IS SEA LEVEL RISE ACCELERATING ON U.S. COASTS?

Recent publications have presented calculations of acceleration from roughly century-long tide records of sea level in the U.S. and around the world. In general, they have fit quadratics to the long-term records and found small or statistically insignificant accelerations. However, when using traditional methods with long-term records, the signal to noise ratio makes it challenging to detect recent sea level rise (SLR) accelerations with statistical confidence. With shorter-term records, we showed in Sallenger et al (2012) that there is statistically significant acceleration along more than 1,000 km of the U.S. Atlantic coast from Cape Hatteras, North Carolina to north of Boston, Massachusetts. The data are suggestive that the increased rate of SLR began approximately 1990, the onset of the recent warming period. Using the same shorter analysis windows elsewhere in the continental U.S., accelerations are generally negative or statistically insignificant. Further analyses since our paper was published indicate that during a previous warm period in 1920-1940, the same regional fingerprint of SLR in the northeastern U.S. did not develop. The recent observations of regional differences were unique over the measured record, suggesting that the hotspot of accelerated SLR was not part of a global or full-basin cycle with period less than the measurement record. The fingerprint of acceleration in the northeast U.S. is consistent with dynamic SLR from slowing of the Atlantic Meridional Overturning Current in a warming world.