{"id":154,"date":"2005-05-15T18:55:19","date_gmt":"2005-05-15T22:55:19","guid":{"rendered":"\/?p=154"},"modified":"2006-02-01T13:14:05","modified_gmt":"2006-02-01T17:14:05","slug":"global-dimming-may-have-a-brighter-future","status":"publish","type":"post","link":"https:\/\/www.realclimate.org\/index.php\/archives\/2005\/05\/global-dimming-may-have-a-brighter-future\/","title":{"rendered":"Global Dimming may have a brighter future Un avenir brillant pour l’assombrissement global ?<\/lang_fr>"},"content":{"rendered":"
\n

A while ago, we wrote about Global Dimming<\/a> – a reduction in downward solar radiation of about 4% or about 7W\/m2 from 1961 to 1990 was found at stations worldwide. We said at the time that there were hints of a recovery underway post-1990; now research has been published showing this. From Dimming to Brightening: Decadal Changes in Solar Radiation at Earth’s Surface<\/a> by Martin Wild et al. (Science 6 May 2005; 308: 847-850; subscription required for link) uses surface measurements; Do Satellites Detect Trends in Surface Solar Radiation?<\/a> by Pinker et al., Science 2005 308: 850-854 uses satellites; both find a recovery of surface downward radiation since about 1990.
\nIl y a quelques temps, nous \u00e9crivions \u00e0 propos de l’assombrissement global<\/a> \u2013 une r\u00e9duction de l’irradiation solaire de 4% ou environ 7W\/m_ entre 1961 et 1990 observ\u00e9e dans des stations m\u00e9t\u00e9orologiques autour du monde. Nous disions alors qu’il y avait des indices de reprise en cours apr\u00e8s 1990. Des recherches qui le montrent ont maintenant \u00e9t\u00e9 publi\u00e9e. De l’assombrissement \u00e0 l’\u00e9claircissement: changements d\u00e9cennaux de l’irradiation solaire \u00e0 la surface de la Terre (From Dimming to Brightening: Decadal Changes in Solar Radiation at Earth’s Surface<\/a>) de Martin Wild et al. (Science 6 Mai 2005; 308: 847-850; abonnement n\u00e9cessaire pour lire l’article) utilise des mesures faites en surface; Les satellittes d\u00e9tectent-ils des tendances dans l’irradiation solaire ai niveau de la surface? (Do Satellites Detect Trends in Surface Solar Radiation?<\/a>) de Pinker et al., Science 2005 308: 850-854, utilise des satellites. Les deux \u00e9tudes identifient une reprise de l’irradiation solaire de la surface depuis environ 1990.<\/p>\n

(suite…)<\/a><\/lang_fr>
\n<\/p>\n

Wild et al. use high-quality surface observations primarily from Europe, North America, China, Australia, Japan and Antarctica but also some from Africa and India. The densest network of observations is over Europe: binning the observations into equal-area cells, and considering the two periods 1950-1990 and 1985-2000, they find 24 showing decreases and 8 increases for the earlier period. For the latter, this reverses with 26 showing increase and 6 decrease (and none of those 6 are statistically significant). Around the world (although there are large gaps in the network) a similar pattern of recent increase is seen. Evidence for continued dimming seems to be restricted to India and Zimbabwe. The average increase, estimated from the 8 most accurate stations, was 0.66 W\/m2\/year.<\/p>\n

Pinker et al. derive surface downward shortwave radiation from satellite measurements since 1983. There must be some slight cautions about the quality of the satellite data, and Pinker et al. devote considerable space to an analysis of why they think their data can be trusted. For their period, they find a (significant) global linear trend of 0.16 W\/m2\/year, which is about 0.1%\/year. Fitting a second-order polynomial to the same data shows a small decreasing trend to about 1992, with increases since then. Since they have global data, they can split it into land and ocean, and do: finding an insignificant negative trend over land and a significant positive trend, 0.24 W\/m2\/year, over the oceans. The Wild et al. paper discussed first used land stations only, of course. The Wild trends are larger, but comparing 8 land points to global data is difficult.<\/p>\n

So what does this all mean? The “dimming” may have lead to a slight negative radiative forcing, somewhat masking the global warming signal; the reversal, Wild et al. suggest, may have removed this masking effect and lead to the signal being more obvious in the 1990s. Aerosol emissions have decreased, particularly in Europe and the US over the 1990s, largely due to clean air legislation. Thus relative to the 1980s there was probably an additional positive forcing from the aerosol decrease. However, as before<\/a> we cautioned against over-interpreting the importance of the dimming, we offer similar cautions for the brightening.<\/p>\n


