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Global mean sea level (GMSL) has risen about 21cm since 1900, at an accelerating rate. GMSL reached its highest value ever in 2021. GMSL will likely rise by 0.28-0.55m under a very low emissions scenario (SSP1-1.9) and 0.63-1.02m under a very high emissions scenario (SSP5-8.5) by 2100, relative to the 1995-2014 average. GMSL simulations that include the possibility of fast disintegration of the polar ice sheets project a rise of up to 5m by 2150. Most coastal regions in Europe have experienced an increase in sea level relative to land, except for the northern Baltic Sea coast.
The global mean sea level (GMSL) in 2021 was the highest ever measured. GMSL reconstructions based on tide gauge observations show a rise of 21cm from 1900 to 2020 at an average rate of 1.7 mm/year . The rate of GMSL rise accelerated to 3.3mm/year over the period 1993-2018 and 3.7mm/year over the period 2006-2018, more than twice as fast as during the 20th century .
Since 1970, anthropogenic forcing has been the predominant cause of this accelerating sea level rise both globally and in European regional seas. Thermal expansion of ocean water was initially the main driver, but melting of glaciers and of the Antarctic and Greenland ice sheets have exceeded the effects of thermal expansion since about 2000 .
Global climate models project that the rise in GMSL during the 21st century (i.e. in 2100, relative to the period 1995-2014) will likely (66% confidence) be in the range of 0.28-0.55m for a very low emissions scenario (SSP1-1.9), 0.44-0.76m for an intermediate emissions scenario (SSP2-4.5) and 0.63-1.02m for a very high emissions scenario (SSP5-8.5). Model simulations that include the possibility of fast disintegration of the polar ice sheets, which is assessed to have a low likelihood, project a GMSL rise of up to about 5m by 2150 under a very high emissions scenario (SSP5-8.5).
The future behaviour of the Greenland and Antarctic ice sheets is still rather uncertain, particularly under higher emissions scenarios. Studies considering processes that can lead to a faster disintegration of the Antarctic ice sheet, including a potential collapse of marine-based sectors, have estimated a GMSL rise of up to 2.3m by 2100 and up to 5.4m by 2150 . The consideration of such high-end scenarios is important for long-term coastal risk management, in particular in densely populated coastal zones. Each 5-year delay in the peaking of global greenhouse gas emissions increases the median sea-level rise projections for 2300 by 0.2m and extreme sea-level rise projections (95th percentile) by up to 1m.
Most European coastal regions experience increases in both absolute sea level (as measured by satellites) and relative sea level (as measured by tide gauges), the latter being more relevant for coastal protection. There are sizeable differences in the rates of sea level change across Europe. Notably, sea levels relative to land along the northern Baltic Sea coast and — to a lesser degree — the northern Norwegian coast are sinking. This is due to rising land levels caused by post-glacial rebound since the last ice age.
In future, relative sea level change along most of the European coastline is projected to be reasonably similar to the global average. The main exceptions are the northern Baltic Sea and the northern Norwegian coasts, which are experiencing considerable land rise as a consequence of post-glacial rebound and changes in the gravity field of the Greenland ice sheet. As a result, sea level relative to land in these regions will continue to rise more slowly than elsewhere or may even decrease .