scholarly journals Why Is the Mediterranean a Climate Change Hot Spot?

2020 ◽  
Vol 33 (14) ◽  
pp. 5829-5843 ◽  
Author(s):  
A. Tuel ◽  
E. A. B. Eltahir

AbstractHigher precipitation is expected over most of the world’s continents under climate change, except for a few specific regions where models project robust declines. Among these, the Mediterranean stands out as a result of the magnitude and significance of its winter precipitation decline. Locally, up to 40% of winter precipitation could be lost, setting strong limits on water resources that will constrain the ability of the region to develop and grow food, affecting millions of already water-stressed people and threatening the stability of this tense and complex area. To this day, however, a theory explaining the special nature of this region as a climate change hot spot is still lacking. Regional circulation changes, dominated by the development of a strong anomalous ridge, are thought to drive the winter precipitation decline, but their origins and potential contributions to regional hydroclimate change remain elusive. Here, we show how wintertime Mediterranean circulation trends can be seen as the combined response to two independent forcings: robust changes in large-scale, upper-tropospheric flow and the reduction in the regional land–sea temperature gradient that is characteristic of this region. In addition, we discuss how the circulation change can account for the magnitude and spatial structure of the drying. Our findings pave the way for better understanding and improved modeling of the future Mediterranean hydroclimate.

2021 ◽  
Author(s):  
Roman Brogli ◽  
Silje Lund Sørland ◽  
Nico Kröner ◽  
Christoph Schär

<div> <p><span>It has long been recognized that the Mediterranean is a ‘hot-spot’ of climate change. The model-projected year-round precipitation decline and amplified summer warming are among the leading causes of the vulnerability of the Mediterranean to greenhouse gas-driven warming. We investigate large-scale drivers influencing both the Mediterranean drying and summer warming in regional climate simulations. To isolate the influence of multiple large-scale drivers, we sequentially add the respective drivers from global models to regional climate model simulations. Additionally, we confirm the robustness of our results across multiple ensembles of global and regional climate simulations.</span></p> </div><div> <p><span>We will present in detail how changes in the atmospheric stratification are key in causing the amplified Mediterranean summer warming. Together with the land-ocean warming contrast, stratification changes also drive the summer precipitation decline. Summer circulation changes generally have a surprisingly small influence on the changing Mediterranean summer climate. In contrast, changes in the circulation are the primary driver for the projected winter precipitation decline. Since land-ocean contrast and stratification changes are more robust in global climate simulations than circulation changes, we argue that the uncertainty associated with the projected climate change patterns should be considered smaller in summer than in winter.</span></p> </div><div> <p><span>References:</span></p> </div><div> <p><span>Brogli, R., S. L. Sørland, N. Kröner, and C. Schär, 2019: Causes of future Mediterranean precipitation decline depend on the season. Environmental Research Letters, 14, 114017, doi:10.1088/1748-9326/ab4438.</span></p> </div><div> <p><span>Brogli, R., N. Kröner, S. L. Sørland, D. Lüthi and C. Schär, 2019: The Role of Hadley Circulation and Lapse-Rate Changes for the Future European Summer Climate. Journal of Climate, 32, 385-404, doi:10.1175/JCLI-D-18-0431.1</span></p> </div>


2020 ◽  
Author(s):  
Roman Brogli ◽  
Silje Lund Sørland ◽  
Nico Kröner ◽  
Christoph Schär

