Sea level rise in Finland

Past trends and future projections

Long-term absolute sea level rise – from the early 20th century to 2018 – at the various locations on the Finnish coast vary from 1.2 to 1.5 mm per year. These historical trends of absolute sea level rise at the Finnish coast, excluding the effect of land uplift and wind- induced changes in Baltic Sea level, are in accordance with global mean rates. Absolute sea level rise in the period 1993–2018 according to satellite altimetry data is 3.0 to 3.8 mm per year (20), in accordance with the global mean rate of 3.25 ± 0.37 mm per year (21).

Future projections of relative sea level rise include the land uplift and the wind-induced component related to the sea level dynamics within the Baltic Sea basin. The median values of the projections of relative mean sea level change in Finland for 2100 relative to 1995–2014 range from −43 to +16 cm for the low-emission scenario of climate change (RCP2.6), −28 to +31 cm for the medium scenario (RCP4.5), and +1 to +61 cm for the high scenario (RCP8.5) depending on location. The lowest values occur in the area of strong land uplift in the north and the highest ones in the Gulf of Finland in the south. The negative values refer to a decline in relative sea level (20).

Future projections of the upper tail of the probability distribution of relative sea level rise characterizes the risk of higher sea level rise. The 95th percentiles range from −9 to +50 cm (low scenario), +24 to +83 cm (medium scenario), and +93 to +152 cm (high scenario) depending on location (20).

Land uplift will continue at a constant rate, while acceleration in global sea level rise is expected together with a small increase in westerly winds in the northeast Atlantic, causing additional wind-induced sea level rise in the Baltic Sea. Due to accelerating absolute sea level rise, a reversal of the historical declining sea level trend is expected at the southern Finnish coast. In the north, in the Bothnian Bay, postglacial land uplift is probably strong enough to compensate for absolute sea level rise so that significant relative sea level rise is unlikely over this century, at least if the emissions of greenhouse gases are mitigated (20).

Additional information

In Finland, sea level rise with respect to the land (relative sea level rise) is the combination of absolute sea level rise and land uplift since the most recent glacial period. In Finland, the rate of land uplift varies greatly along the coastline, being strongest around Vaasa and weakest on the coast of the Gulf of Finland. Besides, absolute sea level along the Finnish coastline is the combination of global sea level rise and water level fluctuations due to changes in the water balance for the Baltic Sea. Coastal construction and planning usually deals with structures with a lifetime of several decades, and thus estimates of the behavior of sea level in the distant future are also needed (1).

The total water volume inside the semi-enclosed Baltic Sea can vary by some 365 km3, which corresponds to a variation in mean sea level of approximately 1 m. These variations in the water balance do not level out on an annual time scale; they explain most of the year-to-year variability of annual mean sea level. The variations in the water balance are mainly caused by inflow and outflow of water through the Danish Straits. This exchange is controlled by meteorological conditions, such as wind and air pressure over the Straits area. In particularly westerly winds push water into the Baltic Sea. The Baltic Sea level is affected on time scales of typically about two weeks, because the narrow Straits have a limited flow capacity (1).

The North Atlantic Oscillation (NAO) is the main source of interannual climate variability in the North Atlantic region.The NAO is essentially a measure of the atmospheric pressure difference between the Icelandic Low and the Azores High. A large pressure gradient between a well-developed Icelandic Low and a strong Azores High (termed a positive NAO) results in a strong westerly air flow on a more northerly track over the eastern North Atlantic and Europe. This wind forces  water through the Danish Straits into the Baltic Sea and also forces an east-west directed slope on the water surface within the Baltic Sea (1).

Until now, land uplift around the coasts of Finland has been greater than the rise in the sea level, with new land appearing. The sea level is expected to rise by 5–30 centimetres during the next 50 years and by 10–90 centimetres by the end of this century due to glacial melting and the thermal expansion of water. North Atlantic Oscillation (NAO) also affects the sea level in the Baltic Sea. It caused the relative decrease in the sea level in the Gulf of Finland to stop 30 years ago (2). A study based on 13 tide gauges starting from  1887 and 1933 (at least 80 years of data) showed that sea level fell (declined) in all Finnish time series up to 1980. During the last two decades of the 20th century the steady linear decreasing trend of sea level was no longer followed (1).

