Extreme sea level rise events along the northeast coast of North America are partly driven by internal ocean dynamics according to a study published in Nature Communications. The findings suggest that extreme sea level rise events could become more frequent in the future through continued ocean weakening due in part to rising levels of atmospheric CO2.

Extreme sea levels are listed by the Intergovernmental Panel on Climate Change (IPCC) as one of the top impacts of climate change. However, while events associated with storms and tsunamis are well documented, events that occur as the result of internal ocean dynamics have received little attention. Jianjun Yin and colleagues analysed tide gauge records (records of changes in sea level) and identified an unprecedented, 1-in-850 year, sea level rise event along the northeast coast of North America, during 2009-10. During this period the coastal sea level north of New York City rose by up to 128 mm.

Through a combination of observations and numerical simulations from state-of-the-art climate models, the authors show that a 30% weakening of the Atlantic Meridional Overturning Circulation (AMOC) played a major role in generating the event. Additional climate modelling experiments, wherein CO2 levels were increased by 1% per year for 100 years, indicate further weakening of the AMOC. Together with thermal expansion of the oceans, land ice melt and atmospheric variability, this weakening will likely cause more extreme sea level rise events along the densely populated coastline of North America in the future.