We’ve been warned that heat is a silent killer — and new research from the University of Washington confirms the extreme heat wave that hit the state two summers ago was, in fact, responsible for more than 150 deaths.
In some ways, the recent UW study, which relied on statistics analyzing how much certain types of deaths in Washington spiked over about three weeks in late June and early July 2021, verified what the state Department of Health already knew: Dozens of people died from the high temperatures, which soared above 100 degrees for several days.
But UW researchers, led by environmental epidemiologist Joan Casey, focused specifically on “injury” deaths, including deaths that might not have been directly caused by overheating, including drowning, transportation accidents, violence and mental health crises. Understanding the extent of these types of deaths and their connection to rising temperatures can help the region reduce the toll of future heat waves, Casey said.
“When we don’t count or we undercount the damages, we don’t put the necessary resources into doing similar research,” she said. “This is a warning to the Pacific Northwest that we really need to think about how we’re going to prepare for these types of events.”
The UW research team used weekly Centers for Disease Control and Prevention mortality data to calculate how many people might have been expected to die from injuries over the same time period had the heat wave not happened, Casey said. They then compared that estimate with official death records, ultimately finding the heat wave was responsible for 159 injury deaths.
Connections to behavior
Although the UW study doesn’t analyze the social or behavioral factors that could be linking higher temperatures and accidents or violence, researchers have analyzed the relationship for decades.
Some behavioral observations sound obvious, such as how more people might flock to bodies of water or go swimming when it’s hot outside, which could explain a rise in drownings, Casey said. More people also leave their homes to spend time outside when it’s warm, leading to more traffic and therefore, more accidents or collisions, she added.
Many studies, however, have also linked physiological and psychological changes to extreme heat, meaning people’s behavior and decision-making likely also shifts.
“One of the dominant psychological theories is the idea that when you’re exposed to uncomfortable heat, that induces a negative, angry or hostile state,” said Kim Meidenbauer, a psychologist who runs a social, cognitive and environmental neuroscience lab at Washington State University.
In lab studies that induce heat, Meidenbauer has found there are also increases in people’s impulsivity. A rise in temperatures can also impair our cognitive control, she said.
“So not only do people have a lot of impairments in things like memory or things that require sustained attention, you also see an inability to override impulsive responses,” she said.
While limited research explores what exactly heat triggers in the brain, a group of Chinese scientists has found evidence of changes in neural activity when people experience increased temperatures.
“It’s thought that by disrupting these pathways you’re interfering with the prefrontal cortex’s ability to put a stop to the emotional reaction that you’re having,” Meidenbauer said. “This might be one way that heat is actually impairing people’s decision-making and in this case increasing the likelihood they will react with violence.”
Some studies have also looked at potential effects of heat in situations of self-harm, though many emphasize that rising temperatures and climate change should not be viewed as direct motivations. Instead, researchers share evidence that heat increases the risk in individual scenarios.
In 2018, a Stanford University economist led research that projected temperature increases through 2050 could lead to an additional 21,000 suicides in the United States and Mexico.
Data from the CDC between 1971 and 2000 confirmed suicide rates peaked in the United States in the early summer during that time, and from Johns Hopkins Medicine also reports rates are highest in the spring and early summer, and lowest in December.
The 2018 study noted that projected changes in suicide rates as climate change intensifies could be “as important as other well-studied societal or policy determinants of suicide rates.”
“The large magnitude of our results adds further impetus to better understand why temperature affects suicide and to implement policies to mitigate future temperature rise,” wrote the team, many of whom study environmental science or economics at institutes in California, Massachusetts, Canada and Chile.
Northwest worries
The state’s official count of the heat wave’s toll is similar to UW’s, counting about 150 heat-related deaths over that same three-week period. But that data delineates the deaths differently, focusing solely on deaths that occurred with “evidence of heat-related stress,” such as hyperthermia or heat stroke, said DOH spokesperson Emily O’Donnell-Pazderka.
Some of the deaths the state is counting, such as those caused by heart attack or stroke, aren’t included in UW’s report because they aren’t considered “injury” deaths. Those differences make the data difficult to compare, and Casey added that her team’s goal wasn’t to compare the state’s preliminary count to theirs.
Regardless, both numbers remind us that living in the Pacific Northwest comes with some particular concerns as temperatures warm.
“This period of anomalously warm temperatures centered on … a region with minimal history of extreme heat events and thus relatively unprepared regarding infrastructure and prevalence of air conditioning,” UW researchers wrote.
The 2021 heat dome, which was caused when a large ridge of high atmospheric pressure trapped hot air over the region and brought unprecedented temperatures to the region, will likely not be the last such event, the team said.
According to climate models that project 2 degrees Celsius of warming, similar heat waves could occur every five to 10 years at even higher temperatures, researchers wrote in the paper.
The study concluded with recommendations for stronger public health interventions, including increasing efforts to contact isolated members of communities, leading campaigns promoting safe swimming and providing additional mental health services.
According to DOH, the region’s lack of cooling infrastructure does increase risk of heat-related illnesses, hospitalizations and deaths for those with certain medical conditions and those without access to air conditioning.
“But, heat-related deaths are preventable,” O’Donnell-Pazderka said. “The timely communication of clear, actionable heat health and safety recommendations is critical to reduce future heat-related deaths, illnesses and injuries.”
Since 2021, the King County Regional Homelessness Authority started providing more cooling (and warming) centers, many specifically for those who are unhoused, said Brendan McCluskey, director of the county’s Office of Emergency Management. The agency is also working with the National Weather Service to improve some of its heat-related products, like the HeatRisk forecast, which provides a quick view of heat risk potential over the upcoming week, he said.
Last summer, the King County Council also passed legislation that requires the county to develop a regional operational plan for extreme weather centers and disaster sheltering, which includes investigating different locations that could be used to create new cooling centers, McCluskey added.
In Olympia, a bill this session that hoped to expand air conditioning use in adult family homes never made it out of the Senate. But another that would protect access to electricity and running water during extreme heat easily passed.
“With each year, we continue to apply lessons learned to our plans, processes and procedures,” McCluskey said. “The extreme heat playbook has been updated.”
