Whether rapid climate mitigation can reverse regional hydroclimate extremes remains a fundamental, unresolved question for climate risk management. Here, using large ensemble simulations from the GFDL SPEAR (Seamless system for Prediction and EArth system Research) model under an aggressive overshoot scenario, we show that extreme precipitation over the Pacific Northwest exhibits pronounced irreversibility. Despite declining net radiative forcing and global surface cooling following mid-twenty-first-century mitigation, precipitation in the mid-latitude North Pacific continues to intensify and becomes increasingly skewed toward extreme events. This hysteresis arises from asymmetric atmospheric circulation responses driven by a persistently weakened Atlantic Meridional Overturning Circulation (AMOC). Specifically, during the global warming phase, El Niño-like tropical Pacific warming excites a Rossby wavetrain that deepens the Aleutian Low. In contrast, during the subsequent cooling phase, enhanced mid-to-high latitude Northern Hemisphere cooling associated with AMOC weakening strengthens the Ferrel Cell and increases baroclinicity over the mid-latitude North Pacific. Circulation anomalies in both phases invigorate storm tracks and atmospheric river activity, sustaining elevated precipitation extremes over the Pacific Northwest even as global temperature declines. These findings highlight the central role of ocean circulation in shaping the reversibility of regional climate hazards.

极端降水，,气候适应