From June 25 to July 2, 2021, the Pacific Northwest experienced a record-breaking heat wave that sent the normally temperate region into Death Valley-like extremes that took a heavy toll on trees as well as people. … In a matter of a few days, the 2021 heat dome turned many of the green leaves and needles on the region’s trees to orange, red and brown. …Still is part of a growing number of scientists investigating what they say is a new, woefully underestimated threat to the world’s plants: climate change-driven extreme heat. …Driven by above-normal temperatures, hot droughts can be far more damaging to trees than droughts that result simply from a lack of moisture. Hot droughts not only dry out soil; they also dry out the air. This stresses trees, and can cause water-carrying tissues inside them to collapse — a process called “hydraulic failure.”