The impact of NAO will cease in the long-term, but the rise in the sea level will also be reflected in the Baltic Sea. In the Gulf of Finland, the past declining trend of the mean sea level will probably not continue in the future, because the accelerating rise in the mean sea level will balance the land uplift. The sea level in the Gulf of Finland will remain roughly at the present level until the end of the century (2). The uncertainties are large, however, amounting to several tens of centimeters at the end of the 21st century. The maximum scenario predicts a sea level rise of 50 cm at Hamina, in the eastern part of the Gulf of Finland, while the minimum scenario results in a still falling mean sea level (1).

In the Gulf of Botnia the stronger land uplift results in probable fall of the mean sea level in the future. The uncertainties are of the same order as those for the Gulf of Finland. According to the maximum scenario for greenhouse gas emissions, the mean sea level will start to rise after the middle of the 21st century even in the area of the strongest land uplift, at Vaasa (1).

Global sea level rise

Observations

For the latest results: see Europe Coastal floods

Projections

For the latest results: see Europe Coastal floods

Extreme water levels - Global trends

More recent studies provide additional evidence that trends in extreme coastal high water across the globe reflect the increases in mean sea level (7), suggesting that mean sea level rise rather than changes in storminess are largely contributing to this increase (although data are sparse in many regions and this lowers the confidence in this assessment). It is therefore considered likely that sea level rise has led to a change in extreme coastal high water levels. It is likely that there has been an anthropogenic influence on increasing extreme coastal high water levels via mean sea level contributions. While changes in storminess may contribute to changes in sea level extremes, the limited geographical coverage of studies to date and the uncertainties associated with storminess changes overall mean that a general assessment of the effects of storminess changes on storm surge is not possible at this time.

On the basis of studies of observed trends in extreme coastal high water levels it is very likely that mean sea level rise will contribute to upward trends in the future.

Short-term water level fluctuations on the Baltic Sea

The sea level is expected to rise by 0.1–0.9 metres by 2100. The increase in the ocean level, together with increased precipitation and potential increases in windiness and storms, will also raise the level of the Baltic Sea and intensify short-term variation in the water level. Potential increases in the sea level and strong winds may boost the exchange of water into the Baltic Sea. However, it is not certain whether the salinity of the Baltic Sea will increase even if the sea level does rise (2).

Estimates indicate that the ice coverage on the Baltic Sea will decrease, the ice-winter will become shorter and the ice cover will become thinner. The ice season in the Finnish waters of the Baltic Sea normally lasts 5–7 months. According to the central SILMU scenario, ice cover would appear about 20 days later in 2050 and melt 10 days earlier than today (3).

The decreased ice cover on the Baltic Sea may increase windiness and sea swells, which would impair marine traffic. At the end of the century, the duration of the ice winter is estimated to have shortened to half of that at present on the southern and southwestern coasts of Finland, and to 70–80% of the present in the Gulf of Bothnia (2).

Storm surges on the Baltic Sea and in the Gulf of Finland

For the case of the Baltic Sea, earlier studies in historical storm surge trends have reported no statistically significant increasing trend (17). Future projections, however, indicate an increase of storm surge levels (18,19). In the Gulf of Finland sea level is now decreasing due to land uplift. Projected storm surge level increase could balance a potential decrease in future sea levels, resulting in comparable levels of coastal hazard in the future (19). 

