The Climate of the Mediterranean Region: From the Past to the Future

The Mediterranean region contains a diverse and interesting climate ranging from areas with permanent glaciers to areas of subtropical, semiarid regions. The region is potentially sensitive to climate change and its progress has environmental, social, and economic implications within and beyond the region. Produced by the Mediterranean Climate Variability and Predictability Research Networking Project, this book reviews the evolution of the Mediterranean climate over the past two millennia with projections further into the twenty-first century as well as examining in detail various aspects of the Mediterranean region’s climate including evolution, atmospheric variables, and oceanic and land elements. Integrated with this, the book also considers the social and economic problems or vulnerabilities associated with the region. Written and reviewed by multiple researchers to ensure a high level of information presented clearly, Mediterranean Climate Variables will be an invaluable source of information for geologists, oceanographers, and anyone interested in learning more about the Mediterranean climate.

• Written by leading experts in the field
• Presents clear, compelling, and concise evidence
• Includes the latest thinking in Mediterranean climate research

• Language: English
• Publisher: Elsevier Science
• Release date: Apr 19, 2012
• ISBN: 9780123914774

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Preface

The climate of the Mediterranean region—its past evolution, present variability, trends, and changes projected for the next decades—has been the object of many research studies and has attracted the interest of a large group of scientists. Such focus of international climate research on a relatively small region can be explained by three fundamental facts—its specific phenomenology, the well-developed cultural background of most Mediterranean countries, and the important social–economical–environmental impacts of climate variability and change.

The Mediterranean region presents a large spectrum of mesoscale processes relevant for the description of both the sea and the atmospheric components of the regional climate. This complexity and richness of phenomena is caused by the morphology of the Mediterranean region and by its geographical location. Two important examples are the weather regimes and the thermohaline circulation for the atmosphere and the sea, respectively. When interacting with the global atmospheric circulation, the morphology of the Mediterranean region induces regional features, such as the Mediterranean branch of the storm track and the associated areas of cyclogenesis, with consequences for storminess and precipitation regimes. Mesoscale processes and wind regimes peculiar to the region (such as Mistral and Bora) are responsible for strong air–sea interactions and considerably affect the thermohaline circulation of the Mediterranean Sea, the regional equivalent of the global thermohaline cell. The location of the Mediterranean Sea in a transitional band between subtropical and midlatitude regimes produces a large climate variability at multiple timescales and a strong seasonal variability of precipitation in many areas. The vulnerability of the southernmost region to climate variability and change is caused by scarce and irregular water availability. The exposure of the Mediterranean environment to continental air masses from the north and subtropical air masses from the south is another aspect of this complexity, which implies a richness of interesting phenomena suitable for specialized research. Furthermore, the large amount of various sources of information from ancient and historical times combined with centennial (and longer) observational time series provide a unique opportunity for the reconstruction of the past climate.

The traditionally high cultural level of this region, which has been a cradle of civilization and has been strongly involved in the development of the modern world, provides cultural resources and highly educated scientists interested in the regional climate. Education (supported by many universities and institutes) is traditionally strong in most countries around the Mediterranean and provides the basis for the existing large research literature. In this region, the richness of processes and climatic features of the different areas has an analogy in the diversity of cultures and societal structures among countries. The consequence is a complex interplay among cultures, with leadership moving in time among the shores of the Mediterranean, with both synergistic and competitive interactions, which can produce conflicts, and also positive cultural exchanges. The present challenge is to prevent these conflicts and to retain the unique richness of cultural diversity stimulating positive interactions. Scientific cooperation can have a key role in this effort.

Finally, vulnerability of society and environment is a key factor that determines a growing set of questions and demands posed by citizens and politicians to scientists. Criticalities are due to both socioeconomic factors and climate, with climate variability and change acting as new source of problems that can trigger very negative scenarios. The Mediterranean is a hot spot for climate-related issues. The water cycle and its extremes are one of the major concerns. Many countries are overexploiting water resources, and water scarcity is a crucial problem for them, on that is expected, in many cases, to worsen in the future. On the other hand, episodes of exceptionally intense precipitation constitute a major hazard, and disastrous floods are a risk for many vulnerable regions around the Mediterranean coast. These problems require research and monitoring for the correct evaluation of the present risk and of its change in future climate scenarios. In this century, changes in the hydrological cycle are likely to affect both the terrestrial and marine environment in the Mediterranean region. The ecosystems in the sea will be affected by increasing temperature and salinity, the thermohaline circulation may weaken with important effects on sea stratification, sea-level rise has a strong regional connotation that contributes to the large uncertainty of its future evolution, and the interaction with the Atlantic Ocean can induce global effects caused by water-mass changes inside the Mediterranean Sea. These are only a few examples of issues of paramount importance that need to be investigated and understood to be able to propose mitigation and adaptation measures.

This book is an important product of the Mediterranean Climate Variability and Predictability (MedCLIVAR) program. MedCLIVAR was initiated at European Geophysical Society (EGS) in Nice in 2003, when a group of scientists met and began working at a scientific program of common interest. The next year, a first MedCLIVAR workshop was held in Rome with the support of the ESF (European Science Foundation). In 2004, the project white paper was written. In January 2005, MedCLIVAR was endorsed by CLIVAR and few months later the MedCLIVAR-RNP (Research Networking Programme) was approved by the ESF and launched in May 2006. Since then, with the support of the ESF (~800,000 euros in 5 years) MedCLIVAR has held 6 strategic workshops and 2 summer schools, assigned 34 grants for young scientist exchange and 8 for senior scientist short visits, sponsored or cosponsored 11 scientific meetings, and organized a major conference. Furthermore, every year since 2003, a session organized by MedCLIVAR has been held at the European Geosciences Union general assembly (formerly EGS). Information on MedCLIVAR activities can be found in the short appendix to this preface.

MedCLIVAR aims to coordinate and promote research on the Mediterranean climate. It covers its past evolution, its present space–time variability and trends, and regional future climate scenarios. It is motivated by the sensitivity of the Mediterranean region to climate change and by the critical environmental, societal, and economic issues that exist in this region. The success of MedCLIVAR is due to the bottom-up approach supported by a culturally strong community. The high scientific profile of many countries around the Mediterranean Sea and the ongoing research have made it possible to build a productive and integrated network. The vulnerability and risks associated with climate variability and change have added further ground for a common international effort. At present, MedCLIVAR represents a forum for scientific discussion in a free community, independent from individual projects and open to the new issues that are proposed.

This new book, The Climate of the Mediterranean Region: From the Past to the Future, has been written 5 years after the book Mediterranean Climate Variability. As the previous one, this book is a multi-authored manuscript written by a team of scientists very active in Mediterranean climate research. In a coordinated sequence of chapters, the book provides the present status of the knowledge on different aspects of the Mediterranean climate. Both books are main outcomes of the MedCLIVAR program and are meant to represent the result of a community effort. They address scholars, students, and experts from other fields with a basic expertise on climate science. They contain very useful reviews of the present research and overviews of recent developments and of new research interests. Environmentalists and policymakers will find in them clear and correct information on climate change at the regional Mediterranean scale. The comparison of this new book with the previous one shows the progress of the MedCLIVAR program and of Mediterranean climate research during the past 5 years. The most evident differences include more material on climate modeling and projections, a wider treatment of sea-level issues, a larger contribution from the paleoclimate component, an extended discussion on climate extremes.

This book consists of eight chapters and an Introduction providing a complete description of the Mediterranean climate evolution from paleoclimate to the twenty-first-century projections.

The Introduction, Mediterranean Climate: Background Information (Lionello et al.), is meant for all readers—unlike the other chapters, which separately address selected topics—because it provides essential information on the regional climate and a general view of the subjects that are considered in detail in the rest of the book, to which readers are directed for specialized discussions.

