week I attended a talk by Dennis Avery, author with Fred Singer of Unstoppable Global Warming Every 1500 Years (there is a summary here). The talk (and tasty lunch) was sponsored by the Heartland Institute, and was apparently enthusiastically received by its audience. Still whoozy from a bit of contention during the question period, a perplexed member of the audience told me privately that he thought a Point/CounterPoint discussion might be useful (he didn’t know I wrote for realclimate; it was just a hypothetical thought). But here’s my attempt to accommodate. [Read more…] about Avery and Singer: Unstoppable hot air

Revealed: Secrets of Abrupt Climate Shifts

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This story is the dream of every science writer. It features some of the most dramatic and rapid climate shifts in Earth’s history, as well as tenacious scientists braving the hostile ice and snows of Greenland and Antarctica for years on end to bring home that most precious material: kilometre-long cores of ancient ice, dating back over a hundred thousand years. Back in their labs, these women and men spend many months of seclusion on high-precision measurements, finding ingenious ways to unravel the secrets of abrupt climate change. Quite a bit has already been written on the ice core feat (including Richard Alley’s commendable inside story “The Two Mile Time Machine”), and no doubt much more will be.

It was the early, pioneering ice coring efforts in Greenland in the 1980s and 90s that first revealed the abrupt climate shifts called “Dansgaard-Oeschger events” (or simply DO events), which have fascinated and vexed climatologists ever since. Temperatures in Greenland jumped up by more than 10 ºC within a few decades at the beginning of DO events, typically remaining warm for several centuries after. This happened over twenty times during the last great Ice Age, between about 100,000 and 10,000 years before present.

The latest results of the EPICA team (the European Project for Ice Coring in Antarctica) are published in Nature today (see also the News & Views by RealClimate member Eric Steig). Their data from the other pole, from the Antarctic ice sheet, bring us an important step closer to nailing down the mechanism of the mysterious abrupt climate jumps in Greenland and their reverberations around the world, which can be identified in places as diverse as Chinese caves, Caribbean seafloor sediments and many others. So what are the new data telling us?
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How much CO2 emission is too much?

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Translations: (Slovenčina) (English)

This week, representatives from around the world will gather in Nairobi, Kenya for the latest Conference of Parties (COP) meeting of the Framework Convention of Climate Change (FCCC) which brought us the Kyoto Protocol. The Kyoto Protocol expires in 2012, and the task facing the current delegates is to negotiate a further 5-year extension. This is a gradual, negotiated, no doubt frustrating process. By way of getting our bearings, a reader asks the question, what should the ultimate goal be? How much CO2 emissions cutting would it take to truly avoid “dangerous human interference in the climate system”? [Read more…] about How much CO2 emission is too much?

Rasslin’ swamp gas

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In the early 1990’s, in defiance of IPCC projections, the methane concentration in the atmosphere abruptly stopped rising, and has remained nearly constant since then. Methane is a crouching tiger in the carbon cycle, with potentially enough available as hydrates and from peats to really clobber the Earth’s heat budget. The big question is, will atmospheric methane start rising again? [Read more…] about Rasslin’ swamp gas