Regional Impacts of Climate Sensitivity on Projected Temperature Trends and Extremes

This study examines the influence of climate sensitivity on future projections of surface temperature and extreme events. Here, we develop a novel modeling framework that couples the emissions-driven Integrated Global System Model (IGSM), a human–Earth system modeling framework, with the Community Earth System Model version 1 (CESM1), which has been enhanced to explore the range of plausible climate sensitivities. We conduct simulations using the IGSM-CESM1 framework under a “Current Trends” (CT) scenario, focusing on the near (2021–2040), mid (2041–2060), and far (2081–2100) periods compared to the baseline period of 1986-2005. Our findings reveal that climate sensitivity has an asymmetric hemispheric effect to long-term warming trends, with higher sensitivity leading to stronger temperature increases in the Northern Hemisphere (NH), reaching approximately 3°C above pre-industrial levels by the end of the century, whereas the Southern Hemisphere, excluding Antarctica and its adjacent regions, continues to experience weaker warming, with temperatures up to 3°C lower than those in the NH. In contrast, low-sensitivity pathways project warming below 2°C. These differences in climate sensitivity also substantially impact the frequency of extreme heat events. For example, the number of “summer hot days” (i.e., maximum daily temperature exceeding 35˚C) that are projected can increase by up to 90 days under high climate sensitivity, compared to an increase of 30 days under low sensitivity, with the most pronounced changes occurring across South America. For precipitation indices, higher climate sensitivity is projected to strongly increase consecutive dry days over the tropics, in contrast to the weaker response under lower sensitivity. Overall, our findings underscore how variations in climate sensitivity influence the magnitude, spatial distribution, and intensity of surface warming and extreme events. These results provide critical insights for risk assessment and highlight the urgent need for policymakers to strengthen climate resilience strategies, particularly in vulnerable regions.