The first two chapters consider past climate in two different time ranges: millions of years in Chapter 1, Paleoclimate Variability in the Mediterranean Region (Abrantes et al.), and thousands of years in Chapter 2, A Review of 2000 Years of Paleoclimatic Evidence in the Mediterranean (Luterbacher et al.). Chapter 1 describes the fascinating history of the Mediterranean climate, when millions of years ago differences with respect to the present condition were substantial. The chapter describes how the present climate evolved through dramatic changes. It considers warm climate intervals, abrupt climate shifts (in particular from cold to warm periods) and the glacial millennial-scale variations, describing the variability of the regional climate system on very long timescales. The comparatively constant climate of recent millennia is described in Chapter 2, which exploits the unique possibility offered by the Mediterranean region for integrating instrumental data, paleo-ecological, and archeological records and information from natural and historical archives for describing the climate in the Mediterranean region over the past 2000 years. This includes episodes such as the Medieval Climate Anomaly and the Little Ice Age.

The following four chapters consider the present climate. The first two analyze the sea component, an essential constituent of the regional climate system. Chapter 3, Circulation of the Mediterranean Sea and its variability (Schroeder et al.), describes data, research results, and key findings that have been reported in the most recent literature about Mediterranean Sea circulation. Chapter 4, Mediterranean Sea-Level Variability and Trends (Gomis et al.), examines sea-level variability and the different processes/contributions responsible for its observed changes and its different behavior with respect to the global mean value. Chapter 5, Climate of the Mediterranean: Synoptic Patterns, Temperature, Precipitation, Winds, and Their Extremes (Ulbrich et al.), describes the synoptic climatology of the Mediterranean region and its links with means and extremes of temperature, precipitation, wind, and storminess. Chapter 6, Large-Scale Atmospheric Circulation Driving Extreme Climate Events in the Mediterranean and its Related Impacts (Xoplaki et al.), discusses atmospheric circulation regimes leading to drought episodes and severe heat waves, two natural hazards that are particularly critical in the Mediterranean because of their socioeconomic impacts and the recent trends toward a hotter and drier climate.

Climate models and regional climate-change scenarios are the topics of the two final chapters. Chapter 7, Modeling of the Mediterranean Climate System (Li et al.), discusses the basic performances of both global and regional climate models in simulating the Mediterranean climate. They also include the general circulation of the Mediterranean Sea. Regional coupled models are an important new topic considered in this chapter. Future climate change is discussed in Chapter 8, The Climate of the Mediterranean Region in Future Climate Projections (Planton et al.), which presents a synthesis of expected changes from recent regional simulations. It considers mean climate and climate extremes, changes in Mediterranean Sea temperature, salinity, circulation, water and heat budgets, and sea level and their uncertainties.

It is my pleasure, at the end of this preface, to acknowledge the contribution of the reviewers (see the list below) who accepted the heavy task of reviewing the chapters and with their very useful comments and suggestions have contributed to the quality of this book. Finally, last but not least, a deep thank to the scientific secretaries of MedCLIVAR, Roberta Boscolo and Annalisa Tanzarella, for all their excellent work, which was a great contribution to the success of the project.

Piero Lionello, chair of the MedCLIVAR program

Reviewers

Introduction: Antonio Busalacchi, Paola Malanotte-Rizzoli

Chapter 1: Alessandra Asioli, Alan Haywood

Chapter 2: Joel Guiot, Danny McCarroll

Chapter 3: Radan Huth, Isabel F Trigo

Chapter 4: Steve Brenner, Harry Bryden

Chapter 5: John Church, Per Knudsen

Chapter 6: Clare Gooddes, Henry Diaz, Javier Martín-Vide

Chapter 7: Vincenzo Artale, Michel Déqué

Chapter 8: Daniela Jacob

Appendix: List of MedCLIVAR Activities

MedCLIVAR Workshops

• Reconstruction of Past Mediterranean Climate (Spain, November 9–11, 2006), convened by R. García-Herrera.

• Connections Between Mediterranean and Global Climate Variability (France, October 8–10, 2007), convened by Laurent Li.

• Understanding the Mechanisms Responsible for the Mediterranean Sea Circulation and Sea Level Trends (Greece, September 29–October 1, 2008), convened by Alexander Theocharis.

• Feedbacks of the Mediterranean Dynamics in the Global Climate System (Portugal, September 28–30, 2009), convened by F. Abrantes and R. Trigo.

• Scenarios for Mediterranean Climate under the Increase of Radiatively Active Gases and the Role of Aerosols (Italy, September 23–15, 2010), convened by Filippo Giorgi.

• MedCLIVAR Workshop on Scientific Achievements 2005–2011 and Future Research Priorities (Tel Aviv, Israel, September 19–20, 2011), convened by P. Alpert and H. Saaroni.

MedCLIVAR Schools

• First School: Climate Variability, Trends, and the Occurrence of Extreme events (September 17–27, 2008, Greece).

• Second School: MedCLIVAR-ICTP-ENEA international summer school: The Mediterranean Climate System and Regional Climate Change (September 13–22, 2010, Italy).

MedCLIVAR Conference

• Mediterranean Climate: From the Past to the Future (June 6–9, 2011, Lecce, Italy).

Workshops Cosponsored by MedCLIVAR

• Provision of Climate Model Data to Hydrological Models for the Eastern Mediterranean and Middle East, March 3–5, 2008, University of Reading, UK. Convenor: Emily Black.

• Oxygen isotopes as tracers of Mediterranean climate variability: linking past, present, and future, June 11–13, 2008, University of Pisa, Italy. Convenor: Neil Roberts.

• Extreme Climate Events of the Last 1000–2000 Years in the Greater Mediterranean Region and Their Impact on Mediterranean Societies, September 14–16, 2008, Athens, Greece. Convenor: Elena Xoplaki (CH).

• Climate Change Modeling for the Mediterranean Region, October 13–15, 2008, ICTP, Trieste, Italy. Convenors: Filippo Giorgi and Piero Lionello.

• Climate Impact Models for the Mediterranean Region—Focus Session within the COSMOS (COmmunity earth System MOdelS) 2009 General Assembly, Berlin, Germany, June 15–17, 2009, Uwe Ulbrich, Germany.

• International Workshop on Climate Change in the Mediterranean and Middle East, June 9–11, 2008, Magdi Abdel Wahab, Cairo, Egypt.

• Hydrological Cycle in the Mediterranean Experiment (HyMeX) Gouves, Heraklion Crete-Greece, January 6, 2009–May 6, 2009, Themis Chronis, Anavissos, Greece.

• MedCLIVAR–HyMeX–MedFriend Side Event on the Recovery and Extension of Precipitation Time Series, Held during the 11th Plinius Conference on Mediterranean Storms Barcelona, July 9, 2009, Maria del Carmen Llasat Botija, Barcelona, Spain.

• Impacts of the Mediterranean Climate Change on Human Health, Paphos, Cyprus (hosted by The Cyprus Institute), October 19, 2009–October 21, 2009, Shlomit Paz, Haifa, Israel.

• Severe Thunderstorm Reporting in Europe and the whole Mediterranean Region—Focus session and dedicated side meeting at the 5th European Conference on Severe Storms, Landshut, Germany, October 12–13, 2009, Nikolai Dotzek, Wessling, Germany.

• Hydrological, Climatic and Social-Economic Impacts of NAO in the Mediterranean, May 24–27, 2010, Ricardo Trigo, Saragoza, Spain.

• Precipitation over Mediterranean Region: Advancing in Recovery and Homogenization of Long Time Series, held during the 12th Plinius Conference on Mediterranean Storms. September 4, 2011, Piero Lionello, Vasso Kotroni, Annalisa Tanzarella, Corfu Island, Greece.

