The coastal sea levels along the Northeast Coast of North America show significant year-to-year fluctuations in a general upward trend. The analysis of long-term tide gauge records identified an extreme sea-level rise (SLR) event during 2009–10. Within this 2-year period, the coastal sea level north of New York City jumped by 128 mm. This magnitude of interannual SLR is unprecedented (a 1-in-850 year event) during the entire history of the tide gauge records. Here we show that this extreme SLR event is a combined effect of two factors: an observed 30% downturn of the Atlantic meridional overturning circulation during 2009–10, and a significant negative North Atlantic Oscillation index. The extreme nature of the 2009–10 SLR event suggests that such a significant downturn of the Atlantic overturning circulation is very unusual. During the twenty-first century, climate models project an increase in magnitude and frequency of extreme interannual SLR events along this densely populated coast
Sea levels north of New York City rose by 128mm in two years, according to a report in the journal, Nature Communications.
Coastal areas will need to prepare for short term and extreme sea level events, say US scientists.
Climate models suggest extreme sea level rises will become more common this century.
“The extreme sea level rise event during 2009-10 along the northeast coast of North America is unprecedented during the past century,” Prof Jianjun Yin of the University of Arizona told BBC News.
“Statistical analysis indicates that it is a 1-in-850 year event.”
Scientists at the University of Arizona and National Oceanic and Atmospheric Administration (NOAA) in New Jersey studied records of tidal levels along the east coast of the US and Canada.
They divided the coastline into three areas: north of New York City, New York City to Cape Hatteras on the coast of North Carolina, and south of Cape Hatteras.
They identified what they call an extreme sea-level rise during 2009-10, when the coastal sea level north of New York City jumped by 128mm.
“When coastal storms occur, extreme sea levels can lead to elevated storm surge,” said Prof Jianjun Yin.
“In addition to long-term and gradual sea level rise, coastal communities will need to prepare for short and extreme sea level rise events.”
Commenting on the study, Prof Rowan Sutton, climate scientist at the National Centre for Atmospheric Science, University of Reading, said climate models suggest an increase in such events.
“This study identifies a record breaking high sea level event that occurred along part of the US east coast in 2009-10.
“There is strong evidence that the likelihood of such events has been increased by climate change, and that we should expect more such events in the future.
“This example illustrates how individual extreme events are influenced by multiple factors – in this case the global rise of sea levels, regional changes in ocean circulation, and wind patterns.”
Dr Dan Hodson, also from the University of Reading, said the analysis underlined the importance of understanding the connections between surges in sea levels and ocean currents.
“Sea level change is a complex phenomenon, especially on the regional scale, where changes to the global ocean circulation can play a major role,” he said.
“The east coast of North America is quite close to an area of active, fast ocean currents, and so is quite sensitive to changing ocean circulation.”
He said the Atlantic Meridional Overturning Circulation (AMOC), a major current in the Atlantic Ocean, had implications for Europe and Africa as well as the US.
Research at the University of Reading has shown how it could make British summers wetter and may influence rainfall patterns in parts of Africa.