Search

Changes in Mediterranean circulation patterns due to global warming may have strong socio‐economic and environmental impacts. We analyze the future evolution of the Mediterranean surface circulation under different levels of global warming by using 28 multi‐decadal simulations from a set of fully coupled and high‐resolution regional climate models of the Med‐CORDEX multi‐model initiative. There is no model agreement for a significant basin‐scale modification of the surface circulation. However significant and robust local circulation changes are identified. In particular, the circulation is expected to shift from cyclonic to predominantly anticyclonic in the northern Balearic, while a strengthening of the cyclonic circulation is expected in the southern Adriatic. Furthermore, our results show an increase in the Mediterranean circulation variability primarily associated with a general increase of meso‐scale activity. Generally, we find a linear increase of the identified changes with global warming levels. Plain Language Summary: Changes in the current flow of Mediterranean waters due to global warming could significantly impact the environment and local populations. This study analyzes the impact of climate change on the surface circulation of the Mediterranean Sea. For this purpose, we use a set of regional climate scenarios under different future greenhouse gas emissions, carried out by the Mediterranean modeling community. Under global warming, the models do not agree in predicting robust changes in surface circulation at the basin scale. However, we find significant circulation changes in specific regions. In particular, the circulation in the northern Balearic is expected to shift from counterclockwise to predominantly clockwise, while the counterclockwise circulation in the southern Adriatic is expected to strengthen. Finally, the variability associated with Mediterranean circulation is expected to increase, mainly as a consequence of an enhanced eddy activity. The response of the mean surface circulation and variability to global warming is stronger as the global warming level increases. Key Points: A large regional climate ensemble to study the future evolution of the Mediterranean Sea has been built for various global warming levelsSignificant, linear and robust changes in surface circulation are projected for the northern Balearic and southern Adriatic regionsSignificant, linear and robust increase in the circulation variability is detected in open‐sea regions [ABSTRACT FROM AUTHOR]

Genesis Potential Indices (GPIs) link the occurrence of Tropical Cyclones (TCs) to large‐scale environmental conditions favorable for TC development. In the last few decades, they have been routinely used as a way to overcome the limitations of climate models (GCM), whose resolution is too coarse to produce realistic TCs. Recently, the first GCM ensemble with high enough horizontal resolution to realistically reproduce TCs was made available. Here, we address the questions of whether GPIs are still relevant in the era of TC‐permitting climate model ensembles, and whether they have sufficient predictive skills. The predictive skills of GPIs are assessed against the TCs directly simulated in a climate model ensemble. We found that GPIs have poor skill in two key metrics: inter‐annual variability and multi‐decadal trends. We discuss possible ways to improve the understanding of the predictive skill of GPIs and therefore enhance their applicability in the era of TC‐permitting GCMs. Plain Language Summary: Tropical Cyclones are extreme weather events which cause large damage when they hit inhabited areas. Understanding future cyclone activity in advance is very important to limit the damage. Until recently, climate models that scientists use to study future extremes where not able to reproduce realistic tropical cyclones because available computers were not powerful enough. Scientists used to look at indicators of cyclone activity ‐known as genesis potential indices—based on a number of quantities responsible for cyclone formation, rather than looking at cyclones themselves. Using cyclone data from a new set of climate model projections, we show that genesis potential indices are not always accurate in explaining future cyclone activity. We discuss how future research could help us improve the understanding of the drivers of tropical cyclone activity, and therefore the accuracy of genesis potential indices. Key Points: A recently produced high‐resolution GCM ensemble allows for the first time a systematic assessment of Genesis Potential Indices (GPIs) performanceAll the analyzed GPIs show poor skill in reproducing the interannual variability and future trends of modeled cyclonesPossible ways forward include adding variables related to Tropical Cyclones small‐scale dynamics, and using advanced statistical techniques based on Machine Learning [ABSTRACT FROM AUTHOR]

We investigate the effects of realistic oceanic initial conditions on a set of decadal climate predictions performed with a state-of-the-art coupled ocean-atmosphere general circulation model. The decadal predictions are performed in both retrospective (hindcast) and forecast modes. Specifically, the full set of prediction experiments consists of 3-member ensembles of 30-year simulations, starting at 5-year intervals from 1960 to 2005, using historical radiative forcing conditions for the 1960-2005 period, followed by RCP4.5 scenario settings for the 2006-2035 period. The ocean initial states are provided by ocean reanalyses differing by assimilation methods and assimilated data, but obtained with the same ocean model. The use of alternative ocean reanalyses yields the required perturbation of the full three-dimensional ocean state aimed at generating the ensemble members spread. A full-value initialization technique is adopted. The predictive skill of the system appears to be driven to large extent by trends in the radiative forcing. However, after detrending, a residual skill over specific regions of the ocean emerges in the near-term. Specifically, natural fluctuations in the North Atlantic sea-surface temperature (SST) associated with large-scale multi-decadal variability modes are predictable in the 2-5 year range. This is consistent with significant predictive skill found in the Atlantic meridional overturning circulation over a similar timescale. The dependency of forecast skill on ocean initialization is analysed, revealing a strong impact of details of ocean data assimilation products on the system predictive skill. This points to the need of reducing the large uncertainties that currently affect global ocean reanalyses, in the perspective of providing reliable near-term climate predictions. [ABSTRACT FROM AUTHOR]

Within the CIRCE project 'Climate change and Impact Research: the Mediterranean Environment', an ensemble of high resolution coupled atmosphere-ocean regional climate models (AORCMs) are used to simulate the Mediterranean climate for the period 1950-2050. For the first time, realistic net surface air-sea fluxes are obtained. The sea surface temperature (SST) variability is consistent with the atmospheric forcing above it and oceanic constraints. The surface fluxes respond to external forcing under a warming climate and show an equivalent trend in all models. This study focuses on the present day and on the evolution of the heat and water budget over the Mediterranean Sea under the SRES-A1B scenario. On the contrary to previous studies, the net total heat budget is negative over the present period in all AORCMs and satisfies the heat closure budget controlled by a net positive heat gain at the strait of Gibraltar in the present climate. Under climate change scenario, some models predict a warming of the Mediterranean Sea from the ocean surface (positive net heat flux) in addition to the positive flux at the strait of Gibraltar for the 2021-2050 period. The shortwave and latent flux are increasing and the longwave and sensible fluxes are decreasing compared to the 1961-1990 period due to a reduction of the cloud cover and an increase in greenhouse gases (GHGs) and SSTs over the 2021-2050 period. The AORCMs provide a good estimates of the water budget with a drying of the region during the twenty-first century. For the ensemble mean, he decrease in precipitation and runoff is about 10 and 15% respectively and the increase in evaporation is much weaker, about 2% compared to the 1961-1990 period which confirm results obtained in recent studies. Despite a clear consistency in the trends and results between the models, this study also underlines important differences in the model set-ups, methodology and choices of some physical parameters inducing some difference in the various air-sea fluxes. An evaluation of the uncertainty sources and possible improvement for future generation of AORCMs highlights the importance of the parameterisation of the ocean albedo, rivers and cloud cover. [ABSTRACT FROM AUTHOR]