<p>The Mediterranean is among the global 'hot-spots' of climate change, where severe consequences of climate change are expected. Changes in the atmospheric water cycle are among the leading causes of the vulnerability of the Mediterranean to greenhouse gas-driven warming. Specifically, precipitation is projected to decrease year-round, which is expected to have major impacts on hydrology, biodiversity, agriculture, hydropower, and further economic sectors that rely on sufficient water supply.</p><p>We investigate possible causes of the Mediterranean drying in regional climate simulations. To isolate the influence of multiple large-scale drivers on the drying, we sequentially add the respective drivers from global models to regional climate model simulations. We show that the causes of the Mediterranean drying depend on the season. We will present in detail how the summer drying is driven by the land-ocean warming contrast, lapse-rate and other thermodynamic changes, while it only weakly depends on circulation changes. In contrast, changes in the circulation are the primary driver for the projected winter precipitation decline. Since land-ocean contrast, thermodynamic and lapse-rate changes are more robust in climate simulations than circulation changes, the uncertainty associated with the projected drying should be considered smaller in summer than in winter.</p><p>Reference: Brogli, R., S. L. Sørland, N. Kröner, and C. Schär, 2019: Causes of future Mediterranean precipitation decline depend on the season. Environmental Research Letters, 14, 114017, doi:10.1088/1748-9326/ab4438.</p>


2021 ◽  
Author(s):  
Alba de la Vara ◽  
William Cabos ◽  
Dmitry V. Sein ◽  
Claas Teichmann ◽  
Daniela Jacob

AbstractIn this work we use a regional atmosphere–ocean coupled model (RAOCM) and its stand-alone atmospheric component to gain insight into the impact of atmosphere–ocean coupling on the climate change signal over the Iberian Peninsula (IP). The IP climate is influenced by both the Atlantic Ocean and the Mediterranean sea. Complex interactions with the orography take place there and high-resolution models are required to realistically reproduce its current and future climate. We find that under the RCP8.5 scenario, the generalized 2-m air temperature (T2M) increase by the end of the twenty-first century (2070–2099) in the atmospheric-only simulation is tempered by the coupling. The impact of coupling is specially seen in summer, when the warming is stronger. Precipitation shows regionally-dependent changes in winter, whilst a drier climate is found in summer. The coupling generally reduces the magnitude of the changes. Differences in T2M and precipitation between the coupled and uncoupled simulations are caused by changes in the Atlantic large-scale circulation and in the Mediterranean Sea. Additionally, the differences in projected changes of T2M and precipitation with the RAOCM under the RCP8.5 and RCP4.5 scenarios are tackled. Results show that in winter and summer T2M increases less and precipitation changes are of a smaller magnitude with the RCP4.5. Whilst in summer changes present a similar regional distribution in both runs, in winter there are some differences in the NW of the IP due to differences in the North Atlantic circulation. The differences in the climate change signal from the RAOCM and the driving Global Coupled Model show that regionalization has an effect in terms of higher resolution over the land and ocean.


2021 ◽  
Author(s):  
Josep Cos ◽  
Francisco J Doblas-Reyes ◽  
Martin Jury

<p>The Mediterranean has been identified as a climate change hot-spot due to increased warming trends and precipitation decline. Recently, CMIP6 was found to show a higher climate sensitivity than its predecessor CMIP5, potentially further exacerbating related impacts on the Mediterranean region.</p><p>To estimate the impacts of the ongoing climate change on the region, we compare projections of various CMIP5 and CMIP6 experiments and scenarios. In particular, we focus on summer and winter changes in temperature and precipitation for the 21st century under RCP2.6/SSP1-2.6, RCP4.5/SSP2-4.5 and RCP8.5/SSP5-8.5 as well as the high resolution HighResMIP experiments. Additionally, to give robust estimates of projected changes we apply a novel model weighting scheme, accounting for historical performance and inter-independence of the multi-member multi-model ensembles, using ERA5, JRA55 and WFDE5 as observational reference. </p><p>Our results indicate a significant and robust warming over the Mediterranean during the 21st century irrespective of the used ensemble and experiments. Nevertheless, the often attested amplified Mediterranean warming is only found for summer. The projected changes vary between the CMIP5 and CMIP6, with the latter projecting a stronger warming. For the high emission scenarios and without weighting, CMIP5 indicates a warming between 4 and 7.7ºC in summer and 2.7 and 5ºC in winter, while CMIP6 projects temperature increases between 5.6 and 9.2ºC in summer and 3.2 to 6.8ºC in winter until 2081-2100 in respect to 1985-2005. In contrast to temperature, precipitation changes show a higher level of uncertainty and spatial heterogeneity. However, for the high emission scenario, a robust decline in precipitation is projected for large parts of the Mediterranean during summer. First results applying the model weighting scheme indicate reductions in CMIP6 and increases in CMIP5 warming trends, thereby reducing differences between the two ensembles.</p>


