| ABSTRACT | Climate fluctuations are the end result of a number of processes acting on a multitude of timescales. For a long time, century-scale climate change simulations initialized from arbitrary model states and forced with prescribed anthropogenic and natural forcings have been the only available product to inform decision-makers on future climate-related risks. A major limitation of non-initialized climate projections is their lack of information regarding the current state of the Earth’s climate system. Decadal climate predictions, obtained by constraining the initial conditions of an ensemble of model simulations through a best estimate of the observed climate state, provide an accurate assessment of climate fluctuations in the near-term range (typically up to 10 years) and a useful tool to inform decision makers on future climate-related risks. First, we present results from the CMIP6 DCPP-A decadal hindcasts produced with the operational CMCC decadal prediction system (CMCC DPS), based on the fully-coupled CMCC-CM2-SR5 dynamical model. A 20-member suite of 10-year retrospective forecasts, initialized every year from 1960 to 2020, is performed using a full-field initialization strategy. The predictive skill for key quantities is assessed and compared with that of an ensemble of non-initialized historical simulations, so as to assess the added value of initialization. In particular, the CMCC DPS is capable to skilfully reproduce past-climate surface temperature fluctuations, while, in terms of precipitation, decadal predictability is bounded to a few specific regions, significantly improving predictions over central Europe and the Iberian peninsula. Second, we assess the predicted near-term climate of the Mediterranean region, one of the most sensitive to climate change. This region has undergone an intense warming and drying trend during the last decades, dominantly caused by the increase of anthropogenic greenhouse gasses. Using the aforementioned CMCC DPS and the respective ensemble of non-initialized projections, we evaluate future climate changes focusing on both the annual mean and seasonal responses. Beyond the contribution of external forcings, the role of internal variability is also investigated since part of the detected predictability arises from internal climate variability patterns affecting the Mediterranean. |