Economic impacts of sea level rise for Europe

The direct and indirect costs of sea level rise for Europe have been modelled for a range of sea level rise scenarios for the 2020s and 2080s (8). The results show:

1. First, sea-level rise has negative economic effects but these effects are not particularly dramatic. In absolute terms, optimal coastal defence can be extremely costly. However, on an annual basis, and compared to national GDP, these costs are quite small. On a relative basis, the highest value is represented by the 0.2% of GDP in Estonia in 2085.
2. Second, the impact of sea-level rise is not confined to the coastal zone and sea-level rise indeed affects landlocked countries as well. Because of international trade, countries that have relatively small direct impacts of sea-level rise, and even landlocked countries such as Austria, gain in competitiveness.
3. Third, adaptation is crucial to keep the negative impacts of sea-level rise at an acceptable level. This may well imply that some European countries will need to adopt a coastal zone management policy that is more integrated and more forward looking than is currently the case.

Adaptation strategies - The costs of adaptation

Both the risk of sea-level rise and the costs of adaptation to sea-level rise in the European Union have been estimated for 2100 compared with 2000 (9). Model calculations have been made based on the IPCC SRES A2 and B1 scenarios. In these projections both flooding due to sea-level rise near the coast and the backwater effect of sea level rise on the rivers have been included. Salinity intrusion into coastal aquifers has not been included, only salt water intrusion into the rivers. Changes in storm frequency and intensity have not been considered; the present storm surge characteristics are simply displaced upwards with the rising sea level following 20th century observations. The assessment is based on national estimates of GDP.

The projections show that without adaptation (no further raising of the dikes and no beach nourishments), the number of people affected annually by coastal flooding would be 20 (B1 scenario) to 70 (A2 scenario) times higher in 2100 than in 2000. This is about 0.05 - 0.13% of the population of the 27 EU countries in 2010 (9).

Without adaptation, damage costs would increase roughly by a factor of 5 during the century under both scenarios, up to US$ 17×109 in 2100. Total damage costs would amount to roughly 0.04% of GDP of the 27 EU countries in 2100 under both scenarios. Damage costs relative to national GDP would be highest in the Netherlands (0.3% in 2100 under A2). For all other countries relative damage costs do not exceed 0.1% of GDP under both scenarios (9).

Adaptation (raising dikes and beach nourishments in response to sea level rise) would strongly reduce the number of people flooded by factors of 110 to 288 and total damage costs by factors of 7 to 9. In 2100 adaptation costs are projected to be US$ 3.5×109 under A2 and 2.6×109 under B1. Relative to GDP, annual adaptation costs constitute 0.005 % of GDP under B1 and 0.009% under A2 in 2100. Adaptation costs relative to GDP are highest for Estonia (0.16% under A2) and Ireland (0.05% under A2). These results suggest that adaptation measures to sea-level rise are beneficial and affordable, and will be widely applied throughout the European Union (9).

References

The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Finland.

1. Johansson et al. (2004)
2. Marttila et al.(2005)
3. Ministry of the Environment of Finland (2006)
4. Bindoff et al. (2007), in: IPCC (2012)
5. Church and White (2011), in: IPCC (2012)
6. Velicogna (2009); Rignot et al. (2011); Sørensen et al. (2011), all in: IPCC (2012)
7. Marcos et al. (2009); Haigh et al. (2010); Menendez and Woodworth (2010), all in: IPCC (2012)
8. Bosello et al. (2012)
9. Hinkel et al. (2010)
10. Cazenave et al. (2014)
11. IPCC (2014)
12. Watson et al. (2015)
13. Yi et al. (2015)
14. Church et al. (2013), in: Watson et al. (2015)
15. Shepherd et al. (2012), in: Watson et al. (2015)
16. Church et al. (2013), in: Watson et al. (2015)
17. Baerens and Hupfer (1999); Menéndez and Woodworth (2010); Suursaar et al. (2015), all in: Vousdoukas et al. (2016)
18. Debernard and Røed (2008); Gräwe and Burchard (2012); Meier (2006); Weisse et al. (2009); Woth et al. (2006), all in: Vousdoukas et al. (2016)
19. Vousdoukas et al. (2016)
20. Pellikka et al. (2023)
21. Fox-Kemper et al. (2021), in: Pellikka et al. (2023)