Speed of sea level rise may be twice as fast or more

Sea levels may rise a lot more this century than is assumed in the IPCC report. This is the conclusion drawn by Dr Riccardo Riva and his colleagues in a recent article in Climate Research.

Riccardo Riva, lecturer in the Department of Geoscience and Remote Sensing (Faculty of Civil Engineering and Geosciences) and the TU Delft Climate Institute, published an article in Climate Research last summer together with colleagues from Copenhagen, Liverpool and Beijing on sea level rise predictions in the 21st century for northern Europe.

There is no doubt that sea levels will rise, due to the accelerated melting of glaciers, the loss of land-based ice masses on Greenland and the South Pole that run into the sea, and expansion of the world’s oceans as they warm. These various contributions together tell us what the global average sea level rise will be.

The water will not rise uniformly across the globe. Local effects such as the uplift of continents that were covered with ice during the Ice Age may cause an annual sea level drop of one metre. The melting of the ice sheets also reduces the local gravitational pull, which means that melting ice on Greenland may cause a local fall in sea level as far away as Norway or Ireland. Such factors can impact local sea levels.

The researchers took the business-as-usual scenario of the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) as their reference point. This scenario assumes only a slight decrease in CO2 emissions, and continued economic growth, resulting in an average temperature by the end of the century that is five degrees higher than pre-industrial levels.

For cities near the North Sea (from London to Hamburg), this means a sea level rise of 80 centimetres by the end of the century.
However, the researchers claim that an additional rise of 95 centimetres is also possible, due to melting ice on the South Pole. Riva and his colleagues point to other studies showing that the rate of melting of glaciers on Antarctica is accelerating, which is associated with a local knock-on effect. Therefore, 80 centimetres is the most likely scenario, but there is a significant risk of water levels rising more than twice as fast. Water levels will also continue to rise, and more rapidly, after 2100. The researchers therefore recommend this to be taken into account in climate change policies.

Waslak Grinsted, Svetlana Jevrejeva, Riccardo Riva, Dorthe Dahl-Jensen, Sea level rise projections for northern Europe under RCP8.5, Climate Research, 17 June 2015

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