![]() ![]() The rings showed that Pacific Northwest conifers grew throughout temperature fluctuations over the past 1,000 years, though there has been significantly more warming in the past few decades. The reflectance of a ring’s surface is related to the ring’s density and is used as a proxy for the average ambient summer temperature-when a tree does most of its growing-during that year. Heeter describes blue intensity as a “very, very up-close remote sensing,” in which the blue wavelet of the visible light spectrum is reflected off the tree ring and measured. ![]() Using a method called blue intensity, the team measured ring densities to infer past temperatures. “We’re much warmer now than we were back then.” Once you’re confident in that, you can keep pushing it back in time.” “Wherever they match up, you can validate the dates. Tree rings are like barcodes, and comparing the codes is like pattern matching, Heeter explained. To make sure they had a continuous record, the researchers overlapped the cores from dead and live trees. To extend the record back, the team also sampled dead wood. “In the Pacific Northwest, there are long-lived species of Douglas fir and mountain hemlock,” said Heeter, adding that land preservation efforts helped protect these old trees. Heeter and her colleagues collected cores from 29 conifer trees in the United States and Canada. Typically, denser rings mean warmer temperatures. A tree records summer temperature in its ring density. Tree rings capture years of climate signatures: temperature, soil moisture, and wind stressors. The data hint at a future full of heat waves. They found that 2021 was a scorcher-hotter than any other year in the past millennium. In a new study in npj Climate and Atmospheric Science, Heeter and her colleagues used tree ring records from the Pacific Northwest to reconstruct summer temperatures for the past 1,000 years.
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