Present-day climatology and projected changes of warm and cold days in the CNRM-CM3 global climate model.

J. Ballester (1) , H. Douville (2) , F. Chauvin (2)

1 Climate Research Laboratory (LRC)
2 CNRM - Centre national de recherches météorologiques

The impact of global warming on the warmest and coldest days of the annual cycle is explored according to an A2 scenario simulated by the CNRM-CM3 climate model in the framework of the IPCC AR4 intercomparison. Given the multi-model spread in IPCC projections, a validation strategy is proposed using the NCEP/NCAR reanalysis. Validation of the late twentieth century model climatology shows that warm and cold model events are slightly too long and infrequent. Although interannual trends in the warm (cold) day occurrence were positive (negative) only for six (three) of the nine considered sub-continental regions, simulated model trends are always positive (negative). This different behaviour suggests that simulated non-anthropogenic decadal variability is small relative to anthropogenic trends. Large-scale synoptic processes associated with European regional warm and cold peaks are also described and validated. Regional cold peaks are better reproduced than warm peaks, whose intensity accuracy is limited by other physical variables. Positive (negative) winter anomalies of sea and land surface temperature lead to summers with severe (weak) temperatures. These inter-annual anomalies are generated by a persistent pressure dipole over Europe. Regarding climate change, warm (cold) events will become more (less) frequent and longer (shorter). The number of warm days will largely rise and the number of cold days will dramatically decrease. The intensity of warm days will be particularly pronounced over Europe, given the projected summer drying in this region. However, according to the limited skill of the CNRM model, these results must be considered with caution

Mots clés: Global warming; IPCC-AR4; Warm and cold day; Regional temperature peak; Model validation Réchauffement climatique; Températures extrêmes; Jours chauds et jours froids; Pics de températures par région; Variabilité décadaire; Variabilité inter-anuelle; Tendances; Validation de modèles de climat; Inter-comparaison de modèles

Domaines: Physique Atmosphérique et Océanique [physics.ao-ph]; Météorologie

J. Ballester, H. Douville, F. Chauvin. Present-day climatology and projected changes of warm and cold days in the CNRM-CM3 global climate model.. Climate Dynamics, 2008, 32, pp.PP. 35-54. ⟨10.1007/s00382-008-0371-0⟩. ⟨meteo-00345208⟩