Sea level rise (CLIM 012) - Assessment published Sep 2008
Climate change (Primary topic)
Coasts and seas
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)
- CLIM 012
Key policy question: .
- Global average sea level rose by around 0.17 m (1.7 mm/year) during the 20th century. In Europe rates of sea-level rise (SLR) ranged from - 0.3 mm/year to 2.8 mm/year. Recent results from satellites and tide gauges indicate a higher average rate of global SLR in the past 15 years of about 3.1 mm/year.
- Projections by the IPCC for the end of the 21st century suggest an additional SLR of 0.18 to 0.59 m above the average 1980-2000 level. Based on the latest observations, recent projections indicate a future SLR that may exceed the IPCC upper limit.
- SLR can cause flooding, coastal erosion and the loss of flat and low-lying coastal regions. It increases the likelihood of storm surges, enforces landward intrusion of salt water and endangers coastal ecosystems and wetlands. An additional 1.6 million people living in Europe's coastal zones could experience coastal flooding by 2080.
Sea-level change at different European tide-gauge stations 1896-2004
Note: Data (mm/year) corrected with regard to postglacial land movement and gravity-field variation.
Novotny, K. and Groh, A., 2007. Untersuchung von Pegelreihen zur Bestimmung der Änderung des mittleren Meeresspiegels an den europäischen Küsten; Technical University of Dresden; internal report prepared for the German Federal Environment Agency (UBA).
Changes in global sea level 1870-2006
Church, J. A. and White, N. J., 2006. A 20th century acceleration in global sea-level rise. In Geophysical Research Letters 33, L01602.
Sea-level changes in Europe October 1992-May 2007
Note: Based on satellite data; trends in mm/year, inverted barometer included, seasonal signal removed
Guinehut, S. and Larnicol, G., 2008. Produced for EEA by Collecte Localisation Satellites (CLS). http://www.cls.fr/.
Projected global average sea-level rise 1990-2100
Note: Six SRES scenarios are shown
UNEP, 2007. Global Outlook for Ice & Snow; UNEP/GRIDArendal, 2007. IPCC, 2001. Climate Change 2001: The scientific basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Houghton, J. T. et al. (eds.), Cambridge University Press, UK.
Tide gauge-based data e.g. from the Permanent Service for Mean Sea Level (PSMSL), show that the long-term average sea level on European coasts changed, depending on the region, at a rate between -0.3 mm/year and 2.8 mm/year during the 20th century (Figure 1). In this period, global sea level rose by an average of 1.7 mm/year (Church and White, 2006). Recent satellite data-sets indicate an accelerated global trend in sea-level rise to about 3.1 mm/year (Figure 2) in the past 15 years which is almost backed by tide-gauge data from this period (Nerem et al., 2006; Church and White, 2006; Rahmstorf et al., 2007). It is very likely that the observed trend in sea-level rise over the past 100 years is attributable mainly to an increase in the volume of ocean water as a consequence of temperature rise, although inflow of water from melting glaciers and ice-sheets is playing an increasing role (Table 1). Several recently-published papers underline the relatively small, but significantly increasing contribution of ice-sheets, e.g. from Greenland (Cazenave, 2006; Chen et al., 2006; Rignot and Kangaratnam, 2006). Satellite observations indicate a large spatial variability of SLR trends in the European seas (Figure 3; Table 2). For instance in the Mediterranean and the Levantine Sea positive trends are observed while negative trends are observed in the northern Ionian Sea. These local variations could be explained by variability of the North Atlantic Oscillation (NAO), inter-annual wind variability, changes in global ocean circulation patterns, or specific local structures of the circulation (e.g. gyres) (Demirov and Pinardi, 2002).
Sea-level rise by the end of this century (2090-2099) is projected, under the SRES-scenarios, to be 0.18-0.59 m above the present (1980-1999) level, with a maximum rate of rise three times that in the past decade (Figure 4). Thermal expansion is the largest component, contributing 70-75 % of the central estimate of these projections for all scenarios. Glaciers, ice caps and the Greenland ice sheet are also projected to contribute to sea-level rise (IPCC, 2007a). Sea-level rise during the 21st century is projected to have substantial geographic variability (IPCC, 2007a). In Europe, regional influences in the Arctic Ocean and the northern North Atlantic may result in SLR being up to 50 % higher than these global estimates (Woodworth et al., 2005). The impact of the NAO on winter sea levels adds an uncertainty of 0.1-0.2 m to these estimates (Hulme et al., 2002; Tsimplis et al., 2004). A slowing of the Atlantic Meridional Overturning Circulation (MOC), also known as great conveyor belt, in the North Atlantic would result in a further rise in relative sea level at European coasts (IPCC, 2007b). SLR projections for the Baltic and Arctic coasts based on SRES scenarios indicate an increased risk of flooding and coastal erosion after 2050 but always lower than the risk in the North Sea and the Mediterranean (Johansson et al., 2004; Meier et al., 2004, 2006b; Nicholls, 2004). The A1F1-scenario, which assumes very high greenhouse gas emission from fossil-fuel combustion, would lead to a greater impact of SLR in the northern Mediterranean, as well as in northern and western Europe. While it was highly unlikely that the populations in these coastal areas would experience flooding in 1990, up to 1.6 million people might experience coastal flooding each year by 2080 (Nicholls, 2004). Various adaptation measures are available to reduce these risks. But there are limits to adaptation: due to the thermal inertia of the oceans, sea-level rise would not stop by 2100 even if greenhouse gas concentrations were stabilised. Over a period of centuries and millennia, a very large SLR could result from the melting of the world's major ice sheets in Greenland and on the West Antarctic ice shelf, which have an SLR potential of about 7 and 5-6 m respectively, should they melt completely (IPCC, 2007a).
Table 1 Contribution of different processes to global sea-level rise (1993-2006)
Contribution to global sea-level rise
Ocean thermal expansion
1.6 +/- 0.5
Melting of glaciers and ice caps
0.8 +/- 0.2
Melting of the Greenland ice sheet
0.2 +/- 0.1
Melting of the west Antarctic ice sheet
0.2 +/- 0.4
Total global sea level rise
3.1 +/- 0.4
Table 2 Average sea-level rise in some European seas (satellite observations)
October 1992-May 2007)
North Atlantic (50 to70N)
Central North Atlantic (30 to 50N)
Changes in mean sea level along European coasts
provided by Federal Environmental Agency (UBA)
Sea-level changes in Europe
provided by Collecte Localisation Satellite (CLS)
Global sea-level change rates
provided by UNEP/GRID-Arendal
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