{"id":86,"date":"2004-12-22T07:20:55","date_gmt":"2004-12-22T11:20:55","guid":{"rendered":"\/?p=86"},"modified":"2009-12-26T12:34:34","modified_gmt":"2009-12-26T17:34:34","slug":"just-what-is-this-consensus-anyway","status":"publish","type":"post","link":"https:\/\/www.realclimate.org\/index.php\/archives\/2004\/12\/just-what-is-this-consensus-anyway\/","title":{"rendered":"Just what is this Consensus anyway? En quoi consiste le “Consensus” ?<\/lang_fr>"},"content":{"rendered":"
\n

We’ve used the term “consensus” here a bit recently (see our earlier post on the subject<\/a>), without ever really defining what we mean by it. In normal practice, there is no great need to define it – no science depends on it. But it’s useful to record the core that most scientists agree on, for public presentation. The consensus that exists is that of the IPCC reports, in particular the working group I report (there are three WG’s. By “IPCC”, people tend to mean WG I). Fortunately that report is available online for all to read at http:\/\/www.grida.no\/climate\/ipcc_tar\/wg1\/<\/a>. It’s a good idea to realise that though the IPCC report contains the consensus, it didn’t form it. The IPCC process was supposed to be – and is – a summary of the science (as available at the time). Because they did their job well, it really is a good review\/summary\/synthesis.
\n
\nPar William Connolley (traduit par Pierre Allemand)<\/small><\/p>\n

Nous avons utilis\u00e9 le terme “consensus” ici tr\u00e8s r\u00e9cemment (voir l\u2019 article pr\u00e9c\u00e9dent sur le sujet<\/a>) sans r\u00e9ellement d\u00e9finir ce que nous entendions par l\u00e0. Normalement, il n\u2019y a pas vraiment besoin de le d\u00e9finir \u2013 rien de scientifique n\u2019en d\u00e9pend. Mais, il est d\u2019usage de noter le c\u0153ur du sujet sur lequel la plupart des scientifiques sont d\u2019accord, pour des pr\u00e9sentations publiques. Le consensus existant est celui des rapports du GIEC, en particulier le groupe de travail n\u00b0I (il y a trois groupes de travail. Par “GIEC”, on a tendance \u00e0 vouloir parler du groupe de travail n\u00b0I).
\n(suite…)<\/a><\/lang_fr>
\n<\/p>\n

The main points that most would agree on as “the consensus” are:<\/p>\n

    \n
  1. The earth is getting warmer (0.6 +\/- 0.2 oC in the past century; 0.1<\/strike> 0.17 oC\/decade over the last 30 years (see update<\/i>)) [ch 2<\/a>]\n<\/li>\n
  2. People are causing this [ch 12<\/a>] (see update<\/i>)\n<\/li>\n
  3. If GHG emissions continue, the warming will continue and indeed accelerate [ch 9<\/a>]\n<\/li>\n
  4. (This will be a problem and we ought to do something about it)\n<\/li>\n<\/ol>\n

    I’ve put those four points in rough order of certainty. The last one is in brackets because whilst many would agree, many others (who agree with 1-3) would not, at least without qualification. It’s probably not a part of the core consensus in the way 1-3 are. Most (all?) of us here on RealClimate are physical scientists – we can talk sensibly about past, present and future changes in climate, but potential impacts on ecosystems or human society are out of our field. If you want to see the IPCCs own summary, it’s here<\/a>.<\/p>\n

    Other things we have mentioned in other posts come in as supporting evidence. That the increase in atmospheric CO2 is anthropogenic is so obvious that few people question it and in consequence few people rebut skepticism of it (though Eric has done so recently here<\/a>; and the IPCC mention it<\/a>). That the recent increase in temperature is unprecedented in the last 1000 years (see e.g. posts 64<\/a> or 7<\/a> by Mike) is one (but by no means the only) line of evidence indicating that recent change is likely to be unnatural (see update<\/i>).<\/p>\n

