A study from the Columbia Climate School placed the blame for an extraordinary and deadly event in 2021 that threatened and killed many people from British Columbia to Oregon and beyond squarely on climate change.
At the time, regional temperatures soared over eighteen degrees Fahrenheit above average from late June to early July 2021- temperatures exceeded a jaw-dropping 54 F above the norm on some days during this period. The record temperature for Canada was shattered at 121.3 F in Lytton, British Columbia. The next day the town incinerated in a wildfire sparked by the high temperatures and a drought that desiccated the region's forests. Over 1400 people died during the heat dome and wildfires in both the US and Canada.
Within a few weeks, climate change was blamed for the devastating event. The new study affirms that conclusion. "And for the first time comprehensively elucidates the multiple mechanisms—some strictly climate-related, others more in the realm of disastrous coincidences—that they say led to the mind-bending temperatures."
From the Columbia Climate School presser:
Average global temperatures have risen less than 2 degrees F in the last century. But small upward increments may shift interactions between atmosphere and land in ways that drive chances of extreme temperature spikes far beyond just the average temperature rise. Boiled down to the simplest terms, the study says much of the 2021 heat wave arose from the multiplying effects of higher overall temperatures, including drying of soils in some areas. Additionally, about a third of the heat wave came from what the researchers call "nonlinear" forces—short-term weather patterns that helped lock in the heat that may also have been amplified by changing climate.
One major driver, they say, was a disruption of the jet stream, which normally carries air west to east across the Northern Hemisphere midlatitudes along a more or less circular path. Preceding the heat wave, though, the jet stream stalled and bent into huge waves, with four north-south peaks and troughs. These concentrated high-pressure systems underneath each peak; high pressure compresses air more and more as it approaches the surface, and this generates heat. One of those systems settled on western North America, then stayed there there day after day, creating what meteorologists call a "heat dome."
Some scientists believe big jet-stream waves are becoming more frequent and extreme due to human-induced warming. The jet stream normally forms a boundary between frigid polar air and warmer southern air, but recent outsize warming in the Arctic is breaking down the temperature difference, destabilizing the system, they say. This idea is still being debated. That said, part of the groundwork for the new study was laid by coauthor Kai Kornhuber, who published a 2019 study identifying such meanders as threats to world food security should they hit multiple major agricultural regions simultaneously. In 2021, concurrent major heat waves tied to the meanders hit not just North America, but within a dome spanning much of Scandinavia, Eastern Europe, western Russia and the Caucasus; and another over northwestern Siberia.
Western North America's was by far the worst. One factor, the authors say, was a series of smaller-scale atmospheric waves generated in the western Pacific Ocean. These moved east, and upon hitting land, latched onto the larger jet-stream wave and amplified it. Meteorologists could see these patterns coming some 10 days out, and thus accurately warned of the heat wave well in advance.
The Pacific Northwest is becoming drier, notes the researchers. A heat event of this magnitude was a once-in-a-two-hundred-year event, they conclude. Due to increasing greenhouse gases in the atmosphere, projections of reoccurrence could be as frequent as once every ten years by 2050, per co-author of the study, Mingfang Ting, at the Lamont-Doherty laboratory.
The study mentions the unusual October 2022 heatwave as proof of their analysis. They point to the heavy and acrid smoke blanketing Seattle from multiple wildfires. Seattle, at the time, had the world's dirtiest air, surpassing Delhi and Beijing.