2018 ◽  
Vol 31 (8) ◽  
pp. 3249-3264 ◽  
Author(s):  
Michael P. Byrne ◽  
Tapio Schneider

AbstractThe regional climate response to radiative forcing is largely controlled by changes in the atmospheric circulation. It has been suggested that global climate sensitivity also depends on the circulation response, an effect called the “atmospheric dynamics feedback.” Using a technique to isolate the influence of changes in atmospheric circulation on top-of-the-atmosphere radiation, the authors calculate the atmospheric dynamics feedback in coupled climate models. Large-scale circulation changes contribute substantially to all-sky and cloud feedbacks in the tropics but are relatively less important at higher latitudes. Globally averaged, the atmospheric dynamics feedback is positive and amplifies the near-surface temperature response to climate change by an average of 8% in simulations with coupled models. A constraint related to the atmospheric mass budget results in the dynamics feedback being small on large scales relative to feedbacks associated with thermodynamic processes. Idealized-forcing simulations suggest that circulation changes at high latitudes are potentially more effective at influencing global temperature than circulation changes at low latitudes, and the implications for past and future climate change are discussed.


2021 ◽  
Author(s):  
David Crookall ◽  
Isabel Caballero-Leiva ◽  
Laksh Sharma ◽  
Pimnutcha Promduangsri ◽  
Pariphat Promduangsri

<p>Modern, educational simulation/games (s/g) have a rich legacy, stretching back to the 1960s.  They are used today for communicating science in educational, environmental or governmental organizations.  Other uses are to help groups and organizations conduct research, solve complex problems or make collective decisions.</p><p>Over the last two decades, a particularly powerful, but underused, form of s/g has developed, called participatory simulation (PS).  It contains (elements of) game, simulation, role-play, experience, human interaction, decision-making, negotiation, engagement, stakeholder, etc.  It is often large scale, open ended, goal and results oriented, free form and data driven.  Of course, debriefing is a crucial component.</p><p>Last summer (2020), the International Oceans-Climate School (IOCS), of the Ocean Open University (OOP), France, planned to organize an in-person summer school with a PS as its capstone event.  We then postponed and made it an autumn school.  It then became clear that this also was impossible, and so, after some hesitation, we scrambled to turn it into an online PS (OPS).</p><p>The theme was “<em>The Mediterranean and climate change: Impacts, people, action</em>”.  Our overarching goal was to help participants understand the <strong>oceans-climate nexus</strong> and to become better <strong>ocean-climate-literate stakeholders</strong>.  The IOCS is an official event of the <strong>Intergovernmental Oceanographic Commission</strong> (IOC) of UNESCO, as part of the <strong>UN Decade of Ocean Science for Sustainable Development</strong>.</p><p>The school ran over three days, with the OPS over two days.  We searched for a platform that would accommodate the flexibility needed for the OPS; we chose Discord.  We had participants originating from Brazil, France, India, Italy, Iran, Spain, Tunisia and the UK; ages ranged from 19 to 60 years.  It was a great success.  A detailed, online feedback form two weeks after the event collected participants’ opinions, including:</p><ul><li><em>“It was a wonderful experience.”, :I felt very good with all the participants.”, “When I describe the experience to friends I always say that it was something really useful for my personal and professional growth.”, “It was a very enriching experience for me to meet all these people with different training and knowledge, coming from different countries.”, “Enriching moments, so much more to discover.”, “What a great experience! I felt happy, engaged and surrounded by beautiful minds.”</em></li> </ul><p>We will run the event again in the Spring and the late summer or autumn, with different geoscience themes.  The success of the October 2020 event raises several research questions, including:</p><ul><li>How do the online and the in-person versions compare?</li> <li>What are the advantages and drawbacks of each?</li> <li>Which is more effective for what objectives and what results?</li> <li>How do the two versions stack up in regard to conducting research on such events?</li> <li>What are the implications of OPS for geoliteracy?</li> </ul><p>Our presentation will describe the event in more detail, offer tentative answers to the above questions, and help you decide if you wish to participate in the next event.  Co-authors include both organizers and participants.</p>


2021 ◽  
Vol 8 ◽  
Author(s):  
Jean-François Legeais ◽  
Benoît Meyssignac ◽  
Yannice Faugère ◽  
Adrien Guerou ◽  
Michaël Ablain ◽  
...  

