This study investigates the variations of the cyclonic activity in the Mediterranean region that would be produced by doubling the CO 2 atmospheric content. The analysis is based on the SLP (sea-level pressure) fields produced by two 30 yr long time slice experiments of the ECHAM-4 model at T106 resolution, carried out by DMI, simulating the present and doubled CO 2 scenarios. The cyclonic activity in the Mediterranean region is similar in the 2 climate scenarios. The present climate is characterized with a slightly, but statistically significant, higher overall number of cyclones. The doubled CO 2 simulation is characterized with more extreme weather events, but the difference between the 2 scenarios is hardly significant. No variation in the regions of formation of the cyclones was clearly identified. An, admittedly small, number of cyclones of both scenarios was simulated using a limited area model (LAM) with 0.25°resolution. These simulations do not suggest that an increased model resolution should add new major findings to the results of this study, but the possibility that a climate change signal is not evident because of the coarse T106 model resolution remains open for further investigations. However, this study does not show a large change in the regime of the cyclones in the Mediterranean region due to the atmospheric CO 2 doubling. KEY WORDS: Cyclones · Regional scenarios · Climate change · CO 2 doubling · Mediterranean region · Extreme eventsResale or republication not permitted without written consent of the publisher Clim Res 22: 147-159, 2002 atmosphere general circulation model has shown a decreased total number of storms in the northern hemisphere and a tendency towards deeper low centers (Carnell & Senior 1998). These changes were, however, not generally statistically significant. A different analysis, based on the identification of cyclonic vorticity centers and applied to the results of a different model (the CSIRO9 general circulation model, including a slab ocean with prescribed heat fluxes), has shown a decrease of 10 to 15% in cyclonic activity (Sinclair & Watterson 1999). The changes in the cyclonic activity over the North Atlantic and Europe have been evaluated using a 240 yr long run of the ECHAM/OPYC3 coupled ocean-atmosphere general circulation model with transient greenhouse forcing (Knippertz et al. 2000). The analysis has shown a north-eastward shift of the cyclone activity accompanied by a decrease in the number of cyclones and an increase in deep cyclones. Therefore, these studies agree that there is reduced cyclonic activity in a doubled CO 2 climate. Marginally lower values of the pressure minima in the cyclone centers have also been suggested, but it has been pointed out that this result might be produced by a decreased mean SLP (sealevel pressure) and is not a necessary indication of more intense cyclones (Sinclair & Watterson 1999). All these analysis were carried out with coarse resolution datasets: 2.5°latitude × 3.25°longitude for the Hadley Centre model; 3....

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This study attempts to estimate the effect of CO 2 doubling on the frequency and intensity of high wind waves and storm-surge events in the Adriatic Sea. The meteorological forcings were derived from two 30-yr-long time-slice experiments that simulated the global atmospheric circulation in the present and the doubled-CO 2 climate scenarios. These time-slice experiments were carried out by the Danish Meteorological Institute using the ECHAM-4 model at T106 resolution. Unfortunately, the resolution of the T106 wind is inadequate for simulation of the wave field and the storm surge in the Adriatic Sea, and it results in a gross underevaluation of extreme events. In this study, regional surface wind fields have been derived from T106 sea-level-pressure fields by statistical downscaling. Downscaled wind fields have been used to force a wave and an ocean model during the two 30-yrlong simulations. The downscaled wind fields produce a large improvement with respect to the T106 fields, but a systematic underestimation with respect to the observed wave height and surge levels remains present. This shortcoming of the analysis might prevent identification of very intense events. Consequently, extreme-value analysis of the results of the present climate simulation produces values lower than observed, and obviously the same systematic bias is expected in the evaluation of the future climate. Some caution is therefore necessary in the interpretation of the results of this study. Nonetheless, the comparison between the present and future climate simulations shows no substantial change in the extreme surge level and a decrease in the extreme wave height.KEY WORDS: Regional climate scenarios · Storm surges · Wave height · Extremes · CO 2 doublingResale or republication not permitted without written consent of the publisher