This study quantifies the historical (1850–2020) climate contributions of China and Japan using the normalized marginal attribution method within a multi-forcer framework. Emission datasets from CEDS, EDGAR, and BB4CMIP are combined across all major sectors to estimate radiative forcing ( \(\Delta F\) ) and temperature change ( \(\Delta T\) ) from long-lived greenhouse gases (LLGHGs) and short-lived climate forcers (SLCFs). For China, post-1980 industrial expansion led to steep CO \({}_{2}\) growth and high aerosol emissions, with aerosols historically offsetting a substantial portion of GHG-driven warming. Recent declines in SO \({}_{2}\) and other precursors have begun to unmask this warming, making coordinated aerosol-GHG mitigation essential. In 2020, China’s \(\Delta F\) was dominated by CO \({}_{2}\) and CH \({}_{4}\) , with aerosols contributing notable opposing effects. Japan’s emissions have stabilized or declined since the late twentieth century, with strong air-quality controls yielding modest aerosol cooling. Japan’s 2020 \(\Delta F\) peaked at 0.06–0.07 W m \({}^{-2}\) and \(\Delta T\) at 0.03–0.04  \({}^{\circ }\) C, primarily from CO \({}_{2}\) -FF. The comparison reveals larger absolute contributions and stronger masking in China, versus Japan’s smaller, smoother warming trajectory. Results inform region-specific mitigation strategies that integrate climate and air-quality objectives.