Drivers of exceptional coastal warming in the northeastern United States

The coastal northeastern United States is a warming hotspot, and observations identify a slower Atlantic overturning circulation and a positive North Atlantic Oscillation phase as drivers. Analysis suggests that low horizontal resolution probably hampers models' ability to capture the spatial pattern of enhanced warming. The northeastern United States (NEUS) and the adjacent Northwest Atlantic Shelf (NWS) have emerged as warming hotspots, but the connection between them remains unexplored. Here we use gridded observational and reanalysis datasets to show that the twentieth-century surface air temperature increase along the coastal NEUS is exceptional on the continental and hemispheric scale and is induced by a combination of two factors: the sea surface temperature (SST) increase in the NWS associated with a weakening Atlantic Meridional Overturning Circulation (AMOC), and atmospheric circulation changes associated with a more persistent positive North Atlantic Oscillation. These connections are important because AMOC slowdown and NWS warming are projected to continue. A survey of climate model simulations indicates that realistic SST representation at high spatial resolution might be a minimum requirement to capture the observed pattern of coastal warming, suggesting that prior projection-based assessments may not have captured key features in this populous region.

Automated summary

The coastal northeastern United States is a warming hotspot driven by a slower Atlantic overturning circulation and a positive North Atlantic Oscillation. The exceptional surface air temperature increase in this region is induced by a combination of sea surface temperature rise in the Northwest Atlantic Shelf associated with a weakening AMOC, and atmospheric circulation changes linked to a more persistent positive NAO. It is important to consider these connections for future projections as AMOC slowdown and NWS warming are expected to continue.