{"id":95,"date":"2005-02-07T06:29:26","date_gmt":"2005-02-07T10:29:26","guid":{"rendered":"\/?p=95"},"modified":"2009-07-03T08:51:38","modified_gmt":"2009-07-03T13:51:38","slug":"exeter-conference-avoiding-dangerous-climate-change","status":"publish","type":"post","link":"https:\/\/www.realclimate.org\/index.php\/archives\/2005\/02\/exeter-conference-avoiding-dangerous-climate-change\/","title":{"rendered":"Exeter conference: Avoiding Dangerous Climate Change Conf\u00e9rence d’Exeter (G-B): \u00e9viter un changement climatique dangereux <\/lang_fr>"},"content":{"rendered":"
\n

The conference last week in Exeter on “Avoiding Dangerous Climate Change” grew out of a speech by UK Prime Minister Tony Blair. He asked “What level of greenhouse gases in the atmosphere is self-evidently too much?” and “What options do we have to avoid such levels?”. The first question is very interesting, but also very difficult. As Roger Pielke<\/a> has noted the conference organisers actually choose three “key questions”:<\/p>\n

    \n
  1. For different levels of climate change what are the key impacts, for different regions and sectors, and for the world as a whole?\n<\/li>\n
  2. What would such levels of climate change imply in terms of greenhouse gas stabilisation concentrations and emission pathways required to achieve such levels?\n<\/li>\n
  3. What technological options are there for achieving stabilisation of greenhouse gases at different stabilisation concentrations in the atmosphere, taking into account costs and uncertainties?\n<\/li>\n<\/ol>\n

    It is worth thinking about the difference between the initial aim and the “key questions” chosen. Question 1 is essentially IPCC WGII impacts<\/a>); question 2 is firmly WGI<\/a> (how-much-climate-change); question 3 is fairly WG III<\/a> (mitigation, including technical options). I guess they switched questions 1 and 2 round to avoid making the identification too obvious. The conference steering committee report<\/a> makes it very clear that they are building on the IPCC TAR foundation.<\/p>\n


    \nPar William Connoley (traduit par Thibault de Garidel)<\/small><\/p>\n

    La conf\u00e9rence ayant eu lieu la semaine derni\u00e8re \u00e0 Exeter intitul\u00e9e “Eviter un changement climatique dangereux<\/a>” a pour origine un discours du premier ministre britannique Tony Blair. Celui-ci avait alors pos\u00e9 deux questions “quel niveau de concentration de gaz \u00e0 effet de serre dans l’atmosph\u00e8re peut \u00eatre consid\u00e9r\u00e9 comme excessif ?” et “quelles options avons-nous pour \u00e9viter de tels niveaux ?”. La premi\u00e8re question est tr\u00e8s int\u00e9ressante, mais \u00e9galement probl\u00e9matique. Comme Roger Pielke<\/a> l’a not\u00e9, les organisateurs de cette conf\u00e9rence ont en fait choisi trois “questions principales” :<\/p>\n

    1.\tPour diff\u00e9rents niveaux de changement climatique, quels sont les impacts principaux, pour les diff\u00e9rentes r\u00e9gions et secteurs, et pour le monde entier ?
    \n2.\tPour que de tels niveaux de changement climatique soient atteints, quelles sont les implications en terme de stabilisation des concentrations en gaz \u00e0 effet de serre, et des options d’\u00e9mission ?
    \n3.\tQuelles options technologiques existent pour arriver \u00e0 stabiliser les gaz \u00e0 effet de serre \u00e0 diff\u00e9rentes concentrations, en tenant compte des co\u00fbts et incertitudes?<\/p>\n

    (suite…<\/a>)
    \n<\/lang_fr>
    \n<\/p>\n

    All in all it would seem that the bold vision of the politicians has been tempered by the conference organisers into something more manageable – a set of questions that can be discussed within the usual scientific framework and by the usual people. And probably that was sensible, because the initial question really is very hard – not merely because all the science isn’t in, but because even if it was what is “dangerous” is probably a political rather than scientific question. And this was a largely scientific meeting.<\/p>\n