    The skeptic attitude to consensus usually starts with “there is no consensus”. That’s wrong, and they usually retreat from it to “but consensus science is meaningless”, and\/or “consensus has nothing to do with science”. The latter is largely true but irrelevant. The existence of the consensus doesn’t do a lot to determine what science is done; it doesn’t prevent contrary lines being explored. But the consensus view does come into the tricky interface between science and policy, and science and the media.<\/p>\n

    The existence of the consensus shouldn’t be used to hide the fact that there are areas of doubt. Climate models clearly aren’t perfect. There are questions about the differences between surface and tropospheric temperature trends<\/a>. Conversely the existence of some areas of doubt shouldn’t be used to try to hide the many areas of understanding and agreement.<\/p>\n

    Update<\/strong> 2004\/12\/23: this post needs one correction and also clarification in a couple of places. Firstly, for point 1 I wrote “0.1 oC\/decade over the last 30 years”. This is actually a bit of an understatement. 0.15 would be better, and the years since 2001 have been warm, pushing it up further. I’ve now replaced my first figure with the figure of 0.17 oC\/decade since 1976, from the IPCC report.<\/p>\n

    For point 2, I wrote “People are causing this”. That was far too brief to cover the complexities concerned. Comments 5 and 6, and my responses, address this.<\/p>\n

    Lastly, I wrote “That the recent increase in temperature is unprecedented in the last 1000 years … is one (but by no means the only) line of evidence indicating that recent change is likely to be unnatural”. This is true, but incomplete and possibly misleading, in that it may appear to overstate the importance of the proxy record. If you follow the link to the TAR chapter 12, you’ll have found that the IPCC based its conclusion of human influence on climate on:<\/p>\n

    A longer and more closely scrutinised observational record
    \nNew model estimates of internal variability
    \nNew estimates of responses to natural forcing
    \nImproved representation of anthropogenic forcing
    \nSensitivity to estimates of climate change signals
    \nQualitative consistencies between observed and modelled climate changes
    \nA wider range of detection techniques<\/p>\n

    …and all of this lead them to write: The increase in the number of studies, the breadth of techniques, increased rigour in the assessment of the role of anthropogenic forcing in climate, the robustness of results to the assumptions made using those techniques, and consistency of results lead to increased confidence in these results<\/i>. Detection and attribution have rapidly developed into an entire discipline and deserves its own post, sometime.<\/p>\n

    Heureusement, ce rapport est disponible en ligne in extenso<\/i> : http:\/\/www.grida.no\/climate\/ipcc_tar\/wg1\/<\/a>. C\u2019est une bonne id\u00e9e de r\u00e9aliser que bien que le rapport du GIEC contienne le consensus, il ne se limite pas \u00e0 lui. L\u2019objet du GIEC \u00e9tait suppose \u00eatre \u2013 et il l\u2019est \u2013 un r\u00e9sum\u00e9 des connaissances scientifiques (disponibles au temps t). Etant donn\u00e9 que le GIEC a bien fait son travail, il est en est aussi un examen, un r\u00e9sum\u00e9, et une synth\u00e8se.
    \nLes principaux points sur lequel la plupart s\u2019accordent (“le consensus”), sont les suivants :
    \nLa terre se r\u00e9chauffe (0,6 +\/- 0,2\u00b0C au cours du dernier si\u00e8cle ; 0,1 0,17 \u00b0C \/ d\u00e9cennie au cours des 30 derni\u00e8res ann\u00e9es (voir mise \u00e0 jour) [    ch 2<\/a>]
    \nL\u2019Homme en est la cause [    ch 12<\/a>] (voir mise \u00e0 jour)
    \nSi les \u00e9missions de gaz \u00e0 effet de serre continuent, le r\u00e9chauffement se poursuivra, et m\u00eame plus rapidement [    ch 9<\/a>]
    \n[Cela constituera un probl\u00e8me, et nous serons dans l\u2019obligation de faire quelque chose \u00e0 ce sujet].
    \nJ\u2019ai class\u00e9 ces quatre points dans leur ordre en gros, de certitude. Le dernier est entre crochets, parce que bien que beaucoup soient d\u2019accord, beaucoup d\u2019autres (qui sont d\u2019accord avec les points 1 \u00e0 3) ne le sont pas, du moins pas sans r\u00e9serve.
    \nCe dernier point n\u2019appartient pas au c\u0153ur du consensus comme les autres points (1 \u00e0 3). La plupart d\u2019entre nous (tous ?) \u00e0 RealClimate sommes des scientifiques physiciens \u2013 nous pouvons parler des changements climatiques pass\u00e9s, pr\u00e9sents et futurs, mais les impacts potentiels sur les \u00e9cosyst\u00e8mes ou sur la soci\u00e9t\u00e9 humaine sont hors de nos comp\u00e9tences. Si vous voulez consulter le r\u00e9sum\u00e9 des recommandations du GIEC, c\u2019est     ici<\/a>. <\/p>\n

