Anthropogenic influence on fixed threshold-based heatwave in China and constrained future projection

Abstract The 35 °C threshold-based heatwave (HW) holds particular significance for human health, energy supply and animal welfare, serving as a critical criterion for issuing high-temperature warnings in China. However, the quantified influence of greenhouse gases (GHGs) and anthropogenic aerosols (AA) on HW days (HWD) and cumulative intensity (HWS) remains underexplored. Here, we investigated these influences based on a threshold adjustment method and optimal fingerprint method. Using observations from 1961–2020, we found that both HWD and HWS experienced a clear increase across most of China, with the largest changes centered in eastern and northwestern China. Bias-corrected Coupled Model Intercomparison Project Phase 6 (CMIP6) climate models successfully reproduced the observed changes as well as the regional differences. Anthropogenic forcing dominated by GHGs was robustly detected, with the influence of GHGs and AA successfully separated. Attribution analysis revealed that GHGs explained about 126.3% of HW changes. Constrained projections indicated that both HWD and HWS would continue to increase until 2050, even under the most optimistic low-emission scenario. Eastern China was projected to experience fast HW increase, likely due to intensified GHG emission combined with anticipated reduction in AA in the future, highlighting the urgency of developing mitigation and adaptation policies.