Halifax sea levels spiked by 11cm in two years

A new study from a group of U.S. scientists is raising concerns about the potential for extreme sea-level rises in Atlantic Canada in the years to come. 

The report is in the journal Nature Communications.

Scientists at the University of Arizona and the National Oceanic and Atmospheric Administration (NOAA) in New Jersey looked at tide level records going back to 1920 along the east coast from Key West, Florida, all the way north to Newfoundland. 

Researchers divided the coastline into three areas, and the zone north of New York City saw an overall sea-level increase of 94 millimetres during the two-year period of 2009 and 2010. 

Halifax saw a sea-level rise of 110 millimetres during that time. Portland, Maine saw the largest increase — 128 millimetres. 

Paul Goddard is the lead author of the study and a PhD student at the University of Arizona. He works primarily on climate change issues.

He says sea-levels north of New York City have gone down slightly since 2010, but they remain well above 2008 levels. 

Gulf stream behind spike

Goddard says sea levels in Atlantic Canada and New England are heavily influenced by the Atlantic meridional overturning circulation (AMOC), a complex movement of water in the North Atlantic that includes the prevailing gulf stream. 

"The gulf stream curls off North Carolina through the North Atlantic, and to the south of the gulf stream you have high sea level. But to the north of it, it's relatively low sea level. When the gulf stream is strong that gradient is maintained," he said. 

"However, when the gulf stream slows down the gradient actually reduces, which allows for the waters north of the gulf stream to rise a little bit, and that was the impact you saw in Halifax." 

Goddard says the strength of the gulf stream dropped by 30 per cent in 2009 and 2010, hence the sea level spike. 

He says climate models suggest extreme sea-level rises will become more common this century, especially for the coastline north of New York. 

The implications of a sudden jump in sea-level is the potential for accelerated shoreline erosion and a rapid increase in the power of storm surges within a relatively short amount of time, as opposed to a gradual, predictable sea-level rise. 

Goddard says he hopes these findings will be integrated into coastal management strategies along the east coast of North America.