Editing IPCC:AR6/WGII/Cross-Chapter-Paper-4 (section)

== Frequently Asked Questions ==

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=== FAQ CCP4.1 | Is the Mediterranean Basin a ‘climate change hotspot’? ===

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''Is the Mediterranean ‘a geographical area characterised by high vulnerability and exposure to climate change’? Climate change projections for the Mediterranean Basin indicate with very high consistency that the region will experience higher temperatures, less rainfall and continued sea level rise during the coming decades. Given that summers are already comparatively dry, these factors together will likely cause substantially drier and hotter conditions as well as coastal flooding, impacting people directly but also harming ecosystems on land and in the ocean.''

For the Mediterranean Basin, climate models consistently project regional warming at rates about 20% above global means and reduced rainfall (–12% for global warming of 3°C). While it is not the region with the highest rate of expected warming on Earth, the Mediterranean Basin is considered particular in comparison to most other regions due to the high exposure and vulnerability of human societies and ecosystems to these changes: a ‘climate change hotspot’.

Rising temperatures trigger extensive evaporation of water from all wet surfaces, notably the sea, lakes and rivers, but also from soils. Along with decreasing rainfall, this evaporation leads to shrinking water resources on land, drier soils, reduced river flow, and significantly longer and more intensive drought spells. Since the Mediterranean climate is already relatively dry and warm in the summer, any additional drought (and also heat) will affect plants, animals and people significantly, and ultimately entire societies and economies.

In general, increasing temperatures and more intensive heat waves in the basin threaten human well-being, economic activities, and also many ecosystems on land and in the ocean. Extreme rainfall events, which despite the lower total rainfall are expected to increase in intensity and frequency in some regions, generate significant risks for infrastructure and people through flash floods. Warming also affects the ocean and its ecosystems, jointly with acidification caused by atmospheric carbon dioxide. Finally, sea level rise, currently accelerating because of global ice loss, threatens coastal ecosystems, historical sites and a growing human population.

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'''Figure FAQ CCP4.1.1 |''' '''Key risks across the Mediterranean region by 2100.''' The symbols above the map highlight risks enhanced by climate change which apply to the entire region with ''high confidence'' . Other risks are localised in the map.

Risks associated with projected climate change are particularly high for people and ecosystems in the Mediterranean Basin due to the unique combination of many factors, including:

* A large and growing urban population exposed to heat waves, with limited access to air conditioning
* A large and growing number of people living in settlements impacted by rising sea level
* Important and increasing water shortages, already experienced by 180 million people today
* Growing demand for water by agriculture for on irrigation
* High economic dependency on tourism, which is likely to suffer from increasing heat but also from the consequences of international emission reduction policies on aviation and cruise-ship travel
* Loss of ecosystems in the ocean, wetlands, rivers and also uplands, many of which are already endangered by unsustainable practices (e.g., overfishing, land use change).

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=== FAQ CCP4.2 | Can Mediterranean countries adapt to sea level rise? ===

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''The rates of observed and projected sea level rise in the Mediterranean are similar to the Northeast Atlantic, potentially reaching 1.1 metres at the end of the present century. Erosion, flooding and the impacts of salinisation are projected to be particularly severe due to the special conditions of the coastal zones in the region. Beyond a few tens of centimetres, adaptation to sea level rise will require very large investments and may be impossible in some regions'' .

Sea level in the Mediterranean has been rising by only 1.4 mm yr -1 during the 20th century, more recently by 2.4±0.5 mm yr −1 from 1993 to 2012, and it is bound to continue rising in the future. Future rates are projected to be similar to the global mean (within an uncertainty of 10–20 cm), potentially reaching 1.1 m or more around 2100 in the event of 3°C of global warming (Figure FAQ CCP4.2; Table SMCCP4.4). Due to the ongoing ice loss in Greenland and Antarctica, this trend is expected to continue in coming centuries. Sea level rise already impacts extreme coastal waters around the Mediterranean and it is projected to increase coastal flooding, erosion and salinisation risks. These impacts would affect agriculture, fisheries and aquaculture, urban development, port operations, tourism, cultural sites and many coastal ecosystems.

Most of the Mediterranean Sea is a micro-tidal environment, which means that the difference between regular high and mean water levels (astronomical tides) is very small. Storm surges and waves can produce coastal floods that persist for several hours, causing particularly large impacts on sandy coasts and eventually also on coastal infrastructure. Mediterranean coasts are also characterised by narrow sandy beaches that are highly valuable for coastal ecosystems and tourism. These beaches are projected to be increasingly affected by erosion and eventually disappear where sedimentary stocks are small.

