The Northwest will experience extreme heat more frequently by the middle half of the century if efforts to combat climate change aren't taken, according to a new study.
By mid-century, defined as 2036-2065 by the Union of Concerned Scientists, the Northwest will see the average number of days of 105 degree heat increase from zero to two if no action is taken. Late in the century (2070-2099), that number will increase to an average of five days, according to the study.
Temperatures considered "off the charts" will be seen up to an average of two days per year by late in the century.
Though the Northwest is only expected to see extreme temperatures a few days out of the year if little to no action to combat climate change is taken, the number of 90-degree days will rapidly increase, according to the study. Using a historic, 30-year baseline (1971-2000) the Northwest saw an average of six 90-degree days, according to the study. That could rise to 37 days by late in the century for portions of the Northwest, though the Seattle area will be on the lower end of that total.
According to historical data from the National Weather Service, Seattle saw an average of three days of 90-degree heat or more per year between 1971-2000. Between 2015-2018, that increased to an average of 10.
The hottest day for the Seattle area is 103 degrees, recorded on July 29, 2009, according to data from the National Weather Service.
Researchers with the science-based advocacy group predicted temperatures across the U.S. based on three models: one where the U.S. takes no action to combat climate change, one with slow action and one with rapid action.
In the "no action" model, UCS predicts global average temperatures will rise by 8 degrees by mid-century, defined as 2036-2065. With "rapid action," that number is reduced to 3.6 degrees.
The study looked at the likelihood of increasing heat index values, which quantify "feels like" heat levels when humidity is taken into account.
Without action, the average number of days per year with a heat index above 100 degrees will more than double, while the number of days per year above 105 degrees will quadruple.
In this scenario, more than one third of the U.S. will experience one day per year, on average, that reaches a temperature "off the charts" of the current National Weather Service heat index range, the study found.
Currently, the National Weather Service does not have standard guidance for the health risks that come with these unprecedented "off the charts" temperatures. Any level of exposure is assumed to be "extremely dangerous for all people and likely to result in heat-related illness or even death," according to the study.
The hardest hit areas in the U.S. would be the Southeast, Southern Great Plains and the Southwest, the study found.