Projections of relative sea level in Canada until 2100 from IPCC AR5
2022-11-21. Changes in relative sea level at a particular location depend not only on changes in absolute sea level, but also on changes in land elevation. In 2020, Natural Resources Canada (NRCan) published a three-dimensional velocity grid for Canada’s Earth crust known as NAD83v70VG (Robin et al. 2020). This crucial piece of information permitted NRCan to publish revised and expanded estimates of projected changes in relative sea level across Canada.
Vertical crustal velocity grid
The vertical crustal velocity in NAD83v70VG is shown below.
Geophysical processes responsible for this distribution of vertical velocities are primarily related to plate tectonics in southwestern British Columbia and to post-glacial isostatic rebound in the remainder of Canada (Robin et al. 2020). Due to the irregular spatial coverage of vertical motion measurements from long-term GPS stations, gridded estimates of vertical crustal motion have a spatially varying uncertainty, shown below.
Maps of projected changes in relative sea level
Shortly after the publication by Church et al. (2013) of the IPCC fifth assessment report (AR5) projections of sea level change across the global ocean, James et al. (2014) published estimates of projected changes in relative sea level at Canadian coastal sites equipped with long-term GPS stations. Publication in 2020 of NAD83v70VG allowed James et al. (2021) to expand the spatial coverage of projections in relative sea level to all of Canada.
A clickable map of the James et al. (2021) dataset on Canada’s climate data website allows users to plot and download time series of relative sea level anywhere in Canada on a grid with a spatial resolution of 0.1° in latitude and longitude.
Large variations in relative sea level change are projected across Canada. While relative sea level is projected to rise fastest in the Maritime provinces and in the Beaufort Sea, relative sea level will be falling in the Hudson Bay and Foxe Basin areas. This spatial pattern of relative sea level change is closely related to the spatial pattern of vertical crustal velocity (see first figure of this article).
Ten maps covering all of Canada display the relative sea level change that could occur up to 2100 according to three levels of global greenhouse gas (GHG) emissions intensity: RCP2 .6 for low GHG emissions, RCP4.5 for medium GHG emissions, RCP8.5 for high GHG emissions. Note: RCP = Representative Concentration Pathways (van Vuuren et al. 2011).
- RCP2.6 lower (5th percentile)
- RCP2.6 median (50th percentile)
- RCP2.6 upper (95th percentile)
- RCP4.5 lower (5th percentile)
- RCP4.5 median (50th percentile), shown in map above
- RCP4.5 upper (95th percentile)
- RCP8.5 lower (5th percentile)
- RCP8.5 median (50th percentile)
- RCP8.5 upper (95th percentile)
- RCP8.5 enhanced scenario (RCP8.5 median plus 65cm of extra sea level rise due to accelerated ice melting in Antarctica).
These ten maps can be viewed on Canada’s climate data portal.
Time series of projected relative sea level change
We can obtain local projections of relative sea level change at any site along the coast of Canada by clicking on the interactive maps. In the time series graphics that follow, solid lines show the median (50th percentile) projections of relative sea level change for the RCP2.6, RCP4.5 and RCP8.5 GHG emission scenarios. Dashed lines show the 5th and 95th percentiles associated by color to each of the three GHG emissions scenarios. Thus, for each of the RCPs, a probability of 90% is associated with the area between its two dashed lines. A red circle indicates the enhanced RCP8.5 upper (95th percentile) scenario for which 65cm of extra sea level rise was added due to accelerated ice melting in Antarctica.
A companion blog post written in French plots the relative sea level time series at Umiujaq and four southern Québec municipalities: Québec City, Rimouski, Sept-Îles and Îles-de-la-Madeleine.
Time series interpretation
By 2100, relative sea level is always lowest for the low GHG emissions scenario RCP2.6. At the other extreme, relative sea level is always highest for the high GHG emissions scenario RCP8.5.
The commitments made by the international community in 2021 at the COP26 Glasgow meeting to reduce GHG emissions roughly correspond to the RCP4.5 medium GHG emissions scenario. This intensity level of GHG emissions would result in intermediate values of relative sea level rise compared to the RCP2.6 and RCP8.5 scenarios.
Vertical crustal motion is the main factor explaining differences in relative sea level projections from place to place. Most localities in southern Canada and the Beaufort Sea can expect sea level rise over the next decades. But at other places such as Churchill, the uplift rate of the earth’s crust exceeds the rate at which absolute sea level rises, causing a local drop in relative sea level.
References
Church, J.A., P.U. Clark, A. Cazenave, J.M. Gregory, S. Jevrejeva, A. Levermann, M.A. Merrifield, G.A. Milne, R.S. Nerem, P.D. Nunn, A.J. Payne, W.T. Pfeffer, D. Stammer and A.S. Unnikrishnan, 2013. Chapter 13, Sea Level Change. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
James, T.S., Henton, J.A., Leonard, L.J., Darlington, A., Forbes, D.L., and Craymer, M., 2014.Relative Sea-level Projections in Canada and the Adjacent Mainland United States; Geological Survey of Canada, Open File 7737, 72 p. https://doi.org/10.4095/295574
James, T S; Robin, C; Henton, J A; Craymer, M. 2021. Relative sea-level projections for Canada based on the IPCC Fifth Assessment Report and the NAD83v70VG national crustal velocity model. https://doi.org/10.4095/327878
Robin, C. M. I.; Craymer, M; Ferland, R; James, T.S.; Lapelle, E; Piraszewski, M; Zhao, Y.; 2020. NAD83v70VG: a new national crustal velocity model for Canada https://doi.org/10.4095/327592.
Van Vuuren, D.P., Edmonds, J., Kainuma, M., Riahi, K., Thomson, A., Hibbard, K., Hurtt, G.C., Kram, T., Krey, V., Lamarque, J.F. and Masui, T., 2011. The representative concentration pathways: an overview. Climatic change, 109(1), pp.5-31. https://doi.org/10.1007/s10584-011-0148-z