Sources of 21st century regional sea-level rise along the coast of northwest Europe

Abstract

Abstract. Changes in both global and regional mean sea level, and changes in the magnitude of extreme flood heights, are the result of a combination of several distinct contributions most, but not all, of which are associated with climate change. These contributions include effects in the solid earth, gravity field, changes in ocean mass due to ice loss from ice sheets and glaciers, thermal expansion, alterations in ocean circulation driven by climate change and changing freshwater fluxes, and the intensity of storm surges. Due to the diverse range of models required to simulate these systems, the contributions to sea-level change have usually been discussed in isolation rather than in one self-consistent assessment. Focusing on the coastline of northwest Europe, we consider all the processes mentioned above and their relative impact on 21st century regional mean sea levels and the 50-year return flood height. As far as possible our projections of change are derived from process-based models forced by the A1B emissions scenario to provide a self-consistent comparison of the contributions. We address uncertainty by considering both a mid-range and an illustrative high-end combination of the different components.For our mid-range ice loss scenario we find that thermal expansion of seawater is the dominant contributor to change in northwest European sea level by 2100. However, the projected contribution to extreme sea level, due to changes in storminess alone, is in some places significant and comparable to the global mean contribution of thermal expansion. For example, under the A1B emissions scenario, by 2100, change in storminess contributes around 15 cm to the increase in projected height of the 50-year storm surge on the west coast of the Jutland Peninsula, compared with a contribution of around 22 cm due to thermal expansion and a total of 58 cm from all of the contributions we consider. An illustrative combination of our high-end projections suggests increases in the 50-year return level of 86 cm at Sheerness, 95 cm at Roscoff, 106 cm at Esbjerg, and 67cm at Bergen. The notable regional differences between these locations arise primarily from differences in the rates of vertical land movement and changes in storminess.

Projections of extreme storm surge levels along Europe

“…Furthermore, previous studies report results relatively similar to the present patterns along the south east coast of UK, i.e. small, or no projected storm surge change (Debernard and Røed 2008;Gaslikova et al 2013;Howard et al 2014;Lowe et al 2009;Woth et al 2006); as well as along the Dutch coast (Howard et al 2014;Sterl et al 2009). …”

Sea level rise projections for northern Europe under RCP8.5

“…There have been several national projections of regional sea level for the Netherlands (Katsman et al 2008, Norway (Simpson et al 2012), Finland (Johansson et al 2014), and the British Isles (Lowe et al 2009, Howard et al 2014. Most of these studies focus on providing a best-guess or a high-end estimate of future relative sea level rise, which does not have any probability attached (with exception of Johansson et al 2014).…”

Separation of the Baltic Sea water level into daily and multi-weekly components

“…This assumption makes it possible to single out the signal of each mechanism from the overall course of water level and to analyse separately its progression, timing and contribution to the flooding (e.g., Losada et al, 2013). It also allows in-depth analysis of gradual changes in the averages and extremes caused by a single driver (e.g., Howard et al, 2014;Weisse et al, 2014) and finally constructing a projection of joint changes in mean and extreme water levels and return periods of dangerous events.…”