• Regional Climate Dynamics in the Mediterranean and Beyond: An Earth System perspective, Course XIX, June 20–29, 2011, Valsavarenche, A. Provenzale, Valle d’Aosta, Italy.

Collective Publications and Reports of MedCLIVAR Events

• Lionello, P., Malanotte-Rizzoli, P., Boscolo, R. (Eds.), 2005. Mediterranean Climate Variability. Elsevier, Amsterdam, The Netherlands. ISBN: 0-444-52170-4, 438 pp.

• Lionello, P., Malanotte-Rizzoli, P., Alpert, P., Artale, V., Boscolo, R., Garcia-Herrera, R., et al., 2006. MedCLIVAR: Mediterranean CLImate VARiability and predictability project PAGES News, 13 (3), 23.

• Cattle, H., Boscolo, R. (Eds.), 2006. CLIVAR Exchanges No 37. Special Issue: MedCLIVAR, vol. 11. International CLIVAR Project Office, Southampton, UK, 32 pp.

• Lionello, P., Malanotte-Rizzoli, P., Alpert, P., Artale, V., Boscolo, R., Li, L., et al., 2006. MedCLIVAR: Mediterranean CLImate VARiability Exchanges 37, 3–5.

• García-Herrera, R., Luterbacher, J., Lionello, P., González-Rouco, F., Ribera, P., Rodó, X., Kull, C., Zerefos, C., 2007. Reconstruction of past Mediterranean climate. Eos Trans. AGU, 88 (9), 111.

• Tsimplis, M., Xoplaki, E., Theocharis, A., Sioulas, A., 2008. The third Mediterranean Climate Variability and Predictability—European Science Foundation (MedCLIVAR-ESF), Workshop and the First MedCLIVAR-ESF Summer School, Exchanges, 48, 10.

• Lionello, P., Llasat, M.C., 2010. Promoting a Precipitation Database for the Mediterranean Region: MedCLIVAR–HyMeX–MedFriends Workshop, 7 September 2009, Barcelona, Spain. Eos Trans. AGU, 91 (8), 76, doi:10.1029/2010EO080005.

• Trigo, R.M., Vicente Serrano, S.M., 2010. Understanding the North Atlantic Oscillation and its Effects in the Mediterranean: ESF-MedCLIVAR Workshop on Hydrological, Socioeconomic and Ecological Impacts of the North Atlantic Oscillation in the Mediterranean, 24–27 May 2010, Zaragoza, Spain. Eos Trans. AGU, 91 (44), 407. doi:10.1029/2010EO440004.

• Serrano, S.M.V., Trigo, R.M., 2011. Hydrological, socioeconomic and ecological impacts of the North Atlantic Oscillation in the Mediterranean region. Adv. Global Change Res. 46, 1–8. doi:10.1007/978-94-007-1372-7_1.

Special Issues

• Natural Hazards and Earth System Sciences dedicated to Understanding dynamics and current developments of climate extremes in the Mediterranean region (Eds. R. Garcia-Herrera, P. Lionello, U. Ulbrich).

• Physics and Chemistry of the Earth dedicated to Venetia and Northern Adriatic climate (Ed. P. Lionello).

• Global and Planetary Change dedicated to Oxygen isotopes as tracers of Mediterranean variability: linking past, present and future (Eds. M.D. Jones, C.N. Roberts, G. Zanchetta).

• Global and Planetary Change dedicated to Mediterranean climate variability (Eds. P. Lionello, S. Planton, X. Rodò).

The following organizations have provided the funding for ESF MedCLIVAR activities:

• Austria: Fonds zur Förderung der Wissenschaftlichen Forschung (FWF)

• Cyprus: Research Promotion Foundation

• France: Centre National de la Recherche Scientifique (CNRS)/Institut National des Sciences de l’Univers (INSU)

• Germany: Deutsche Forschungsgemeinschaft (DFG)

• Greece: National Hellenic Research Foundation (NHRF)

• Israel: Israel Academy of Sciences and Humanities

• Italy: Ministry for the Environment and Territory

• Portugal: Fundação para e Ciência e a Tecnologia (FCT)

• Spain: Consejo Superior de Investigaciones Cientificas (CSIC), Ministerio de Educacion y Ciencia

• Switzerland: Schweizerischer Nationalfonds zur Förderung der wissenschaftlichen Forschung

• Turkey: Scientific and Technical Research Council of Turkey (TUBITAK)

• United Kingdom: Natural Environment Research Council (NERC)

MedCLIVAR Grants

Foreword

The Mediterranean region has contributed significantly to the development of important human civilizations; however, what is still a matter of scientific debate is the relevance of Mediterranean climatic conditions and its climate variability to the rise and fall of some of these civilizations. It is widely accepted that ancient societies were highly sensitive to famine, disease, and war, which were often driven by drought, flood, frost, or fire events. Therefore, agrarian wealth and overall economic growth might be related to climate change on interannual to decennial timescales. As shown recently by Büntgen et al. (2011), reduced climate variability in Roman times, relative to its surroundings, matched a sustained demographic growth and civilization expansion. Wet and warm summers occurred during periods of Roman prosperity; on the other hand, increased climate variability from ~250 to 600 CE coincided with the demise of the western Roman Empire.

Although it is likely that preindustrial civilizations were highly sensitive to climatic conditions, it is wise to argue that present-day societies are also dependent on variations in the climate and natural environment. The Mediterranean climate is characterized by its accentuated interannual variability, defined also as climatic infidelity, and this area is one of the world’s hot spots of climate change, where forecasted global warming and dryness are likely to greatly affect the environment and human activities (IPCC, 2007). An increase in atmospheric temperature ranging between 2.2 and 5.1 °C is expected by the end of this century, as is a significant decrease in rainfall (ranging between 4% and 27%), and an increase in drought periods. These will result in a higher frequency of days during which the temperature would exceed 30 °C and will trigger extreme events such as heat waves, droughts, or floods that could become more frequent and violent.

Consequently, climate-change impacts on the Mediterranean environment will affect particularly the availability and quality of water resources, via a change in its cycle due to a rise in evaporation and a reduction in rainfall. This water issue will be a core concern in the sustainability challenge of the whole region. Land degradation and desertification will also be exacerbated, and animal and plant biodiversity will be at risk because of a displacement of species natural ranges toward the north and toward higher altitudes, the extinction of less mobile or more climate-change-sensitive species, and the appearance or even invasions of new species. Forests will most probably experience an increase in fire and parasitic risks. These forcings will amplify the already existing pressures on the natural environment related to anthropogenic activities; in fact, a whole range of local meteorological and physical risks already affecting the Mediterranean area will have their impacts aggravated by rapid coastal urbanization and global change (Plan Bleu and EIB, 2008).

Mediterranean climate and its impacts on land processes and on human activities are also tightly connected with the circulation of water masses and the ecological processes of the Mediterranean Sea. Because of its relatively small size, its geographical location, and its semi-land-locked nature, this marine basin is very sensitive and responds quickly to atmospheric forcings and/or anthropogenic influences. The Mediterranean is, on average, a typical concentration basin, with the annual evaporation exceeding annual rainfall and river runoff, thus transforming the Atlantic water that enters through the Strait of Gibraltar on surface into a denser and more saline form. The Mediterranean Water flows out as a dense bottom current, which cascades down the continental slope of the Gulf of Cadiz, mixing with the surrounding Atlantic waters. This saline water flows westward along the Iberian southern continental slope and spreads over the North Atlantic at intermediate levels. The presence of this saline water in the Atlantic has important consequences in both the mesoscale and large-scale processes occurring in the Atlantic, an important example being the meridional overturning circulation that is highly relevant for European climate. Besides the important role that the Mediterranean plays directly in the Atlantic circulation and European climate, this semi-enclosed basin is a very interesting system by itself. The climate and its variability in the Mediterranean area constitute a challenging subject, especially for the European scientific community, since there is still insufficient knowledge about the regional climate forcing, internal variability, and system feedbacks. The Mediterranean basin has a large enough scale to experience most of the main processes that occur in the world ocean but has also a small enough scale to be monitored with a good time–space observation network. In addition, the understanding of the present state and the future of the Mediterranean basin circulation and of its climate system has to be grounded on the paleoclimate and paleo-oceanography knowledge, for which the European science community has developed a global leadership. However, more studies are still needed to reconstruct past Mediterranean climates using different well-dated and well-calibrated proxy terrestrial and marine records and to model climate and climate variability at different timescales.

