Our changing climate isn’t just raising temperatures and bringing heavier rains to the Northeast. Atmospheric and ocean circulation patterns may also be shifting.
In our March 2018 newsletter article, What's Going on with Our Winter Weather?, we discussed new research that shows how the jet stream is changing. These jet stream changes are leading to more persistent weather patterns where we get “stuck” longer in one weather type or another. As a case in point, this summer we experienced a persistent wet pattern that repeatedly plagued Maryland and central Pennsylvania with bouts of heavy rainfall. In some areas, rainfall totals have been running 12 to 20 inches above normal through the end of August. The heavy rains led to fields being inaccessible for long periods and also caused crop damage due to flooding.
Another “hot” research topic in climate science is whether changes are taking place in ocean currents too. Of special importance to us in the Northeast is an apparent slowdown in the Atlantic Meridional Overturning Circulation (AMOC). This is a process that moves warm, shallow water up to the north Atlantic via the Gulf Stream and cooler, deeper water back south. The AMOC is closely watched by Europeans because changes in this circulation strongly affect their weather and climate. Evidence suggests that these flows have slowed by about 15% since measurements started in 2004.
The connection with the Northeast U.S.? The warm water has to go somewhere, and as part of these changes, the Gulf Stream has moved closer to shore. This migration has caused the waters along the Northeast coast to warm at record rates and contributed to on-shore warming as well, especially off the coast of Maine. Further expected slowing of these currents would intensify the warming along the Northeast coast and possibly across the globe. Warmer coastal waters contribute to the humidity in our region as well. The record high humidity across the Northeast this summer is partially due to these very warm near-shore waters.
Another local impact is on sea level. When the circulation slows, the sea level rises all along the US east coast. A temporary slowdown in the AMOC in 2009-2010 resulted in a record 1-year sea-level rise of over 1.5 inches, compared to the long term trend of 0.1 inch per year.