As much of Oregon endures consecutive days of high heat, climate data shows the state has seen more 90 degree Fahrenheit or hotter days over the past 10 years than in the decades that came before. It’s part of a trend playing out this week, and likely to continue in the years ahead.
“Over the last few years, we have experienced almost double the number of these hot days compared with historical occurrences,” state climatologist Larry O’Neill said.
Days that reach 90 degrees are happening more frequently, Portland State University associate professor of weather and climate science Paul Loikith said.
“This is not a thing that is going to go away,” he said. “We’re dealing with more heat than we used to, now we deal with more heat. So this is a staple of our summer, and it’s something that we should continue to be cognizant of because it is important. And just because we have some summers that have exceptional heat and some that maybe don’t have exceptional heat, that doesn’t mean that the risk goes away.”
Since 1940, the number of 90 degree days in Portland has climbed, according to National Weather Service data.
“The last several years we’ve been averaging between around 20 to 25 days above 90 degrees, which is substantially more than the mid-20th century when we didn’t exceed 20 days above 90 degrees very often,” Loikith said.
Each year from 2021 through 2024 the city saw at least 24 days of about 90.
“It’s in some sense pretty expected from a warming climate,” he said. “So we know that the average temperature is increasing. We know that that’s true globally and locally, and this is a reflection of that overall increase in global temperature on our local climate.”
The continued burning of fossil fuels like coal, oil and natural gas is driving that human-caused climate change. The resulting greenhouse gas emissions trapped in the atmosphere raise average temperatures, resulting in extreme weather like warmer, hotter, drier summers.
In 2021, the Pacific Northwest experienced a heat dome event which trapped scorching hot air above the region for nearly a week during the summer. The extreme heat broke records across the state and temperatures in Portland ticked as high as 116 degrees. The heat also killed nearly 100 people across the state. Many were found home and alone without an air conditioning system.
Although the region has not otherwise experienced extreme temperatures of that magnitude, data shows 90 degree days are occurring more frequently. According to the NWS, during the summer of 2018, Portland experienced 31 days of above 90.
Summer nights are also getting warmer, Loikith said. Since 1940, summer nights have increased by about 5.4 degrees.
That makes it harder for people to recover from high temperatures during the day and to continue to endure high temperatures for longer periods of time.
“If you’re not recovering to sufficiently cool values, homes don’t cool off enough, people don’t get that relief, the effects of hot days can be compounded,” he said.
That could lead to serious heat related health risks, like heat exhaustion or heat stroke, like the many people who died during the heat dome event.
This story comes to you from the Northwest News Network, a collaboration between public media organizations in Oregon and Washington.
