‘Warmer no matter what’: Boise weathered hottest summer on record, for now
In what may not come as a surprise to residents who’ve spent the season in Idaho’s capital city, the summer of 2021 was the hottest on record in Boise, according to the National Weather Service.
Unlike the astronomical summer season, which ends on Sept. 22, the meteorological summer begins on June 1 and ends Aug. 31. The average temperature from June through August was 78 degrees. That beats the previous record of 76.6, which was set in 2015, by 1.4 degrees.
“It’s a huge difference,” Mojtaba Sadegh, an assistant professor of civil engineering at Boise State University who studies climate extremes, told the Idaho Statesman.
After an off-the-charts heat wave struck the Pacific Northwest in late June, hot weather settled in the Treasure Valley for much of the summer. On July 7, Boise broke a daily temperature record when the thermometer hit 107 degrees, according to the weather service. It was 100 degrees or hotter for 12 days in July, and the lowest high temperature was 91 degrees, which came on July 22, according to weather service data.
Scientists have attributed the summer’s extreme heat in the Pacific Northwest — which extended inland to Boise — to climate change, with one study finding the excessive temperatures would have been “almost impossible” without global warming, which scientists say is primarily caused by human emissions of greenhouse gases.
“Because of all the emissions that we’ve had, some of the solar radiative power that comes in does not exit the atmosphere,” Sadegh said.
In general, variability in the climate causes some years to be colder and wetter, and others to be hotter and drier, Sadegh added. This year, a season that would have likely already been hot and dry was “compounded” by the effects of climate change. And that extra heat is only likely to worsen.
“As we go into the future, this exogenous extra heat that we get from climate change is going to be more and more,” Sadegh said.
Of the top 10 hottest summers on record since 1877, nine of them have come in the last 20 years, according to the National Weather Service.
In August, a United Nations panel of scientists released a report which said that human influence on the changing atmosphere is unequivocal, and that the rapid impact is noticeable all over the world. While the report said the effects of climate change over the next 30 years are essentially unavoidable, even more severe, longer-term impacts could be avoided if nations drastically cut their emissions.
“Do we want to see those mega heatwaves every couple of years or every year, or do we want to cut our emissions and maybe see that every decade?” Sadegh said. “It’s going to get warmer no matter what we do now, but how much warmer and what rate it becomes warmer is what we can determine with our emissions now.”
The blistering heat extended outside of the Treasure Valley, too, with McCall in Idaho and Burns and Ontario in Oregon also marking their hottest recorded summer temperatures, according to a Weather Service tweet. Jerome tied its hottest record, at 74.2 degrees.
This summer, Boise also had nine consecutive days with temperatures exceeding 100 degrees, tying the previous record first set in 2003 and repeated in 2006 and 2015. It was over 100 degrees on 18 total days, which is just two days shy of the record of 20, set in 2003, according to the agency.
Daily low temperatures also hovered above normal this summer. The lows were 70 degrees or higher on 11 consecutive days in the city, beating a previous record of five set in 2015.
The weather affected workers in the region, some of whom changed their outdoor working hours in an effort to cope with the dangerous temperatures. So far this year, there have been eight heat-related deaths reported in Idaho, according to the Department of Health and Welfare.
The hot weather and drought this year have also caused issues for Idaho farmers, some of whom are having trouble with crop yields. More than half the state is experiencing exceptional or extreme drought, according to U.S. Drought Monitor.
A meteorologist with the weather service, Bill Wojcik, told the Statesman that one factor that affected the season’s heat was a lack of soil moisture, which usually decreases the amount of sensible heat.
“When you have moisture in the soil (that evaporates), that can keep the temperature not as hot,” Wojcik said. “Since much of the West was dry, that can have an effect on these extreme temperatures.”
Since 1850, Idaho has warmed slightly less than California. While parts of the Golden State have warmed 1.5 degrees Celsius, according to Carbon Brief, the Boise region has warmed 1.3 degrees Celsius. The state of California saw massive wildfires this year, including its second-largest fire in history, the more than 800,000-acre Dixie Fire. While the two states have different climates, Sadegh said there are enough similarities to suggest that Idaho may experience similar effects as temperatures continue to rise.
“Those fires might happen in Idaho soon enough,” he said.