The efforts that are bringing together leading European marine and terrestrial scientific communities to advance our understanding of climate variability and the underlying physical, chemical, and biological processes are also at the forefront in the strategic view of the Life, Earth and Environmental Sciences (LESC) Standing Committee of the European Science Foundation (ESF-LESC, 2009). In the context of current concerns about the future sustainability of our planet and our society, ESF-LESC identified such issues as deserving the highest priority for research and international cooperation in the coming decade. A wide range of ESF activities have been put into action toward this aim. This book is a result of a multi-annual research networking activity conducted in the framework of the Mediterranean Climate Variability (MedCLIVAR, www.esf.org/medclivar) Research Networking Program on the variability of Mediterranean climate and its links with marine circulation, land–atmosphere interactions, and future climate projections. This ESF program has been endorsed by the LESC Standing Committee and supported by research organizations in 12 countries.

In this context, this book presents a logical series of chapters starting with a review of the paleoclimatic variability of the Mediterranean region and its possible causes. This is essential for validating model simulations of past climate, which can then improve future climate simulations. Chapter focuses on the main aspects of the circulation in the Mediterranean Sea and its variability, identifying some priorities for future research on the forcing mechanisms of the main modes of temporal and spatial variability of the circulation. This is followed by a chapter about the long-term (interannual to interdecadal) sea-level variability and trends, paying special attention to the processes contributing to the observed changes. Chapters 5 and 6 offer a review of the synoptic and of the large-scale atmospheric circulation. Finally, a perspective of the state-of-the-art of regional climate modeling over the Mediterranean is presented in chapter 7, ending with new insights on future climate projections and expected changes of the Mediterranean regional climate in chapter 8.

All these chapters correspond to the major results obtained by many scientists who contributed to the MedCLIVAR program, whose main goals were the description and understanding of climate past evolution and variability at different scales and the identification of trends and climate-change impacts. The authors raise several issues whose full understanding is still pending and thus offer suggestions for future research. It is very much hoped that the fundamental research conducted and networked within the MedCLIVAR framework will contribute to the further development of science-based mitigation and adaptation strategies in the Mediterranean area.

Prof. Isabel Ambar, University of Lisbon, Portugal

Prof. Giuseppe Scarascia-Mugnozza, Agricultural Research Council of Italy, Roma, Italy

Members of the Life, Earth and Environmental Sciences (LESC) Standing Committee

European Science Foundation (ESF) July 2011

References

1. Büntgen U, Tegel W, Nicolussi K, et al. 2500 years of European climate variability and human susceptibility. Science. 00FC;ntgen et al., 2011;331:578–582.

2. ESF-LESC, 2009. LESC Strategic Science Position: The View Ahead. An ESF-LESC Science Position Paper. European Science Foundation, Strasbourg, p. 16. <http://www.esf.org/lesc>.

3. IPCC, 2007. In: Solomon, S., Qin, D., Manning, M., et al. (Eds.), Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. <http://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm>.

4. Plan Bleu and European Investment Bank, 2008. Climate Change and Energy in the Mediterranean. <http://www.planbleu.org/publications/changement_clim_energie_med_EN.pdf>.

List of Contributors

Fatima Abrantes

Laboratório Nacional de Energia e Geologia—LNEG, Unidade de Geologia Marinha, Amadora, Portugal; Centro de Investigação Marinha e Ambiental—CIMAR, Porto, Portugal

Sena Akcer-On

ITU Eastern Mediterranean Centre for Oceanography and Limnology (EMCOL) and Eurasia Institute of Earth Sciences, Istanbul, Turkey; ITU Eastern Mediterranean Centre for Oceanography and Limnology (EMCOL), Faculty of Mines, Istanbul, Turkey

Rob Allan

Met Office Hadley Centre, Exeter, UK

Maria-Carmen Alvarez-Castro

Departamento de Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, Seville, Spain

Daniel Ariztegui

Section of Earth and Environmental Sciences, University of Geneva, Geneva, Switzerland

Vincenzo Artale

ENEA, Rome, Italy

Rolland Aznar

Área de Medio Físico, Dirección de Relaciones Institucionales e Innovación, Tecnológica, Puertos del Estado, Madrid, Spain

David Barriopedro

IDL at University of Lisbon, Lisbon, Portugal

Departamento Astrofisica y CC de la Atmosfera / Instituto de Geociencias UCM-CSIC, Universidad Complutense de Madrid, Madrid, Spain

Luis Batista

Laboratório Nacional de Energia e Geologia—LNEG, Unidade de Geologia Marinha, Amadora, Portugal

Danijel Belušić

School of Mathematical Sciences, Monash University, Victoria, Australia

Gerardo Benito

Museo Nacional de Ciencias Naturales-CSIC, Serrano 115bis, Madrid

Jonathan Booth

Centre for Catchment and Coastal Research and the River Basin Dynamics and Hydrology Research Group, Institute of Geography and Earth Sciences, University of Wales, Aberystwyth, UK

David Brayshaw

National Centre for Atmospheric Sciences, Department of Meteorology, University of Reading, Reading, UK

Ulf Büntgen

Swiss Federal Research Institute WSL, Birmensdorf, Switzerland and Oeschger Centre for Climate Change Research (OCCR), University of Bern, Bern, Switzerland

Isabel Cacho

GRC Geociències Marines, Department Estrat. Paleont. i Geoc. Marines Facultat de Geologia, Universitat de Barcelona, Barcelona, Spain

Namik Cagatay

ITU Eastern Mediterranean Centre for Oceanography and Limnology (EMCOL) and Eurasia Institute of Earth Sciences, Istanbul, Turkey; ITU Eastern Mediterranean Centre for Oceanography and Limnology (EMCOL), Faculty of Mines, Istanbul, Turkey

Adriana Carrillo

ENEA Casaccia, Roma, Italy

Alberto Casado

Laboratoire de Météorologie Dynamique, IPSL/CNRS/UPMC, Paris, France

Jeanne Colin

Centre National de Recherches Météorologiques—Groupe d’études de l’Atmosphère Météorologique, Météo-France, Toulouse, France

Daniele Colombaroli

Institute of Plant Sciences and Oeschger Centre for Climate Change Research (OCCR), University of Bern, Bern, Switzerland

Letizia Congedi

Department of Material Science, University of Salento, Salento, Italy

Fabio D’Andrea

LMD, Paris, France

Basil Davis

ARVE Group, School of Architecture, Civil and Environmental Engineering, Station 2 Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland

Alessandro Dell’Aquila

ENEA, Rome, Italy

Clotilde Dubois

Centre National de Recherches Météorologiques—Groupe d’études de l’Atmosphère Météorologique, Météo-France, Toulouse, France

Alberto Elizalde

Max Planck Institute for Meteorology, Hamburg, Germany

Jan Esper

Department of Geography, University of Mainz, Mainz, Germany

Thomas Felis

MARUM – Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany

Luciana Fenoglio-Marc

Institute of Physical Geodesy, Technical University Darmstadt, Germany

Erich M. Fischer

Institute for Atmospheric and Climate Science, ETH, Zurich, Switzerland

Dominik Fleitmann

Institute of Geological Sciences and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland

