by As a huge heat dome linged over the Pacific Northwest three years ago, swaths of North America simmered – and then burned. Wildfires have killed more than 18.5 million acres across the continent, with most of the land burned in Canada and California.
A new study has revealed how much human-caused climate change has accelerated the extraordinary event, with researchers theorizing that the heat dome was 34% larger and lasted nearly 60% longer than it would have otherwise. it in the absence of global warming. The heat dome, in turn, was responsible for up to a third of the area burned in North America that year, according to the study, published in Communications Earth & Environment.
“What happens is you get a stagnant weather pattern — it’s very hot and very dry,” said study author Piyush Jain, a research scientist with Natural Resources Canada. “And it dries up all the vegetation and makes anything that is on the ground combustible.”
The study adds to a body of literature documenting how the fingerprints of climate change can be detected in events such as heat waves, droughts and wildfires.
Jain was living in Edmonton in late June 2021 when the mercury in North America’s northernmost city of one million people exceeded 100 degrees. “I was shaking,” he said. “I’ve never experienced those temperatures anywhere I’ve lived.”
Further south, the hottest recorded temperature in Canada, 119 degrees, was recorded in the town of Lytton, British Columbia, on June 29, and was largely destroyed by a wildfire the next day.
The heat dome lasted for a whopping 27 days, from June 18 to July 14, and hundreds of people were killed by sky-high temperatures across the western United States and Canada, leaving a massive die-off in marine life, a devastating result. crop and timber and infrastructure damage. , buckling highways in Washington and melting train power lines in Portland. Over a five-day period in June, locations in seven US states, including California, broke all-time maximum temperature records, according to the National Oceanic and Atmospheric Administration.
The heat wave also increased the fire danger, breaking fire weather records across a wide area and helping to stop blazes in British Columbia, California, Arizona, Colorado, Utah and Montana. More than 7.9 million acres burned in North America in July alone — at the time, the largest area in a single month since record-keeping began, according to the study. Smoke traveled across the continent, prompting air quality alerts across the East Coast.
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Jain previously worked with other researchers to develop a method to estimate such extreme events by looking at anomalies in geopotential height, which indicate whether there are high or low pressure systems in the upper atmosphere. Long-lasting high pressure systems tend to correspond with heat waves and increased fire risk, he said. And climate change has contributed to the trend of rising altitudes, which could increase these events.
In this study, Jain and his colleagues analyzed what the heat dome would look like without this trend. They estimated that it would be 34% smaller, 59% shorter and 6% lower.
The researchers also found strong links between the extreme heat and wildfire activity in 2021. That year, 21% of the burned land in North America was scorched by fires that started during and within the heat dome, and the figure that rising to 34% when adopted. included fires that started within 10 days, the researchers found.
The size of the heat dome made him particularly concerned because of what the study authors called widely synchronous, with many different areas burning at the same time. That has been a challenge for fire agencies because they tend to seek help from other places when they don’t have enough resources locally.
“If other areas are also facing the same resource pressure, you may hit a bottleneck at some point,” Jain said.
When there are not enough resources to attack fires when they first start, blazes that might otherwise have been snuffed out when they were small grow large and difficult to contain, resulting in the need for more even more resources, said John Abatzoglou, professor with. climatology at UC Merced who also worked on the study. If this type of synchronous activity continues in the coming years, it could force fire managers to reevaluate the reliability of resource-sharing arrangements, he said.
The study did not specifically look at the impact of the heat dome, which extended into Northern California, on the state’s fire season. That summer, the 963,000-acre Dixie fire, which started on July 13, was the first to burn from one side of the Sierra Nevada to the other, followed in short order by the 221,000-acre Caldor fire.
In general, it’s difficult to attribute a fire entirely to any single factor, because flames are often fueled by a complex interplay of conditions — anything from overstocked forests to wind, Abatzoglou said. Still, in 2021, California had its hottest June through July in the observation period, and researchers have established a strong relationship between hot, dry summers and area burned in the state’s forests, he said.
“Obviously it’s hard to say how much the heat dome itself was responsible for those fires,” Abatzoglou said. “But based on the hellaciously hot temperatures in that month, the significant heat wave events, we can say that those conditions certainly helped to enable the availability of fuels to be extremely great and made less resistance against fire, when a fire broke out.”
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The findings add to the understanding of how climate change can affect extreme weather events — and the role these events may play in fire activity.
“This is the latest in a growing body of evidence about the causes of wildfires around the world but particularly in western North America,” said Noah Diffenbaugh, a climate scientist at Stanford University who was not involved. with the study. “I think this is a breakthrough, in particular, in terms of linking excellent fire weather conditions with specific atmospheric conditions for a specific event.”
It is important to address the impact of climate change on extreme weather events such as the heat dome, which are increasing in frequency and intensity, Diffenbaugh said. A lot of infrastructure and risk management systems are based on assumptions about how these events will play out, so if that changes, those systems will be stressed, he said.
“Linking, through this careful analysis, the contribution of climate change to the record heat dome fire weather conditions is an excellent example of the kind of research we need to quantify the risk of climate change exactly,” Diffenbaugh said. “The climate change we are already living with, and the climate change we can expect in the future, even if the world’s ambitious global warming targets are met.”
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Studies that attempt to quantify the role of climate change in individual events can also help calculate the health costs and financial toll of planetary warming from carbon emissions, which is cited by a growing number of lawsuits seeking damages.
Learning about the conditions under which these events occur can help people understand how a warming climate can lead to more extremes in the future, Jain said.
And all signs point to that future being fast approaching. Since the study was written, Canada’s 2021 wildfire season was worse than the 2023 season, when more than 45 million acres burned. Jain now has a preprint that examines the role of heat waves. While no single event was as large as the 2021 heat dome, some regions in Canada saw much larger than average heat events, he said.
“So none of the events alone dominated 2023, but when you looked at the total number of events that occurred, it was a very big year in terms of heat waves,” he said . “And, of course, 2023 was the hottest year on record worldwide.”
This story originally appeared in the Los Angeles Times.
