In summer of 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. What become known as the “heat dome” is estimated to have killed hundreds of people in Oregon, Washington and British Columbia. The heat also turned many green leaves and needles on the region’s trees to orange, red and brown. Researchers say the foliage didn’t simply dry out, but instead underwent “widespread scorching.” A growing number of scientists are investigating what they say is a new and underestimated threat to the world’s plants: climate change-driven extreme heat.