{"id":118,"date":"2005-02-08T16:15:24","date_gmt":"2005-02-08T20:15:24","guid":{"rendered":"\/?p=118"},"modified":"2010-04-26T14:27:20","modified_gmt":"2010-04-26T19:27:20","slug":"strange-bedfellows","status":"publish","type":"post","link":"https:\/\/www.realclimate.org\/index.php\/archives\/2005\/02\/strange-bedfellows\/","title":{"rendered":"Strange Bedfellows En Etrange Compagnie<\/lang_fr>"},"content":{"rendered":"
\n

Here’s a curious observation. Some commentators<\/a> who for years have been vocally decrying the IPCC consensus are lining up to support the ‘Ruddiman’ hypothesis. A respected paleoceanographer, Bill Ruddiman has recently argued that humans have been altering the level of important greenhouse gases since the dawn of agriculture (5 to 8000 years ago), and in so doing have prevented a new ice age from establishing itself. This intriguing idea is laid out in a couple of recent papers (Ruddiman, 2003<\/a>; Ruddiman et al, 2005<\/a>) and has received a fair degree of media attention (e.g. here<\/a>, and here<\/a>). <\/p>\n


\npar Gavin Schmidt (traduit par Thibault de Garidel)<\/small><\/p>\n

Voici une curieuse observation. Les m\u00eames commentateurs<\/a> qui pendant des ann\u00e9es ont d\u00e9cri\u00e9 le consensus autour du GIEC s’alignent d\u00e9sormais pour soutenir l’hypoth\u00e8se dite de ‘Ruddiman’. Bill Ruddiman, un pal\u00e9oc\u00e9anographe respect\u00e9, a en effet r\u00e9cemment sugg\u00e9r\u00e9 que l’action humaine avait chang\u00e9 la concentration de certains gaz \u00e0 effet de serre, depuis le d\u00e9veloppement de l’agriculture (il y a 5 \u00e0 8000 ans), emp\u00eachant ainsi la mise en place d’une nouvelle p\u00e9riode glaciaire. Cette id\u00e9e intrigante est pr\u00e9sent\u00e9e dans deux articles r\u00e9cents ( Ruddiman, 2003<\/a> ; Ruddiman et autres, 2005<\/a> ), et a suscit\u00e9 depuis une certaine attention des m\u00e9dias (voir par exemple ici<\/a> , et ici<\/a> ).
\n(suite…<\/a>)
\n<\/lang_fr><\/p>\n


\nThe basic idea mainly relies on paleoclimatic evidence that there would have been a new ice age by now under ‘normal’ circumstances, and since there isn’t one, anthropogenic influences are presumably to blame. Whether this is valid or not is now the topic of some debate at scientific conferences. One can argue about the details (and I have here<\/a> for instance), but the relevant issues are quite technical and not really what I want to talk about. Instead, I will explore what acceptance of this idea implies.<\/p>\n

The attraction to this idea for the contrarians is not hard to see. They have seen quickly that this is a controversial and non-mainstream idea (and even Bill Ruddiman will allow that!), and that Ruddiman appears to be ‘battling’ against the science establishment. So, following a sort of ‘the enemy of my enemy is my friend’ logic, they have been vocal in supporting Ruddiman’s ideas (I should hasten to add that this support does not reflect on the quality of Ruddiman as a scientist, nor on the validity of his thesis). <\/p>\n

For instance, take this quote from TCS<\/a><\/p>\n

Given Ruddiman’s findings the key question now is not “is industrial-age, human-caused global warming occurring?”, but rather “are we sure that the human effect on climate over the last 8,000 years has helped to prevent the occurrence of another glaciation?” Should the answer to that question be yes, then it prompts the further question: “do we wish to maintain the human warming effect, or instead to counteract it and allow Earth’s climatic cycle to drop back into its next (natural) glacial episode?”.<\/p><\/blockquote>\n

Or from the Idso’s site: <\/p>\n

\nHence, even if the IPCC is correct in their analysis of climate sensitivity and we are wrong in suggesting the sensitivity they calculate is way too large, the bottom line for the preservation of civilization and much of the biosphere is that governments ought not interfere with the normal progression of fossil fuel usage, for without more CO2 <\/sub> in the atmosphere, we could shortly resume the downward spiral to full-fledged ice-age conditions.\n<\/p><\/blockquote>\n

There are multiple strands of intellectual incoherence here. Firstly, people who have argued that there really hasn’t been a significant rise in CO2 <\/sub> since the 1800s, now accept the ice core results that show there was a much smaller rise from 8000 yrs ago. Secondly, those that argued that the 20th Century CO2 <\/sub> rise cannot be anthropogenic, appear to accept that the post-8000 BP change was. Thirdly, those who argue that the current increase in greenhouse gases has no significant climate effect, now appear to believe that the much smaller changes in the pre-industrial prevented an ice age. <\/p>\n

