2021 Western North America heat wave

The 2021 Western North America heat wave was an extreme heat wave that affected much of Western North America from late June through mid-July 2021. The heat wave affected Northern California, Idaho, Western Nevada, Oregon, and Washington in the United States, as well as British Columbia, and in its latter phase, Alberta, Manitoba, the Northwest Territories, Saskatchewan, and Yukon, all in Canada. It also affected inland regions of Central and Southern California, Northwestern and Southern Nevada and parts of Montana, though the temperature anomalies were not as extreme as in the regions farther north.

The heat wave appeared due to an exceptionally strong ridge centered over the area, whose strength was linked to the effects of climate change. Extreme event attribution found this was a 1000-year weather event, made 150 times more likely by climate change. A study in Nature Climate Change estimated that its occurrence was projected to increase rapidly with further global warming, possibly becoming a 10-year event in a climate warmed 2°C relative to pre-industrial levels. The heat wave resulted in some of the highest temperatures ever recorded in the region, including the highest temperature ever measured in Canada at 49.6 °C (121.3 °F), as well as the highest temperatures in British Columbia, in the Northwest Territories, in the state of Washington as well as a tied record in Oregon. The record-high temperatures associated with the heat wave stretched from Oregon to northern Manitoba, and daily highs were set as far east as Labrador and as far southwest as Southern California.

The extreme heat sparked numerous, extensive wildfires, some reaching hundreds of square kilometers in area, leading to widespread destruction. The eponymous Lytton wildfire destroyed the village of Lytton, British Columbia, the day after the city set the record high temperature for Canada. Extreme heat also damaged road and rail infrastructure, forced closures of businesses, disrupted cultural events, and melted snowcaps, in some cases resulting in flooding. The heat wave also caused extensive damage to agriculture across the region, resulting in a one-third decrease in yield from the worst affected crops and a loss of at least 651,000 farm animals. The National Oceanic and Atmospheric Administration (NOAA) estimated that the heatwave caused at least $8.9 billion (2021 USD) in damages in the USA.

The death toll exceeded 1,400 people, with at least 808 estimated in western Canada. The Chief Coroner of British Columbia reported that in the week from June 25 to July 1, 619 deaths were recorded due to heat exposure. Confirmed deaths in the United States include at least 116 in Oregon (of which 72 are in Multnomah County, which includes Portland), at least 112 in Washington and one death in Idaho; An analysis by The New York Times suggests that around 600 excess deaths occurred the week the heat wave passed through Washington and Oregon.