{"id":216,"date":"2005-11-30T03:15:27","date_gmt":"2005-11-30T07:15:27","guid":{"rendered":"\/?p=216"},"modified":"2009-06-01T07:36:18","modified_gmt":"2009-06-01T12:36:18","slug":"greenhouse-gases-help-seasonal-predictions","status":"publish","type":"post","link":"https:\/\/www.realclimate.org\/index.php\/archives\/2005\/11\/greenhouse-gases-help-seasonal-predictions\/","title":{"rendered":"Greenhouse gases help seasonal predictions Gaz \u00e0 effet de serre et pr\u00e9dictions saisonni\u00e8res<\/lang_fr>"},"content":{"rendered":"
\n

The conventional wisdom in meteorology has been that certain factors such as the complete<\/em> oceanic state and the exact concentrations of greenhouse gases are of minor importance for a normal weather forecast. Moreover, whereas sea surface temperatures (SST) are important, the deep sea temperatures are believed to have little impact for predictions for the next few days. The reason is that the ocean reacts slowly to changes in the atmosphere (has much higher inertia and much higher heat capacity). Hence, the most important information needed for such a weather forecast is the atmospheric initial conditions<\/em>, a description of what the atmosphere and the SST look like when the weather model starts computing the weather evolution.
\nIl est g\u00e9n\u00e9ralement admis en m\u00e9t\u00e9orologie que certains facteurs, tels que l’\u00e9tat global des oc\u00e9ans et la concentration exacte de gaz \u00e0 effet de serre sont de faible importance pour une pr\u00e9vision m\u00e9t\u00e9o normale. De plus, si les temp\u00e9ratures de surface des oc\u00e9ans (TSO) sont importantes, les temp\u00e9ratures des eaux profondes semblent avoir peu d’influence sur les pr\u00e9visions pour les prochains jours. La raison en est que les oc\u00e9ans r\u00e9agissent lentement aux changements atmosph\u00e9riques (leur inertie et capacit\u00e9 thermique est beaucoup plus \u00e9lev\u00e9e). D\u00e8s lors, l’information la plus importante pour de telles pr\u00e9visions m\u00e9t\u00e9o est l’ensemble des conditions initiales de l’atmosph\u00e8re, c’est-\u00e0-dire une description des caract\u00e9ristiques de l’atmosph\u00e8re et des TSO au moment o\u00f9 le mod\u00e8le commence \u00e0 calculer l’\u00e9volution du temps.
\n(suite…)<\/a>
\n <\/lang_fr>
\n<\/p>\n

If we want to make predictions over longer periods<\/em>, such as the subsequent months, then the effects of boundary conditions<\/em> become more important than the atmospheric initial conditions (due to internal chaos and the lack of predictability from the initial state). The oceans, which provide part of the boundary conditions for the atmosphere, also have sufficient time to change appreciably, and the change in the oceanic state must be taken into account. Such long forecasts are often referred to as seasonal forecasting<\/em>. Seasonal forecasts are often made with coupled ocean-atmoaphere models (more like climate models), as opposed to atmosphere-only models for ordinary weather forecasts. Until now, it has been assumed that factors such as greenhouse gas concentrations play a minor role for the skill of the seasonal forecasts. However, a new study by Doblas-Reyes and co-authors<\/a> at the European Centre for Medium-Range Weather Forecasts (ECMWF) – the ‘European weather centre’ – suggests that by updating the greenhouse conditions with the observed annual mean values, the skill of the seasonal forecasts improve noticeably. <\/p>\n

The implications of these findings are quite subtle, but important: we are already feeling the climatic effects of rising greenhouse gas concentrations. These findings also open for more practical use of our knowlegde about climate change: by taking these trends (i.e. extra information) into account, we improve our ability to make predictions seasons ahead. This is also something that has been observed, e.g. in Norway, where the climatic trends result in more warm than cold seasons.<\/p>\n

Reference: <\/em><\/p>\n

Doblas-Reyes, F.J., R. Hagedorn, T.N. Palmer and J.-J. Morcrette:
\nImpact of increasing greenhouse gas concentrations in seasonal ensemble forecasts.
\nECMWF Tech. Mem. #476, October 2005<\/p>\n