    Les autres points que nous avons mentionn\u00e9s dans d\u2019autres articles viennent en renfort d\u2019\u00e9vidence : Le fait que l\u2019accroissement du CO atmosph\u00e9rique soit anthropog\u00e9nique est si \u00e9vident qu\u2019il est remis en question par tr\u00e8s peu de gens et qu\u2019en cons\u00e9quence, le scepticisme sur la question est peu combattu (bien que Eric l\u2019ai fait r\u00e9cemment ici<\/a> ; et que le GIEC le mentionne<\/a>).<\/p>\n

    Le fait que l\u2019accroissement r\u00e9cent de la temp\u00e9rature n\u2019ait pas eu de pr\u00e9c\u00e9dent depuis 1000 ans (voir les articles 64<\/a> ou 7<\/a> par Mike) constitue (mais n\u2019est pas la seule) ligne d\u2019\u00e9vidence indiquant que ce changement r\u00e9cent n\u2019est probablement pas naturel (voir la mise \u00e0 jour).
    \nL\u2019attitude des sceptiques au consensus commence g\u00e9n\u00e9ralement par \u201cil n\u2019y a pas de consensus\u201d. C\u2019est faux, et ils continuent en g\u00e9n\u00e9ral par “mais le consensus en science n\u2019a pas de signification”, et\/ou “le consensus n\u2019a rien \u00e0 faire avec la science”. Ce dernier point est largement vrai, mais sans rapport avec la question. L\u2019existence d\u2019un consensus ne fait pas grand chose dans la d\u00e9termination du travail scientifique ; elle n\u2019emp\u00eache pas des pistes contraires d\u2019\u00eatre explor\u00e9es. Mais, la vision consensuelle intervient \u00e0 l\u2019interface compliqu\u00e9 entre la science et la politique, ou entre la science et les m\u00e9dias.
    \nL\u2019existence d\u2019un consensus ne doit pas \u00eatre utilis\u00e9e pour cacher le fait qu\u2019il reste des zones d\u2019ombre. Les mod\u00e8les climatiques ne sont clairement pas parfaits. Des questions demeurent sur les diff\u00e9rence entre les tendances des temp\u00e9ratures de surface et les     temp\u00e9ratures troposph\u00e9riques<\/a>. Par contre, l\u2019existence de zones d\u2019ombre ne doit pas \u00eatre utilis\u00e9e pour essayer de cacher les nombreux domaines compris et admis.<\/p>\n