It is essential to monitor accurately current sea level changes to better understand and project future sea level rise (SLR). This is the basis to support the design of adaptation strategies to climate change. Altimeter sea level products are operationally produced and distributed by the E.U. Copernicus services dedicated to the marine environment (CMEMS) and climate change (C3S). The present article is a review paper that intends to explain why and to which extent the sea level monitoring indicators derived from these products are appropriate to develop adaptation strategies to SLR. We first present the main key scientific questions and challenges related to SLR monitoring. The different processing steps of the altimeter production system are presented including those ensuring the quality and the stability of the sea level record (starting in 1993). Due to the numerous altimeter algorithms required for the production, it is complex to ensure both the retrieval of high-resolution mesoscale signals and the stability of the large-scale wavelengths. This has led to the operational production of two different sea level datasets whose specificities are characterized. We present the corresponding indicators: the global mean sea level (GMSL) evolution and the regional map of sea level trends, with their respective uncertainties. We discuss how these products and associated indicators support adaptation to SLR, and we illustrate with an example of downstream application. The remaining gaps are analyzed and recommendations for the future are provided.


2008 ◽  
Vol 17 ◽  
pp. 87-91 ◽  
Author(s):  
A. V. Mehta ◽  
S. Yang

Abstract. Climatological features of mesoscale rain activities over the Mediterranean region between 5° W–40° E and 28° N–48° N are examined using the Tropical Rainfall Measuring Mission (TRMM) 3B42 and 2A25 rain products. The 3B42 rainrates at 3-hourly, 0.25°×0.25° spatial resolution for the last 10 years (January 1998 to July 2007) are used to form and analyze the 5-day mean and monthly mean climatology of rainfall. Results show considerable regional and seasonal differences of rainfall over the Mediterranean Region. The maximum rainfall (3–5 mm day−1) occurs over the mountain regions of Europe, while the minimum rainfall is observed over North Africa (~0.5 mm day−1). The main rainy season over the Mediterranean Sea extends from October to March, with maximum rainfall occurring during November–December. Over the Mediterranean Sea, an average rainrate of ~1–2 mm day−1 is observed, but during the rainy season there is 20% larger rainfall over the western Mediterranean Sea than that over the eastern Mediterranean Sea. During the rainy season, mesoscale rain systems generally propagate from west to east and from north to south over the Mediterranean region, likely to be associated with Mediterranean cyclonic disturbances resulting from interactions among large-scale circulation, orography, and land-sea temperature contrast.


2020 ◽  
Author(s):  
Giulio Nils Caroletti ◽  
Roberto Coscarelli ◽  
Tommaso Caloiero

