Heat extremes threaten cattle and outdoor workers across northern Australia’s extensive grazing systems

Australia is projected to warm throughout the 21st century, raising the risk of dangerous heat for livestock and the people who work with them, yet these changes have not been quantified for the extensive grazing systems of northern Australia. Here we employ a seven-model ensemble of regionally downscaled climate projections to quantify future changes in cattle heat load and the maximum safe metabolic rate for outdoor work under lower- and higher-emission pathways (Shared Socioeconomic Pathway (SSP) 1-2.6 and SSP3-7.0) at mid- and late-century. Days exceeding the heat load accumulation threshold increase throughout the region. Heat-tolerant Bos indicus cattle at the Barkly are projected to experience 105.6 days per year above their threshold (HLI MAX > 96) by the late century under SSP3-7.0, compared with 15.2 days per year historically, while Bos taurus exposure exceeds 300 days per year in parts of the semi-arid interior. Days unsafe for outdoor work increase by 31–60% over the same interval. Effective shade provision offsets approximately the entire projected late-century increase in cattle heat load at five of the six site-genotype combinations. These projections indicate that integrated adaptation across livestock management and labour scheduling will likely be required to sustain northern Australia’s red-meat sector.