Extrêmes de température en Europe : mécanismes et réponses au changement climatique.

Europe witnessed a spate of record-breaking warm seasons during the 2000s, inducing particularly strong societal and environmental impacts. This thesis aims to contribute to the understanding of physical mechanisms responsible for such extremes, in order to anticipate their responses to future climate change. Involved processes are assessed by both statistical data-analysis of observations and climate projections and regional modeling experiments. First we show that while the inter-annual European temperature variability appears driven by disturbances in the North-Atlantic dynamics, the recent warming is likely to be dissociated with potential circulation changes. This inconsistency climaxes during the exceptionally mild autumn of 2006. Recent warm surface conditions in the North-Atlantic ocean seem to substantially contribute to the European warming in autumn--winter, while more local processes appear predominant in spring--summer (e.g., influence of soil moisture). Then multi-model analysis, based on climate projections of the International Panel on Climate Change, show that the inconsistency noticed over recent decades is likely to continue in future years. In particular, it appears that climate change does not affect the internal variability of the North-Atlantic dynamics in a significant manner. Thus future temperature extremes should be associated with circulations similar to those observed during recent episodes. In this context the European winter of 2009/10 can be considered as a cold extreme in a warming climate.Le climat des années 2000 a été marqué en Europe par une vague d'épisodes chauds battant tous les précédents records saisonniers de température et s'accompagnant d'impacts sociétaux et environnementaux particulièrement sévères. Cette thèse se propose de contribuer à la compréhension des mécanismes physiques responsables de tels extrêmes, dans le but d'anticiper leurs réponses au changement climatique futur. Ce travail mêle ainsi analyses statistiques de données d'observations et de projections climatiques, et expériences de modélisation régionale. Nous montrons dans un premier temps que si la variabilité inter-annuelle du climat européen est pilotée par les fluctuations de la dynamique atmosphérique nord-atlantique, le récent réchauffement apparaît dissocié de potentiels changements dans la circulation. Cette divergence s'illustre particulièrement lors de l'automne exceptionnellement doux de 2006. Les récentes conditions chaudes en surface de l'océan Atlantique nord semblent contribuer au réchauffement européen en automne--hiver, tandis que des processus amplificateurs plus locaux apparaissent au printemps--été (e.g., influence de l'humidité des sols). La seconde partie de notre travail, basée sur les projections climatiques de l'International Panel on Climate Change, montre que la divergence constatée sur la période présente semble se poursuivre dans les projections futures. En particulier la variabilité interne de la dynamique nord-atlantique n'apparaît que peu affectée par le changement climatique. Les futurs extrêmes de température seraient alors associés à des circulations similaires aux circulations observées lors des extrêmes récents. Dans ce cadre, l'hiver européen de 2009/10 fournit une illustration d'un événement extrême froid dans un climat déjà plus chaud

Defining Single Extreme Weather Events in a Climate Perspective

International audienc

Opposite CMIP3/CMIP5 trends in the wintertime Northern Annular Mode explained by combined local sea ice and remote tropical influences

International audienc

U.S. heat waves of spring and summer 2012 from the flow-analogue perspective

International audienc

Contribution of atmospheric circulation to wet Southern European winter of 2013

International audienceWinter 2013 was the second wettest since 1948 in southern Europe. This is partially explained by the atmospheric circulation. We suspect the warm Atlantic Ocean to have amplified the precipitation extreme

North-Atlantic SST amplified recent wintertime European land temperature extremes and trends

International audienc

Dynamics of future seasonal temperature trends and extremes in Europe: a multi-model analysis from CMIP3

International audienc

Searching for the most extreme temperature events in recent history

International audienceBecause they are rare, extreme weather events have critical impacts on societies and ecosystems and attract public and scientific attention. The most unusual events are regularly documented as part of routine climate monitoring by meteorological services. A growing number of attribution studies also aim at quantifying how their probability has evolved under human induced climate change. However, it is often recognized that (i) the selection of studied events is geographically uneven, and (ii) the definition of a given event, in particular its spatio-temporal scale, is subjective, which may impact attribution statements. Here we present an original method that objectively selects, defines, and compares extreme events that have occurred worldwide in the recent years. Building on previous work, the event definition consists of automatically selecting the spatio-temporal scale that maximizes the event rarity, accounting for the non-stationary context of climate change. We then explore all years, seasons, and regions and search for the most extreme events. We demonstrate how our searching procedure can be both useful for climate monitoring over a given territory, and resolve the geographical selection bias of attribution studies. Ultimately, we provide a selection of the most exceptional hot and cold events in the recent past, among which are iconic heatwaves such as those seen in 2021 in Canada or 2003 in Europe

Evaluation and response of winter cold spells over Western Europe in CMIP5 models

International audienc