"Seattle doesn't get very many heat waves. Houston gets more heat waves but they're better prepared for them -- everything from air conditioning to how the city is built," Ebi said.
Of the 15 cities studied, Seattle ranked fourth-highest in the number of deaths projected from heat waves for every 100,000 residents.
"We're not a city that's adapted well to higher temperatures," Ebi said. "We need to take more action intermediately to adapt."
Heat kills by myriad methods.
People can simply overheat, which can progress, if not treated, to heat stroke, said Jeff Duchin, health officer for Public Health -- Seattle & King County.
"When temperature regulation of the body can't cope, organs basically start to fry," Duchin said. Heat can also exacerbate symptoms from underlying ailments like cardiac disease, diabetes or kidney problems.
The elderly, the very young and pregnant women are most at risk, Duchin said.
Wealth can also be a factor, said Mark Stephan, an associate professor in political science at Washington State University Vancouver.
"Heat waves have a bias in terms of who is affected, partly based on age, but also based on income," he said. "Climate change only exacerbates this, arguably."
People's ability to afford air conditioning, live in a home with effective air circulation, or leave town for places where it's cooler, gives them advantages.