{"id":18,"date":"2004-12-03T21:17:42","date_gmt":"2004-12-04T01:17:42","guid":{"rendered":"\/?p=18"},"modified":"2009-01-31T21:06:23","modified_gmt":"2009-02-01T02:06:23","slug":"antarctic-cooling-global-warming","status":"publish","type":"post","link":"https:\/\/www.realclimate.org\/index.php\/archives\/2004\/12\/antarctic-cooling-global-warming\/","title":{"rendered":"Antarctic cooling, global warming? Refroidissement de l’Antarctique, r\u00e9chauffement global ? <\/lang_fr>"},"content":{"rendered":"
\n

by Eric Steig and Gavin Schmidt<\/small>
\nLong term temperature data from the Southern Hemisphere are hard to find, and by the time you get to the Antarctic continent, the data are extremely sparse. Nonetheless, some patterns do emerge from the limited data available. The Antarctic Peninsula, site of the now-defunct Larsen-B ice shelf<\/a>, has warmed substantially. On the other hand, the few stations on the continent and in the interior appear to have cooled slightly (Doran et al, 2002<\/a>; GISTEMP<\/a>). At first glance this seems to contradict the idea of \u201cglobal\u201d warming, but one needs to be careful before jumping to this conclusion.
\n
\npar Eric Steig et Gavin Schmidt (traduit par Claire Rollion-Bard)<\/small><\/p>\n

Les donn\u00e9es de temp\u00e9rature \u00e0 long terme de l’h\u00e9misph\u00e8re sud sont difficiles \u00e0 trouver, et au moment o\u00f9 vous acc\u00e9dez au continent Antarctique, les donn\u00e9es sont extr\u00eamement \u00e9parses. N\u00e9anmoins quelques tendances \u00e9mergent des quelques donn\u00e9es disponibles. La P\u00e9ninsule Antarctique, lieu de la barri\u00e8re de glace Larsen-B<\/a>, maintenant disparue, s’est r\u00e9chauff\u00e9e substantiellement. D’un autre c\u00f4t\u00e9, les quelques stations sur le continent et \u00e0 l’int\u00e9rieur semblent s’\u00eatre l\u00e9g\u00e8rement refroidies. (Doran et al., 2002<\/a> ; GISTEMP<\/a>). Au premier coup d’\u0153il, cela semble contradictoire avec l’id\u00e9e de r\u00e9chauffement “global”, mais on a besoin d’\u00eatre prudent avant de sauter sur cette conclusion. <\/lang_fr>
\n<\/p>\n

A rise in the global mean temperature does not imply universal warming. Dynamical effects (changes in the winds and ocean circulation) can have just as large an impact, locally as the radiative forcing from greenhouse gases. The temperature change in any particular region will in fact be a combination of radiation-related changes (through greenhouse gases, aerosols, ozone and the like) and dynamical effects. Since the winds tend to only move heat from one place to another, their impact will tend to cancel out in the global mean.<\/p>\n

It is important to recognize that the widely-cited \u201cAntarctic cooling\u201d appears, from the limited data available, to be restricted only to the last two decades, and that averaged over the last 40 years, there has been a slight warming (e.g. Bertler et al. 2004<\/a>. At present, it is not possible to say what the long term change over the entire last century or more has been. The lesson here is that changes observed over very short time intervals do not provide a reliable picture of how the climate is changing.<\/p>\n

Furthermore, there are actually good reasons to expect the overall rate of warming in the Southern Hemisphere to be small. It has been recognized for some time that model simulations result in much greater warming in the high latitudes of the Northern Hemisphere than in the South, due to ocean heat uptake by the Southern Ocean. Additionally, there is some observational evidence that atmospheric dynamical changes may explain the recent cooling over parts of Antarctica. .<\/p>\n

Thompson and Solomon (2002) <\/a> showed that the Southern Annular Mode (a pattern of variability that affects the westerly winds around Antarctica) had been in a more positive phase (stronger winds) in recent years, and that this acts as a barrier, preventing warmer air from reaching the continent. There are also some indications from models that this may have been caused by a combination of stratospheric ozone depletion and stratospheric cooling due to CO2<\/sub> (Gillett and Thompson, 2002 ;<\/a> Shindell and Schmidt, 2004)<\/a>. It is important to note, though, that there is evidence from tree-ring based climate reconstructions that the phase of the Southern Annular Mode has changed similarly in the past (Jones and Widman, 2004<\/a>). We cannot, therefore, ascribe observed recent temperature changes to any one particular cause.<\/p>\n

