{"id":13,"date":"2004-12-03T09:42:20","date_gmt":"2004-12-03T13:42:20","guid":{"rendered":"\/?p=13"},"modified":"2007-08-25T11:37:14","modified_gmt":"2007-08-25T16:37:14","slug":"co2-in-ice-cores","status":"publish","type":"post","link":"https:\/\/www.realclimate.org\/index.php\/archives\/2004\/12\/co2-in-ice-cores\/","title":{"rendered":"What does the lag of CO2<\/sub><\/small> behind temperature in ice cores tell us about global warming? Quelle information sur le r\u00e9chauffement climatique nous apportent les \u00e9tudes qui concluent \u00e0 un retard du CO2<\/sub> sur la temp\u00e9rature, r\u00e9alis\u00e9es \u00e0 partir des carottes de glace?<\/lang_fr>"},"content":{"rendered":"
\n

This is an issue that is often misunderstood in the public sphere and media, so it is worth spending some time to explain it and clarify it. At least three careful ice core studies have shown that CO2<\/sub><\/small> starts to rise about 800 years (600-1000 years) after Antarctic temperature during glacial terminations. These terminations are pronounced warming periods that mark the ends of the ice ages that happen every 100,000 years or so. <\/p>\n

Does this prove that CO2<\/sub><\/small> doesn’t cause global warming? The answer is no.
\n Par Jeff Severinghaus (traduit par Nicolas Caillon)<\/small><\/p>\n

Les r\u00e9sultats de ces \u00e9tudes ne sont pas toujours bien compris par le public, souvent mal restitu\u00e9s par les m\u00e9dias, et m\u00e9ritent donc davantage d’explications. Au moins 3 \u00e9tudes d\u00e9taill\u00e9es r\u00e9alis\u00e9es \u00e0 partir de carottes de glace montrent que le CO2<\/sub> commence \u00e0 augmenter autour de 800 ans (entre 600 \u00e0 1000 ans) apr\u00e8s le d\u00e9marrage de l’augmentation de temp\u00e9rature lors des terminaisons glaciaires. Ces terminaisons sont les p\u00e9riodes de r\u00e9chauffement qui marquent la fin des p\u00e9riodes glaciaires et qui se produisent tous les 100 000 ans.<\/lang_fr>
\n<\/p>\n

The reason has to do with the fact that the warmings take about 5000 years to be complete. The lag is only 800 years. All that the lag shows is that CO2<\/sub><\/small> did not cause the first 800 years of warming, out of the 5000 year trend. The other 4200 years of warming could in fact have been caused by CO2<\/sub><\/small>, as far as we can tell from this ice core data. <\/p>\n

The 4200 years of warming make up about 5\/6 of the total warming. So CO2<\/sub><\/small> could have caused the last 5\/6 of the warming, but could not have caused the first 1\/6 of the warming.<\/p>\n

It comes as no surprise that other factors besides CO2<\/sub><\/small> affect climate. Changes in the amount of summer sunshine, due to changes in the Earth’s orbit around the sun that happen every 21,000 years, have long been known to affect the comings and goings of ice ages. Atlantic ocean circulation slowdowns are thought to warm Antarctica, also.<\/p>\n

From studying all the available data (not just ice cores), the probable sequence of events at a termination goes something like this. Some (currently unknown) process causes Antarctica and the surrounding ocean to warm. This process also causes CO2<\/sub><\/small> to start rising, about 800 years later. Then CO2<\/sub><\/small> further warms the whole planet, because of its heat-trapping properties. This leads to even further CO2<\/sub><\/small> release. So CO2<\/sub><\/small> during ice ages should be thought of as a “feedback”, much like the feedback that results from putting a microphone too near to a loudspeaker. <\/p>\n

In other words, CO2<\/sub><\/small> does not initiate the warmings, but acts as an amplifier once they are underway. From model estimates, CO2<\/sub><\/small> (along with other greenhouse gases CH4<\/sub><\/small> and N2<\/sub><\/small>O) causes about half of the full glacial-to-interglacial warming.<\/p>\n

So, in summary, the lag of CO2<\/sub><\/small> behind temperature doesn’t tell us much about global warming. [But it may give us a very interesting clue about why CO2<\/sub><\/small> rises at the ends of ice ages. The 800-year lag is about the amount of time required to flush out the deep ocean through natural ocean currents. So CO2<\/sub><\/small> might be stored in the deep ocean during ice ages, and then get released when the climate warms.]<\/p>\n

To read more about CO2<\/sub><\/small> and ice cores, see Caillon et al., 2003, Science magazine<\/a><\/p>\n

Guest Contributor: Jeff Severinghaus<\/a>
\nProfessor of Geosciences
\nScripps Institution of Oceanography
\nUniversity of California, San Diego.<\/p>\n

Update May 2007<\/strong>: We have a fuller exposition of this on a more recent post.<\/a>
\nPeut-on d\u00e9duire de ces \u00e9tudes que le CO2<\/sub> n’est pas responsable du r\u00e9chauffement de la plan\u00e8te? La r\u00e9ponse est non.<\/p>\n

