Thursday, February 21, 2013

Sea Level rising 3 to 4 times faster on US Atlantic coast

One of the impacts of the Greenland Ice sheet melt is the increase in cold fresh water impacting on the themohaline circulation, the great ocean conveyor belt. There are signs the Gulf Stream has slowed down by a third due to this influx of melt water. The Gulf Stream acts to drag water away from the coast of North America, so a slowing current will add to greater sea level rise along the east coast of north America: increasing sea level rise by up to 4 times the global average.

Scientists from the US Geological Survey (USGS) identified that since about 1990, sea-level rise in the 1,000-km (600 mile) stretch of coastal zone from Cape Hatteras, North Carolina, to north of Boston, Massachusetts is a sea level rise hotspot. This is based on tide gauge data and concurs with sea level rise modelling.


Caption: Differences in rates of sea-level rise from tide-gauge records across North America over a 60-year period (1950-2009). Circles are color coded to reflect computed differences; no color fill indicates differences in rates of sea-level rise that are not statistically different from zero. Cool colors indicate decreasing rates of sea-level rise over the 60-year period; warm colors indicate increasing rates of sea-level rise over the 60-year period. Note "hotspot" between Cape Hatteras and Cape Cod. After figure 2 in "Hotspot of Accelerated Sea-Level Rise on the Atlantic Coast of North America."


"Cities in the hotspot, such as Norfolk, New York, and Boston, already experience damaging floods during relatively low intensity storms," said Abby Sallenger, USGS oceanographer and project lead for a 2012 study. "Ongoing accelerated sea-level rise in the hotspot will make coastal cities and surrounding areas increasingly vulnerable to flooding by adding to the height that storm surge and breaking waves reach on the coast."

So United States east coast cities like New York and Boston are going to need to prepare expensive coastal defences. The Boston Harbor Association has just released the Preparing for the Rising Tide Report which identifies flood risks and estimates some of the costs of adaptation. The major impacts will occur with coastal flooding with storm surges associated with storms like ex-tropical hurricane Sandy riding upon higher sea levels.

Sources:
  • Melanie Glade, US Geological Survey (USGS) Soundwaves newsletter Sept/Oct 2012 - Sea-Level Rise Accelerating on U.S. Atlantic Coast
  • Asbury H. Sallenger Jr et al (2012) Nature Climate Change 2, 884-888 (2012) doi:10.1038/nclimate1597 Hotspot of accelerated sea-level rise on the Atlantic coast of North America (abstract)