North America’s 2021 ‘heat dome’ has caused catastropic ecological damage: study

People make their way through downtown Ottawa on Tuesday, June 18, 2024, as temperatures hit 32C in what meteorologists are calling a heat dome. (Sean Kilpatrick/THE CANADIAN PRESS)

PARIS - Billions of mussels scorched and baby birds dropping from sweltering nests: North America’s 2021 heatwave caused a cascade of ecological damage, some of it catastrophic, some unexpected, a new study showed Wednesday.

The “heat dome” that hit the western United States and Canada, fuelled by human-induced climate change, was among the most extreme ever recorded globally, with temperatures sometimes exceeding 50 C.

“The heatwave had widespread ecological effects, including an almost 400 per cent increase in wildfire activity and negatively affecting more than three-quarters of the species studied,” said study co-author Diane Srivastava, professor at the University of British Columbia.

To assess the heatwave’s impact, researchers combined weather, ecological and hydrological data with information on wildfires and scientific models.

Of the 49 terrestrial and marine species studied, over 75 per cent were negatively affected, according to the study published in the journal Nature Ecology and Evolution.

But the effects were highly variable: some populations fell by nearly 99 per cent, while others increased by up to 89 per cent.

The variability depends on factors such as vegetation cover, a species’ intrinsic heat tolerance and behaviour -- especially the ability to seek shade.

More than half the thatched barnacle population died as well as 92 per cent of Bay mussels.

The number of surf scoters, a native sea duck, dropped by 56 per cent while daily camera trap detections of caribou fell by half.

“Basically, any animal that couldn’t escape the heat was hard hit by it,” said Julia Baum, the lead author and biology professor at the University of Victoria.

“This included mobile animals at vulnerable stages of life, such as baby birds that couldn’t yet fly and were trapped in their heat-retaining nests,” she said.

Some species thrived.

Sea lettuce benefited from the die-off of other algae and expanded, increasing its coverage on beaches by 65 per cent after the heatwave.

Moose returned to the same level of daily camera trap sightings after the heatwave as they had before.

“We know from previous studies that moose are sensitive to high temperatures, so it’s possible they were able to avoid the hottest areas by selecting cooler microclimates, such as sites with denser forest cover,” said co-author Cole Burton, an associate professor at UBC.