 In 2021, several major cities experienced extreme heat events that were much hotter than usual, with temperatures up to 20 degrees Celsius above the average. This was caused by a combination of factors including climate change, the El Nino southern oscillation, and local weather patterns such as ocean breezes and urban heat islands. These findings highlight the importance of understanding how different scales interact to create extreme heat events and emphasize the need for holistic approaches to heat mitigation strategies. This article was authored by Kaiyu Chen, Jacob Boomsma, and Heather A. Holmes.