A new study suggests the deadly 2021 heat dome that hit B.C. and the U.S. Pacific Northwest was amplified by climate change and could become a once-in-10-year event if global temperatures aren’t kept below 2 C above the pre-industrial average.
The study, which was published this month in the journal Nature Climate Change cites the interaction between factors, including climate change, atmospheric weather patterns and dry soils in the region as factors that allowed the heat wave to reach extreme levels.
The heat dome, which hit western Canada and the U.S. at the end of June and beginning of July is believed to be responsible for more than 600 deaths, set national temperature records and preceded the fire that razed the community of Lytton to its foundations.
Study co-author and Columbia University PhD candidate Sam Bartusek said he and his team built a statistical model using temperature records dating back seven decades to come to their conclusions.
“Just a few decades ago … it’s estimated that this event would have been virtually impossible, so at a way lower probability of happening, but then because of the warming, since then it’s its likelihood as it has increased drastically,”
“And so we presently estimate that it’s about a one in 200-year event … One of the implications is that if temperatures rise to two degrees above pre-industrial conditions, the estimated likelihood of this of an event of this magnitude is about one in ten every year.”
Bartusek’s team looked at how a “wavy” pattern in the jet stream — disrupted from its usual east-west flow to a north-south flow — and another “wavy” atmospheric pattern coming off the Pacific Ocean reinforced one another in order to allow an “unprecedented atmospheric ridge” to stall over the west coast for days, setting up the heat wave.
They then looked at dry soil and surface temperature interacting with that ridge, which they found could increase the likelihood of “month-long high-temperature anomalies.”
“It turns out that it’s probable that in some areas of the Pacific Northwest, the dry soils that were in place throughout the summer and earlier … potentially allowed the heat to become more extreme, and so they amplified the heat that was already a really high level because of the dynamics of the atmosphere,” he explained.
“What really allowed this heat wave to become so extreme was the interaction between a combination of factors that led up to the heat wave really becoming more than sort of a sum of its parts alone.”
Ongoing climate-change-driven trends both in drying soil and atmospheric patterns have accelerated such extreme interactions, they found.
Rachel White, an assistant professor at UBC’s Department of Earth, Ocean and Atmospheric Sciences, said the study raised important questions about potentially hard-to-predict interactions between land and the atmosphere amid a changing climate.
“For me, it’s sort of one of those scary possibilities of this could be a way that climate change is going to impact us that we don’t understand a lot about yet,” she said.
But she said the study’s eye-catching projection of once-in-a-decade heat domes should be viewed cautiously, noting there remains significant uncertainty and debate in the scientific community about how to model extreme heat events like 2021’s.
White pointed to a September study in the journal Geophysical Research Letters, which used climate model computer simulations, rather than seven decades of temperature records, and concluded the heat dome was a one-in-more-than-10,000-year event.
“So that discrepancy is what needs to it needs to close before we can really say that we actually have a scientific consensus and we have a full understanding and that just we need more researchers looking into this,” she said.
“I think this is a great contribution, and I don’t think it’s going to be the last word on this particular heat wave and the heat waves more generally.”
White said what is clear is that the warming climate is increasing both the frequency and severity of heat waves.
That’s a concern, given that the latest statement from the U.N. Environment Program suggested current government policies have the world on track for 2.8 C temperature warming by the end of the century.
“That, to me, says this problem is serious and we should be doing something about it, and that something is both reducing greenhouse gas emissions to try to limit the warming — because at the moment, the pathway we’re going, we are going to exceed two degrees warming — but also really trying to understand what’s going on between behind these extreme events to really get a more exact value on that figure,” she said.
“So, yes, there is uncertainty, but saying, oh, we have to wait to do something until we 100 per cent understand everything about this problem. It’s going to be too late.”