1,000 Years of Tree Rings Show Just How Hardcore the 2021 Pacific Northwest Heat Wave Was
In June and July 2021, an extreme heat wave swept across the historically temperate Pacific Northwest, killing hundreds of people and cooking over a billion sea creatures. Now, scientists have used information etched into tree rings to demonstrate that, yes, the heat wave was unlike anything the region had seen in a millennium.
A study published in the journal Climate and Atmospheric Science looked at tree rings in the Pacific Northwest going back over 1,000 years—as far back as the year 950. The rings showed how the last 40 years have been some of the hottest on record.
Read more
These Winning Close-Up Photos Show Life That's Often Overlooked
Remembering Enterprise: The Test Shuttle That Never Flew to Space
The team looked at tree rings across northern Idaho and the Cascade Range of Oregon and Washington, as well as rings from samples taken in the 1990s by other researchers in British Columbia. “Across many regions of the Northern Hemisphere, the annual variability of tree growth, particularly metrics for wood density, strongly reflects the variation of summer season temperature,” the paper notes.
The researchers cored into trees with a T-shaped hand drill to pull out a pencil-sized piece of the tree. In the lab, the team shaved and sanded the wood to better examine the rings (trees add new rings annually as they grow; size, color, and other information in the rings can reveal ancient climate events, insect attacks, and more). For this study, they used a method called blue intensity, in which they look at the amount of blue light reflected back from each portion of the ring.
Study author and scientist at Columbia University’s Lamont-Doherty Earth Observatory Karen Heeter described how, during unusually hot years, tree rings are denser.
“I’m looking at how dense the later growing portion of the ring is,” Heeter told Earther during a phone call. “When it’s really warm [that year], typically I’m seeing these really dark dense fans of the late wood portion of the ring.” Those denser sections reflect back less blue light, which can mean the tree experienced higher temperatures that year. “You see this very dark band,” she said, referring to 2021 rings from north Idaho.
The researchers noticed historical clusters of warmer years, such as the Medieval Climate Anomaly, which was a warm, dry period that lasted from about 950 to 1250 CE. “Even during the warmest interval of the [Medieval Climate Anomaly], mean of summer temperatures during this time are approximately 0.59 °C cooler than those documented since 1979,” the study says.
They also noted that the largest rates of temperature change have occurred in the last decades of the 1900s. “While the 2021 value substantially increases the period’s average anomaly, even without its inclusion, the period from 1979—2020 CE is still the warmest on record,” the team wrote.
The tree rings help fill in blanks about historic temperatures in the Pacific Northwest region, which is important because official temperature records for the U.S. only go back to the 1800s, according to the National Weather Service.
Heeter said she hopes to see more research in the near future into how trees interact with temperature. “The tree ring record can tell us a whole lot about the imprint of extreme heat and wildfire activity—whether it’s burn severity or burned area.”
More from Gizmodo
Sign up for Gizmodo's Newsletter. For the latest news, Facebook, Twitter and Instagram.