David Frank

Swiss Federal Research Institute WSL, Birmensdorf, Switzerland and Oeschger Centre for Climate Change Research (OCCR), University of Bern, Bern, Switzerland

GacicMiroslav GaČić

OGS, Trieste, Italy

David Gallego

Departamento de Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, Seville, Spain

Elena Garcia-Bustamante

Department of Geography, Climatology, Climate Dynamics and Climate Change, Justus Liebig University, Giessen, Germany

Garcia-HerreraRicardo García-Herrera

Dpto. Astrofisica y CC. de la Atmosfera / Instituto de Geociencias (UCM-CSIC)

Garcia-LafuenteJesus Garcìa-Lafuente

Departamento de Física Aplicada II, University of Málaga, Málaga, Spain

Gian Pietro Gasparini

CNR-ISMAR, Forte Santa Teresa, La Spezia, Italy

Luis Gimeno

Ephyslab. Facultad de Ciencias de Ourense, Universidad de Vigo, Ourense, Spain

Ruediger Glaser

Department of Geography, University of Freiburg, Freiburg, Germany

Damià Gomis

IMEDEA, Universitat de les Illes Balears—CSIC, Mallorca, Spain

Fidel J. Gonzalez-Rouco

Dpto. Astrofisica y CC. de la Atmosfera / Instituto de Geociencias (UCM-CSIC)

Hugues Goosse

Lemaitre Center for Earth and Climate Research, Earth and Life Institute, Université Catholique de Louvain, Belgium

Celia Gouveia

IDL at University of Lisbon and Universidade Lusófona, Lisbon, Portugal

Silvio Gualdi

Instituto Nazionale di Geofisica e Vulcanologia, Bologna, Italy

HernandezEmiliano Hernández

Departamento de Física de la Tierra II, Universidad Complutense, Madrid, Spain

Marine Herrmann

CNRM-GAME, Météo-France/CNRS, Toulouse, France

Elke Hertig

Institute of Geography, University of Augsburg, Augsburg, Germany

Jucundus Jacobeit

Institute of Geography, University of Augsburg, Augsburg, Germany

JordaGabriel Jordà

Institut Mediterrani d’Estudis Avançats, Esporles, Spain

Simon A. Josey

National Oceanography Centre, Southampton, UK

Thorsten Kiefer

PAGES International Project Office, Bern, Switzerland

Peter Knippertz

Institute for Atmospheric Physics, Johannes Gutenberg University, Mainz, Germany

Franz G. Kuglitsch

Institute of Geography, Climatology and Meteorology, University of Bern, Bern, Switzerland; Institute of Geography and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland

L’HevederBlandine L’Hévéder

Laboratoire de Météorologie Dynamique, IPSL/CNRS/UPMC, Paris, France

Gregor C. Leckebusch

School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK

Laurent Li

Laboratoire de Météorologie Dynamique, IPSL/CNRS/UPMC, Paris, France

Piero Lionello

DISTEBA, Dipartimento di Scienze e Tecnologie Biologiche e Ambientali, University of Salento, Lecce and CMCC, Centro euroMediterraneo per i Cambiamenti Climatici, Lecce, Italy

Wolfgang Ludwig

CEFREM, University of Perpignan, Perpignan, France

Jürg Luterbacher

Department of Geography, Climatology, Climate Dynamics and Climate Change, Justus Liebig University, Giessen, Germany

Mark G. Macklin

Centre for Catchment and Coastal Research and the River Basin Dynamics and Hydrology Research Group, Institute of Geography and Earth Sciences, University of Wales, Aberystwyth, UK

Panagiotis Maheras

Department of Meteorology and Climatology, Aristotle University of Thessaloniki, Thessaloniki, Greece

Sturt W. Manning

Malcolm and Carolyn Wiener Laboratory for Aegean and Near Eastern Dendrochronology, Cornell Tree Ring Laboratory, Cornell University, Ithaca, NY

Marta Marcos

IMEDEA, Universitat de les Illes Balears—CSIC, Mallorca, Spain

Annarita Mariotti

NOAA, Office of Atmospheric and Oceanic Research, Silver Spring, USA

Maurizio Maugeri

Dipartimento di Fisica, Università degli studi di Milano, Milan, Italy

Claude Millot

LOPB-COM-CNRS, La Seyne/mer, France

Sebastià Monserrat

IMEDEA, Universitat de les Illes Balears—CSIC, Mallorca, Spain

Paolo Montagna

Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY and Laboratoire des Sciences du Climat et de l’Environnement, Avenue de la Terrasse, Gif-sur-Yvette, France

Bruno Buongiorno Nardelli

CNR-ISAC, Roma, Italy

Filipa Naughton

Laboratório Nacional de Energia e Geologia—LNEG, Unidade de Geologia Marinha, Amadora, Portugal; Centro de Investigação Marinha e Ambiental—CIMAR, Porto, Portugal

Louise Newman

PAGES International Project Office, Bern, Switzerland

Raquel Nieto

Ephyslab. Facultad de Ciencias de Ourense, Universidad de Vigo, Ourense, Spain

Katrin M. Nissen

Institut für Meteorologie, Freie Universität Berlin, Germany

OzsoyEmin Özsoy

Institute of Marine Sciences, Middle East Technical University, Erdemli, Turkey

Valentina Pavan

ARPA-SIMC, Bologna, Italy

PerezBegoña Pérez

Área de Medio Físico, Puertos del Estado, Madrid, Spain

Claudio Piani

International Centre for Theoretical Physics, Trieste, Italy

Joaquim G. Pinto

Institute for Geophysics and Meteorology, University of Cologne, Cologne, Germany

Giovanna Pisacane

ENEA Casaccia, Roma, Italy

Serge Planton

Centre National de Recherches Météorologiques—Groupe d’études de l’Atmosphère Météorologique, Météo-France, Toulouse, France

Mitchell J. Power

Utah Museum of Natural History, Department of Geography, University of Utah, Salt Lake City, Utah

Pozo-VazquezDavid Pozo-Vázquez

Department of Physics, University of Jaén, Jaen, Spain

Fabio Raicich

Istituto di Scienze Marine, Consiglio Nazionale delle Richerche, Trieste, Italy

Volker Rath

Dpto. Astrofisica y CC. de la Atmosfera (UCM)

Pedro Ribera

Departamento de Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, Seville, Spain

Dirk Riemann

Department of Geography, University of Freiburg, Freiburg, Germany

Neil Roberts

School of Geography, Earth and Environmental Sciences, University of Plymouth, Plymouth, UK

Teresa Rodrigues

Laboratório Nacional de Energia e Geologia—LNEG, Unidade de Geologia Marinha, Amadora, Portugal

Centro de Investigação Marinha e Ambiental—CIMAR, Porto, Portugal

Paolo Ruti

ENEA, Rome, Italy

Hadas Saaroni

Department of Geography and the Human Environment, Tel Aviv University, Tel Aviv, Israel

Sanchez-GarridoJose C. Sánchez-Garrido

Departamento de Física Aplicada II, University of Málaga, Málaga, Spain

Emilia Sanchez-Gomez

Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique, Toulouse, France

Gianmaria Sannino

ENEA Casaccia, Roma, Italy

Rosalia Santoleri

CNR-ISAC, Roma, Italy

Katrin Schroeder

CNR-ISMAR, Forte Santa Teresa, La Spezia, Italy

Stefanie Seubert

Institute of Geography, University of Augsburg, Augsburg, Germany

Florence Sevault

Centre National de Recherches Météorologiques—Groupe d’études de l’Atmosphère Météorologique, Météo-France, Toulouse, France

