Changes in Mean Relative Sea Level around Canada in the Twentieth and Twenty-First Centuries

Abstract

Trends in regional mean sea levels can be substantially different from the global mean trend. Here, we first use tide-gauge data and satellite altimetry measurements to examine trends in mean relative sea level (MRSL) for the coasts of Canada over approximately the past 50–100 years. We then combine model output and satellite observations to provide sea level projections for the twenty-first century. The MRSL trend based on historical tide-gauge data shows large regional variations, from 3 mm y−1 (higher than the global mean MRSL rise rate of 1.7 mm y−1 for 1900–2009) along the southeast Atlantic coast, close to or below the global mean along the Pacific and Arctic coasts, to –9 mm y−1 in Hudson Bay, as indicated by the vertical land motion. The combination of altimeter-measured sea level change with Global Positioning System (GPS) data approximately accounts for tide-gauge measurements at most stations for the 1993–2011 period. The projected MRSL change between 1980 and 1999 and between 2090 and 2099 under a medium-high climate change emission scenario (A2) ranges from −50 cm in northeastern Canada to 75 cm in southeastern Canada. Along the coast of the Beaufort Sea, the MRSL rise is as high as 70 cm. The MRSL change along the Pacific coast varies from −15 to 50 cm. The ocean steric and dynamical effects contribute to the rise in MRSL along Canadian coasts and are dominant on the southeast coast. Land-ice (glaciers and ice sheets) melt contributes 10–20 cm to the rise in MRSL, except in northeastern Canada. The effect of the vertical land uplift is large and centred near Hudson Bay, significantly reducing the rise in MRSL. The land-ice melt also causes a decrease in MRSL in northeastern Canada. The projected MRSL change under a high emission scenario (Representative Concentration Pathway 8.5) has a spatial pattern similar to that under A2, with a slightly greater rise in MRSL of 7 cm, on average, and some notable differences at specific sites.