So what does this all of this imply? First, short term observations should be interpreted with caution: we need more data from the Antarctic, over longer time periods, to say with certainly what the long term trend is. Second, regional change is not the same as global mean change. Third, there are very reasonable explanations for the recent observed cooling, that have been recognized for some time from model simulations. However, the models also suggest that, as we go forward in time, the relative importance of increasing radiative effects, compared with atmosphere and ocean dynamic effects, is likely to increase. In short, we fully expect Antarctica to warm up in the future.
\nUne augmentation de la temp\u00e9rature moyenne globale n’implique pas un r\u00e9chauffement universel. Les effets dynamiques (changements dans la circulation des vents et des oc\u00e9ans) peuvent avoir un impact aussi large, localement, que le for\u00e7age radiatif des gaz \u00e0 effet de serre. Le changement de temp\u00e9rature dans une r\u00e9gion particuli\u00e8re sera, en fait, une combinaison des changements reli\u00e9s \u00e0 la radiation (par l’interm\u00e9diaire des gaz \u00e0 effet de serre, des a\u00e9rosols, de l’ozone etc.) et des effets dynamiques. Puisque les vents tendent \u00e0 seulement bouger la chaleur d’un lieu vers un autre, leur impact aura tendance \u00e0 neutraliser dans la moyenne globale.
\nIl est important de reconna\u00eetre que le largement cit\u00e9 “refroidissement antarctique” appara\u00eet, \u00e0 partir des donn\u00e9es disponibles, \u00eatre restreint aux deux derni\u00e8res d\u00e9cades, et que moyenn\u00e9 sur les 40 derni\u00e8res ann\u00e9es, il y a eu un faible r\u00e9chauffement (e.g. Bertler et al., 2004<\/a>). \u00c0 pr\u00e9sent, il n’est pas possible de dire comment a \u00e9t\u00e9 le changement \u00e0 long terme sur le dernier si\u00e8cle ou plus. La le\u00e7on ici est que les changements observ\u00e9s sur de petits intervalles de temps ne fournissent pas une image fid\u00e8le de la mani\u00e8re dont le climat est en train de changer.
\nDe plus, il y a actuellement de bonnes raisons d’attendre un taux de r\u00e9chauffement dans l’H\u00e9misph\u00e8re Sud faible. Il a \u00e9t\u00e9 reconnu depuis quelque temps que les simulations des mod\u00e8les r\u00e9sultent dans un r\u00e9chauffement beaucoup plus important dans les hautes latitudes de l’H\u00e9misph\u00e8re Nord que dans le Sud, \u00e0 cause de la prise de chaleur oc\u00e9anique pour l’Oc\u00e9an Austral. De plus, il y a des \u00e9vidences \u00e0 partir des observations que les changements dynamiques atmosph\u00e9riques pourraient expliquer le refroidissement r\u00e9cent sur des certaines parties de l’Antarctique.
\nThomson et Salomon (2002)<\/a> ont montr\u00e9 que le Mode Annulaire Austral (une variabilit\u00e9 qui affecte les vents ouest autour de l’Antarctique) avait \u00e9t\u00e9 dans une phase plus positive (vents plus forts) au cours des derni\u00e8res ann\u00e9es, et que cela joue comme une fronti\u00e8re, emp\u00eachant l’air plus chaud d’atteindre le continent. Il y a aussi quelques indications des mod\u00e8les que cela pourrait avoir \u00e9t\u00e9 caus\u00e9 par une combinaison de l’appauvrissement de l’ozone stratosph\u00e9rique et le refroidissement stratosph\u00e9rique \u00e0 cause du CO2 (Gillet et Thompson, 2002<\/a> ; Shindell et Schmidt, 2004<\/a>). Il est important de noter qu’il y a des preuves, \u00e0 partir des reconstructions climatiques bas\u00e9es sur les cernes d’arbres, que la phase du Mode Annulaire Austral a chang\u00e9 de mani\u00e8re comparable dans le pass\u00e9 (Jones et Widman, 2004<\/a>). On ne peut pas, alors, attribuer les changements de temp\u00e9ratures r\u00e9cemment observ\u00e9s \u00e0 une seule cause en particulier.<\/p>\n

Alors qu’est-ce que tout cela implique ? Tout d’abord, les observations \u00e0 court terme devraient \u00eatre interpr\u00e9t\u00e9es avec prudence : nous avons besoin de plus de donn\u00e9es sur l’Antarctique, sur des p\u00e9riodes de temps plus longues, pour dire avec certitude ce qu’est la tendance \u00e0 long terme. <\/p>\n

Deuxi\u00e8mement, un changement r\u00e9gional n’est pas pareil \u00e0 un changement global moyen. <\/p>\n

Troisi\u00e8mement, il y a des explications tr\u00e8s raisonnables pour le refroidissement r\u00e9cemment observ\u00e9 qui ont \u00e9t\u00e9 reconnues, il y a d\u00e9j\u00e0 quelques temps, \u00e0 partir des simulations des mod\u00e8les. Cependant, les mod\u00e8les sugg\u00e8rent aussi que, plus on va dans le temps et plus l’importance relative des effets radiatifs qui augmentent, compar\u00e9s avec les effets de la dynamique de l’atmosph\u00e8re et de l’oc\u00e9an, est susceptible d’augmenter. En r\u00e9sum\u00e9, nous nous attendons pleinement \u00e0 ce que l’Antarctique se r\u00e9chauffe dans le futur. <\/lang_fr><\/p>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

by Eric Steig and Gavin Schmidt Long term temperature data from the Southern Hemisphere are hard to find, and by the time you get to the Antarctic continent, the data are extremely sparse. Nonetheless, some patterns do emerge from the limited data available. The Antarctic Peninsula, site of the now-defunct Larsen-B ice shelf, has warmed […]<\/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":[12,5,1,3],"tags":[],"class_list":{"0":"post-18","1":"post","2":"type-post","3":"status-publish","4":"format-standard","6":"category-arctic-and-antarctic","7":"category-climate-modelling","8":"category-climate-science","9":"category-greenhouse-gases","10":"entry"},"aioseo_notices":[],"post_mailing_queue_ids":[],"_links":{"self":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts\/18","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=18"}],"version-history":[{"count":0,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts\/18\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/media?parent=18"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/categories?post=18"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/tags?post=18"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}