Key findings at a glance
Why was this heat event so deadly?
Nighttime cooling plays a key role in health risks: when nighttime temperatures remain high, there’s no relief. During the late June heat event, Seattle and Portland both broke their previous records for high minimum nighttime temperatures.
But possibly the largest factor in the high mortality rate was geographic. Per-capita heat-related death rates are highest in northern states and lowest in the South, where air conditioning is ubiquitous and people are acclimatized to high temperatures. The Pacific Northwest is known for its moderate climate, and most people there are not prepared for extreme heat—certainly not the kind they experienced at the end of June. Only about 44% of homes in Seattle and 78% in Portland have some form of air conditioning, as households have historically been able to get through short warm spells in the summer without it.
The health risks of extreme heat
In addition to mortality from cardiac, respiratory, or other causes, exposure to extreme heat can cause heat exhaustion, heat stroke, dehydration, and kidney failure. It can exacerbate existing cardiopulmonary diseases, and may accentuate side effects from certain medications. In addition to physiological impacts, research has found evidence for impacts on mental health, including a direct linear relationship between temperature and the incidence of suicide.
Inequitable exposure and vulnerability
These disparities drive differences in vulnerability across populations. The three components of vulnerability—sensitivity, exposure, and adaptive capacity—are at play here: an older adult who is sensitive to extreme heat but can afford air conditioning will avoid exposure and thus will not be vulnerable (as long as the power stays on). In contrast, a renter in a low-income housing development may not be able to afford to run air conditioning even if it is available.
As with other types of extreme events, the heatwaves in the Pacific Northwest likely had disproportionate impacts on the health and wellbeing of frontline communities—those that have contributed the least to climate change but will be the most affected. Due to historical redlining, for example, Black individuals are more likely to live in areas with less green space and street trees. A study conducted by King County and the City of Seattle found that areas with less landscaping and tree cover were as much as 20 degrees hotter compared with greener areas; these more urbanized areas were also disproportionately affected by COVID-19. Some vulnerable populations such as individuals with a mental illness, individuals with a disability, and older adults may have less access to cooling centers either due to distance or ability to access or travel to those centers. For example, as noted in King County’s Strategic Climate Action Plan, communities in southern King County have less access to cooler green spaces, which are concentrated in northern areas of the county. LGBTQ+ communities may be able to access cooling centers, but can face discrimination from staff or others using the facility due to lack of cultural competence training.
There are indirect impacts of higher temperatures on frontline communities as well. Black individuals, other communities of color, and same-sex couples are more likely to live in areas with higher air pollution, which interacts with and is exacerbated by high temperatures. This is on top of the already high rates of chronic illnesses within these groups. Power outages due to increased strain on the electrical grid could lead those with disabilities and/or chronic illnesses to lose access to life-saving medications or technologies.
The heat wave also detrimentally affected some species of fish, such as the endangered sockeye salmon, culturally important to the Shoshone-Bannock Tribes, and likely had a negative impact on other species of fish and crops important to food security, subsistence, or aquaculture for the region.
Implications for electric power and emissions
Some utilities in the region have had to install extra cooling systems to keep their own equipment from overheating, and if the extreme heat events continue in the future (spoiler alert: they will), there will be other strains on electricity infrastructure; above-ground power lines will suffer reduced transmission capacity and thermal power generation plants will suffer reduced efficiency.
Climate change and the future of extreme heat in the Pacific Northwest
Climate change increases the severity, duration, and frequency of extreme heat events by increasing global average temperatures. It may also increase the likelihood of very deep high-pressure systems called “heat domes,” which helped cause the record-smashing temperatures in the Pacific Northwest. Global climate models (GCMs) project that extreme heat events will become more frequent, more intense, and longer-lasting in the decades ahead, especially in higher latitudes.
Projections drawn from GCMs provide insights into how the Pacific Northwest heat event might look in a changing climate. We queried ICF’s climate analytics platform, which includes 32 downscaled GCMs, to determine whether temperatures like those we saw in late June would be anomalous under future climate conditions. The recent heat wave was a nearly “once in a millennium” event based on historical observations. However, projections from 2036 through 2065 at Portland International Airport (see Figure 1) show that temperatures in excess of 115°F could occur as often as every 25 years.* The average of the models suggests that by 2050, daily high temperatures of 100°F could be expected in Portland on average about 3–4 times per year and 105°F about once per year.
