Abstract
We synthesized more than 70 articles, most peer-reviewed, that addressed the heat wave that occurred across the Pacific Northwest of the United States and Canada in late June 2021, breaking hundreds of daily and all-time daily maximum temperature records across the region. A persistent, extraordinarily strong ridge of high pressure was a primary driver of the heat wave. Contributing mechanisms were moisture originating in the tropical western Pacific Ocean, high solar radiation, low pressure offshore, large-scale subsidence over land, and unusually dry soils. Climate change contributed to the heat wave’s magnitude by increasing mean temperature, although it is unclear whether the trend in extreme temperature is steeper than the trend in mean temperature. Mortality, heat-induced illness, and the number of visits to emergency departments during the 2021 heat wave were anomalously high. Individual and compounded social determinants of adverse outcomes included older age, living alone, lower income, and lack of functioning air conditioning. Browning or scorch of tree leaves and needles following the heat wave was extensive, although the extent of long-term tree mortality is not yet clear. Following the heat wave, Oregon, Washington, and British Columbia established new regulations and programs to reduce the risk of heat-related illness in the workplace. It is not yet feasible to rigorously evaluate the effectiveness of these new initiatives.
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