Sea level rise projections, published in 2021 by the Intergovernmental Panel on Climate Change (IPCC) in the AR6 Report, would be underestimated along the coasts. This is the result of the research , just published in the international journal Environmental Research Letters by a team of researchers fromNational Institute of Geophysics and Volcanology (INGV) and Radboud Radio Lab of the Department of Astrophysics of Radboud University (Holland).
“Subsidence, the slow downward movement of soil due to natural or anthropogenic causes, plays a crucial role in accelerating the rise in sea levels along the coasts, triggered by global warming since 1880”, explains Marco Anzidei, INGV researcher and co-author of the study.
“Our analyzes show that, precisely because of subsidence, in some areas of the Mediterranean the sea level is rising almost three times faster than in stable areas”, he adds Antonio Vecchio, researcher at Radboud Universiteit Nijmegen and first author of the study.
“The Mediterranean, in fact, is characterized by a strong variability in the vertical movements of the coasts, which vary from area to area due to tectonic, volcanic and anthropic activity”, keep it going Enrico Serpelloni, INGV researcher and co-author of the study. “For our research, conducted within the projects SAVEMEDCOASTS, SAVEMEDCOASTS2 e Dynamic Planet, we used data from the numerous GNSS satellite geodetic stations located within 5 km of the sea, with which we can calculate, with millimeter precision, the speed of vertical movement of the ground".
In light of this evidence, the team of researchers recalculated the IPCC projections up to 2150 in 265 areas of the Mediterranean, also corresponding to the 51 tide gauges of the international monitoring networks, including data relating to subsidence in the analyses.
“The results show maximum and minimum differences compared to the IPCC Report ranging, respectively, from approximately +109 cm to -77 cm, with a higher average value of approximately 8 cm”, explains Antonio Vecchio.
“Sea level rise and subsidence mean that approximately 38.500 km2 of Mediterranean coasts - of which approximately 19.000 km2 in the northern sector of the basin alone - will soon be more exposed to the risk of marine flooding, with consequent greater impacts on the environment, human activities and infrastructure. It is therefore necessary to take concrete actions to support coastal populations who will be increasingly vulnerable to rising sea levels and the increased risks associated with this by the end of this century and beyond."he concludes Marco Anzidei.
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National Institute of Geophysics and Volcanology (INGV)
Figure 1: The GNSS stations considered in the study, located within 5 km from the coast. The colors represent the subsidence speeds in mm/year according to the scale shown below. 
Figure 2:
Highlighted in red are 163 major coastal plains most exposed to sea level rise by 2100-2150. The total area that could be submerged corresponds to approximately the surface of Switzerland or even 38.529 km2. 
Figure 3:
Maps with projections of sea level rise for different coastal areas of the Mediterranean and in correspondence with tide gauge stations (green dots). On the left up to 2100 and on the right up to 2150 for different SSP and Tlim climate scenarios of the IPCC AR6 Report (2021) to which the subsidence value calculated at the GNSS geodetic stations has been added. The size of the dots and the colors represent the sea level rise values according to the scale shown below.
Panels (a)/(b): SSP1-1.9 2100/2150; Panels (c)/(d): Tlim 1.5 °C 2100/2150; Panels (e)/(f): SSP5-8.5 2100/2150; Boxes (c)/(d): Tlim 5 °C 2100/2150.