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

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

<div id="h2-22-siblings" class="h2-siblings"></div>

''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.

<div id="_idContainer010y" class="Figure"></div>

[[File:e074e0b914ae2f40b134b86ed12243a3 IPCC_AR6_WGII_Figure_CCP4_FAQ_4_2_1.png]]

'''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.

<span id="faq-ccp4.3-what-is-the-link-between-climate-change-and-human-migration-in-the-mediterranean-basin"></span>