Overall, Mediterranean low-lying areas of significant width occur along 37% of the coastline and currently host 42 million inhabitants. The coastal population growth projected until 2050 mostly occurs in southern Mediterranean countries, with Egypt, Libya, Morocco and Tunisia being the most exposed countries to future sea level rise. The area at risk also hosts 49 cultural World Heritage sites, including the city of Venice and the early Christian monuments of Ravenna. The Mediterranean also includes areas subjected to sinking of the land (subsidence), including the eastern Nile Delta (Egypt) and the Thessaloniki flood plain (Greece), where local relative sea level rise can exceed 10 mm yr -1 today.

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'''Figure FAQ CCP4.2.1 |''' '''Mediterranean Sea level projections.''' These projections translate the global estimates in WGI AR6 [[IPCC:Wg2:Chapter:Chapter-9|Chapter 9]] to the Mediterranean Basin (Fox-Kemper et al., 2021). They assume that sea level change in the Mediterranean continues to be forced by Atlantic Sea level change seen at the Gibraltar Strait (Section CCP4.1) and thus follow the global mean beyond 2100. Vertical ground motions induced by glacial isostatic adjustments are also included, but not those due to other natural or anthropogenic processes such as tectonics or groundwater extractions. Intra-basin sea level changes are not included. Data available as supplementary material.

Adaptation to sea level rise in the Mediterranean includes engineering or soft/ecosystem-based protection, accommodation, and retreat or managed realignment. Despite various limitations, adaptation already happens today to some extent, as for example the coastal flood and erosion protections along the subsiding Nile Delta coast. Only massive coastal protection and other sustainable development policies could reduce the growing number of people exposed to sea level rise by 20%. It appears therefore ''likely'' that the number of people exposed could increase by up to 130% by 2100.

Without drastic mitigation of climate change, sea level rise is projected to accelerate and will require additional coastal engineering protection projects (e.g., dykes or groynes). Despite their efficiency for the few next decades, these engineering options have also adverse impacts for coastal ecosystems and may not ensure that the recreative value of Mediterranean coasts can be sustained (see Box 13.1 on Venice on the movable barriers protecting the Venice Lagoon). Among nature-based solutions, there are immediate benefits of restoring dunes and coastal wetlands to restore a buffer zone between coastal infrastructure and the sea and therefore reduce coastal risks (Cross-Chapter Box SLR in Chapter 3). Yet, this kind of protection is not feasible everywhere, particularly in urbanised areas, where it faces its limits. The limits for adaptation in the Mediterranean to further acceleration of sea level rise have stimulated ideas of large-scale geoengineering projects such as surface height control dams at Gibraltar. However, such projects come with unknown risks for humans and ecosystems.

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=== FAQ CCP4.3 | What is the link between climate change and human migration in the Mediterranean Basin? ===

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''Climate change already influences conflict and migrations occurring within countries or regions. However, climate is only one of the multiple factors affecting conflict and migration decisions across countries and regions. It is currently not possible to attribute particular conflicts or migrations to climate change and also in the future migration will most likely depend on the economic, social and governance context.''

The Mediterranean Sea is the world’s most dangerous place for migrants, with more than 20,000 deaths reported since 2014. Although empirical evidence indicates that migration related to climate impacts is mostly internal to national borders, climate change is likely to contribute to migration in the Mediterranean Basin as one out of several factors. Climate impacts contribute to migration flows particularly by affecting the economic and political drivers of migration.

Many migrants attempting to cross the Mediterranean to Europe originate from sub-Saharan Africa, a region heavily affected by climate change. In West Africa, for example, migration decisions are heavily influenced by perceptions of climate change and of its economic impact on resources and income. However, projections are uncertain, because climate impacts in Africa might both increase human suffering and thus enhance mobility, but they could also limit mobility of people through lack of financial resources.

The impacts of climate change on conflicts and security are increasingly documented, especially in Africa. Climate impacts may not in itself have caused social and political unrest but can contribute to them. The conflict in Syria has occurred after the drought that marred the country in the years before, but there is no evidence for direct causal linkage. There is, however, high agreement that food insecurity and land degradation, which can be induced by climate change, are major drivers of political upheavals and instability in northern and sub-Saharan Africa.

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