Contributions of external forcing and internal variability to the multidecadal warming rate of East Asia in the present and future climate

Abstract

External forcing and internal variability contribute to multidecadal variation in the warming rate of East Asia. By rescaling the Coupled Model Intercomparison Project Phase 6 multi-model mean to the temperatures observed for the 1890-2020 period, we find that external forcing contributes about -0.2 to 0.1 K decade-1 to the warming rate until the 1980s, but this rate increases to 0.4 K decade-1 in recent decades. This multidecadal variation in the forced response is decomposed further into contributions by greenhouse gases, anthropogenic aerosols, and natural forcing. Once the external component is removed, the warming rate explained by the internal variability is +/- 0.15 K decade-1 in the twentieth century, reaching about -0.21 K decade-1 in recent decades. We find that 68% of the variance in the internally generated temperature anomaly is explained by the Indian Ocean Basin Mode (IOBM), the Atlantic Multidecadal Oscillation, and the Interdecadal Pacific Oscillation, with the IOBM playing a dominant role. In future Shared Socio-economic Pathway 2-4.5 scenario simulations, the impact of external forcing is projected to triple over the 2020-2100 period. Because the influence of internal variability remains relatively stable over this period, the contribution of external forcing becomes more pronounced in driving East Asian warming. These findings improve our understanding of both external and internal factors that shape trends and variation in the warming rate of East Asia and have implications for constraining future projections.