Research & Developments is a blog for brief updates that provide context for the flurry of news that impacts science and scientists today.
A historic heatwave is sweeping across western North America.
Wednesday, 18 March was the hottest March day in recorded history in dozens of cities across the West, including Phoenix, Palm Springs, and Las Vegas. Temperatures are expected to peak today, with a forecast of 42.2°C (108°F) in Palm Springs and 41.1°C (106°F) in Phoenix. The Bay Area saw its first-ever March heat advisory on Monday. Cities as far east as Texas and as far north as Montana could also see March temperature records, according to The Weather Channel meteorologist Jonathan Erdman.
A new rapid analysis by World Weather Attribution suggests that, based on a combination of observations and modeling, climate change has made the extreme temperatures forecasted for 18-22 March about 800 times more likely and 2.6°C hotter.
“These temperatures are completely off the scale for March and our data shows that they would be virtually impossible in a world without human-caused climate change,” Ben Clarke, a research associate in extreme weather and climate change at Imperial College London, said in a press release.
The study also highlights how much the climate has changed in more recent years: The forecasted temperatures have become about 4 times more likely in the past 10 years alone.
“It’s sobering that a child born in 2016 has already seen a significant shift in the extremes that are possible in this part of the United States before they’ve even finished grade school,” Clarke said.
March Madness
To conduct attribution studies, researchers feed two sets of data into climate models: one set based on observations or forecasts from reality, and one theoretical set of data in which the climate is 1.3°C cooler, as it was in the pre-industrial era. In this way, they can compare extreme weather events to what they might have looked like without the effects of anthropogenic climate change.
At the time the report was done (and that this article was published), the extreme heatwave was still ongoing. The researchers selected 18-22 March as the study period because a forecast of intense heat during this period has remained stable.
Rachel White, an atmospheric scientist at the University of British Columbia who was not involved in the study, said that for a rapid attribution study like this one, it’s not possible to run extensive analyses on observations that are only a day old.
“So to do this study as quickly as possible, they are using the one dataset that does include data for very recent days, but the way that it does that is by including forecast data,” she explained in an email to Eos. “This is a reasonable thing to do if you need to do a study this quickly (and this is a rapid attribution!), but does come with the caveat that the exact numbers they are reporting in terms of return period etc. will likely change as we are able to more carefully analyse observational data.”
Heatwaves of this scale, the report forecasts, are expected to occur just once every 500 years. Such rare occurrences make it challenging for researchers to estimate how often these events might happen if the climate warms further. But the current attribution study estimates that, if the climate warms another 1.3°C, heat events so extreme that they are forecasted to happen just once every 100 years will become 6.4 times more likely and 1.8°C hotter.
“These findings leave no room for doubt. Climate change is pushing weather into extremes that would have been unthinkable in a pre-industrial world,” said Friederike Otto, a climate scientist at Imperial College London, in a press release.
“This study gives us a first estimate of how rare this event is, and how much more likely it has been made due to human-caused climate change,” White said. “And in the months and years to come, other research studies will be able to understand this event more and provide more details and undated estimates.”
—Emily Gardner (@emfurd.bsky.social), Associate Editor
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