Marie-Alexandrine Sicre

Laboratoire des Sciences du Climat et de l’Environnement (LSCE), IPSL-CNRS, Domaine du CNRS, Gif-sur-Yvette Cedex, France

Francisco Javier Sierro

Department of Geology, University of Salamanca, Salamanca, Spain

Sergio Silenzi

Climate and Coastal Research Unit, ISPRA-Institute for Environmental Protection and Research, Rome, Italy and Earth Science Department, University of Rome, La Sapienza, Italy

Samuel Somot

CNRM, Groupe d’Etudes de l’Atmosphère Météorologique, Météo-France, Toulouse, France

Emil Stanev

ICBM, University Oldenburg, Oldenburg, Germany

Mariavittoria Struglia

ENEA Casaccia, Roma, Italy

Isabelle Taupier-Letage

LOPB-COM-CNRS, La Seyne/mer, France

Willy Tinner

Institute of Plant Sciences and Oeschger Centre for Climate Change Research (OCCR), University of Bern, Bern, Switzerland

Andrea Toreti

Department of Geography, Justus-Liebig University of Giessen, Giessen, Germany

Isabel F. Trigo

Instituto de Meteorologia and IDL at University of Lisbon, Lisbon, Portugal

Ricardo M. Trigo

IDL at University of Lisbon and Universidade Lusófona, Lisbon, Portugal

Michael N. Tsimplis

Ocean Observing and Climate, National Oceanography Centre, Southampton, UK

Mikis Tsimplis

National Oceanography Centre, Southampton, UK

P.Chronis Tzedakis

Department of Geography, University College London, London, UK

Uwe Ulbrich

Institut für Meteorologie, Freie Universität Berlin, Germany

Valero-GarcesBlas Valero-Garcés

Pyrenean Institute of Ecology (CSIC), Zaragoza, Spain

Gerard van der Schrier

Royal Netherlands Meteorological Institute (KNMI), De Bilt, The Netherlands

VanniereBoris Vannière

CNRS, UMR Chrono-Environnement, UFC, Besançon, France

Vargas-YanezManuel Vargas-Yáñez

IEO, Centro Oceanográfico de Málaga, Málaga, Spain

Sergio M. Vicente-Serrano

Instituto Pirenaico de Ecología, Consejo Superior de Investigaciones Científicas, Zaragoza, Spain

VilibicIvica Vilibić

Institute of Oceanography and Fisheries, Split, Croatia

Antje (Helga Luise) Voelker

Laboratório Nacional de Energia e Geologia—LNEG, Unidade de Geologia Marinha, Amadora, Portugal

Centro de Investigação Marinha e Ambiental—CIMAR, Porto, Portugal

Steffen Vogt

Department of Geography, University of Freiburg, Freiburg, Germany

Heinz Wanner

Oeschger Centre for Climate Change, University of Bern, Bern, Switzerland

Johannes P. Werner

Department of Geography, Climatology, Climate Dynamics and Climate Change, Justus Liebig University, Giessen, Germany

Gail Willett

Met Office Hadley Centre, Exeter, UK

Megan H. Williams

Department of History, San Francisco State University, San Francisco, California

WoppelmannGuy Wöppelmann

LIENSs, Université de la Rochelle—Centre National de la Recherche Scientifique, La Rochelle, France

Elena Xoplaki

Department of Geography, Climatology, Climate Dynamics and Climate Change, Justus Liebig University, Giessen, Germany; Institute of Geography and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland

Pascal Yiou

LSCE, CEA-CNRS-UVSQ & IPSL, Gif-sur-Yvette, France

Matteo Zampieri

Department of Material Science, University of Salento, Salento, Italy

Christos S. Zerefos

Biomedical Research Foundation, Academy of Athens, N.E.O., Athens, Greece

Vassilis Zervakis

Department of Marine Sciences, University of the Aegean, Mytilene, Greece

Baruch Ziv

Department of Natural Sciences, The Open University of Israel, Raanana, Israel

George Zodiatis

Oceanography Centre, University of Cyprus, Nicosia, Cyprus

Eduardo Zorita

Helmholtz-Zentrum Geesthacht, Geesthacht, Germany

Introduction: Mediterranean Climate—Background Information

Piero Lionelloa,b, Fatima Abrantesc, Letizia Congedia, Francois Dulacd, Miro Gacice, Damià Gomisf, Clare Goodessg, Holger Hoffh, Haim Kutieli, Jürg Luterbacherj, Serge Plantonk, Marco Realea, Katrin Schröderl, Maria Vittoria Strugliam, Andrea Toretin,o, Michael Tsimplisp, Uwe Ulbrichq and Elena Xoplakin,o

aDISTEBA Department of Science and technology for Biology and The Environment, University of Salento, Lecce, Italy

bCMCC, Centro EuroMediterraneao per i Cambiamenti Climatici, Lecce, Italy

cLaboratório Nacional de Energia e Geologia, Unidade de Geologia Marinha, Amadora, Portugal

dIPSL, LSCE (CEA-CNRS-UVSQ) Gif-Sur-Yvette, and LISA (UPEC-UPDP7-CNRS), Créteil, France

eOGS, Trieste, Italy

fIMEDEA (Universitat de les Illes Balears, CSIC), Mallorca, Spain

gClimatic Research Unit, University of East Anglia, UK

hPotsdam Institute for Climate Impact Research, Germany and Stockholm Environment Institute, Sweden

iDepartment of Geography and Environmental Studies, University of Haifa, Haifa, Israel

jDepartment of Geography, Justus Liebig University, Climatology, Climate, Giessen, Germany

kCNRM-GAME, Météo France, Toulouse, France

lCNR-ISMAR, La Spezia, Italy

mENEA, Rome, Italy

nDepartment of Geography, Climatology, Climate Dynamics and Climate Change, Justus-Liebig University of Giessen, Giessen, Germany

oInstitute of Geography, Climatology and Meteorology, University of Bern, Bern, Switzerland

pNational Oceanography Centre Southhampton, Southampton, UK

qFreie Universität, Berlin, Germany

I.1 Introduction

This introductory chapter presents general and consolidated background knowledge to be referred to in the rest of the book and anticipates, though only partially, the information that is provided in the book chapters, where a complete description of scientific issues and recent research results is presented, including technical details and discussion of open issues. The content intends not only to reflect what is known about Mediterranean climate but also to highlight the open issues associated with limitations in data availability or lack of understanding of key processes. It provides essential information, which is not limited to basic climate variables, such as surface temperature and precipitation, but reflects the complexity of the climate system, the role of the main subsystems and factors, and includes also the links among environment, society, and climate.

The Mediterranean Sea is the crucial environmental factor in this region. The presence of a large marginal and almost completely closed sea on the western side of a large continental area is geographically unique. Its size is actually substantial. Its area, excluding the Black Sea, is about 2.5 million km². Its extent is about 3700 km in longitude and 1600 km in latitude and has an average depth of 1500 m. The Strait of Gibraltar, connecting the Mediterranean Sea to the Atlantic is only 14.5 km wide and less than 300 m deep at the shallowest sill. These morphological characteristics make the Mediterranean Sea a large source of moisture and a heat reservoir with a significant capacity for the surrounding land areas (considering the annual average, it acts as a moderate source of heat). The Strait of Gibraltar plays a crucial role for the environment of the Mediterranean Sea. The fluxes through the strait compensate for the mass deficit due to the large evaporation in the basin, supply comparatively freshwater masses to one of the saltiest seas on Earth, and also provide a small supply of heat, because the Mediterranean water (MW) outflow is cooler than the Atlantic water (AW) inflow. The complicated morphology of the region—with its many sharp orographic features, often close to the coastlines, and the presence of distinct basins and gulfs, islands, and peninsulas—has a strong effect on the atmospheric circulation. It is responsible for several cyclogenetic areas, local winds, many mesoscale processes, and intense air–sea interactions, such as those responsible for dense-water formation processes driving the Mediterranean thermohaline cells. Further, the shape of the Mediterranean Sea bottom, with deep basins linked through much shallower straits, strongly constrains the Mediterranean Sea circulation.