This is like someone who believes the earth is flat buying a round-the-world ticket for their vacation. <\/p>\n

Let me make it a little clearer. If one accepts Ruddiman’s hypothesis, one implicitly agrees that: i) CO2 <\/sub> and CH4 <\/sub> can be affected by human activity, ii) greenhouse gases have a significant forcing role, and iii) climate sensitivity is in the ballpark of mainstream estimates. (The opposite is not however true, one can agree on those three points (which is pretty much the IPCC consensus<\/a>) without necessarily thinking that Ruddiman is correct). One must therefore conclude that those contrarians who have warmly welcomed Ruddiman’s thesis have now come around to mainstream opinion. Hmm…<\/p>\n

But wait, they might say, we don’t believe any of those things, but we accept that we may be wrong, in which case, Ruddiman’s theory still implies that we should not do anything about increasing CO2 <\/sub>. No. At minimum it might indicate that reducing CO2 <\/sub> below pre-industrial levels might not be a good idea, but that is far from saying that any amount of further increases are beneficial. It certainly doesn’t follow that if a little bit of CO2 <\/sub> is good for the climate, then a lot more is better. <\/p>\n

I think a more obvious explanation is that, for some critics, any argument will do – regardless of its coherence with the argument they had before, or the one they will pick next. <\/p>\n


\n<\/a>
\nL’id\u00e9e fondamentale de cette hypoth\u00e8se se fonde principalement sur l’\u00e9vidence pal\u00e9oclimatique que dans des conditions ‘normales’, il y aurait, maintenant, une nouvelle p\u00e9riode glaciaire, et comme ce n’est pas le cas, l’action anthropique en est sans doute la cause. Que cette hypoth\u00e8se soit valide ou pas est maintenant un sujet de discussion des conf\u00e9rences scientifiques. On peut argumenter au sujet de d\u00e9tails de cette th\u00e9orie (comme je l’ai fait ici<\/a> par exemple), mais les questions sont relativement techniques, ce que je ne veux pas aborder ici. Dans ce message, j’explorerai ce qu’implique l’acceptation de cette id\u00e9e.<\/p>\n

Il est manifeste que les contradicteurs ont \u00e9t\u00e9 attir\u00e9s par cette id\u00e9e. Ils se sont rapidement aper\u00e7us que c’est une id\u00e9e controvers\u00e9e et \u00e0 contre-courant (et m\u00eame Bill Ruddiman l’accepte !), et que Ruddiman semble ‘lutter’ contre “l’establishment” scientifique. Ainsi, utilisant un raisonnement du type ‘l’ennemi de mon ennemi est mon ami ‘, ils ont publiquement soutenu les id\u00e9es de Ruddiman (et je m’empresse d’ajouter que cet appui n’a aucun rapport avec la qualit\u00e9 de Ruddiman en tant que scientifique, ni sur la validit\u00e9 de sa th\u00e8se).<\/p>\n

Par exemple, prenez cette citation de TCS<\/a> [Tech Central Station-en anglais]<\/p>\n

Etant donn\u00e9s les r\u00e9sultats de Ruddiman, la question principale n’est maintenant plus “est-ce-que le r\u00e9chauffement global de l’\u00e8re industrielle caus\u00e9 par l’action humaine est en cours ?”, mais plut\u00f4t “sommes nous s\u00fbrs que l’action humaine sur le climat au cours des 8000 derni\u00e8res ann\u00e9es a aid\u00e9 \u00e0 emp\u00eacher la mise en place d’une autre glaciation?” Si la r\u00e9ponse \u00e0 cette question est oui, elle soul\u00e8ve la question suivante : ” Souhaitons-nous maintenir le r\u00e9chauffement li\u00e9 a l’action humaine, ou \u00e0 la place voulons-nous le contrecarrer et permettre au cycle climatique de la Terre de retourner vers un prochain \u00e9pisode glaciaire (normal) ?”.<\/p><\/blockquote>\n

Ou sur le site web d’Idso:<\/p>\n

Ainsi, m\u00eame si le GIEC est correct dans son analyse de la sensibilit\u00e9 climatique et que nous avons tort en sugg\u00e9rant que la sensibilit\u00e9 qu’ils calculent est bien trop \u00e9lev\u00e9e, le message fondamental est que pour la pr\u00e9servation de la civilisation et d’une grande partie de la biosph\u00e8re, les gouvernements ne doivent pas interf\u00e9rer avec l’augmentation normale de l’utilisation de combustibles fossiles, parce que sans ce CO2<\/sub> suppl\u00e9mentaire dans l’atmosph\u00e8re, nous pourrions retourner vers un nouvel \u00e2ge glaciaire.<\/p><\/blockquote>\n

