Australia’s 2019/20 Black Summer fire weather exceptionally rare over the last 2000 years

Abstract Australia’s record-breaking 2019/20 Black Summer fire weather resulted from a combination of natural and anthropogenic climate factors, but the full range of natural variability in fire weather is unknown. We reconstruct southeast Australian fire weather over the Common Era based on an East Antarctic ice core sea-salt aerosol record. This record reflects the Southern Ocean synoptic-scale weather patterns and Antarctic stratospheric polar vortex strength that pre-condition elevated fire danger over southeast Australia. We show that the (a) intensity of the 2019/20 fire weather was unprecedented since 1950 and (b) frequency of above average fire weather seasons from 2010–2020 has only occurred once since 1950 (over 1977–1987), but there are analogues for similar extreme fire danger caused by natural variability in the 2000-year reconstruction. This highlights the need for fire risk mitigation that considers the full range of plausible natural variability in Australia’s fire weather as well as anthropogenic forcing.