\nWild et al. utilisent des observations de haute qualit\u00e9 faites en surface, qui viennent principalement d’Europe, d’Am\u00e9rique du Nord, de Chine, d’Australie, du Japon et de l’Antarctique, et quelques-unes proviennent aussi d’Afrique et d’Inde. Le r\u00e9seau d’observation le plus dense est en Europe: en regroupant les observations dans des cellules de m\u00eame surface, et en consid\u00e9rant les p\u00e9riodes 1950-1990 et 1985-2000, ils en trouvent 24 qui montrent une diminution et 8 une augmentation sur la premi\u00e8re p\u00e9riode. Pour la seconde p\u00e9riode, ceci s’inverse avec 26 zones montrant une augmentation et 6 une diminution (et aucune de ces 6 n’est statistiquement significative). Dans le monde (bien qu’il y ait de grands trous dans le r\u00e9seau), un comportement similaire d’augmentation r\u00e9cente est observ\u00e9. Les preuves d’une continuation de l’ assombrissement sont restreintes \u00e0 l’Inde et au Zimbabwe. L’augmentation moyenne, estim\u00e9e sur les 8 stations les plus pr\u00e9cises, \u00e9tait de 0,66 W\/m2\/an. <\/p>\n

Pinker et al. d\u00e9rivent des flux descendants de radiations \u00e0 onde courte des mesures prises par satellite depuis 1983. Il faut faire une l\u00e9g\u00e8re mise en garde \u00e0 propos de l’utilisation de donn\u00e9es de satellites, et Pinker et al. consacre un espace consid\u00e9rable \u00e0 une analyse des raisons pour lesquelles ils pensent qu’on peut se fier \u00e0 leurs donn\u00e9es. Pour leur p\u00e9riode, ils trouvent une tendance globale lin\u00e9aire (significative) de 0,16 W\/m_\/an, soit environ 0,1% par an. L’ajustement d’un polyn\u00f4me du second degr\u00e9 \u00e0 ces m\u00eames donn\u00e9es montre une faible tendance \u00e0 la baisse jusqu’\u00e0 environ 1992 et une augmentation depuis lors. Leurs donn\u00e9es \u00e9tant globale, ils peuvent les diviser entre terres et oc\u00e9ans, ce qu’ils font. Il trouvent une tendance n\u00e9gative non-significative sur les terres et une tendance positive significative sur les oc\u00e9ans, de 0,24 W\/m_\/an. L’article de Wild et al. utilisait uniquement des donn\u00e9es de stations terrestres, \u00e9videmment. Les tendances trouv\u00e9es par Wild et al. sont plus fortes, mais il est difficile de comparer 8 point terrestres \u00e0 des donn\u00e9es globales.
\nQue veut donc dire tout ceci? L’assombrissement peut avoir caus\u00e9 un l\u00e9ger for\u00e7age radiatif n\u00e9gatif, masquant quelque peu le signal du r\u00e9chauffement global. L’inversion de ce for\u00e7age, sugg\u00e8rent Wild et al., peut avoir supprim\u00e9 cet effet de masque et avoir rendu ce signal plus \u00e9vident dans les ann\u00e9es 1990. Les \u00e9missions d’a\u00e9rosols ont diminu\u00e9, particuli\u00e8rement en Europe et aux USA pendant les ann\u00e9es 1990, principalement \u00e0 cause des l\u00e9gislations anti-pollution. Relativement aux ann\u00e9es 1980, il y avait donc probablement un for\u00e7age positif additionnel provenant de la diminution des a\u00e9rosols. Toutefois, comme pr\u00e9c\u00e9demment<\/a> nous mettions en garde contre une trop grande importance que l’on donnerait \u00e0 l’assombrissement, nous faisons la m\u00eame mise en garde \u00e0 propos de l’\u00e9claircissement.<\/p>\n

traduit de l’anglais par A. Henry<\/small>
\n<\/lang_fr><\/p>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

A while ago, we wrote about Global Dimming – a reduction in downward solar radiation of about 4% or about 7W\/m2 from 1961 to 1990 was found at stations worldwide. We said at the time that there were hints of a recovery underway post-1990; now research has been published showing this. From Dimming to Brightening: […]<\/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":[17,1],"tags":[],"class_list":{"0":"post-154","1":"post","2":"type-post","3":"status-publish","4":"format-standard","6":"category-aerosols","7":"category-climate-science","8":"entry"},"aioseo_notices":[],"post_mailing_queue_ids":[],"_links":{"self":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts\/154","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=154"}],"version-history":[{"count":0,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts\/154\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/media?parent=154"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/categories?post=154"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/tags?post=154"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}