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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]

Using the extended ERA5 reanalysis and three state‐of‐the‐art models, this study explores how El Niño‐Southern Oscillation (ENSO) can influence the total frequency, seasonal cycle and preconditioning of sudden stratospheric warmings (SSWs). Reanalysis data shows that in the last seven decades, winters with SSWs were more common than winters without, regardless El Niño (EN) or La Niña (LN) occurrence or the ENSO/SSW definitions. In agreement with previous studies, our models tend to simulate a linear ENSO‐SSW relationship, with more SSWs for EN, around mid‐winter (January–February) as in reanalysis, and less for LN when compared to neutral conditions. Independently of ENSO, the main tropospheric precursor of SSWs appears to be an anomalous wave‐like pattern over Eurasia, but it is dominated by wavenumber 1 (WN1) for EN and shows an enhanced wavenumber 2 (WN2) for LN. The differences in this Eurasian wave pattern, which is largely internally generated, emerge from the distinct configuration of the background, stationary wave pattern induced by ENSO in the North Pacific, favoring a stronger WN1 (WN2) component during EN (LN). Our results suggest that the ENSO‐forced signal relies on modulating the seasonal‐mean polar vortex strength, becoming weaker and more displaced (stronger and more stable) for EN (LN), while ENSO‐unforced wave activity represents the ultimate trigger of SSWs. This supports the view that ENSO and SSWs are distinct sources of variability of the winter atmospheric circulation operating at different time‐scales and may reconcile previous findings in this context. Plain Language Summary: Sudden stratospheric warmings (SSWs) are extreme events of the stratospheric polar vortex that consist in its deceleration and breakdown for several days, with implications on surface weather for several weeks. On the other hand, the atmospheric response to El Niño‐Southern Oscillation (ENSO) has been shown to weaken the stratospheric polar vortex during El Niño and strengthen it during La Niña winters, and hence, potential modulation of the occurrence of SSWs by ENSO is expected. Reanalysis data shows that in the last seven decades, winters with SSWs were more frequent than winters without regardless of ENSO, and instead of having an impact on the SSW total frequency, El Niño seems to favor events in mid‐winter (January–February). The main mechanism driving SSWs is thought to be anomalous upward wave activity from the troposphere into the stratosphere, reaching and perturbing the polar vortex. Independently of the ENSO phase, enhanced wave activity before SSWs is here found over Eurasia, thus pointing to this region as the main precursor of SSWs. While ENSO modulates the polar vortex at monthly/seasonal time‐scales, SSWs do so at daily/weekly time‐scales, representing distinct sources of variability of the polar vortex. Key Points: El Niño‐Southern Oscillation (ENSO) and sudden stratospheric warmings (SSWs) modulate the stratospheric polar vortex at different time‐scalesThe main SSW precursor independently of the ENSO phase is associated with wave activity over EurasiaThe anomalous Eurasian wave pattern can be dominated by different wave numbers depending on the ENSO phase [ABSTRACT FROM AUTHOR]

This article introduces the second generation CMCC Earth System Model (CMCC‐ESM2) that extends a number of marine and terrestrial biogeochemical processes with respect to its CMIP5 predecessor. In particular, land biogeochemistry was extended to a wider set of carbon pools and plant functional types, along with a prognostic representation of the nitrogen cycle. The marine ecosystem representation was reshaped toward an intermediate complexity of lower trophic level interactions, including an interactive benthic compartment and a new formulation of heterotrophic bacterial population. Details are provided on the model setup and implementation for the different experiments performed as contribution to the sixth phase of the Coupled Model Intercomparison Project. CMCC‐ESM2 shows an equilibrium climate sensitivity of 3.57°C and a transient climate response of 1.97°C which are close to the CMIP5 and CMIP6 multi‐model averages. The evaluation of the coupled climate‐carbon response in the historical period against available observational datasets show a consistent representation of both physical and biogeochemical quantities. However, the land carbon sink is found to be weaker than the current global carbon estimates and the simulated marine primary production is slightly below the satellite‐based average over recent decades. Future projections coherently show a prominent global warming over the northern hemisphere with intensified precipitations at high latitudes. The expected ranges of variability for oceanic pH and oxygen, as well as land carbon and nitrogen soil storage, compare favorably with those assessed from other CMIP6 models. Plain Language Summary: Earth System Models integrate our knowledge on the underlying physical and biogeochemical mechanisms that drive or influence the global climate and the biosphere over the land and in the ocean. These models are used to provide realistic estimates of climate variability and its response to perturbations in the chemical constituents of the atmosphere and modifications of the terrestrial surface. This work describes the science at the base of the second generation Earth System Model developed at the Euro‐Mediterranean Centre on Climate Change and the major results obtained from the simulation of historical (from the pre‐industrial period until present) and different future scenarios up to 2100 in the context of the sixth Coupled Model Intercomparison Project. The model provides a solid representation of the present‐day physical climate and biosphere dynamics in comparison to available observations and data reconstruction of the recent past. The projected global warming signal and carbon accumulation within terrestrial and oceanic systems under future climate scenarios are comparable to the findings of other models involved in the sixth intercomparison project. Key Points: This work introduces the second generation CMCC Earth System Model (CMCC‐ESM2) and its configuration for CMIP6Estimated climate sensitivity and carbon‐climate feedbacks are similar to average of CMIP5 and locate in the lower end of CMIP6Both climate and biogeochemical dynamics are assessed through the comparison with observations and previous literature findings [ABSTRACT FROM AUTHOR]

