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What uncertainties exist with the sea level rise and storm surge projections?

The contribution from the polar ice sheet rise is the most uncertain aspect of sea level rise. Reflecting the high degree of uncertainty in modelling, the modelling suggests that climate change is less likely to increase storm surge height and frequency in the North Sea than previously thought.

In detail

There is great uncertainty in many of the contributions to sea level rise, with the contribution from polar ice sheet rise being the most uncertain. At the extreme, recent scientific research into ice sheet dynamics suggests that this melting may raise sea levels up to a total of 2 m by the end of the 21st century, although there is considerable uncertainty and this is thought highly unlikely. To reduce the uncertainty, further research and monitoring is needed. This upper bound total forms part of the Scenario.

Reflecting the high degree of uncertainty in storm surge modelling, the modelling suggests that climate change is less likely to increase storm surge height and frequency in the North Sea than previously thought. The modelling suggests that, as a maximum, additional surge heights due to climate change may reach up to 0.7 m for a 5 year return period event (or 0.95 m for a 50 year event) in the southern North Sea. Adding this to the extreme case of 2 m for sea level rise, suggests a total maximum rise in a 5 year return period extreme sea level of around 2.7 m by the end of the 21st century. Again, there is great uncertainty and low likelihood with this extreme figure, but it is useful to help us adapt to climate change and guide long term contingency planning.