In late June 2021, the Pacific Northwest experienced an unprecedented extreme heat event. A strong high-pressure “heat dome” parked over the region around June 25–30, 2021, leading to record-shattering temperatures:
- Lytton, BC: 121°F (49.6°C), the highest temperature ever recorded in Canada.
- Seattle, WA: 108°F (42.2°C), in a city where June highs are usually in the 70s.
- Spokane, WA: 109°F (42.8°C), the highest temperature ever recorded in the area.
- Portland, OR: 116°F (46.7°C), shattering previous records by more than 10°F.
Climate scientists concluded that an event of this severity was at least 150 times more likely due to human-caused climate change. It would have been virtually impossible in the pre-industrial climate.
Mortality outcomes
The full toll across the region likely exceeded 1,000 lives lost:
- 619 deaths in British Columbia over one week—Canada’s deadliest weather event ever.
- At least 250 excess deaths in Washington and Oregon.
- 63-fold increase in heat illness emergency department visits in Oregon.
Clinical pearl
The vast majority of those who died collapsed in non-air-conditioned settings during peak heat. Many were found alone in their homes, highlighting the importance of community check-ins during heat emergencies.
Why was this so lethal?
Healthcare system response
Hospitals and emergency medical services were stretched beyond capacity:
- Seattle 911 calls overwhelmed—responders had to triage only critical cases.
- Emergency rooms set up overflow cooling areas with IV fluids, ice packs, and fans.
- Cities opened dozens of cooling centers in libraries, community centers, and malls.
Clinical pearl for healthcare providers
This event revealed that prevention is far more effective than treatment. Many patients with full-blown heat stroke could not be resuscitated even with aggressive cooling. Early intervention—checking on high-risk individuals and facilitating access to cooling—is critical.
Understanding the heat dome
This video provides an in-depth look at the meteorology, climate change connection, and disproportionate impacts on vulnerable communities.
Watch to ~5 min. (stop before the wildfire discussion, which is covered in a separate module).
Question
Which factor made the 2021 Pacific Northwest heat dome particularly dangerous?
The lack of air conditioning in most homes, combined with a population unaccustomed to extreme heat, made this event particularly deadly. Many victims were found in non-air-conditioned homes.