Seattle’s hot start to this June was influenced by climate change.
That’s according to Climate Central, a New Jersey-based research nonprofit, that has used modeling to assess how climate change affects local temperatures, among other impacts.
Last weekend’s heat brought the hottest June 8 in the Seattle area since 1948, with Seattle-Tacoma International Airport recording a high of 90 degrees. The city saw above-normal temperatures for several days. Normal for the first week of June is about 70 degrees, said Matthew Cullen, a meteorologist at the National Weather Service in Seattle.
Sunday also brought the highest recorded overnight low for the day at 61 degrees, Cullen said.
Here and elsewhere climate change may be more obviously manifesting through rising low temperatures, rather than highs.
During the day, solar radiation heats the earth’s surface. Overnight, when there’s no more solar radiation coming in, the surface is cooling by emitting infrared radiation.
The effects of greenhouse gases act throughout the day to warm the surface, including at night, when they reduce nighttime cooling that would otherwise cool the surface faster, said Dennis Hartmann, an atmospheric science professor at the University of Washington.
During the day, clouds, haze and smoke, which reflect some of the sun’s warming rays, have increased over time. So daytime temperatures have not warmed as fast as nighttime temperatures, Hartmann said.
Seattle’s recent warmer-than-normal nights — from June 6 to June 9 — were made three to five times more likely because of climate change, said Shel Winkley, a meteorologist at Climate Central. The city saw overnight low temperatures up to 15 degrees above average for this time of year.
Climate change made hot nights 3 to 5 times more likely
From June 6–9, parts of Washington had unusually elevated nighttime low temperatures, which were made 3 to 5 times more likely due to greenhouse gases. The maps below show a new metric developed by Climate Central, which measures how likely it is that temperatures anomalies are related to greenhouse gas emissions.
The city has seen an average of 38 more warmer-than-normal summer nights per year — made at least two times more likely due to climate change — compared to 1970, according to Climate Central.
Summer nighttime temperatures are warming nearly twice as fast as daytime highs across the U.S. Summer nighttime temperatures have warmed on average by about 3 degrees since 1970.
East of the Cascade crest, Yakima saw overnight lows about 15 to 20 degrees above normal June 8 through 10, made three to four times more likely because of climate change, according to Climate Central. And Spokane saw overnight lows about 8 to 15 degrees above normal for this time of year beginning June 6, made nearly two times more likely because of climate change, according to the group.
To produce these analyses, Climate Central runs 22 climate models twice. With one set, they’re running the models with the historical carbon emissions that have been put into the atmosphere by humans since the Industrial Revolution. They run the models again, but without the extra carbon and get a ratio that shows how much more likely an outcome is because of climate change.
Warming is amplified in paved-over cities.
More than half of Seattle’s population resides in “urban heat islands” where daytime temperatures are over 8 degrees higher than they would naturally be as trees are replaced with pavement and other heat-absorbing surfaces. The trapped heat raises nighttime temperatures 2 to 5 degrees above surrounding areas.
Seattle’s historically marginalized neighborhoods have fewer trees and less green space. Residents are more likely to be exposed to air pollution and heat and to be burdened by preexisting health conditions.
These hotter nights are not only uncomfortable, but people also are at greater risk of heat-related illnesses.
Your core body temperature needs to stay within a relatively narrow range to protect cells and organs, said Kristie Ebi, a professor in the University of Washington Center for Health and the Global Environment. Typically, cooler overnight temperatures can help bring that core temperature down to normal, but if it’s hot overnight you start the next day with a higher core body temperature, which puts you at greater risk.
Research has shown that hot nights contribute to excess mortality because people don’t have the time to get their body temperature down in the normal range, Ebi said. Early season heat waves are also associated with higher mortality because people are not yet acclimatized to higher temps.
There are relatively few groups who are not vulnerable to exposure to high temperatures. Outdoor workers, pregnant people, children and people with underlying conditions are particularly vulnerable.
Wrapping a cool, wet towel around your neck, immersing your feet in water and drinking cool water can help keep people cool.
More information on how to stay healthy in the heat is available at the Department of Health’s website and heat.gov.
Material from The Seattle Times archives was used in this story.