Il y a plusieurs arguments incoh\u00e9rents ici. Premi\u00e8rement, ces personnes qui ont argu\u00e9 du fait qu’il n’y a pas eu vraiment d’\u00e9l\u00e9vation significative de CO2<\/sub> depuis les ann\u00e9es 1800, acceptent d\u00e9sormais les r\u00e9sultats des carottes de glace qui montrent une \u00e9l\u00e9vation beaucoup plus faible il y a environ 8000 ans. Deuxi\u00e8mement, ceux qui ont argu\u00e9 que l’\u00e9l\u00e9vation au 20\u00e8me si\u00e8cle du CO2<\/sub> ne pouvait pas \u00eatre anthropog\u00e8ne, semblent accepter que le changement qui a eu lieu il y a 8000 ans l’\u00e9tait. Troisi\u00e8mement, ceux qui arguent du fait que l’augmentation moderne de la concentration en gaz \u00e0 effet de serre n’a aucun effet significatif sur le climat, semblent maintenant croire que des changements beaucoup plus faibles pendant l’\u00e8re pr\u00e9-industrielle ont emp\u00each\u00e9 la mise en place d’une p\u00e9riode glaciaire.<\/p>\n

Ces arguments font penser \u00e0 quelqu’un qui ach\u00e8te un billet pour un tour du monde alors qu’il croit que la terre est plate.<\/p>\n

Je clarifie quelques points. Si on accepte l’hypoth\u00e8se de Ruddiman, on convient implicitement que : i) le CO2<\/sub> et le CH4<\/sub> peuvent \u00eatre affect\u00e9s par l’activit\u00e9 humaine, ii) les gaz \u00e0 effet de serre ont un r\u00f4le de for\u00e7age climatique significatif, et iii) la sensibilit\u00e9 climatique est dans la m\u00eame gamme que celle des \u00e9valuations traditionnelles (l’inverse n’est cependant pas vrai, on peut \u00eatre d’accord sur ces trois points \u2013ce qui correspond approximativement au consensus<\/a> du GIEC\u2013 sans penser n\u00e9cessairement que Ruddiman a raison). On doit donc conclure que ces “contradicteurs” qui ont chaleureusement accueilli la th\u00e8se de Ruddiman acceptent maintenant l’opinion traditionnelle. Hmm…<\/p>\n

Mais ceux-ci pourraient dire : nous ne croyons aucune de ces choses, mais nous acceptons que nous pouvons avoir tort, auquel cas la th\u00e9orie de Ruddiman implique toujours que nous ne devrions rien faire pour att\u00e9nuer l’augmentation du CO2<\/sub>. Non. Au minimum, cette \u00e9tude pourrait indiquer que la r\u00e9duction du CO2<\/sub> au-dessous des niveaux pr\u00e9-industriels pourrait ne pas \u00eatre une bonne id\u00e9e, ce qui est diff\u00e9rent de dire que n’importe quel accroissement sup\u00e9rieur serait salutaire. Il est donc certainement faux que si un peu de CO2<\/sub> est bon pour le climat, alors beaucoup plus est meilleur.<\/p>\n

Je pense que l’explication la plus \u00e9vidente est que, pour quelques critiques, n’importe quel argument sera bon \u2013ind\u00e9pendamment de sa coh\u00e9rence avec le pr\u00e9c\u00e9dent ou le suivant.
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Here’s a curious observation. Some commentators who for years have been vocally decrying the IPCC consensus are lining up to support the ‘Ruddiman’ hypothesis. A respected paleoceanographer, Bill Ruddiman has recently argued that humans have been altering the level of important greenhouse gases since the dawn of agriculture (5 to 8000 years ago), and in […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_exactmetrics_skip_tracking":false,"_exactmetrics_sitenote_active":false,"_exactmetrics_sitenote_note":"","_exactmetrics_sitenote_category":0,"_genesis_hide_title":false,"_genesis_hide_breadcrumbs":false,"_genesis_hide_singular_image":false,"_genesis_hide_footer_widgets":false,"_genesis_custom_body_class":"","_genesis_custom_post_class":"","_genesis_layout":"","footnotes":""},"categories":[1,3,2],"tags":[],"class_list":{"0":"post-118","1":"post","2":"type-post","3":"status-publish","4":"format-standard","6":"category-climate-science","7":"category-greenhouse-gases","8":"category-paleoclimate","9":"entry"},"aioseo_notices":[],"post_mailing_queue_ids":[],"_links":{"self":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts\/118","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/comments?post=118"}],"version-history":[{"count":2,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts\/118\/revisions"}],"predecessor-version":[{"id":3875,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts\/118\/revisions\/3875"}],"wp:attachment":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/media?parent=118"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/categories?post=118"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/tags?post=118"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}