An extreme, prolonged heat wave blanketing California and much of the western U.S. is harming human health and forcing rolling electricity blackouts for the first time in nearly two decades. Officials warned the heat wave could rival that of 2006, which state researchers estimated killed between 350-450 people. The impact of human activities on heat waves is clear, driving up rare heatwave temperatures at least 3°F. Multiple aspects of this heatwave, including the number of consecutive days with temperatures over 100°F, high overnight lows, and high humidity, align with the impacts of climate change. Temperatures hit 129.9°F in Death Valley Sunday, which, if verified, will be the hottest temperature officially verified since July 1913, according to the National Weather Service. The California fire season is just beginning, and the heatwave could undermine firefighting efforts and dry out vegetation across the West. Extreme heat kills an average of more than 600 people in the U.S. every year according to official estimates, more than any other natural disaster. New research, however, puts that number as high as 5,600 deaths annually. The human health harms caused by extreme heat heighten societal inequities — extreme heat danger is often worst in historically redlined neighborhoods. While public cooling centers can mitigate the dangers faced by vulnerable populations, the COVID-19 pandemic has reduced the accessibility of cooling centers while also increasing the danger to those who need them. On Saturday a confluence of factors, including the excessive temperatures, combined to create a rare fire tornado near the California-Nevada border. The extreme heat blanketing much of the West is expected to persist until at least Thursday. (Heat wave and climate: NPR, New York Times $, CNBC, San Francisco Chronicle, Xinhua, Bloomberg $, Washington Post $; 2006 Heat wave: LA Times $, Newsweek, Bloomberg $;Blackouts: LA Times $, Vox, CBS, Modesto Bee, Bloomberg $, Weather Channel, Mercury News, Greentech Media, Wall Street Journal $, Gizmodo, HuffPost, Bloomberg $; Death Valley record: Washington Post $, BBC, The Guardian; Fire tornado: Washington Post $, Weather Channel, NBC, Sacramento Bee, Gizmodo, HuffPost; Heat and Fires across West: NPR, CBS, AP; Climate Signals background: August 2020 California heat wave, 2020 Western wildfire season)