En effet, les r\u00e9chauffements associ\u00e9s aux transitions glaciaire-interglaciaires ont une dur\u00e9e d’environ 5000 ans. Or le retard du CO2<\/sub> sur le d\u00e9but de l’augmentation de la temp\u00e9rature n’est que de 800 ans. Le CO2<\/sub> ne serait, par cons\u00e9quent, pas la cause des 800 premi\u00e8res ann\u00e9es du r\u00e9chauffement, mais a, en revanche, pu \u00eatre responsable du r\u00e9chauffement se produisant pendant les 4200 ann\u00e9es suivantes.<\/p>\n

Ces 4200 ans de r\u00e9chauffement repr\u00e9sentent les 5\/6 du r\u00e9chauffement total. Ainsi, le CO2<\/sub> serait la cause des derniers 5\/6 du r\u00e9chauffement, mais pas du d\u00e9but du r\u00e9chauffement, c’est-\u00e0 -dire 1\/6 du r\u00e9chauffement total.<\/p>\n

Il n’est pas surprenant que des processus autres que l’effet du CO2<\/sub> puissent affecter le climat. Les changements d’insolation, cons\u00e9quence des variations de l’orbite terrestre autour du soleil qui ont lieu tous les 21 000 ans, sont depuis longtemps tenus pour responsables du va et vient des p\u00e9riodes glaciaires. On montre \u00e9galement que des ralentissements de la circulation oc\u00e9anique dans l’Atlantique peuvent \u00eatre \u00e0 l’origine d’un r\u00e9chauffement du secteur antarctique.<\/p>\n

En compilant les donn\u00e9es pal\u00e9o disponibles, et pas seulement celles obtenues \u00e0 partir de carottes de glace, il est possible de proposer une s\u00e9quence d’\u00e9v\u00e9nements se produisant lors d’une terminaison. Un processus (encore mal connu) provoque le r\u00e9chauffement du secteur antarctique. Ce processus est \u00e9galement \u00e0 l’origine du d\u00e9marrage de l’augmentation du CO2<\/sub> atmosph\u00e9rique 800 ans apr\u00e8s celui de la temp\u00e9rature. Ensuite, le CO2<\/sub> contribue au r\u00e9chauffement de toute la plan\u00e8te de part son r\u00f4le de gaz \u00e0 effet de serre, un r\u00e9chauffement qui provoque \u00e0 son tour une intensification du relargage de CO2<\/sub> dans l’atmosph\u00e8re.
\nC’est ainsi que l’on parle de l’effet de r\u00e9troaction du CO2<\/sub>, effet comparable aux r\u00e9actions parasites qui ont lieu quand on approche un microphone trop proche d’une enceinte.<\/p>\n

En d’autres termes, le CO2<\/sub> ne d\u00e9clenche pas le r\u00e9chauffement, mais joue un r\u00f4le d’amplificateur une fois que celui-ci est en cours. Selon des estimations de mod\u00e8les, l’effet du CO2<\/sub> (avec celui du CH4<\/sub> et du N2<\/sub>O) permet d’expliquer la moiti\u00e9 du r\u00e9chauffement total se produisant lors des transitions glaciaire-interglaciaires.<\/p>\n

Pour r\u00e9sumer, le retard du CO2<\/sub> sur la temp\u00e9rature ne nous dit pas grand-chose sur le r\u00e9chauffement global actuel. Son estimation est cependant un \u00e9l\u00e9ment int\u00e9ressant pour comprendre le m\u00e9canisme \u00e0 l’origine de l’augmentation du CO2<\/sub> \u00e0 la fin des p\u00e9riodes glaciaires. Ces 800 ans sont \u00e9quivalents au temps n\u00e9cessaire pour ventiler l’oc\u00e9an profond sous l’effet de courants oc\u00e9aniques. Ainsi, le CO2<\/sub> serait stock\u00e9 dans l’oc\u00e9an profond au cours des p\u00e9riodes glaciaires, puis r\u00e9inject\u00e9 dans l’atmosph\u00e8re lorsque le climat se r\u00e9chauffe).<\/p>\n

Pour une lecture plus d\u00e9taill\u00e9e : Caillon et al., 2003, Science magazine<\/a><\/p>\n

Mai 2007<\/strong>: Plus r\u00e9cemment.<\/a>
\n<\/lang_fr><\/p>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

This is an issue that is often misunderstood in the public sphere and media, so it is worth spending some time to explain it and clarify it. At least three careful ice core studies have shown that CO2 starts to rise about 800 years (600-1000 years) after Antarctic temperature during glacial terminations. These terminations are […]<\/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":[13,3,2],"tags":[],"class_list":{"0":"post-13","1":"post","2":"type-post","3":"status-publish","4":"format-standard","6":"category-faq","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\/13","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=13"}],"version-history":[{"count":0,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts\/13\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/media?parent=13"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/categories?post=13"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/tags?post=13"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}