All IPCC AR6 regions are close to their 1.5 °C- and 2 °C-equivalent warming limits

Key Points:

• The Paris Agreement aims to limit global warming to well below 2 °C and pursue efforts to keep it under 1.5 °C above pre-industrial levels, necessitating regional estimates of attributable warming to guide adaptation and loss-and-damage negotiations.
• Due to sparse historical temperature observations in many regions, especially Africa, South America, and polar areas, estimating regional human-induced warming relative to pre-industrial baselines is challenging and uncertain.
• The study employs a Bayesian observational-constraint method called Kriging for Climate Change (KCC) to estimate attributable warming up to 2025 across all IPCC AR6 regions, integrating climate model simulations and observational data to improve attribution accuracy even in data-poor regions.
• Multiple constraint schemes combining regional, continental, and global temperature data were evaluated, with the approach combining global and regional constraints providing the best balance of precision and reliability in estimating regional warming.
• Results project that the 1.5 °C global warming threshold will be reached by 2029 and the 2 °C threshold by 2042 under a high emissions scenario, with regional warming estimates at these milestones informing the remaining warming "budget" for adaptation planning.