{"id":221,"date":"2005-11-24T22:26:26","date_gmt":"2005-11-25T02:26:26","guid":{"rendered":"\/?p=221"},"modified":"2016-09-23T20:27:40","modified_gmt":"2016-09-24T01:27:40","slug":"650000-years-of-greenhouse-gas-concentrations","status":"publish","type":"post","link":"https:\/\/www.realclimate.org\/index.php\/archives\/2005\/11\/650000-years-of-greenhouse-gas-concentrations\/","title":{"rendered":"650,000 years of greenhouse gas concentrations 650 000 ann\u00e9es de concentrations de gaz \u00e0 effet de serre<\/lang_fr>"},"content":{"rendered":"
\n

The latest results from the EPICA core in Antarctica have just been published this week in Science<\/em> (Siegenthaler et al<\/a>. and Spahni et al.<\/a>). This ice core extended the record of Antarctic climate back to maybe 800,000 years, and the first 650,000 years of ice have now been analysed for greenhouse gas concentrations saved in tiny bubbles. The records for CO2<\/sub>, CH4<\/sub> and N2<\/sub>O both confirm the Vostok records that have been available for a few years now, and extend them over another 4 glacial-interglacial cycles. This is a landmark result and a strong testament to the almost heroic efforts in the field to bring back these samples from over 3km deep in the Antarctica ice. So what do these new data tell us, and where might they lead? Les derniers r\u00e9sultats du forage EPICA en Antarctique viennent juste d’\u00eatre publi\u00e9s dans le num\u00e9ro de cette semaine de Science<\/em> (Siegenthaler et al.<\/a> et Spahni et al.<\/a>). Cette carotte glaciaire a permis d’\u00e9tendre l’enregistrement du climat Antarctique jusqu’\u00e0 800 000 ans, alors que les concentrations de gaz \u00e0 effet de serre, pi\u00e9g\u00e9es sous forme de minuscules bulles de gas, ont \u00e9t\u00e9 analys\u00e9es pour les 650 000 derni\u00e8res ann\u00e9es. Ces enregistrements de CO2<\/sub>, CH4<\/sub> et N2<\/sub>O sont en accord avec ceux de Vostok (\u00e9galement en Antarctique) disponibles depuis quelques ann\u00e9es, et permettent d’observer 4 cycles d’alternance glaciaire\/interglaciaire suppl\u00e9mentaires. Ces travaux sont remarquables, et justifient des efforts gigantesques effectu\u00e9s sur le terrain pour ramener des \u00e9chantillons enfouis jusqu’\u00e0 3km de profondeur dans la glace Antarctique. Que nous disent ces nouvelles donn\u00e9es, et dans quelle direction peuvent elles nous mener ?
\n(suite…)<\/a>
\n<\/lang_fr><\/p>\n

\"Composite<\/a>First of all, the results demonstrate clearly that the relationship between climate and CO2<\/sub> that had been deduced from the Vostok core appears remarkably robust. This is despite a significant change in the patterns of glacial-interglacial changes prior to 400,000 years ago. The ‘EPICA challenge’ was laid down a few months ago for people working on carbon cycle models to predict whether this would be the case, and mostly the predictions<\/a> were right on the mark. (Who says climate predictions can’t be verified?). It should also go almost without saying that lingering doubts about the reproducability of the ice core gas records should now be completely dispelled. That a number of different labs, looking at ice from different locations, extracted with different methods all give very similar answers, is a powerful indication that what they are measuring is real. Where there are problems (for instance in N2<\/sub>O in very dusty ice), those problems are clearly found and that data discarded. <\/p>\n

Secondly, these results will allow paleoclimatologists to really look in detail at the differences between the different interglacials in the past. The previous 3 before our current era look quite similar to each other and were quite short (around 10,000 years). The one 400,000 years ago (Marine Isotope Stage 11, for those who count that way) was hypothesised to look more like the Holocene and appears to be significantly longer (around 30,000 years). Many of the details though weren’t completely clear in the Vostok data, but should now be much better resolved. This may help address some of the ideas put forward by Ruddiman<\/a> (2003, 2005), and also help assess how long our current warm period is likely to last.<\/p>\n

More generally, since the extra interglacials that are now resolved have very different characteristics from the previous ones, they may allow us to test climate theories and models over a whole new suite of test cases. To quote Richard Alley “Whether you’re a physicist, a chemist, a biologist, a geologist, or any other “ist” studying the Earth system, there is something in these data that confirms much of your understanding of the planet and then challenges some piece of your understanding”. It’s all very exciting (for us ‘ists’ at least!).<\/p>\n


