1.5 °C Looks Inevitable

The 1991 eruption of Mount Pinatubo, a volcano in the Philippines, belched so much SO 2 into the stratosphere that it cooled the entire Earth.Approximately 1.36 × 10 7 t of the gas reacted with water to form a planet-wide blanket of aerosol particles that absorbed and scattered sunlight, lowering the average global temperature by 0.6 °C for nearly two years [1-3].Now, according to a new report on the state of the global climate system from an international team of researchers [4,5], drastic emissions reductions or additional major volcanic eruptions are effectively the only way to prevent the Earth from passing 1.5 °C of warming, a key goal of the Paris Agreement [6][7][8], within about five yearsand the latter would only delay it by a few years.The report, published in June 2025 in the journal Earth System Science Data, is the latest in a series of papers aiming to provide annual updates on key indicators of climate change.The effort mirrors that of the Assessment Reports produced by the Intergovernmental Panel on Climate Change (IPCC) [9], but at a higher frequency.''The IPCC reports are published every five to eight years, and we are in times where that is too slow," said Joeri Rogelj, one of the new report's 61 coauthors and professor of climate science and policy at Imperial College London (London, United Kingdom).''With global warming nearing key limits in the Paris Agreement, we consider it essential to give this annual update of where we stand."The report comes on the heels of the first year, 2024, in which the average global temperature reached 1.5 °C above preindustrial levels [4,10,11].While hitting that threshold in a single year does not mean it has been crossed for good, the world is currently on track for that to happen in roughly five years.To maintain even a 50% chance of avoiding that outcome, the report contends, humanity could only afford roughly three more years at the current rate of global carbon emissions [4].After that, emissions reductions alone would no longer suffice to limit global warming to levels that would avoid the worst impacts on people and the planet-the only way to do that would be through removing CO 2 from the atmosphere [11].''What this is effectively telling us is that there is, in practice, a 100% chance we are blowing past 1.5," said