Model projections of rapid sea-level rise on the northeast coast of the United States

Human-induced climate change could cause global sea-level rise. Through the dynamic adjustment of the sea surface in response to a possible slowdown of the Atlantic meridional overturning circulation1,2, a warming climate could also affect regional sea levels, especially in the North Atlantic region3, leading to high vulnerability for low-lying Florida and western Europe4–6. Here we analyse climate projections from a set of state-of-the-art climate models for such regional changes, and find a rapid dynamical rise in sea level on the northeast coast of the United States during the twenty-first century. For New York City, the rise due to ocean circulation changes amounts to 15, 20 and 21 cm for scenarios with low, medium and high rates of emissions respectively, at a similar magnitude to expected global thermal expansion. Analysing one of the climate models in detail, we find that a dynamic, regional rise in sea level is induced by a weakening meridional overturning circulation in the Atlantic Ocean, and superimposed on the global mean sea-level rise. We conclude that together, future changes in sea level and ocean circulation will have a greater effect on the heavily populated northeastern United States than estimated previously7–9. In the current climate, sea level is anomalously low along the east coast of the United States, with a steep sea-level slope just offshore. This sharp sea surface height (SSH) gradient is required by geostrophy (the balance between Coriolis and pressure-gradient forces) to maintain the strong and narrow Gulf Stream and North Atlantic Current, which are components of the Atlantic meridional overturning circulation (AMOC). The high-latitude deep convection and deep-water formation associated with the AMOC drives the North Atlantic Current and accelerates the Gulf Stream, thereby contributing to the steep dynamic SSH gradient on the east coast of the United States. In addition to the dynamic sea level, the AMOC is also closely linked to the steric sea level10 (see the Methods section for terminologies). Owing to the deep-water formation, the entire ocean column in the northernNorthAtlantic is occupied by very dense seawater, thereby significantly lowering the sea level. Model simulations suggest that a collapse of the AMOC could cause a large regional sea-level rise (SLR) in the North Atlantic3. Here we report a rapid SLR on the northeast coast of the United States during the twenty-first century projected by the climate models used for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). The projected ensemblemean (tenmodels) shows that the SLR during the twentyfirst century is uneven, with some regions such as the northeast coast of the United States experiencing rises considerably faster and larger than the global mean (Fig. 1). In addition, the northeast coast