The sequence of the sections in this introductory chapter is meant to follow the logic of the Mediterranean Climate Variability and Predictability (MedCLIVAR) project, merging the different topics and timescales that are needed for a comprehensive description of the Mediterranean climate. This is a region with large socioeconomic contrasts and sectors that are very vulnerable to climate change (Section I.2). Though this book and MedCLIVAR do not actually deal with socioeconomic issues, it is important to be aware of the information that is needed by policymakers and stakeholders in the Mediterranean region. Some general characteristics of the Mediterranean region are described in Section I.3. Specifically, it is well known that reaching the spatial resolution required to study local impacts is a formidable task for which climate research is required to dedicate a strong effort, especially for the Mediterranean region, where environmental and morphological gradients are particularly large. Sections I.4–I.8 describe past evolution of the climate and its present condition and trends. Its complicated past evolution (Section I.4), with dramatic events that have left clear marks in the Mediterranean geological history, is by itself a fascinating research subject with interesting specific problems (Section I.4), but also poses the problem of whether any of these past conditions, such as the anoxic states documented in the past, can occur again in the next decades and centuries. The presence of archeological records since ancient times and documentary proxies to complement the natural archives offers a unique (with the only possible exception of China) opportunity for reconstructing the climate in historical times (Section I.5). The interpretation of this information is not straightforward, but gives to the Mediterranean region an exceptional opportunity to assess whether the recent pace of climate variations is unprecedented in the history of the past millennia. Trends in temperature and precipitation (Sections I.6 and I.8) have been observed in the twentieth century and for temperature their consistency with global warming is not controversial, even if a demonstration of the consistency between the patterns in observations and climate simulations remains challenging (Section I.17).

Sections I.9–I.15 describe components and factors and their Mediterranean specificities, beginning with the marine component. The Mediterranean Sea circulation (Section I.9) presents three main thermohaline cells driven by dense-water formation: a basinwide open cell, with a freshwater inflow from the Atlantic counteracted by a salty outflow of water formed in the Levantine basin across the Gibraltar Strait, and two separated closed cells, one for the western and one for the eastern part of the basin. This last one is peculiar, as it has been observed that it can operate in two different regimes, with dense-water formation in different areas, which are suggestive of possible multiple equilibriums. The shift of the formation site of deep waters from the Adriatic to the Aegean took place in the late 1980s and it is called EMT (eastern Mediterranean transient). The Mediterranean Sea level (Section I.10) has been shown to depart in its trends and variability from the nearby Atlantic Ocean, because of important local factors, which make it very uncertain to link its evolution to that of global sea level for the next decades.

Rivers, atmospheric cyclones, winds, ocean waves, and aerosols are briefly discussed in Sections I.11–I.15. Rivers (Section I.11) are a key component to close the hydrological cycle and the mass balance of the Mediterranean Sea. Atmospheric cyclones in the Mediterranean (Section I.12) determine a separate branch of the northern hemisphere storm track, with several areas of cyclogenesis, mainly in the western Mediterranean, and prevalent cyclolysis in the central and eastern Mediterranean. Spatially and seasonally varying wind regimes are summarized in Section I.13. Ocean waves (Section I.14) are a factor to be accounted for the management and evolution of the coasts. A high aerosol load over the basin, dominated by continental sources, significantly impact the radiation budget (Section I.15), with consequences for evaporation and regional climate that are not yet quantified.

Finally, Section I.16 discusses the climate projections that are an attempt to establish possible future climate scenarios in the Mediterranean region and their uncertainty. Section I.17 discusses the most relevant issues with regard to the main objectives of present climate research.

I.2 Socioeconomic Characteristics and Main Vulnerabilities

The Mediterranean basin is characterized by strong socioeconomic differences, in particular, between the northern Mediterranean countries (NMCs) and the southern and eastern Mediterranean countries (SEMCs). Though the situation is changing rapidly, and the SEMCs are increasing their annual primary energy demand at more than 4% per year, at present, the NMCs have about a four times higher per capita gross domestic product than the SEMCs, a three times higher per capita energy supply, more than twice as high per capita CO2 emissions, and four times more tourist arrivals, with the Mediterranean accounting for 30% of the world’s international tourism (Plan Bleu, 2009).

While population development in the north is almost stagnant, strong population growth in the southeast (in combination with a lack of effective policies) results in overexploitation of water, land, and other resources, driven by land clearing, cultivation of marginal land, overgrazing, and firewood harvesting. Currently, 80% of all dry lands in the SEMCs are affected by desertification (Plan Bleu, 2005). Land productivity is decreasing accordingly. In contrast, many rural areas in the NMC experience abandonment of agricultural land, with subsequent encroachment of shrubs and trees and a greening of the land. Forest cover in the NMCs is much higher than in the SEMCs. The SEMCs are rapidly urbanizing—with almost all of the future population growth projected to be in the cities—while urbanization rates in the north are more or less stable (Plan Bleu, 2005).

Precipitation in the Mediterranean in unevenly distributed (see also Section I.6), being scarce and irregular in many southern areas, where water availability is already a problem. There is a significant risk of reaching climate conditions (see Section I.15 and Chapter 8) that will imply a much drier state of the land and atmosphere than at present. Likely, the simultaneous action on the environment of climate and other anthropic factors (such as deforestation, draining of wetlands, and adoption of water-saving technologies in irrigation) will produce further land degradation, to which the Mediterranean social-ecological systems seem to be quite vulnerable.

Per capita water availability in the NMCs is three times higher than in the SEMCs. Water scarcity in the south is compounded by higher loss rates and lower water productivity in all sectors. The gap between water availability and demand is currently widening further in the south because of rapid population growth and is projected to become even wider in the future because of conditions becoming progressively drier than in the north with climate change. Irrigation accounts for 40% (80%) of total water demand in the NMCs (the SEMCs). While irrigation is primarily an adaptation strategy to climate variability, the growing dependence on irrigation in the Mediterranean is likely to increase economic and social vulnerability further, given projections of reduced total water availability and rapidly growing competing urban water demands. An indication for water-quality problems is the fact that 10% (50%) of the cities and 5% (20%) of population in the NMCs (the SEMCs) are not connected to any wastewater treatment (Plan Bleu, 2005, 2009).

Agricultural (water) productivity is low in most SEMCs, with frequent crop failure due to droughts. Yield increases have remained below the world average over the past few decades, aggravating the problems due to higher climate variability and lower per capita water availability as compared with the NMCs. Cultivation of more marginal land and urbanization (often resulting in a loss of the most productive agricultural land) further suppress agricultural productivity in the south. north African countries have already experienced a sharp decline in per capita rain-fed agricultural production in years (IAASTD, 2008). As a result (also in response to the overuse and depletion of groundwater), SEMCs have become net importers of virtual water (Yang et al., 2007; Fernandez and ENGREF, 2007). Their dependence on virtual water imports is growing rapidly, already being higher than in any other region of the world. Net virtual water imports in several SEMCs are approaching or even exceeding the renewable blue water resources. This situation makes them increasingly vulnerable to price hikes in international markets.

All of these factors in combination indicate a higher vulnerability to climate change of the SEMCs, given the lower adaptive capacity and at the same time higher exposure to droughts and desertification as compared with NMCs. SEMC economies, employment, and livelihoods depend more strongly on agriculture and hence on water resources and climate. Greater climate-change impacts in the south are met by a lack of technical, financial, and institutional means to implement climate adaptation solutions on a large scale. With respect to the NMCs, SEMCs generally have lower literacy rates and rank lower on indexes of good governance, democracy, and corruption.

