SANTA MONICA, Calif. — The deadly heat wave that brought triple-digit temperatures to the Pacific Northwest and western Canada and killed hundreds of people was virtually impossible without human-caused climate change, according to a new analysis by an international team of 27 scientists.
The temperature records were so extreme — 116 degrees Fahrenheit in Portland, Oregon, and 121 degrees Fahrenheit in Canada's British Columbia — that researchers said it was difficult to quantify just how rare the heat wave was. The team, working under the umbrella of Oxford University-based World Weather Attribution, estimated it was a once-in-a-millennium event.
The scientists, who are based in the U.S., Canada, the U.K., the Netherlands, France, Germany and Switzerland, estimated that human-caused climate change increased the likelihood of such a heat wave by at least 150 times.
"An event such as the Pacific Northwest 2021 heatwave is still rare or extremely rare in today's climate, yet would be virtually impossible without human-caused climate change," the team of scientists wrote. "As warming continues, it will become a lot less rare."
The researchers urged adaptation measures that account for the rising risk of heat waves, including action plans that incorporate early warning systems for high temperatures, as well as more ambitious targets to drastically reduce planet-warming greenhouse gas emissions.
Researchers also found that in a world with 2 degrees Celsius of warming, which could happen this century unless there are significant cuts to greenhouse gas emissions, such a heat event would occur about every five to 10 years.
The Earth has already heated up more than 1 degree Celsius compared with preindustrial levels, according to the World Meteorological Organization.
The analysis by World Weather Attribution, which conducts quick analyses to determine if there is a link between climate change and specific extreme weather events, has not yet been peer-reviewed. However, it uses processes that have been peer-reviewed in the past 10 years.
Scientists used computer simulations that compared a hypothetical world without greenhouse gas emissions to the existing world in order to assess the impact of climate change on weather events. The research will later be published in peer-reviewed journals.
The study, published on Wednesday, is in line with previous research on the impact climate change has on the frequency and severity of heat waves and drought.
The recent historic heat wave, which started at the end of June, fueled wildfires, threatened water shortages and was linked to hundreds of deaths in Oregon, Washington and British Columbia. The official death count is expected to rise.
More than one-third of global heat-related deaths during warm seasons can be attributed to climate change, experts have said. Heat also kills more people than any other weather-related disaster in the U.S.
"Our results provide a strong warning: our rapidly warming climate is bringing us into uncharted territory that has significant consequences for health, well-being and livelihoods," the scientists wrote.
North America just recorded its hottest June on record, according to scientists with the Copernicus Climate Change Service, with 2021 virtually certain to be among the 10 hottest years on record.
