US N. East coast sea levels rising fast

US N. East coast sea levels rising fast

Sea levels north of New York City rose by 128mm in the two years 2009-2010, an event described as unprecedented during the past century, according to an article in the journal Nature Communications. A 1-in-850 year event, such a big interannual SLR (Sea Level Rise) has never before happened in the entire history of the tide gauge records.

The coastal sea levels along the northeast coast of North America show significant year-to-year fluctuations in a general upward trend, according to Prof Jianjun Yin of the University of Arizona, who carried out the research.

The scientists showed that the extreme SLR event was 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,” the published research abstract said.

The meridional overturning circulation(MOC) is a global circulation cell whereby surface waters in the high latitudes are cooled, thereby becoming denser; this dense water sinks and flows towards the equatorial regions.

The North Atlantic Oscillation (NAO) is a climatic phenomenon in the North Atlantic ocean of fluctuations in the difference of atmospheric pressure between the Icelandic low and the Azores high.

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.

Climate models project an increase in magnitude and frequency of extreme interannual SLR events along the densely populated north east seaboard during the twenty-first century. “When coastal storms occur, extreme sea levels can lead to elevated storm surge,” Prof Jianjun Yin told the BBC. “In addition to long-term and gradual sea level rise, coastal communities will need to prepare for short and extreme sea level rise events.”

Earlier this year, US-based scientists found that the rate at which the global oceans have risen in the past two decades is more significant than previously recognised. A reassessment of tide gauge data from 1900-1990 found that the world’s seas went up more slowly than earlier estimates - by about 1.2mm per year.

But that made the 3mm per year tracked by satellites since 1990 a much bigger trend change as a consequence.

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