*These projections assume Representative Concentration Pathway 8.5, which represents a high greenhouse gas concentration future without major greenhouse gas emissions mitigation.
Projected increase in daily maximum temperature in Portland
Figure 1. Projected daily maximum temperatures at Portland International Airport. Dots in orange are projected daily maximum temperatures from 32 GCMs for the climate period 2036-2065, with temperatures above 115°F highlighted in red. Superimposed in black are observed daily maximum temperatures from 1992–2021. The record-breaking temperatures of 2021 would still be considered quite high in 2050, but not unusual.
Estimating future heat-related health risks in the Pacific Northwest
Building the Pacific Northwest’s resilience to future heat events
To better prepare for extreme heat, communities in the Pacific Northwest should focus on two main fronts: 1) reduce exposure to heat events—especially among vulnerable populations, and 2) adapting to warmer temperatures and implementing measures to reduce the urban heat island effect, which magnifies the impacts of heat waves by making urban areas hotter than the surrounding countryside.
King County’s Strategic Climate Action Plan, which it updated in 2020, includes a priority action to develop and implement an urban heat island strategy that will incorporate nature-based solutions. Similarly, the 2015 Climate Action Plan for Multnomah County and City of Portland includes several strategies to reduce heat-related risks and impacts, including addressing the urban heat island effect, increasing the resilience of natural systems and built infrastructure, and improving emergency preparedness.
The Centers for Disease Control and Prevention (CDC) provides solid, evidence-based strategies to prevent heat-related illness under the general categories of “stay cool, stay hydrated, and stay informed.” The CDC also provides recommended actions to protect the most vulnerable, such as older adults and those living in low-income communities. It’s valuable for information resources to be available in several languages (see examples in the call-out box), since immigrant communities tend to be particularly exposed to heat stress.
To help provide state and local public health officials with information about heat waves in the coming month and season, CDC has developed a Heat Tracker tool that uses short-term climate forecasts produced by the National Oceanic and Atmospheric Administration (NOAA) to identify parts of the country that will be most at risk from heat extremes.
Early warning systems (e.g., CDC’s Heat Tracker tool, National Weather Service heat advisory alerts, and local heat warning systems) are critical to reducing exposure to the impacts of rising temperatures and the increase in frequency and intensity of heat waves.
Communities also need current, comprehensive data to inform them on which areas of the community—and which groups of the population—are most at risk. CDC’s National Syndromic Surveillance Program provides data essential now and into the future.
Adapting to heat
Comprehensive adaptation to heat extremes should incorporate long-term actions, such as interventions in physical infrastructure (e.g., power plant and electricity grid adjustments), creating accessible cooling centers, and upgrading housing (e.g., installing central AC and outdoor awnings and blinds, as well as using energy-efficient design in new construction and major renovations. Studies indicate that central air conditioning may have a stronger protective effect than room air conditioners).
Cooling centers are an important approach to reducing exposure among vulnerable populations, and communities need to carefully plan locations to ensure cooling centers are easily accessible to those who most need them. In an analysis ICF conducted for the City of Philadelphia in 2015, for example, we found that some potentially vulnerable populations were not within easy walking distance of a cooling center.
In urban settings, the heat island effect compounds the negative impacts of extreme heat. At the community level, actions to address the heat island effect also contribute to reduce vulnerability to extreme heat events.
The U.S. Environmental Protection Agency’s Heat Island Reduction Program provides information on strategies to mitigate heat islands, including smart growth planning, planting trees and vegetation, green roofs, cool roofs, and cool pavements. These approaches provide co-benefits for air quality, energy use, greenhouse gas emissions, public health, and quality of life. Additionally, cool pavements can improve nighttime visibility and safety while reducing tire noise, while nature-based solutions such as urban green spaces and green infrastructure (e.g., shade trees, green roofs, etc.), benefit water quality and stormwater management.