\nSi nous voulons faire des pr\u00e9visions sur de plus longues p\u00e9riodes, par exemple les prochains mois, alors les influences des conditions aux limites deviennent plus importante que celles des conditions initiales (\u00e0 cause du chaos interne et du manque de pr\u00e9dictabilit\u00e9 de l’\u00e9tat initial). Les oc\u00e9ans, qui fournissent certaines des conditions aux limites pour l’atmosph\u00e8re, ont \u00e9galement assez de temps pour \u00e9voluer sensiblement, et le changement d’\u00e9tat oc\u00e9anique doit \u00eatre pris en compte. De telles pr\u00e9visions \u00e0 long terme sont souvent appel\u00e9es des pr\u00e9visions saisonni\u00e8res. Les pr\u00e9visions saisonni\u00e8res sont souvent r\u00e9alis\u00e9es avec des mod\u00e8les coupl\u00e9s atmosph\u00e8re-oc\u00e9ans (plus proche des mod\u00e8les climatiques), par opposition aux mod\u00e8les utilis\u00e9s pour les pr\u00e9visions m\u00e9t\u00e9o ordinaires qui n’incluent que l’atmosph\u00e8re. Jusqu’\u00e0 pr\u00e9sent, il \u00e9tait suppos\u00e9 que des facteurs tels que les concentrations de gaz \u00e0 effet de serre jouent un r\u00f4le mineur dans la technique des pr\u00e9visions saisonni\u00e8res. Toutefois, une nouvelle \u00e9tude par Doblas-Reyes et ses co-auteurs<\/a>, du Centre europ\u00e9en de pr\u00e9visions m\u00e9t\u00e9orologiques \u00e0 moyen terme \u2013 le \u00ab centre m\u00e9t\u00e9orologique europ\u00e9en \u00bb (European Centre for Medium-Range Weather Forecasts (ECMWF) <\/a>\u2013 sugg\u00e8re qu’en mettant \u00e0 jour les caract\u00e9ristiques de l’effet de serre avec les moyennes annuelles observ\u00e9es, la technique de pr\u00e9vision s’am\u00e9liore sensiblement. <\/p>\n

Les implications de ces d\u00e9couvertes sont assez subtiles, mais importantes: nous sommes d\u00e9j\u00e0 en train de sentir les effets climatiques de l’augmentation des concentrations de gaz \u00e0 effet de serre. Ces d\u00e9couvertes d\u00e9bouchent \u00e9galement sur des applications plus concr\u00e8tes de nos connaissances sur les changements climatiques: en prenant en compte ces tendances (c’est-\u00e0-dire de l’information suppl\u00e9mentaire), nous am\u00e9liorons notre capacit\u00e9 \u00e0 faire des pr\u00e9visions des saisons \u00e0 l’avance. C’est aussi quelque chose qui a \u00e9t\u00e9 observ\u00e9, par exemple en Norv\u00e8ge, o\u00f9 les tendances climatiques ont comme cons\u00e9quence plus de saisons chaudes que froides. <\/p>\n

R\u00e9f\u00e9rence: <\/em>
\nDoblas-Reyes, F.J., R. Hagedorn, T.N. Palmer and J.-J. Morcrette:
\nImpact of increasing greenhouse gas concentrations in seasonal ensemble forecasts.
\nECMWF Tech. Mem. #476, October 2005 <\/p>\n

(traduit par Alain Henry)<\/lang_fr><\/p>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

The conventional wisdom in meteorology has been that certain factors such as the complete oceanic state and the exact concentrations of greenhouse gases are of minor importance for a normal weather forecast. Moreover, whereas sea surface temperatures (SST) are important, the deep sea temperatures are believed to have little impact for predictions for the next […]<\/p>\n","protected":false},"author":11,"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":[1,3],"tags":[],"class_list":{"0":"post-216","1":"post","2":"type-post","3":"status-publish","4":"format-standard","6":"category-climate-science","7":"category-greenhouse-gases","8":"entry"},"aioseo_notices":[],"post_mailing_queue_ids":[],"_links":{"self":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts\/216","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\/11"}],"replies":[{"embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/comments?post=216"}],"version-history":[{"count":0,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts\/216\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/media?parent=216"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/categories?post=216"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/tags?post=216"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}