{"id":3,"date":"2004-12-01T18:59:46","date_gmt":"2004-12-01T22:59:46","guid":{"rendered":"\/?p=3"},"modified":"2007-08-01T23:14:46","modified_gmt":"2007-08-02T04:14:46","slug":"scenarios","status":"publish","type":"post","link":"https:\/\/www.realclimate.org\/index.php\/archives\/2004\/12\/scenarios\/","title":{"rendered":"Climate model scenarios Les sc\u00e9narios des mod\u00e8les climatiques<\/lang_fr>"},"content":{"rendered":"
\n

A couple of commentators (Pat Michaels<\/a>, Roy Spencer<\/a>) recently raised an issue about the standard scenarios used to compare climate models, in this case related to a study on the potential increase in hurricane activity.<\/p>\n

The biggest uncertainty in what will happen to climate in the future (say 30 years or more) is the course that the global economy will take and the changes in technology that may accompany that. Since climate scientists certainly don’t have a crystal ball, we generally take a range of scenarios or projections of future emissions of CO2 <\/sub> and other important forcings<\/a> such as methane and aerosols.
\nQuelques commentateurs (Pat Michaels<\/a>, Roy Spencer<\/a>) ont r\u00e9cemment relanc\u00e9 une question au sujet des sc\u00e9narios standard utilis\u00e9s pour comparer les mod\u00e8les climatiques, dans ce cas reli\u00e9 \u00e0 une \u00e9tude sur l’augmentation potentielle de l’activit\u00e9 des ouragans.
\nLa plus grande incertitude dans ce qui va se passer pour le climat du futur (dans 30 ans ou plus) est le cours que va suivre l’\u00e9conomie globale et les changements technologiques qui peuvent l’accompagner. Puisque les climatologues n’ont certainement pas une boule de cristal, nous consid\u00e9rons g\u00e9n\u00e9ralement une gamme de sc\u00e9narios ou de projections des \u00e9missions futures de CO 2 <\/sub> et d’autres for\u00e7ages<\/a> importants comme le m\u00e9thane et les a\u00e9rosols. <\/lang_fr><\/p>\n

<\/p>\n

For each scenario, the models will project a course of climate change. Of course, this is not a prediction – climate change in the real world will depend on which of the scenarios turns out to be more accurate. However, there are a number of scenarios that have become de-facto standards – not because they are more likely than others, but due to historical reasons. i.e. they are simple, and there is substantial exisiting work that you can compare the results to. <\/p>\n

The most common de-facto standard is the equilibrium doubled CO 2 <\/sub> run. i.e. you just double the amount of CO2 <\/sub> in the model and you see what happens. Only slightly more realistic is the 1% increasing equivalent CO2 <\/sub> case. i.e. every year the amount of CO2 <\/sub> increases by 1% for 100 years. By the time you get to about 2080, CO2 <\/sub> has doubled. Even if we take account of methane, N2 <\/sub>O and CFC contributions, this too is an unlikely scenario. The maximum growth rate occured in the 1980’s (due to the rapid growth of CFCs) and was equivalent to about 0.7% increase per year. Currently, the forcing is around 0.6% increase of equivalent CO2 <\/sub> per year. Does this mattter? In most cases, the answer is no. <\/p>\n

Both these simple scenarios are used mainly to be able to characterise the behaviour of different models. The existence of a ‘date’ attached to the results is really rather misleading. The models are not going to be able to tell you what will happen in 2080, but more what may happen at the time of doubling of CO2 <\/sub>, whenever that may be<\/em>. It turns out the much of the climate is only weakly dependent on the rate of change of the greenhouse gases (though there are some important exceptions). So the result at the time of doubling doesn’t much matter whether it takes 70 or 100 years to get there. <\/p>\n

More complex scenarions that also include aerosol and other GHG changes have been developed by the IPCC. Models are using these (which range from no further change in greenhouse gases to a ‘Business as usual’ continuation of the past increases) to run simulations for the next IPCC report due 2007. In the meantime, the simple standards can continue to tell us a lot about the models, and hopefully, the real world.<\/p>\n


