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It is generally accepted that volcanic eruptions may have a climatic impact involving overall cooling of the troposphere, as the sulfur injected into the stratosphere is transformed into sulfate. However, it is intrinsically difficulty to distinguish this impact because of natural climate variability. In this paper, we look for a relationship between sulfate in the Northern Hemisphere (NH) and European temperature during the last 500 years using two independent data sets: stratospheric sulfate retrieved from ice cores and European seasonally and annually averaged temperature. Relationships between temperature and sulfate are obtained as a function of the season (summer and winter) and location (tropics vs extra‐tropics) one and two years after the sulfate record year. After one year, we always find a negative correlation in the winter for both tropical and extra‐tropical eruptions. A correlation value of ‐0.56 is obtained for the relationship between sulfate and annually averaged temperature anomalies after one year, and a linear regression predicts a cooling of 1 °C for an eruption of 100 Tg of sul‐ fate, an amount similar to that estimated to have been emitted by the Laki eruption in 1783.The variability of the cooling effect after one year is evaluated by introducing a multiplicative error model for sulfate that accounts for sys‐ tematic as well as random errors in retrieved sulfate. To evaluate the impact of sulfate uncertainties on the regression slope, a resampling approach with 104 simulations is applied. Results indicate that when uncertainties in sulfate are introduced, the variability of cooling is in the order of several 10‐3 °C/Tg. Temperature anomaly uncertainties impact slope uncertainty but have little influence on slope variability.

This article investigates the role of sea surface temperature (SST) as well as the effects of evaporation and moisture convergence on the evolution of cyclone Klaus, which occurred on January 23 and 24, 2009. To elucidate the role of sea surface temperature (SST) and air–sea fluxes in the dynamics of the cyclone, ten hydrostatic mesoscale simulations were performed by Bologna Limited Area Model (BOLAM). The first one was a control experiment with European Centre for Medium-Range Weather Forecasts (ECMWF) SST analysis. The nine following simulations are sensitivity experiments where the SST are obtained by adding a constant value by 1 to 9 K to the ECMWF field. Results show that a warmer sea increases the surface latent heat fluxes and the moisture convergence, favoring the development of convection in the storm. Convection is affected immediately by the increased SST. Later on, drop of mean sea level pressure (MSLP) occurs together with increasing of surface winds. The cyclone trajectory is not sensitive to change in SST differently from MSLP and convective precipitation.