Like in ‘Postapocalyptic Movies’: Heat Wave Killed Marine Wildlife en Masse

Dead mussels and clams coated rocks in the Pacific Northwest, their shells gaping open as if they’d been boiled. Sea stars were baked to death. Sockeye salmon swam sluggishly in an overheated Idaho river, prompting wildlife officials to truck them to cooler areas.

The combination of extraordinary heat and drought that hit the Western United States and Canada over the past two weeks has killed hundreds of millions of marine animals and continues to threaten untold species in freshwater, according to a preliminary estimate and interviews with scientists.

“It just feels like one of those postapocalyptic movies,” said Christopher Harley, a marine biologist at the University of British Columbia who studies the effects of climate change on coastal marine ecosystems and who calculated the death toll.

Such extreme conditions will become more frequent and intense, scientists say, as climate change, driven by humans burning fossil fuels, wreaks havoc on animals and humans alike. Hundreds of people died last week when the heat wave parked over the Pacific Northwest. A study by an international team of climate researchers found it would have been virtually impossible for such extremes to occur without global warming.

Just before the heat wave, when Dr. Harley took in the eye-popping weather forecasts, he thought about how low the tide would be at midday, baking the exposed mussels, sea stars and barnacles. When he walked to the beach last week on one of the hottest days, the smell of decay hit him immediately. The scientist in him was excited, he admitted, to see the real-life effect of something he’d been studying for so long.

But his mood quickly changed.

“The more I walked and the more I saw, the more sobering it all became,” Dr. Harley said. “It just went on and on and on.”

The dead sea stars, usually the most eye-catching creatures in tidal pools, hit him particularly hard. But the obvious mass victims were blue mussels, an ecologically important species that feeds sea stars and sea ducks and creates habitat for other animals. Dr. Harley estimated losses for the mussels alone in the hundreds of millions. Factoring in the smaller creatures that live in the mussel beds — barnacles, hermit crabs and other crustaceans, various worms, tiny sea cucumbers — puts the deaths at easily over a billion, he said.

Scientists have only begun to consider the domino effects. One concern is that the sea ducks, which feast on mussels in the winter before migrating to their summer breeding grounds in the Arctic, will have enough food to survive the journey.

“It’s at least something that we’re starting to think about,” he said.

Species that live in intertidal zones are resilient, he noted, and the mussels on the shady north side of boulders seem to have survived. But if these extreme heat waves become too frequent, species won’t have time to recover.

While the heat wave over the Pacific Northwest has eased, punishing temperatures have persisted across much of the American West. Now, another heat wave appears to be building, only worsening the ongoing drought.

That means biologists are watching river temperatures with alarm. Salmon make an extraordinary migration, often hundreds of miles, from the inland rivers and lakes where they are born, out to sea, and then back again to spawn the next generation. A network of longstanding dams in western states already makes the journey perilous. Now, with climate change worsening heat waves and droughts, scientists say the conditions look grim without intense intervention, which comes with its own risks.

Heat Wave Hits North America

As suffocating heat hits much of Western North America, experts are concerned about human safety and power failures.

    • Western Canada: Canada broke a national heat record on June 27, when the temperature in a small town in British Columbia reached almost 116 degrees Fahrenheit, breaking an 84-year-old record by nearly 3 degrees, with dangerously hot weather expected to continue for several more days.
    • Pacific Northwest U.S.: A heat dome has enveloped the region driving temperatures to extreme levels — with temperatures well above 100 degrees — and creating dangerous conditions in a part of the country unaccustomed to oppressive summer weather or air-conditioning.
    • Severe Drought: Much of the Western half of the United States is in the grip of a severe drought of historic proportions. Conditions are especially bad in California and the Southwest, but the drought extends into the Pacific Northwest, much of the Intermountain West, and even the Northern Plains. The extreme heat is exacerbating the dry conditions.
    • Growing Energy Shortages: Power failures have increased by more than 60 percent since 2015, even as climate change has made heat waves worse, according to new research published in the journal Environmental Science & Technology.
    • Baseline Temperatures Are Rising: New baseline data for temperature, rain, snow and other weather events reveal how the climate has changed in the United States. One key takeaway, the country is getting hotter.

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