{"id":65,"date":"2004-12-08T18:13:33","date_gmt":"2004-12-08T22:13:33","guid":{"rendered":"\/?p=65"},"modified":"2005-02-16T18:28:15","modified_gmt":"2005-02-16T22:28:15","slug":"ok-perhaps-recent-20th-century-warmth-is-anomalous-over-the-past-millennium-or-two-but-wasnt-it-warmer-during-the-holocene-optimum-some-6000-years-ago","status":"publish","type":"post","link":"https:\/\/www.realclimate.org\/index.php\/archives\/2004\/12\/ok-perhaps-recent-20th-century-warmth-is-anomalous-over-the-past-millennium-or-two-but-wasnt-it-warmer-during-the-holocene-optimum-some-6000-years-ago\/","title":{"rendered":"OK, But we do<\/i> know it was warmer than present 6000 years ago, don’t we? Sommes nous s\u00fbrs<\/i> qu’il faisait plus chaud il y a 6000 ans ?<\/lang_fr>"},"content":{"rendered":"
\n

This is yet another oft-repeated but problematic assertion based in this case on the mis-characterization of the so-called Mid-Holocene Climatic Optimum”<\/a> or “Mid-Holocene Warm Period”. Paleoclimate experts now know that the mid-Holocene warmth centered roughly 8000 to 6000 years ago was probably restricted to high latitudes and certain seasons (summer in the Northern Hemisphere and winter in the southern hemisphere). Because much of the early paleoclimate evidence that was available (for example, fossil pollen assemblages) came from the Northern Hemisphere extratropics, and is largely reflective of summer conditions, decades ago some scientists believed that this was a time of globally warmer conditions. More abundant evidence now demonstrates, for example, that the tropical regions were cooler over much of the year.<\/p>\n

par Michael Mann (traduit par Thibault de Garidel)<\/small><\/p>\n

Cette assertion est tr\u00e8s souvent r\u00e9p\u00e9t\u00e9e mais reste probl\u00e9matique en raison de la mauvaise caract\u00e9risation de cette p\u00e9riode appel\u00e9e ““Optimum climatique de l’Holoc\u00e8ne moyen<\/a>” ou “p\u00e9riode chaude de l’Holoc\u00e8ne moyen”. Les experts des pal\u00e9oclimats, savent maintenant que cette phase chaude \u00e0 l’Holoc\u00e8ne (il y a approximativement 8000 \u00e0 6000 ans) \u00e9tait probablement limit\u00e9e aux hautes latitudes et \u00e0 certaines saisons (\u00e9t\u00e9 dans l’h\u00e9misph\u00e8re nord et hiver dans l’h\u00e9misph\u00e8re sud). Comme la majorit\u00e9 des indicateurs du climat pass\u00e9 disponibles (comme par exemple, assemblages de pollens fossiles) provenaient des latitudes moyennes \u00e0 hautes de l’h\u00e9misph\u00e8re Nord, et \u00e9taient diagnostiques des condition climatiques d’\u00e9t\u00e9, certains scientifiques ont cru que cette p\u00e9riode de temps \u00e9tait plus chaude globalement. Cependant, d\u00e9sormais, de nombreuses \u00e9tudes montrent que les r\u00e9gions tropicales \u00e9taient plus fra\u00eeches pendant la plus grande partie de l’ann\u00e9e.
\n(suite…)<\/a>
\n<\/lang_fr><\/p>\n

All of these changes are consistent with the expected response of surface temperatures to the known changes in the Earth\u2019s orbital geometry relative to the Sun during that time period and associated climate feedbacks, as detailed in the peer-reviewed literature (see Ganopolski et al, 1998; Hewitt and Mitchell, 1998). The best available evidence suggests that annual, global mean warmth was probably similar to pre-20th century warmth, but less than late 20th century warmth, at this time (see Kitoh and Murakami, 2002).<\/p>\n

More information about the Mid-Holocene warm period can be found here.<\/a><\/p>\n

References:<\/b><\/font><\/p>\n

\n Ganopolski, A., C. Kubatzki, M. Claussen, V. Brovkin, and V. Petoukhov, The Influence of Vegetation-Atmosphere-Ocean Interaction on Climate During the Mid-Holocene, Science<\/i>, 280, 1916-1919, 1998.<\/font><\/font><\/p>\n

\n Hewitt, C.D. and J.F.B. Mitchell, A Fully Coupled GCM Simulation of the Climate of the Mid-Holocene, Geophys. Res. Lett.<\/i>, 25, 361-364, 1998.<\/font><\/font><\/p>\n

Kitoh, A., and S. Murakami, Tropical Pacific Climate at the mid-Holocene and the Last Glacial Maximum simulated by a coupled ocean-atmosphere general circulation model, Paleoceanography<\/i>, 17, 1-13, 2002. <\/font><\/font><\/p>\n


\n<\/a>
\nTous ces changements sont conformes \u00e0 la r\u00e9ponse des temp\u00e9ratures de surface aux changements bien document\u00e9s de la g\u00e9om\u00e9trie orbitale de la Terre par rapport au soleil pendant cette p\u00e9riode de temps et aux r\u00e9troactions associ\u00e9es du climat, comme d\u00e9taill\u00e9 dans la litt\u00e9rature scientifique (voir Ganopolski et al., 1998; Hewitt et Mitchell, 1998). L’\u00e9tude de Kitoh et Murakami fournit une des meilleures preuves disponibles que la temp\u00e9rature moyenne globale \u00e9tait pendant cette p\u00e9riode de temps probablement semblable aux conditions pr\u00e9datant le 20ie si\u00e8cle, mais plus faible que celle du 20ie si\u00e8cle (Kitoh et Murakami, 2002).<\/p>\n

Pour trouver plus d’informations sur la p\u00e9riode chaude de l’Holoc\u00e8ne moyen, le site de la NOAA<\/a> fournit une bonne r\u00e9f\u00e9rence (en anglais) :<\/p>\n

R\u00e9f\u00e9rences :<\/b><\/font><\/p>\n

\n Ganopolski, A., C. Kubatzki, M. Claussen, V. Brovkin, and V. Petoukhov, The Influence of Vegetation-Atmosphere-Ocean Interaction on Climate During the Mid-Holocene, Science<\/i>, 280, 1916-1919, 1998.<\/font><\/font><\/p>\n

\n Hewitt, C.D. and J.F.B. Mitchell, A Fully Coupled GCM Simulation of the Climate of the Mid-Holocene, Geophys. Res. Lett.<\/i>, 25, 361-364, 1998.<\/font><\/font><\/p>\n

Kitoh, A., and S. Murakami, Tropical Pacific Climate at the mid-Holocene and the Last Glacial Maximum simulated by a coupled ocean-atmosphere general circulation model, Paleoceanography<\/i>, 17, 1-13, 2002. <\/font><\/font><\/p>\n

<\/lang_fr><\/><\/p>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

This is yet another oft-repeated but problematic assertion based in this case on the mis-characterization of the so-called Mid-Holocene Climatic Optimum” or “Mid-Holocene Warm Period”. Paleoclimate experts now know that the mid-Holocene warmth centered roughly 8000 to 6000 years ago was probably restricted to high latitudes and certain seasons (summer in the Northern Hemisphere and […]<\/p>\n","protected":false},"author":4,"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":[1,13,2],"tags":[],"class_list":{"0":"post-65","1":"post","2":"type-post","3":"status-publish","4":"format-standard","6":"category-climate-science","7":"category-faq","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\/65","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\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/comments?post=65"}],"version-history":[{"count":0,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts\/65\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/media?parent=65"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/categories?post=65"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/tags?post=65"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}