\nPour chaque sc\u00e9nario, les mod\u00e8les vont concevoir un d\u00e9roulement du changement climatique. Bien s\u00fbr, ce n’est pas une pr\u00e9diction – le changement climatique dans le monde r\u00e9el d\u00e9pendra de quel sc\u00e9nario se r\u00e9v\u00e8lera le plus fid\u00e8le. Cependant, il y a plusieurs sc\u00e9narios qui sont devenus, de fait, des r\u00e9f\u00e9rences – pas parce qu’ils sont plus probables que les autres, mais \u00e0 cause de raisons historiques. i.e. ils sont simples, et il y a un travail substantiel existant auquel on peut comparer les r\u00e9sultats.<\/p>\n

La r\u00e9f\u00e9rence de facto la plus commune est un doublement du CO 2 <\/sub> \u00e0 l’\u00e9quilibre, i.e. vous doublez juste la quantit\u00e9 de CO 2 <\/sub> dans le mod\u00e8le et vous regardez ce qui se passe. Un mod\u00e8le un peu plus r\u00e9aliste est le cas d’une augmentation de 1% d’\u00e9quivalent CO 2 <\/sub>, i.e. chaque ann\u00e9e la quantit\u00e9 de CO 2 <\/sub> augmente de 1% pour 100 ans. Quand vous atteignez environ l’ann\u00e9e 2080, le CO 2 <\/sub> a doubl\u00e9. M\u00eame si vous prenez en compte des contributions du m\u00e9thane, de N2 <\/sub>O et des CFC, c’est aussi un sc\u00e9nario peu probable. Le taux de croissance maximum a eu lieu dans les ann\u00e9es 80 (\u00e0 cause de l’augmentation rapide des CFC) et \u00e9tait \u00e9quivalent \u00e0 environ 0,7 % d’augmentation par an. Couramment, le for\u00e7age est d’environ 0,6 % d’augmentation en \u00e9quivalent CO 2 <\/sub> par an. Est-ce que cela importe ? Dans la plupart des cas, la r\u00e9ponse est non.<\/p>\n

Ces deux sc\u00e9narios simples sont utilis\u00e9s principalement car ils sont capables de caract\u00e9riser le comportement de diff\u00e9rents mod\u00e8les. L’existence d’une “date” attach\u00e9e aux r\u00e9sultats est vraiment assez trompeuse. Les mod\u00e8les ne vont pas \u00eatre capables de dire ce qui se passera en 2080, mais plus ce qui pourrait se passer \u00e0 l’\u00e9poque o\u00f9 le CO 2 <\/sub> doublera, quelque soit l’\u00e9poque o\u00f9 \u00e7a se passera. Il en ressort qu’une grande partie du climat est faiblement d\u00e9pendante du taux de changement des gaz \u00e0 effet de serre (bien qu’il y ait des exceptions importantes). Ainsi le r\u00e9sultat du doublement ne s’occupe pas si cela prend 70 ou 100 ans pour y arriver.<\/p>\n

Des sc\u00e9narios plus complexes qui incluent aussi des changements dans les a\u00e9rosols et d’autres gaz \u00e0 effet de serre ont \u00e9t\u00e9 d\u00e9velopp\u00e9s par l’IPCC. Ces mod\u00e8les utilisent ces changements (avec des gammes allant de plus aucun changement dans les gaz \u00e0 effet de serre \u00e0 une prolongation des augmentations pass\u00e9es) pour faire des simulations pour le prochain rapport de l’IPCC en 2007. Pendant ce temps, les standards simples peuvent continuer \u00e0 nous dire beaucoup de choses sur les mod\u00e8les et, avec un peu de chance, sur le monde r\u00e9el.<\/p>\n

(traduit de l’anglais par C. Rollion-Bard)<\/small>
\n<\/lang_fr><\/p>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

A couple of commentators (Pat Michaels, Roy Spencer) recently raised an issue about the standard scenarios used to compare climate models, in this case related to a study on the potential increase in hurricane activity. The biggest uncertainty in what will happen to climate in the future (say 30 years or more) is the course […]<\/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":[5,1,3,23],"tags":[],"class_list":{"0":"post-3","1":"post","2":"type-post","3":"status-publish","4":"format-standard","6":"category-climate-modelling","7":"category-climate-science","8":"category-greenhouse-gases","9":"category-ipcc","10":"entry"},"aioseo_notices":[],"post_mailing_queue_ids":[],"_links":{"self":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts\/3","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=3"}],"version-history":[{"count":0,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/posts\/3\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/media?parent=3"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/categories?post=3"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.realclimate.org\/index.php\/wp-json\/wp\/v2\/tags?post=3"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}