    So, what’s new? On the impacts front, the final report says that there is more clarity and less uncertainty since the TAR, which is what you would hope for after 4 years of research. They identify a few “thresholds” that are dangerous for certain processes – 2.7 \u00baC local for melting Greenland; coral bleaching above 1 \u00baC global. Extremes, and the 2003 european heatwave get a mention. On climate change, they note that restricting the global temperature change to 2 \u00baC with a fair degree of confidence would require stabilisation at 400 ppm CO2 equivalent (CO2 itself is at 380 already, but “equivalent” includes other GHG’s and the negative effects of sulphates; see here<\/a> for more). If you were prepared to accept more risk of exceeding 2 \u00baC then 550 ppm would be possible. For technical options, they note that the IEA predict a 63% increase in CO2 levels by 2030, in line with IPCC estimates. There are a whole raft of options that could be taken to reduce emissions, and they do mention the word “nuclear”.<\/p>\n

    All in all, it looks like progress as normal. In summary, they note that work is needed on both mitigation and adaption – which is to recognise that climate change is occuring and will continue, although possibilities for slowing it exist.<\/p>\n

    To pick out some of the science, there is the perennially interesting “will global warming cause cooling” bit that people love so much because it seems paradoxical. This is the “thermohaline circulation (THC) shutdown” or slowdown, caused by freshening of the North Atlantic. Of course it wouldn’t (at its worst) lead to global cooling, it would mostly impact Northern Europe. And the IPCC TAR said even in models where the THC weakens, there is still a warming over Europe<\/a> (because the overall warming outweights the local cooling). This still seems to be true. The conference was presented some results showing what happens if THC shutdown is artifically induced (by Richard Wood<\/a>), and various attempts to explore the probability of a collapse, but coupled AOGCMs seem to be quite resilient to a total collapse. From impacts, they mention that “resilient” societies are better able to survive climate stresses – for example, they downplay the oft-mentioned risk of malaria spreading under increasing temperature: the increase expected is small compared to the total number; all it means is that existing efforts to combat malaria should be strengthened.<\/p>\n

    And finally, since it gets a mention in the report, there are two possible errors to make, apparently labelled Type 1 and Type 2. Type 1 is excess caution, leading to damage by unnecessary action restricting development. Type 2 is insufficient action, leading to damage from climate change. In the face of uncertaintly, it is very hard to steer a true path avoiding these two errors, but it appears that we should be tilting towards taking action.<\/p>\n

    The conference generated a lot of press coverage (thanks Het<\/a>). Nature said UK climate meeting calls for action<\/a>; New Scientist said Climatologists pursue greenhouse gas danger levels<\/a> and Only huge emissions cuts will curb climate change<\/a>. The BBC told us of Scientists’ grim climate report<\/a>, that “The risks from global warming are more serious than previously thought”. The Guardian warned of A grim assessment of the global cost for each degree rise in temperature<\/a> and the Manila Times says Evidence indicates climate change already here<\/a>, which is a mild strengthening of what the IPCC TAR told us. The reporting seems reasonably fair – slightly sexed up headlines, as usual, but the text of the articles quite faithful to the conference.<\/p>\n


    \n    <\/a>
    \nIl est int\u00e9ressant de r\u00e9fl\u00e9chir \u00e0 la diff\u00e9rence entre le but initial et “les questions principales” choisies par les organisateurs. La question 1 rel\u00e8ve essentiellement de la partie “impacts” du GIEC (Groupe de Travail II-     WGII<\/a> ); la question 2 rel\u00e8ve du Groupe de Travail I-WGI<\/a> (amplitude du changement climatique); la question 3 est enfin assez proche du Groupe de Travail III – WGIII<\/a> (mesures d’att\u00e9nuation, y compris les options techniques). Je suppose qu’ils ont \u00e9chang\u00e9 les questions 1 et 2 pour \u00e9viter de rendre l’identification trop \u00e9vidente. Le rapport du comit\u00e9 de coordination de la conf\u00e9rence explique tr\u00e8s clairement qu’ils se sont bas\u00e9s sur le travail du Troisi\u00e8me Rapport d’Evaluation du GIEC.<\/p>\n

