A stunning heat wave swept across western North America in summer of 2021, from British Columbia to Washington, Oregon, and beyond into other inland areas where the climate is generally mild.
Many places set temperature records by tens of degrees, wildfires erupted, and at least 1,400 people died.
Scientists declared the event unprecedented and blamed it largely on human-caused climate change. But, in the absence of reliable weather data dating back more than a century or so, was there really no precedent?
1,000-Plus Years Of Tree Rings Confirm Historic Heatwave
(Photo : AFP via Getty Images)
According to a new study of tree rings from the region, the event was almost certainly the worst in at least the previous millennium, as per Phys.org.
The study, which was published in the journal npj Climate and Atmospheric Science, established a year-by-year record of summer average temperatures dating back to 950. Scores of unusually hot summers emerged, many of which were clustered into multiyear warm periods.
However, the new study shows that the last 40 years have been the hottest on record, owing to human-caused warming and that 2021 was the hottest summer on record.
It's not like the Pacific Northwest has never seen high-temperature waves. However, with climate change, their magnitude is much greater, and their impact on the community is much greater, according to lead author Karen Heeter, a postdoctoral researcher at Columbia University's Lamont-Doherty Earth Observatory.
There is a lot of power in being able to look at the past and compare it to climate models and come to similar conclusions.
The tree-ring reconstruction and modern temperature readings show that the period 1979-2021 saw an unrivaled period of hot summers in the last 1,000 years. Since 2000, the majority of the hottest years have occurred.
The tree rings indicate that the second-warmest period was 1028-1096, during the height of the so-called Medieval Climate Anomaly, when a natural warming trend is thought to have taken hold across large parts of the planet.
Another notable hot period during the Medieval Climate Anomaly occurred between 1319 and 1307. Even so, temperatures were significantly lower than in recent decades.
The 2021 heat wave spanned several weeks from late June to mid-July.
While the researchers did not attempt to isolate such brief periods in the rings, they believe average seasonal temperatures are a good proxy for such events.
Summer 2021 set the annual temperature record at 18.9 degrees Celsius, or about 66 degrees Fahrenheit.
By contrast, the hottest summer in prehistoric times was in 1080, at 16.9 degrees C, or 62.4 F.
This may not appear to be very impressive until you consider that, in part due to the near-complete human destruction of ancient trees in the lowlands, the researchers relied primarily on samples collected at mountain elevations above 10,000 feet.
Temperatures are significantly lower than in the populous lowlands, and snow cover is common in June.
The 2021 seasonal temperature spike was nearly 3 degrees F higher than any annual spike shown by tree rings during the Medieval period.
To collect data, the researchers bore straw-size samples of rings from about 600 old conifers in northern Idaho, Oregon, and Washington's Cascade ranges.
Their oldest sample came from mountain hemlock near Oregon's Crater Lake, which sprouted in the 1300s.
They supplemented these with samples collected by other Lamont-Doherty researchers in the 1990s, mostly in British Columbia.
The oldest of these dates from 950 and came from a Douglas fir on Vancouver Island. Loggers have since clear-cut the area.
Humans affect climate
There is overwhelming evidence that human activities, particularly the use of fossil fuels, are increasing levels of carbon dioxide and other greenhouse gases in the atmosphere, amplifying the natural greenhouse effect and raising the temperature of the Earth's atmosphere, oceans, and land surface.
Laboratory experiments dating back to 1856, when Eunice Foote first measured the effect, show that greenhouse gases "trap" infrared heat, as per CLEAN.
The well-documented trend of rising CO2 levels in the atmosphere is caused by the use of fossil fuels and massive changes in land cover.
Carbon isotopes provide the "smoking gun" that clearly shows that human activities are to blame for recent increases in carbon dioxide in the atmosphere (carbon atoms of different atomic weight).
These isotopes enable scientists to "fingerprint" the source of the carbon dioxide molecules, revealing that the increased CO2 in the atmosphere is caused by the combustion of fossil fuels.
Related article: Record-Breaking 2,000-Mile Heatwave to Stretch from Texas to Maine This Week
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