Regional sea-level rise: New York will get 25% more than the global average

Published: 19 December 2016

A study that appeared on Earth’s Future makes a new prediction of the sea-level rise along the Gulf and East Coast of North America in the 21st century. Several large, important cities are located along that coast, such as New York, Washington, Miami and New Orleans.

In several cities, like New York, sea level will rise faster than the global average. It was also found in this study that there are marked differences between regions and cities.

Glacial isostatic adjustment incorporated

The innovative aspect of this study, co-authored by Marc Hijma from Deltares, is the manner in which the influence of glacial isostatic adjustment has been included. It was calculated on the basis of a new database with reconstructed sea levels from the past 10,000 years, 35 variations in the building up and melting of the ice cap from the last ice age, and 363 models of the build-up of the Earth. Changes in the position of ocean currents, the density of seawater, ocean circulation and the melting of continental ice are also included in the estimates of future sea-level rise.

The contribution of glacial isostatic adjustment to projections of sea-level change along the Atlantic and Gulf coasts of North America

Maps of the various components of the sea-level projections at 2085–2100 relative to 2006–2015 for RCP8.5. The sub-plots are as follows: (a) glacial isostatic adjustment (for model parameters that best fit the US Atlantic coast dataset); (b) dynamic/steric; (c) Greenland; (d) Antarctica, (e) glaciers and ice caps; (f) sum of (a–e).

Because the researchers used this database, it has become clear that the glacial isostatic adjustment will ensure that for instance New York will be faced with a decimetre higher sea-level rise than the global estimate. In another region and city along the Gulf and East Coast, this will be different. Note that subsidence due to the extraction of groundwater and/or compaction has not been included in the study. In cities like New Orleans in particular, this subsidence will lead to an even greater relative sea-level rise.

Take especially the regional sea level into account

The study shows the importance of using regional forecasts of sea-level rise when making water security plans or climate adaptation. If managers of cities and coastal regions use a regional relative sea-level rise (including subsidencel), they can fine-tune their adaptive measures.
Co-author Marc Hijma is involved in setting up a global database of sea-level changes from the past. Such a database is necessary to be able to make regional projections. Hijma: ‘The projections should also be made for north-western Europe, but that was not the topic of our study.’