Bruegel : The Harvesters (1565) Mechanisms for European summer temperature response to solar forcing over the last millennium Swingedouw D., Terray L., Servonnat J., Guiot J.

Background IPCC 2007: large increase in temp. and drought in the Med. region, while increase in precip. in Northern Europe « Transition zone » governed by evapotranspiration (Boé and Terray 2008) Evapotranspiration was also playing a crucial role in 2003 heat wave (Fischer et a. 2007) Transition Transition zone zone IPCC 2007, Chap. 11, Fig. 2

Last millennium: a case-test for European summer response to radiative changes? A recent reconstruction now available (Guiot et al. 2010) goes back to 600 Use lots of pollen data which allow a better representation of low frequency Use of this dataset to test a climate model response to solar forcing

Influence du forçage solaire et volcanique Climate simulation with complex land-surface scheme: CNRM-CM3 using SECHIBA (Swingedouw et al. 2011) Solar, GHG and volcanic forcings Last millennium simulation

Solar forcing fingerprints Low but significant correlation with solar forcing both in data and model Summer European temperature Regression over solar variations : 90% : 95% : 99%

Solar forcing impact in the model Schar et al. 1999

Large-scale response Sea ice is responding to solar changes by decreasing its cover in the Nordic Seas The large-scale atmospheric circulation does not exhibit significant changes over the North Atlantic sector in summer

Surface radiative changes in the model

Evapotranspiration driver Evapotranspiration over Central Europe is highly correlated in summer with water content in the soil It is therefore the loading in water of the soil in winter that is mainly driving changes in evapotranspiration Indeed winter precipitation slighty increases with solar forcing due to Clausius-Clapeyron relationship (not shown) (Alkama et al. 2010)

Summary of the mechanism Loading of soil water reservoir in winter Evapotranspiration increases in summer More evaporation in the tropics Mettre un nuage avec pluie pour hiver Utiliser tableau Bruegel pour illustrer hiver et ete…

Summary of the mechanism 55°N 25°N 75°N

Summary of the mechanism 55°N 25°N 75°N Temperature

Conclusions Solar forcing over last millennium has small but significant inprints over Europe in summer with similar latitudinal pattern in reconstruction and model Long time scales useful to increase signal to noise ratio Evapotranspiration responds strongly to solar forcing in Central Europe and damps temperature signal through cloud feedback Sea-ice also responds strongly and enhances solar forcing signal in Northern Europe Too large amplitude of TSI variations in CNRM-CM3 simulation?

Thank you! Swingedouw D., Terray L., Servonnat J., Guiot J. Mechanisms for European summer temperature response to solar forcing over the last millennium. Climate of the past 8, , 2012

TSI Winter precipitation Early spring soil moisture Summer Evapotranspiration Convective clouds Surface SW Surface temperature Convective precipitation Non convective precipitation Soil moisture Schär et al. (1999) positive feedback loop Mechanisms to explain Central Europe response to solar forcing