Vegetation phenology and its variability have substantial influence on land‐atmosphere interaction, and changes in growing season length are additional indicators of climate change impacts on ecosystems. For these reasons, global land surface models are routinely evaluated in order to assess their ability to reproduce the observed phenological variability. In this work, we present a new approach that integrates a wider spectrum of growing season modes, in order to better describe the observed variability in vegetation growing season onset and offset, as well as assess the ability of state‐of‐the‐art land surface models to capture this variability at the global scale. The method is applied to the Community Land Model version 4.5 (CLM4.5) simulations and LAI3g satellite observation. The comparison between data and model outputs shows that CLM4.5 is capable of reproducing the growing season features in the Northern Hemisphere midlatitude and high latitude, but also displays its limitations in areas where water availability acts as the main driver of vegetation phenological activity. Besides, the new approach allows evaluating land surface models in capturing multigrowing‐season phenology. In this regard, CLM4.5 proves its ability in reproducing the two‐growing‐season cycles in the Horn of Africa. In general, the new methodology expands the area of analysis from northern midlatitude and high latitude to the global continental areas and allows to assess the vegetation response to the ongoing climate change in a larger variety of ecosystems, ranging from semiarid regions to rain forests, passing through temperate deciduous and boreal evergreen forests. Key Points: A new phenology analysis method able to validate land surface model at global scale is presentedSatellite observation is used as a benchmark for the evaluation of Community Land Model version 4.5 [ABSTRACT FROM AUTHOR]

Euro‐Mediterranean Centre on Climate Change coupled climate model (CMCC‐CM2) represents the new family of the global coupled climate models developed and used at CMCC. It is based on the atmospheric, land and sea ice components from the Community Earth System Model coupled with the global ocean model Nucleus for European Modeling of the Ocean. This study documents the model components, the coupling strategy, particularly for the oceanic, atmospheric, and sea ice components, and the overall model ability in reproducing the observed mean climate and main patterns of interannual variability. As a first step toward a more comprehensive, process‐oriented, validation of the model, this work analyzes a 200‐year simulation performed under constant forcing corresponding to present‐day climate conditions. In terms of mean climate, the model is able to realistically reproduce the main patterns of temperature, precipitation, and winds. Specifically, we report improvements in the representation of the sea surface temperature with respect to the previous version of the model. In terms of mean atmospheric circulation features, we notice a realistic simulation of upper tropospheric winds and midtroposphere geopotential eddies. The oceanic heat transport and the Atlantic meridional overturning circulation satisfactorily compare with present‐day observations and estimates from global ocean reanalyses. The sea ice patterns and associated seasonal variations are realistically reproduced in both hemispheres, with a better skill in winter. Main weaknesses of the simulated climate are related with the precipitation patterns, specifically in the tropical regions with large dry biases over the Amazon basin. Similarly, the seasonal precipitation associated with the monsoons, mostly over Asia, is weaker than observed. The main patterns of interannual variability in terms of dominant empirical orthogonal functions are faithfully reproduced, mostly in the Northern Hemisphere winter. In the tropics the main teleconnection patterns associated with El Niño–Southern Oscillation and with the Indian Ocean Dipole are also in good agreement with observations. Key Points: New CMCC climate model built coupling atmosphere and land components of NCAR model with NEMO ocean modelRealistic representation of mean climate and main patterns of variability, mostly for the Northern Hemisphere winterImprovements in some aspects of the SST pattern with respect to a previous version of CMCC model [ABSTRACT FROM AUTHOR]