Houses near the shore in Tuktoyaktuk. PATRICK DELL/THE GLOBE AND MAIL

As summer sea ice disappears in the far north due to climate change, massive swells are expected to roil Canada’s Arctic waters later this century with potentially dire consequences for coastal communities and burgeoning shipping traffic, new research has found.

In a study published Tuesday in the Journal of Geophysical Research: Oceans, scientists with Environment and Climate Change Canada project that the average height of the highest waves seen on the Arctic Ocean could increase by nearly two storeys, or six metres.

Closer to shore, the equivalent change is about two-metres higher – enough to batter coastal communities and infrastructure in vulnerable areas. The study also found that floods and other extreme events that currently occur about once every 20 years could show up every two to five years.

“Some of the general patterns were expected but seeing how much it will increase is a bit surprising – I would say alarming,” said Mercè Casas-Prat, a scientist with the climate research division of Environment and Climate Change Canada in Toronto who co-authored the work.

While erosion is already a serious problem for many coastal regions in the North, few studies have tried to quantify the extent to which that threat will grow as climate change eliminates the giant lid of sea ice that currently sits atop much of the Arctic Ocean through the year.

Together with senior scientist Xiaolan Wang, a specialist in ocean wave research, Ms. Casas-Prat set out to investigate the question.

The pair looked at the heights and periods of waves found in the Arctic Ocean between 1979 and 2005 and then used climate models to estimate how much those characteristics are likely to change by 2081-2100, a time when many climate scientists expect that sea ice will be largely absent during the summer months.

With ice removed from the picture, the conditions for the Arctic changes dramatically. More open water means more ‘fetch’, a term that describes the surface area across which wind has an opportunity to generate waves. Ice also suppresses waves because of the additional mass on the water’s surface and protects coastlines, particularly during the fall when Arctic seas are at their stormiest.

To improve the confidence level of their result, the pair ran their projections using five climate models to take uncertainties into account. The changes in wave heights and other characteristics that resulted were large enough to stand out from any differences that arose because of variations between models.

The team went into finer detail than most previous studies by dividing the entire Arctic Ocean into a vast grid of 25-by-25 kilometres square throughout, and 12-by-12 kilometres square at the coasts. The resulting projections encompassed the entire Arctic coastline, including Canada, Alaska, Russia, Scandinavia and Greenland.

“It’s really a step forward,” said Li Erikson, a physical oceanographer with the U.S. Pacific Coastal and Marine Science Center in Santa Cruz, Calif., who was not involved in the study.

Ms. Erikson added that there were some details that the Canadian study did not take into account, such as the extent of the broad continental shelf that fronts Alaska’s north coast, among other areas. That may serve to limit the height of waves closer to land, she said, but as Earth’s climate warms, the overall trend for the Arctic is clear.

“It’s ground zero up there as far as changes to the globe and where it impacts coasts,” she said.

Ms. Casas-Prat said that another factor the study did not take into account is the effect that higher waves will have on sea ice, rather than vice versa. As polar waters become more disturbed it’s likely that the break-up of the ice will be hastened, contributing to an ice-free ocean in the summer well before 2080.

The most vulnerable areas include the eastern shores of Greenland and Canada’s western Arctic, on the rim of the Beaufort Sea. Communities there, including Tuktoyaktuk, have already been assessing strategies for holding back erosion on shorelines made increasingly vulnerable by melting permafrost. The new study indicates this work will likely need to take into account significantly higher waves as well.

“There’s definitely a huge change that highlights how we’ll need to adapt in future,” she said.

In addition to threats to the coast, the higher waves could menace commercial shipping traffic, which is expected to increase with the absence of ice, Ms. Casas-Prat added.

The Globe and Mail, July 7, 2020