A traceable global warming record and clarity for the 1.5 °C and well-below-2 °C goals
Gottfried Kirchengast, Moritz Pichler
Abstract
Abstract Global surface air temperature change versus preindustrial level is a primary metric of global warming. Its 20-year mean serves as the indicator of the Intergovernmental Panel on Climate Change to monitor threshold crossings like of the 1.5 °C target of the Paris Agreement. Here we introduce a new benchmark timeseries 1850–2024 and projection to 2034 for this key metric, which shows a clear exceedance of 1.5 °C in 2024 by the annual mean (1.62 [1.55–1.69] °C). The 20-year mean still stayed below 1.5 °C (1.39 [1.29–1.49] °C) but is set to cross this threshold in 2028 [2025–2032]. Given this imminence, we propose improved quantification of the Paris goals by a simple four-classes definition (Paris compliance Target-1.5 °C, Well-below-2 °C; exceedance Risky-below-2 °C, Exceedance-2 °C) combined with a reliable tracking of goal compliance based on current and projected global warming levels. Such clear quantification can help spur climate action in the policy and legal domains and further standardization can help to also underpin the Paris Agreement’s global stocktake process.