Australians are bracing for a hot spring and summer. The Bureau of Meteorology has finally declared El Niño is underway, making warmer and drier conditions more likely for large parts of the country. And we’ve just watched the Northern Hemisphere swelter through their summer, making July 2023 Earth’s hottest month on record. We studied the effects of extreme heat on urban trees in Western Sydney during Australia’s record-breaking summer of 2019–20.