\n\"Composite<\/a>
\nPremi\u00e8rement, ces r\u00e9sultats d\u00e9montrent clairement que la relation entre climat et CO2<\/sub> d\u00e9duite a partir de l’enregistrement de Vostok est remarquablement robuste – en d\u00e9pit d’un changement majeur dans les caract\u00e9ristiques des alternances glaciaire-interglaciaire avant 400 000 ans. Un exercice international, ‘le challenge EPICA’ avait \u00e9t\u00e9 mis en place il y a quelques mois pour les chercheurs travaillant sur les mod\u00e8les du cycle du carbone, afin de d\u00e9terminer si ce serait le cas ou pas, et la plupart des pr\u00e9dictions<\/a> se sont r\u00e9v\u00e9l\u00e9es justes. (Qui a dit que les pr\u00e9dictions climatiques ne peuvent \u00eatre v\u00e9rifi\u00e9es ?). Ceci va de pair avec le fait que toute incertitude sur la fiabilit\u00e9 et reproductibilit\u00e9 des enregistrements de gaz a effet de serre doit maintenant \u00eatre compl\u00e8tement \u00e9cart\u00e9e. En effet, que diff\u00e9rents laboratoires, \u00e9tudiant de la glace extraite de diff\u00e9rentes mani\u00e8res et provenant de diff\u00e9rents endroits donnent des r\u00e9sultats tr\u00e8s similaires, montre de mani\u00e8re tr\u00e8s claire que ce qu’ils mesurent est r\u00e9el. Dans le cas ou il subsiste des probl\u00e8mes (par exemple pour mesurer le N2<\/sub>O dans de la glace riche en poussi\u00e8res), ces probl\u00e8mes sont clairement identifi\u00e9s et ces donn\u00e9es \u00e9cart\u00e9es.<\/p>\n

Deuxi\u00e8mement, ces r\u00e9sultats vont permettre aux pal\u00e9oclimatologues de regarder en d\u00e9tail les diff\u00e9rences entre les diff\u00e9rents interglaciaires du pass\u00e9. Les 3 pr\u00e9c\u00e9dents interglaciaires a notre \u00e8re se ressemblent beaucoup et furent relativement brefs (environ 10000 ans). Celui qui a eu lieu il y a 400 000 ans (correspondant au stade isotopique marin 11, pour ceux qui comptent de cette mani\u00e8re) \u00e9tait par contre suppos\u00e9 ressembler a l’Holocene (la p\u00e9riode interglaciaire pendant laquelle nous vivons) et semble \u00eatre plus long (environ 30 000 ans). Alors que beaucoup de d\u00e9tails n’\u00e9taient pas compl\u00e8tement r\u00e9solus dans les donn\u00e9es de Vostok, ceux ci devraient maintenant s’\u00e9claircir. Ces enregistrements permettront peut \u00eatre de tester et de r\u00e9soudre certaines des id\u00e9es de Ruddiman<\/a>, et \u00e9galement nous aider a estimer la dur\u00e9e probable de la p\u00e9riode chaude pendant laquelle nous vivons.<\/p>\n

Plus g\u00e9n\u00e9ralement, comme ces interglaciaires semblent assez diff\u00e9rents de ceux pr\u00e9c\u00e9demment d\u00e9crits, ceux-ci vont nous permettre de tester certains mod\u00e8les et th\u00e9ories du climat dans une nouvelle s\u00e9rie de cas. Comme le dit Richard Alley “que vous soyez un physicien, un chimiste, un biologiste, un g\u00e9ologue ou qui que ce soit \u00e9tudiant le syst\u00e8me Terre, il y a dans ces donn\u00e9es a la fois des confirmations majeures de ce que nous comprenons d\u00e9j\u00e0 de cette plan\u00e8te et de nouvelles interrogations sur quelques points”.<\/p>\n

<\/lang_fr><\/p>\n

Update 1 Dec:<\/strong> Thomas Stocker sent in a better figure of the composite results for CO2, CH4, and the isotopes: <\/a>.<\/p>\n


\nMise-a-jour 1er d\u00e9cembre:<\/strong> Thomas Stocker a envoy\u00e9 une image plus claire des donn\u00e9es:.
\n<\/a><\/lang_fr><\/p>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

The latest results from the EPICA core in Antarctica have just been published this week in Science (Siegenthaler et al. and Spahni et al.). This ice core extended the record of Antarctic climate back to maybe 800,000 years, and the first 650,000 years of ice have now been analysed for greenhouse gas concentrations saved in […]<\/p>\n","protected":false},"author":2,"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":[12,1,3,2],"tags":[],"class_list":{"0":"post-221","1":"post","2":"type-post","3":"status-publish","4":"format-standard","6":"category-arctic-and-antarctic","7":"category-climate-science","8":"category-greenhouse-gases","9":"category-paleoclimate","10":"entry"},"aioseo_notices":[],"post_mailing_queue_ids":[],"_links":{"self":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts\/221","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=221"}],"version-history":[{"count":2,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts\/221\/revisions"}],"predecessor-version":[{"id":19622,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts\/221\/revisions\/19622"}],"wp:attachment":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/media?parent=221"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/categories?post=221"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/tags?post=221"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}