Achieving the 2 ℃ climate target requires the coordination of strategies for greenhouse gases (GHGs) and air pollutants mitigation, yet their complex interactions remain insufficiently explored. BCC-ESM1 Earth system model is employed to compare global climate responses under the novel SSP2-com scenario, in which both GHGs and aerosols undergo reduction, with that under the SSP2-4.5 scenario. Moreover, the relative contributions of carbon dioxide (CO₂), sulfur dioxide (SO₂), and black carbon (BC) to future temperature increases are analyzed. Results reveal that compared with the SSP2-4.5 scenario, the SSP2-com scenario can stabilize the end-21st-century temperature rise well below 2 ℃, primarily driven by the reduction of anthropogenic CO₂ emissions. A mid-term warming rebound between 2061 and 2080 is observed due to reduced aerosol cooling. SO₂ reductions result in a weakening aerosol-induced radiative forcing, driving regional warming asymmetries―particularly in northern high latitudes (up to +1.5 ℃ in winter). Compared to CO₂-only mitigation, experiments involving SO₂ reductions also exhibit stronger global precipitation increases, suggesting an acceleration of the hydrological cycle under lower aerosol loading. Energy budget analysis further indicates that SO₂ mitigation results in an increase in net shortwave radiation at the top of the atmosphere by approximately 0.23 W/m² during the mid-term (2061―2080), and consequently leads to an accumulated surface energy gain of about 0.15 W/m². These findings highlight a key trade-off: aerosol mitigation may induce mid-term warming, but remains essential for achieving air quality and climate goals. This work underscores the necessity of balancing mid-term climate―air quality trade-offs with long-term decarbonization, offering actionable insights for policymakers to design integrated pathways align with the Paris Agreement.

This study revisits the influence of the quasi-biennial oscillation (QBO) on the Northern Hemisphere surface climate during the boreal winter by using the QBO index based on the empirical orthogonal function (EOF) of stratospheric equatorial winds. When the QBO is defined with eight phases, the tropospheric anomalies significantly project onto the negative Arctic Oscillation (AO) in phase 1 and onto the positive AO in phases 5 and 6. The underlying mechanism can be partially explained by the Holton–Tan relationship and the associated planetary wave–mean flow interactions. Compared with the known QBO indices defined with the single-level winds, the EOF-based index better captures the AO-like response to the QBO. This may be because the vertical structure, particularly the depth of the QBO’s stratospheric easterly or westerly, is essential for the QBO’s extratropical influence, which is better described by the EOF-based metric. The results remain robust in phases 1 and 5 and become more significant in phase 6 when the El Niño–Southern Oscillation (ENSO) effects are linearly removed. This result suggests that the two-dimensional QBO index is more useful than the one-dimensional index for monitoring and predicting QBO-related tropospheric circulation changes.