Sea-Level Rise and Extremes in Norway: Observations and Projections Based on IPCC AR6

Owing to vertical land movement (VLM), Norway has long had falling or stable relative sea levels and is yet to feel the impacts of sea-level rise. The danger is that this can foster a false sense of security, where the long-term risks are not understood or ignored.

Results from a recent national assessment show that sea-level rise is starting to push up water levels in some parts of the coast, most notably in Western and Southern Norway. Owing to global warming, Norway is transitioning from a country with on average falling or stable relative sea level, to one with rising relative sea levels. Measured coastal average geocentric (the ocean surface) sea-level rise is 2.3 ± 0.3 mm/yr for the period 1960-2022, i.e., an increase of 14 ± 2 cm over that time.

IPCC AR6 sea-level projections are tailored to the Norwegian coast using the semi-empirical model NKG2016LU to estimate VLM and associated geoid changes. Although the broad pattern of regional VLM is caused by glacial isostatic adjustment, there is evidence of other processes driving changes, especially on local scales. Projections show Norway’s coastal average relative sea-level change for 2100, compared to the period 1995-2014, will range from 0.13 m (likely -0.12 to 0.41 m) for the very low emissions scenario (SSP1-1.9) to 0.46 m (likely 0.21 to 0.79 m) for the very high emissions scenario (SSP5-8.5). A rise between 40% and 70% lower than the projected global average. For scenarios with higher greenhouse gas emissions than SSP1-2.6, a majority of the coast will likely experience relative sea-level rise for 2100.

Sea-level rise will increase flood risk in Norway by pushing up the height of sea level extremes (the combination of tides, storm surges, and waves) which will reach higher and further inland. Sea-level rise will also drive sharp increases in flooding frequency. There are large differences in the timing and extent of flooding frequency changes that partly depend on projected sea level and the regional VLM signal. Western and Southern Norway will experience increases in flooding frequency first.

In summary, careful treatment of VLM and its uncertainties is important for assessing observed sea level and tailoring national sea-level projections for their eventual use in adaptation planning. VLM also has important implications for how sea level information is communicated to decision makers and stakeholders.