    Mise \u00e0 jour 23\/12\/2004<\/strong> : cet article doit \u00eatre corrig\u00e9 et clarifi\u00e9 \u00e0 deux endroits : Premi\u00e8rement pour le point 1, j\u2019ai \u00e9crit “0,1 \u00b0C \/ d\u00e9cennie sur les 30 derni\u00e8res ann\u00e9es”. C\u2019est un peu sous estim\u00e9. 0,15 aurait \u00e9t\u00e9 mieux, et, le fait que les ann\u00e9es depuis 2001 ont \u00e9t\u00e9 plus chaudes, remonte encore ce chiffre. J\u2019ai maintenant remplac\u00e9 mon premier chiffre par 0,17 \u00b0C \/ d\u00e9cennie depuis 1976, suivant le rapport du GIEC.
    \nPour le point 2, j\u2019ai \u00e9crit “l\u2019Homme en est la cause”. C\u2019est beaucoup trop court pour couvrir la complexit\u00e9 du probl\u00e8me. Les commentaires 5 et 6, et mes r\u00e9ponses approfondissent ce sujet.
    \nEn fin d\u2019article, j\u2019ai \u00e9crit “Que l\u2019accroissement r\u00e9cent de la temp\u00e9rature n\u2019ait pas eu de pr\u00e9c\u00e9dent depuis 1000 ans\u2026 est une (mais en aucune mani\u00e8re la seule) ligne d\u2019\u00e9vidence indiquant que ce changement r\u00e9cent n\u2019est probablement pas naturel”. C\u2019est vrai, mais incomplet et pouvant induire en erreur en ce que l\u2019importance des indicateurs physiques pourrait en \u00eatre exag\u00e9r\u00e9e. Si vous suivez le lien vers le TAR [NdT : troisi\u00e8me rapport d\u2019\u00e9valuation<\/i>] chapitre 12 vous trouverez que le GIEC a fond\u00e9 ses conclusions sur l\u2019influence humaine sur le climat sur :<\/p>\n

    Des observations plus longues et plus fines
    \nDe nouvelles estimations de mod\u00e8les sur la variabilit\u00e9 interne
    \nDe nouvelles estimations de r\u00e9ponses aux for\u00e7ages naturels
    \nUne repr\u00e9sentation am\u00e9lior\u00e9e du for\u00e7age anthropog\u00e9nique
    \nUne sensibilit\u00e9 aux estimations des signaux de changement climatique
    \nUne concordance qualitative entre les changements climatiques observ\u00e9s et issus de mod\u00e8les
    \nUn \u00e9ventail de techniques de d\u00e9tection plus large.
    \n\u2026et tout cela les conduit \u00e0 \u00e9crire : l\u2019augmentation du nombre d\u2019\u00e9tudes, l\u2019\u00e9largissement des techniques, la rigueur accrue dans l\u2019affirmation du r\u00f4le du for\u00e7age anthropog\u00e9niques sur le climat, la conformit\u00e9 des r\u00e9sultats aux hypoth\u00e8ses faites en utilisant ces techniques et la consistance des r\u00e9sultats conduit \u00e0 une confiance accrue dans ces m\u00eames r\u00e9sultats.
    \nLes \u00e9tudes de d\u00e9tection et d\u2019attribution sont rapidement devenues une discipline \u00e0 part enti\u00e8re, et m\u00e9ritent qu\u2019on leur consacre un article sp\u00e9cifique.
    \n<\/sub2><\/lang_fr><\/p>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

    We’ve used the term “consensus” here a bit recently, without ever really defining what we mean by it. In normal practice, there is no great need to define it – no science depends on it. But its useful to record the core that most scientists agree on, for public presentation. The consensus that exists is that of the IPCC reports, in particular the working group I report<\/p>\n","protected":false},"author":12,"featured_media":0,"comment_status":"closed","ping_status":"closed","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":[1,13],"tags":[],"class_list":{"0":"post-86","1":"post","2":"type-post","3":"status-publish","4":"format-standard","6":"category-climate-science","7":"category-faq","8":"entry"},"aioseo_notices":[],"post_mailing_queue_ids":[],"_links":{"self":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts\/86","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\/12"}],"replies":[{"embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/comments?post=86"}],"version-history":[{"count":3,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts\/86\/revisions"}],"predecessor-version":[{"id":2599,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts\/86\/revisions\/2599"}],"wp:attachment":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/media?parent=86"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/categories?post=86"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/tags?post=86"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}