Clearer metrics for the Paris climate targets: A new compliance quantification approach

In light of seeing temperatures now closely approach the international targets set by the 2015 Paris Agreement for limiting global warming, in particular the 1.5 °C target, an accurate and reliable tracking of changes in the global surface temperature is critical. We introduce a comprehensive benchmark time series for global surface air temperature (GSAT) extending from 1850 to 2024, complemented by a projection up to 2034 and scenarios through to 2050. Building on and advanced from widely recognized global mean surface temperature (GMST) records used by the IPCC, we established a detailed and traceable GSAT annual and 20-year-mean time record in this form, referenced to the conventional preindustrial level (mean 1850-1900). Our record indicates an increase of the 20-year-mean GSAT change to 1.40 [1.30-1.49] °C by 2024 and a subsequent exceedance of the 1.5 °C threshold by 2028 [2025-2032] (uncertainty ranges denote a 90% confidence interval). Given this imminence of 1.5 °C, we propose a new classification system to gauge, with regular updates, the compliance with the Paris goals (1.5 °C goal, well-below-2 °C goal; or exceedance up to 2 °C or even beyond). These improvements in compliance/exceedance quantification may help policymakers, the judiciary and the general public to obtain standardized and thus more reliable assessments of the degree of compliance with the Paris climate targets over the coming years and decades.