When Skamania County’s temperature shot past 110 degrees, Deepti Singh took refuge in the Wind River.

A Washington State University researcher who studies extreme weather events, Singh and her friends unwittingly planned a weekend getaway that coincided with the 2021 Pacific Northwest heat dome. As temperate Western Washington heated up like Death Valley, they abandoned plans for a Columbia River Gorge hike and submerged themselves in the nearby river.

“Luckily, our cabin was air-conditioned, and we also spent hours just sitting in the water,” says Singh, an assistant professor at WSU Vancouver’s School of the Environment. “I even had to put my dog in the river, and she hates the water.”

Smiling woman net to her dog wearing a blue kerchief
Deepti Singh (Courtesy WSU School of the Environment)

The heat dome toppled records across the Northwest and ranked among 2021’s global weather extremes. It’s cited in the Fifth National Climate Assessment as an example of how extreme weather events are becoming more frequent as the climate changes.

Singh is among the climate assessment’s coauthors, who also include WSU colleague Kirti Rajagopalan, assistant professor of biological systems engineering. Released in November, the report outlines how hotter temperatures are already impacting the Northwest, and what we can expect in the future.

Better known for its gray skies and drizzle, the Northwest is a relative stranger to extreme heat, particularly in areas west of the Cascades where many homes lack air-conditioning. But since the 1980s, extreme heat has emerged as a critical concern for the western United States.

The West is experiencing a greater magnitude of warming from climate change than the East Coast, the assessment says. Climate models indicate the Northwest is on a similar path, with higher rates of summertime warming than other parts of the continental United States. That will trigger a new normal for Northwest summers. Even average years will feature more days with uncomfortably hot temperatures. And heat waves and extreme heat events will occur more frequently.

Washington’s and Idaho’s average temperatures have climbed by nearly 2 degrees Fahrenheit since 1900, and Oregon’s by 2.5 degrees. While the increase may seem negligible, it represents a heat accumulation that’s already destabilizing historic climate patterns.

“Even these seemingly small increases have such big impacts on our society,” says Singh⁠— a point she drives home with undergraduate students in an earth climate systems class.

Nearly 14 million people live in the Northwest, where residents already feel the brunt of climate change extending the warmer, drier seasons. Wildfire season lasts longer and fires burn more intensely, filling the skies with smoke and threatening rural communities. More precipitation falls as rain instead of snow in the mountains. Besides shorter ski seasons, the reduced snowpack diminishes water supplies available for cities, irrigators, and migrating salmon. Severe rain events also occur more frequently because warmer air can carry more moisture.

Heat waves are more prevalent, too. Since 1960, Seattle and Portland have experienced four to six additional heat waves each year compared to historic climate conditions, according to the assessment. Urban areas magnify the effect of heat waves, which are characterized by two or more abnormally hot days compared to average temperatures. The built-environment traps heat and provides fewer green spaces for shade and cooling.

The Paris Agreement climate treaty aims to keep the increase in global temperatures well below 2 degrees Celsius (3.6 degrees F) from pre-industrial levels. In the Northwest, warming of that magnitude would upend seasonal weather expectations. More summer days would climb above 95 degrees F, and fewer winter days would drop below freezing.

Searing summer heat would have the greatest impact on parts of central and southeastern Washington, which could expect an average of 19 to 20 additional days above 95 degrees F each year.

The likelihood of regionwide heat domes increases as well.

Some scientists have described the 2021 heat dome as a 1,000-year event made 150 times more likely by climate change. Instead of being a rare anomaly, events like the heat dome could occur every five to 10 years with 2 degrees C of global warming, they say.

During the heat dome, parts of the Northwest recorded temperatures up to 40 degrees F above normal. Even after temperatures peaked, above-average heat lingered into mid-July. It was a stark reminder of how ill-prepared the Northwest is for a hotter climate.

“Everything depends on our climate⁠—from the food we grow, to our water supplies, the buildings we design, and our physical and mental health. When we have these extreme events, we see the impact from fatalities to infrastructure damage to ecosystems in distress,” Singh says.

An estimated 1,400 deaths in the United States and Canada were attributed to the heat dome. Shellfish and other marine animals experienced mass die-offs. Crops were lost, sections of Interstate 5 buckled, and Portland’s Max commuter train shut down when its attached power lines melted.

“Our infrastructure was built for the climate of a few decades ago. And that climate has changed and continues to change,” Singh says.

The Northwest can prepare for a hotter future by adapting infrastructure and putting measures in place to protect vulnerable populations. But the future is in human hands, the National Climate Assessment notes. The volume of emissions from burning fossil fuels and the release of other greenhouse gases will determine the future climate.

Meanwhile, the effects of the 2021 heat dome will be felt in the region for decades to come, Singh says. Salmon populations were lost when streams became too hot for survival. The heat killed young trees and scorched new growth in the Olympic Peninsula’s forests. And the village of Lytton, British Columbia, is still rebuilding after a wildfire destroyed the town and killed two people the day after the temperature hit 121.3 degrees F⁠—the highest recorded in Canada.

“I think the biggest lesson from the 2021 heat dome is that these events are not isolated,” Singh says. “We often remember them as a few bad days, but they have cascading impacts throughout our lives and our ecosystems that last for years.”

Temperature map of North America showing heat dome of 2021 in the Pacific NorthwestThe heat dome toppled records across the Northwest and ranked among 2021’s global weather extremes.
(Image Courtesy NASA Earth Observatory)


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Exploring weather extremes at Deepti Singh’s lab