Relative sea-level projections in Canada and the adjacent mainland United States

Abstract

Relative sea-level projections are provided for 59 locations in Canada and 10 in the adjacent mainland United States (New England and Washington State) through the 21st century, relative to 1986-2005. The projections are based on the Representative Concentration Pathway (RCP) scenarios of the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR5). They include contributions from thermal expansion of the ocean (steric effect), land ice melting and discharge, and anthropogenic influences. The global mean sea-level projection for RCP8.5, the largest emissions scenario, at 2100 is 74 cm (5%-95% range is 54 to 98 cm). Global Positioning System (GPS) measurements of vertical land motion are incorporated into the relative sea-level projections. In the regions presented here, vertical land motion, largely arising from glacial isostatic adjustment, plays a prominent role in determining projected relative sea-level change. On the east coast, crustal subsidence, combined with dynamic oceanographic changes, generates relative sea-level projections that are similar to or larger than the global mean projections in large parts of Atlantic Canada and New England. On the west coast, most relative sea-level projections are smaller than the global means, although some sites in Washington State and southern British Columbia feature relative sea-level projections similar to the global values. The largest variation in projected relative sea-level rise occurs in the Arctic, owing to the very large spatial differences in present-day crustal uplift due to glacial isostatic adjustment. Here, projected relative sea-level at 2100 varies from around 1 m of sea-level fall (median values) where land is rising quickly on Hudson Bay, while it reaches about 70 cm of sea-level rise on the Beaufort coast where the land is subsiding. A scenario featuring partial collapse of a portion of the West Antarctic Ice Sheet provides an additional 65 cm of sea-level rise to RCP8.5, and may be appropriate to consider when tolerance to the risk of sea-level rise is low. The relative sea-level projections given here only provide a trajectory through this century, but the IPCC AR5 projects continued global sea-level rise in coming centuries. As understanding improves of the various components of sea-level rise, it will be necessary to update, on an occasional basis, the relative sea-level projections and re-evaluate the implications for infrastructure, habitat, and marine navigation.

Erosion and Flooding—Threats to Coastal Infrastructure in the Arctic: A Case Study from Herschel Island, Yukon Territory, Canada

“…however, this figure incorporates −1.68 mm·a −1 of submergence due to glacial isostatic adjustment and correction for ice-mass changes (James et al 2014). At Herschel Island, SLR may be as high as ca.…”

Estimating Sea-Level Allowances for Atlantic Canada using the Fifth Assessment Report of the IPCC

“…In Atlantic Canada, the vertical land motion occurs mainly because of GIA (e.g., Koohzare, Vaníček, & Santos, 2008;James et al, 2014). Table 5 (column 2) summarizes the vertical land motion (uplift or subsidence) at tide-gauge stations based on nearby GPS observations.…”

“…The GPS data were processed using the Canadian Geodetic Survey's Precise Point Positioning (PPP) software (Kouba & Héroux, 2001). The rates of vertical land motion from PPP were compared with the rates derived from an analysis of the GPS data using the Bernese GPS Software, version 5.0 (Dach et al, 2007), (James et al, 2014). For Nain, the GPS uplift rate is determined from a Canada-wide GPS velocity field (M. R. Craymer, personal communication, 2011) whose network-adjusted rates have been realigned in a manner consistent with the PPP rates.…”

“…The objectives of this paper are to assess the dual consistency of tide-gauge trends and GPS vertical land motion, compare the GIA model predictions to the global positioning system (GPS) trends, and to describe a procedure to extend the use of GPS data to replace the GIA component of the projections for calculating sea-level allowances (James et al, 2014). While the allowance methodology deals with the effect of SLR on inundation, it does not address coastline recession through erosion (Ranasinghe, Duong, Uhlenbrook, Roelvink, & Stive, 2012).…”

Exposure to Coastal Hazards in a Rapidly Expanding Northern Urban Centre, Iqaluit, Nunavut

“…The IPCC AR5 recognized that additional sea level rise from accelerated drawdown of the West Antarctic Ice Sheet, for which the potential is poorly constrained, would not likely exceed several tenths of a metre during this century (Church et al, 2013). To allow for this scenario, James et al (2014) provided an enhanced projection of +65 cm based on a number of published estimates of the likely effects of marine ice-sheet instability in West Antarctica. Recent work suggests that increased oceanic melting and hydrofracturing of ice shelves could lead to collapse of the West Antarctic Ice Sheet much sooner than previously thought and to accelerated ice loss from the East Antarctic Ice Sheet (Pollard et al, 2015).…”