<p>Due to the importance of precipitation as a climatic and meteorological variable, it is paramount to detect the relationships between teleconnections and precipitation at different temporal and spatial scale. In fact, large-scale systems can i) influence precipitation directly, ii) establish a favourable environment to deep moist convection, and thus extreme precipitation, but also iii) help triggering dry conditions and drought.</p><p>In this study, developed within the INDECIS EU project, the teleconnection influence on precipitation in the Calabria region has been evaluated over the 1981-2010 time period, by means of a database of 79 rain gauge stations and seven teleconnections indices. Calabria, the southernmost region of peninsular Italy, was chosen as a valuable test bed mainly because it is located in the centre of the Mediterranean region, which constitutes a hot spot for climate change. Moreover, Calabria has a high-density, long-time network of precipitation gauges, recently validated and homogenized.</p><p>Statistical relationships between teleconnection indices and precipitation are often developed through well-known correlation analyses techniques, e.g. Pearson, Spearman and Kendall, where a teleconnection index is compared to cumulated precipitation values. In this study, three types of correlation analysis were performed: i) seasonal indices vs seasonal cumulated precipitation; ii) three-month indices vs monthly cumulated precipitation; iii) monthly indices vs monthly cumulated precipitation. These analyses have been performed in five Rainfall Zones (RZs) of the study area, characterised by different climatic conditions: the North-Eastern Zone (I1), the Central-Eastern Zone (I2) and the South-Eastern Zone (I3) on the Ionian side of Calabria and the North-Western Zone (T1) and the South-Western Zone (T2) on the Tyrrhenian part.</p><p>Results showed that the Mediterranean Oscillation and the North Atlantic Oscillation are the most important large-scale contributors to the precipitation regime of Calabria. Moreover, seasonal Eastern Atlantic pattern influenced seasonal precipitation in the RZs I1 and T1; three-monthly East Atlantic/Western Russian pattern influenced monthly precipitation in the RZs I2 and T1; three-monthly Western Mediterranean Oscillation influenced monthly precipitation in the RZs I3 and T1; while three-monthly El Nino-Southern Oscillation influenced monthly precipitation in the RZ T2.</p><p>Investigating changes in the response of local precipitation and teleconnections throughout the 1951-2010 and 1951-1980 time periods, a change in precipitation response to teleconnection patterns emerged, i.e., in the impact that the Mediterranean Oscillation has on the East coast precipitation (RZs I1-I3), a possible result of natural variation or climate change. In addition, these results have been compared to those obtained with the classical correlation analyses between teleconnection indices and single-station precipitation.</p><p>The approach developed for this study is a general method that, in principle, can be reproduced for any variable for any region and for every teleconnection.</p><p>Acknowledgments:</p><p>The Project INDECIS is part of ERA4CS, an ERA-NET initiated by JPI Climate, and funded by FORMAS (SE), DLR (DE), BMWFW (AT), IFD (DK), MINECO (ES), ANR (FR) with co-funding by the European Union (Grant 690462).</p>


2006 ◽  
Vol 6 (4) ◽  
pp. 863-881 ◽  
Author(s):  
A. P. van Ulden ◽  
G. J. van Oldenborgh

Abstract. The quality of global sea level pressure patterns has been assessed for simulations by 23 coupled climate models. Most models showed high pattern correlations. With respect to the explained spatial variance, many models showed serious large-scale deficiencies, especially at mid-latitudes. Five models performed well at all latitudes and for each month of the year. Three models had a reasonable skill. We selected the five models with the best pressure patterns for a more detailed assessment of their simulations of the climate in Central Europe. We analysed observations and simulations of monthly mean geostrophic flow indices and of monthly mean temperature and precipitation. We used three geostrophic flow indices: the west component and south component of the geostrophic wind at the surface and the geostrophic vorticity. We found that circulation biases were important, and affected precipitation in particular. Apart from these circulation biases, the models showed other biases in temperature and precipitation, which were for some models larger than the circulation induced biases. For the 21st century the five models simulated quite different changes in circulation, precipitation and temperature. Precipitation changes appear to be primarily caused by circulation changes. Since the models show widely different circulation changes, especially in late summer, precipitation changes vary widely between the models as well. Some models simulate severe drying in late summer, while one model simulates significant precipitation increases in late summer. With respect to the mean temperature the circulation changes were important, but not dominant. However, changes in the distribution of monthly mean temperatures, do show large indirect influences of circulation changes. Especially in late summer, two models simulate very strong warming of warm months, which can be attributed to severe summer drying in the simulations by these models. The models differ also significantly in the simulated warming of cold winter months. Finally, the models simulate rather different changes in North Atlantic sea surface temperature, which is likely to impact on changes in temperature and precipitation. These results imply that several important aspects of climate change in Central Europe are highly uncertain. Other aspects of the simulated climate change appear to be more robust. All models simulate significant warming all year round and an increase in precipitation in the winter half-year.


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