    Il semble que la vision audacieuse des politiciens a \u00e9t\u00e9 transform\u00e9e par les organisateurs de la conf\u00e9rence en quelque chose de plus maniable – un ensemble de questions qui peuvent \u00eatre discut\u00e9es dans le cadre scientifique habituel et par les personnes habituelles. Et c’\u00e9tait probablement judicieux, car la question initiale est vraiment tr\u00e8s difficile a r\u00e9soudre – pas simplement parce que toute la science n’est pas encore connue, mais parce que m\u00eame si toutes les incertitudes scientifiques \u00e9taient r\u00e9solues, ce qui est “dangereux” est probablement une question politique plut\u00f4t que scientifique. Et cette conf\u00e9rence \u00e9tait principalement scientifique.<\/p>\n

    Quelles sont les nouveaut\u00e9s ? Sur la question des impacts, le rapport final indique qu’il y a plus de clart\u00e9 et moins d’incertitude depuis le Troisi\u00e8me Rapport d’Evaluation du GIEC, ce qui est logique apr\u00e8s 4 ann\u00e9es de recherche. Ils identifient quelques “seuils” qui sont dangereux pour certains processus : – un r\u00e9chauffement local de 2,7\u00baC pour la fonte du Groenland; un r\u00e9chauffement global de 1\u00baC pour le blanchissement du corail. Les extr\u00eames climatiques, et la vague de chaleur de 2003 en Europe sont \u00e9galement mentionn\u00e9s. Sur le changement climatique, ils notent que limiter le changement de temp\u00e9rature global \u00e0 2\u00baC avec un bon niveau de confiance exigerait la stabilisation \u00e0 l’\u00e9quivalent de 400 ppm de CO2<\/sub> (le CO2<\/sub> lui-m\u00eame est d\u00e9j\u00e0 \u00e0 380, mais “l’\u00e9quivalent CO2<\/sub>” inclut la contribution des autres gaz \u00e0 effet de serre et les effets n\u00e9gatifs des sulfates; voyez ici<\/a> pour plus de d\u00e9tail). Si le risque d’augmenter la temp\u00e9rature globale par plus de 2\u00baC est accept\u00e9, alors une concentration de 550 ppm serait acceptable. Pour les options techniques, ils notent que l’IEA [ndt<\/i> : agence Internationale de l’Energie Atomique] pr\u00e9voit une augmentation de 63% des niveaux de CO2<\/sub> d’ici 2030, en accord avec les \u00e9valuations du GIEC. Il y a un grand nombre d’options qui pourraient \u00eatre prises pour r\u00e9duire les \u00e9missions, et parmi celles-ci figure le nucl\u00e9aire.<\/p>\n

    Ainsi, rien de bouleversant. En r\u00e9sum\u00e9, ils notent que du travail reste \u00e0 accomplir sur les mesures d’att\u00e9nuation et d’adaptation – reconnaissance implicite du fait que le changement climatique a bien lieu et continuera, bien que les possibilit\u00e9s pour l’att\u00e9nuer existent.<\/p>\n

