An impressive heat wave hit the American West in the summer of 2021. From British Columbia, the westernmost province of Canada, to California, passing through Oregon, Washington and even moving to more inland states such as Colorado, Idaho and Utah, where the climate is generally more temperate.
The maximum temperature reached record figures. In Salt Lake City they reached 40 degrees and in Grand Junction (Colorado) they even reached 41. But nothing was comparable to the always dangerous Death Valley, where thermometers touched 56.6 degrees, the highest maximum recorded in the entire world. planet.
It wasn't just the heat. Drought and thunderstorms helped create a deadly cocktail that devastated 330,000 hectares from 2,300 recorded fires that killed at least 1,400 people. The figure, however, is small compared to what happened a year earlier, when the flames devastated 1.1 million hectares.
Scientists attributed the devastating event in large part to climate change caused by human activities and even declared it unprecedented. The problem is that the oldest weather data goes back barely a century.
So researchers at the University of Idaho looked for the formula to compare data and opted for a technique that is always effective: the study of tree rings in the region. His article, published in the journal Climate and Atmospheric Science, confirms that what happened in the American West was the worst event in the last 1,000 years.
Their analyzes revealed that the annual record for average summer temperatures dates back to the year 950 and that, throughout history, dozens of abnormally hot moments appeared, many clustered in warm periods of several years. Global warming, however, has made the last 40 years the hottest, surpassing all records in 2021, just as previously believed.
“It's not like the Pacific Northwest has never experienced heat waves before. But with climate change, their magnitude is much greater and they have a higher impact on the community," says researcher Karen Heeter, lead author of the study.
Reconstruction of tree rings and modern readings show that between 1979 and 2021 there was a sustained period of hot summers unmatched in the last millennium. Most of the warmer years have occurred since 2000.
The second hottest period, indicated by tree rings, was between 1028 and 1096, at the height of the so-called Medieval Climate Anomaly, when a natural warming trend is thought to have taken hold across much of the planet. Another period of notable heat extended from 1319 to 1307. But even these periods were considerably colder than the averages recorded in recent decades.
The shocking heat wave of 2021 lasted for several weeks, from late June to mid-July. And its average annual temperature was a record: 18.9 degrees Celsius. By contrast, the hottest summer in prehistoric times was at 1080, with 16.9 degrees.
There is a detail of the study that stands out even above the temperatures. Human activity has caused the almost complete destruction of the ancient trees in the flat areas, forcing the experts to use samples collected in mountainous elevations… more than 3,000 meters high.
Clearly, at this altitude, where there is often snow even in June, temperatures are drastically lower than in populated low-lying areas. “Everything has to be thought of in a larger context,” Heeter says, which would reasonably lead to adding a few tens of degrees for cities like Seattle and Portland.
The specialists were afraid to go looking for samples in forests that were on fire and where, in many cases, evacuation orders prevented them from entering. To obtain the data, they drew straw-sized samples from about 600 ancient conifers in northern Idaho and the Cascade Ranges of Oregon and Washington.
Its earliest sample came from a mountain hemlock near Oregon's Crater Lake, which took root in the 13th century. They supplemented them with samples taken in the 1990s by other Lamont-Doherty researchers, primarily in British Columbia. The oldest of these was from a Douglas fir on Vancouver Island, dating to the year 950. The area has since been cleared by loggers.
To measure the temperature, Heeter and his colleagues used a relatively new technique called blue intensity. This involves shining visible light into a high-resolution scan of each ring and measuring how much of the blue spectrum is reflected. Trees generally build thicker cell walls at higher temperatures, which increases ring density.
Another recent study suggested that by 2050, heat waves like the one that hit in 2021 could occur every 10 years. With a climate that is usually quite moderate, the American West is ill-prepared to deal with these types of events. “It may not be realistic to put air conditioning everywhere, but communities could create shelters where people can go when these things happen again,” he concludes.
