Puget Sound nights are getting warmer, which is concerning experts

As Seattle’s latest heat advisory expires, overnight temps will remain higher than historical norms – it’s part of a growing trend that is getting more attention.

According to Climate Central, the Seattle/Tacoma area has undergone a transition since the 1970s. Overnight lows are now, on average, 2.7 degrees warmer. In Spokane, the nights are growing warmer, faster: the change has been measured at a whopping 4.2 degrees warmer. 

Climate Central trends show a 2.7 degree warming in overnight lows dating back to the 1970s. (Climate Central)

Simply put: summer nights are warming even faster than summer days.

"From a human health perspective, it’s the nighttime temperatures that really make a huge difference in terms of frequency of emergency room visits," said Nick Bond, Washington’s state climatologist.

"I don’t think it’s getting enough attention. Our summer nights are getting warmer and during our heat waves, the nights are also warmer and that’s when people have problems."

Scorching summer temperatures regularly get headlines, but those nighttime trends are becoming a clear threat.

Following last summer’s extreme heat dome Seattle & King County Public Health’s Dr. Jeff Duchin noted: that while tornadoes and hurricanes garner national headlines, extreme heat is the leading cause of weather-related deaths in the U.S.

"Climate change is a health emergency," said Dr. Duchin. "Reducing greenhouse gas emissions is literally a matter of life and death."

In King County, the problem is especially concerning in neighborhoods that reside in "heat islands" – essentially, areas that have hotter surface-level temperatures as a result of paved landscapes, a lack of tree canopies and/or greater industrial activity.

Back in 2020, the county mapped heat-islands with more than 100,000 measurements across the county. Volunteers were able to map how some areas held onto heat throughout the day and night, while others retained less heat as the sun went down.

It’s a health concern that has the greatest impact on younger children, the elderly and those with underlying health conditions.

However, extreme heat – and prolonged exposure to heat – can affect others too. Seattle & King County Public Health warns that athletes who exercise outdoors, outdoor workers and those who are unsheltered face additional risk.

Some medications can also make it harder to stay hydrated and regulate body temperatures, including medications for allergies and colds, thyroid, depression, heart/blood pressure and weight loss. You can read more about heat concerns, and who is most at-risk of high temperatures on the Public Health Insider, here.