    Sur la partie scientifique, il y a \u00e9galement l’\u00e9ternel refrain sur “est-ce que le r\u00e9chauffement global va causer un refroidissement ?” qui accroche beaucoup de monde a cause du paradoxe qu’il sugg\u00e8re. C’est le sc\u00e9nario de “l’arr\u00eat de la circulation thermohaline (THC)” ou son ralentissement, provoqu\u00e9 par un adoucissement des eaux de l’Atlantique nord. Celui-ci ne pourrait pas dans le pire des cas mener \u00e0 un refroidissement global, il affecterait principalement les pays septentrionaux d’Europe. Le Troisi\u00e8me Rapport d’Evaluation du GIEC dit que m\u00eame dans les mod\u00e8les dans lesquels le THC s’affaiblit, il y a toujours un r\u00e9chauffement en Europe (parce que l’effet du r\u00e9chauffement global est plus important que le refroidissement local). Ceci semble toujours \u00eatre vrai. Pendant la conf\u00e9rence ont \u00e9t\u00e9 pr\u00e9sent\u00e9s quelques r\u00e9sultats sur ce qui se produit si l’arr\u00eat de la circulation thermohaline est artificiellement induit (par Richard Wood<\/a> ), et diverses autres tentatives d’explorer l’hypoth\u00e8se d’un arr\u00eat complet de la THC, mais les AOGCMs coupl\u00e9s semblent \u00eatre tout \u00e0 fait r\u00e9sistants \u00e0 cette hypoth\u00e8se. Sur les impacts, ils mentionnent que les soci\u00e9t\u00e9s “r\u00e9sistantes” peuvent mieux survivre au stress climatique – par exemple, ils minimisent le risque souvent mentionn\u00e9 d’extension de la malaria due au r\u00e9chauffement : l’augmentation pr\u00e9vue est faible par rapport aux nombreux cas. Le message est que les efforts existants pour combattre la malaria devraient \u00eatre renforc\u00e9s.<\/p>\n

    Et en conclusion, puisque ce point est mentionn\u00e9 dans le rapport, il y a deux erreurs possibles \u00e0 faire, dites de “type 1” et de “type 2”. Celle du type 1 est une prudence excessive, menant \u00e0 des dommages dus a des actions inutiles limitant le d\u00e9veloppement. Celle du type 2 correspond \u00e0 une action insuffisante, menant \u00e0 des dommages li\u00e9s au changement du climat. En raison des incertitudes, il est tr\u00e8s difficile de tracer un chemin qui \u00e9vite ces deux erreurs, mais il s’av\u00e8re que nous devrions favoriser l’action.<\/p>\n

    La conf\u00e9rence a eu une large couverture dans la presse (merci \u00e0 ). Nature a indiqu\u00e9 <\/a>Une conf\u00e9rence britannique appelle \u00e0 des actions sur le climat<\/a> ; The New Scientist Des niveaux dangereux de gaz \u00e0 effet de serre poursuivis par des climatologistes<\/a> et Seules des r\u00e9ductions \u00e9normes des \u00e9missions limiteront le changement climatique<\/a> . La BBC a indiqu\u00e9 que dans un sombre rapport sur le climat par des scientifiques<\/a>, “les risques du r\u00e9chauffement global sont plus s\u00e9rieux que pr\u00e9c\u00e9demment pens\u00e9s”. The Guardian alerte : “Une \u00e9valuation sombre du co\u00fbt global de chaque degr\u00e9 en plus”<\/a> et le Times de Manille dit que les preuves indiquent que le changement climatique a d\u00e9j\u00e0 lieu, ce qui est une l\u00e9g\u00e8re insistance de ce que le TAR du GIEC a indiqu\u00e9. [N-d-T. En francais, voir Le Monde : Conf\u00e9rence internationale d’Exeter : le r\u00e9chauffement global a d\u00e9j\u00e0 commenc\u00e9<\/a>.] ; Les reportages semblent raisonnablement justes – un peu ‘sexis’ comme d’habitude, mais globalement, le texte des articles est assez fid\u00e8le \u00e0 la conf\u00e9rence.
    \n<\/lang_fr><\/p>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

    The conference last week in Exeter on “Avoiding Dangerous Climate Change” grew out of a speech by UK Prime Minister Tony Blair. He asked “What level of greenhouse gases in the atmosphere is self-evidently too much?” and “What options do we have to avoid such levels?”. The first question is very interesting, but also very […]<\/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":[5,1,3],"tags":[],"class_list":{"0":"post-95","1":"post","2":"type-post","3":"status-publish","4":"format-standard","6":"category-climate-modelling","7":"category-climate-science","8":"category-greenhouse-gases","9":"entry"},"aioseo_notices":[],"post_mailing_queue_ids":[],"_links":{"self":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts\/95","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=95"}],"version-history":[{"count":0,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts\/95\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/media?parent=95"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/categories?post=95"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/tags?post=95"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}