Limiting warming to 1.5° Celsius rather than 2.0° Celsius would maintain significant proportions of systems such as Arctic summer sea ice, forests and coral reefs and have clear benefits for human health and economies, say Ove Hoegh-Guldberg and colleagues in this Review. Their Review expands upon a 2018 special report by the Intergovernmental Panel on Climate Change focused on the effects associated with climate warming to 1.5° Celsius (C) above pre-industrial levels. Hoegh-Guldberg et al. overview a range of scientific approaches that have been used for understanding how the world may change at 1.5°C versus 2.0°C of global warming, all of which show qualitatively consistent results regarding how mean weather extremes would increase in the latter scenario. For example, very intense cyclones are likely to occur more frequently at 2.0°C vs 1.5°C of global warming, they say, with associated increases in heavy rainfall and damage. The authors say that achieving the 1.5°C target requires immediate and transformative actions in the next decade, and even as it would be costly, the benefits would still greatly outweigh the toll likely to be exacted due to inaction. "Aiming to limit warming to 1.5° Celsius is now a human imperative if escalating risks of dangerous if not catastrophic tipping points and climate change hotspots are to be avoided," the authors say.