Titre :	Changes of temperature and hydrology caused by an increase of atmospheric carbon dioxide as predicted by general circulation models
Type de document :	texte imprimé
Auteurs :	Richard T. Wetherald, Auteur
Editeur :	Chapman and Hall
Année de publication :	1991
Importance :	p 1-17
Langues :	Anglais (eng)
Catégories :	SCIENCES DE L'ENVIRONNEMENT
Mots-clés :	CHANGEMENT DE TEMPERATURE  DIOXIDE DE CARBONE  MECANISME ATMOSPHERIQUE  EFFET DE SERRE  GENERAL CIRCULATION MODELS (GCM)
Résumé :	Although there are many areas of disagreement between the various models, it’s worthwhile to highlight the areas of agreement. With regard to temperature, the state-of-the-art GCMs reveal that (1) an increase of global surface temperature due to CO² doubling lies in the range 3.5-5.2°C , (2) over the central United States, the average surface temperature increase ranges from 4 to 6°C during the December-February period and from 3 to 6°C for the June-August period and (3) for all models, the increase of surface temperature is greater in higher latitudes than it is in the tropics. This polar amplification is greatest during the winter and early spring seasons due to the snow/sea ice over albedo process, which opeartes mainly at these times. With regard to hydrology, the latest GCMs reveal that continental snow cover in mid latitudes is less extensive and shallover depth for the higher CO² experiment. This implies that the snow cover there will appear later in fall and disappear earlier in spring and result in less spring runoff from snowmelt (although there will be greater runoff in the form of rainfall). Also the soil surface is exposed earlier in the winter season and therefore, higher rates of evaporation will occur from it which will cause greater soil moisture loss from spring to summer. One of the largest uncertainties in climate-sensitivity studies is the CO² -induced response of precipitation over the continents during the summer season. Whether or not a given GCM will produce a summer dryness scenario appears to be dependent on a poleward shift of the mid latitude storm track (and accompanying rainbelt) and the state of the soil moisture of the standard experiment for both early spring and summer. In the final analysis, a given GCM will produce a tendency for dryer summertime conditions if the projected rainfall is forecast to either decrease or remain the same. Only if the rainfall is forecast to increase at least as much as the projected increase of evaporation will the desication of soil moisture be prevented. Other uncertainties include modeling of cloud processes, active ocean currents and the use of low horizontal resolution. The explicit inclusion of ocean currents can alter the transient or time-dependent phase of a climate sensitivity experiment. Until recently, the use of large grid boxes has hampered the successful simulation of climate, especially on a regional scale. However, the advent of larger and faster supercomputers is making it possible for modelers to rerun their experiments with a higher computational resolution.
Numéro du document :	A/MAC
Niveau Bibliographique :	2
Bull1 (Theme principale) :	METEOROLOGIE ,ATMOSPHERE,CLIMATOLOGIE
Bull2 (Theme secondaire) :	ATMOSPHERE,CLIMATOLOGIE-CONSIDERATION GENERALE

Changes of temperature and hydrology caused by an increase of atmospheric carbon dioxide as predicted by general circulation models [texte imprimé] / Richard T. Wetherald, Auteur . - Chapman and Hall, 1991 . - p 1-17.
Langues : Anglais (eng)

Catégories :	SCIENCES DE L'ENVIRONNEMENT
Mots-clés :	CHANGEMENT DE TEMPERATURE  DIOXIDE DE CARBONE  MECANISME ATMOSPHERIQUE  EFFET DE SERRE  GENERAL CIRCULATION MODELS (GCM)
Résumé :	Although there are many areas of disagreement between the various models, it’s worthwhile to highlight the areas of agreement. With regard to temperature, the state-of-the-art GCMs reveal that (1) an increase of global surface temperature due to CO² doubling lies in the range 3.5-5.2°C , (2) over the central United States, the average surface temperature increase ranges from 4 to 6°C during the December-February period and from 3 to 6°C for the June-August period and (3) for all models, the increase of surface temperature is greater in higher latitudes than it is in the tropics. This polar amplification is greatest during the winter and early spring seasons due to the snow/sea ice over albedo process, which opeartes mainly at these times. With regard to hydrology, the latest GCMs reveal that continental snow cover in mid latitudes is less extensive and shallover depth for the higher CO² experiment. This implies that the snow cover there will appear later in fall and disappear earlier in spring and result in less spring runoff from snowmelt (although there will be greater runoff in the form of rainfall). Also the soil surface is exposed earlier in the winter season and therefore, higher rates of evaporation will occur from it which will cause greater soil moisture loss from spring to summer. One of the largest uncertainties in climate-sensitivity studies is the CO² -induced response of precipitation over the continents during the summer season. Whether or not a given GCM will produce a summer dryness scenario appears to be dependent on a poleward shift of the mid latitude storm track (and accompanying rainbelt) and the state of the soil moisture of the standard experiment for both early spring and summer. In the final analysis, a given GCM will produce a tendency for dryer summertime conditions if the projected rainfall is forecast to either decrease or remain the same. Only if the rainfall is forecast to increase at least as much as the projected increase of evaporation will the desication of soil moisture be prevented. Other uncertainties include modeling of cloud processes, active ocean currents and the use of low horizontal resolution. The explicit inclusion of ocean currents can alter the transient or time-dependent phase of a climate sensitivity experiment. Until recently, the use of large grid boxes has hampered the successful simulation of climate, especially on a regional scale. However, the advent of larger and faster supercomputers is making it possible for modelers to rerun their experiments with a higher computational resolution.
Numéro du document :	A/MAC
Niveau Bibliographique :	2
Bull1 (Theme principale) :	METEOROLOGIE ,ATMOSPHERE,CLIMATOLOGIE
Bull2 (Theme secondaire) :	ATMOSPHERE,CLIMATOLOGIE-CONSIDERATION GENERALE