Beyond the north–south gradient in the Mediterranean, particularly vulnerable landscapes include deltas and coastal zones (vulnerable to sea-level rise), as well as rapidly growing cities without adequate infrastructure and institutions. In the Mediterranean region, 50% of the urban population lives less than 10 m above sea level (Plan Bleu, 2005, 2009). Tourist destinations (concentrated along the coast) are vulnerable not only to sea-level rise but also to higher summer temperatures, which may turn tourists away toward more northern and cooler locations.

I.3 The Mediterranean Region

The characterization of the region is strongly linked to the Mediterranean Sea, a semi-enclosed, mostly deep regional sea. Its presence is, however, not sufficient for determining a uniform climate. Strong contrasts among different areas are present, deriving from the complicated morphology of the Mediterranean region and its location between the subtropical zone to the south and the temperate zone to the north. According to the traditional climate classification (Köppen, 1900) the Mediterranean climate is defined as a midlatitude temperate climate with a dry summer season, which can be either warm or hot (these two types are labeled Csa and Csb, respectively, in the Köppen classification). However, the Csa and Csb classifications apply only to a fraction of the Mediterranean region (Figure I.1). The distance between most parts of this region and the sea is only a couple hundred kilometers; however, other temperate, arid, and snow climate types are present. The contrasts are large: There are permanent glaciers in the humid alpine area north of the Mediterranean Sea and hot subtropical desert areas at the southern African coast, a temperate maritime climate at the north Iberian coast west of the Mediterranean Sea and truly Mediterranean areas, and steppe in the Middle East regions at the eastern coast. Note also the large areas with midlatitude temperate climate and with no dry summer (Cfa and Cfb) in the northern parts of the Mediterranean. The mean annual cycles of the climate types that are present in Figure I.1 are shown in Figure I.2, which shows the large range of temperatures and the different behavior of precipitation among the different zones. Note the scarcity of summer precipitation in many areas.

Figure I.1 Köppen climate types in the Mediterranean region: subtropical steppe (BSh), midlatitude steppe (BSk), subtropical desert (BWh), midlatitude desert (BWk), Mediterranean climate with hot/warm summer (Csa/b), humid subtropical with no dry season (Cfa), maritime temperate (Cfb), humid continental with hot/warm summer (Dfa/b), continental with dry hot/warm summer (Dsa/b), and tundra (ET). This figure is based on Climatic Research Unit (CRU) temperature and precipitation gridded data ( New et al., 2000 ).

Figure I.2 Mean annual cycles of temperature (A, monthly average temperature, °C) and precipitation (B, mm/month) of the Köppen climate types in the Mediterranean. Each line corresponds to the spatial mean over the corresponding areas in Figure I.1 . Data and labels used are the same as in Figure I.1 .

The location of the Mediterranean region in a transitional zone between subtropical and midlatitude regimes (for a review, see Lionello et al., 2006a; Alpert et al., 2006a; Trigo et al., 2006) is another important factor of space and time variability. In general terms, there is a difference between the northwestern and southeastern areas, though this cannot be considered a rigorous distinction. The northern part of the region is strongly linked to the midlatitude variability, characterized by the NAO (north Atlantic oscillation) and other midlatitude teleconnection patterns (Xoplaki, 2002; Dünkeloh and Jacobeit, 2003; Xoplaki et al., 2003, 2004; Lionello and Galati, 2008; and Chapter 3 ). Different from areas in northern Europe or along the European Atlantic coast, many northern hemisphere teleconnection patterns besides the NAO exert a comparable influence on regional variables, such as the Scandinavian Pattern, the East Atlantic, and the East Atlantic/northern Russia pattern (Xoplaki, 2002; Lionello and Galati, 2008; and Chapters 5 and 6). The consequence is that many patterns need to be included for describing a significant fraction of climate variability. The southern part of the region is under the influence of the descending branch of the Hadley cell for a large part of the year and is exposed to the Asian monsoon in summer. The effect of the El Niño Southern Oscillation (ENSO) has been detected mainly on precipitation, and it is variable in time but not negligible (Mariotti et al., 2002a; Alpert et al., 2006a). This northwest (midlatitude influences) versus southeast (subtropical influences) separation allows for many exceptions, such as the effect of ENSO on autumn precipitation in the northwestern Mediterranean region (Knippertz et al., 2003) and the effect of northern hemisphere patterns such as NAO on Middle East precipitation (Alpert et al., 2006b).

The complicated land–sea pattern—with many islands of various sizes and peninsulas dividing the Mediterranean Sea into many subbasins connected by narrow straits and the presence of steep mountain ridges close to the coast—helps to explain the spatial heterogeneity of climate in the Mediterranean region (as shown in Figure I.1) and represent a well-known problem for the correct simulation of its climate. The effect of the mesoscale morphological features on atmospheric circulation and air–sea and land–atmosphere interaction and the constraints they pose on sea circulation are crucial for an adequate simulation of Mediterranean climate (Lionello et al., 2006a, b). All these morphological factors need high resolution to be accounted for in numerical simulations, and this requirement has been for a long time beyond the capabilities of climate models and computers. Figure I.3 shows the representation of bathymetry and topography aggregating data in cells of various size. Approximately, Figure I.3A corresponds to the resolution recently achieved by RCMs (Regional Climate Models) and Figure I.3D corresponds to the average resolution of the global models used in the Intergovernmental Panel on Climate Change 4th Assessment Report (IPCC AR4) and in the analysis by Giorgi and Lionello (2008). The two remaining panels correspond to the resolution of two widely used data sets in climate research: the ERA40 reanalysis data set (Figure I.3B; Uppala et al., 2005) and the CRU (Climatic Research Unit) gridded climatology (Figure I.3C) (New et al., 1999). The more recent E-OBS data set (Haylock et al., 2008) based on gridded station data has a resolution comparable to that shown in Figure I.3A. It is clear that only Figure I.3A and B can be considered adequate for representing realistically the morphology of the region, and even a model working at these high resolutions is far from being adequate for simulating hydrological processes in narrow and steep basins of the Mediterranean region. For precipitation, a field with high spatial variability, the resolution required for producing reasonably accurate simulations of the hydrology is discouragingly high. It can be shown that the ratio between precipitation field resolution and size of the hydrological basin should be less than 0.2 for obtaining a reasonably small error of river runoff, implying a 2 km resolution for a river basin with an area of 100 km² (Sangati and Borga, 2009).

Figure I.3 Representation of bathymetry and topography of the Mediterranean region aggregating data in cells of increasing size: (A) 0.2°, (B) 0.5°, (C) 1.25°, and (D) 2.5°.

I.4 Paleoclimate Reconstruction

Paleoclimate records indicate that climate has varied throughout geological time at different timescales, from millions of years (My) to annual or even seasonal scales. Reconstructions of climate variability on geological timescales are based on the study of climate archives that contain information on climate variables (e.g., temperature, precipitation, and wind) and that extend our understanding of climate far beyond both the approximately 150 years of instrumental records and the 4.5 millennia of historical records. Some climate archives, such as sediment sequences on land or from shallow ocean areas, can provide information dating back millions of years but are mostly limited to specific time windows. Other climate archives, such as tree rings, ice cores, corals, speleothems, lake sediments, and deep-sea sediments, allow us to obtain information from multidecadal to hundred thousands to millions of years—either as short glimpses in time (e.g., life span of a tree or coral) or as continuous records.

Past-climate reconstruction draws upon the knowledge of modern oceanography and climatology. Reconstructions of parameters such as air temperature, precipitation, wind, sea-surface temperature (SST), and ocean salinity at any place and time in