Comprehending the resilience of regional hydroclimate in response to CO₂ removal is essential for guiding future mitigation and adaptation strategies. Using an ensemble of model simulations forced by idealized CO₂ ramp-up followed by ramp-down, here we show that the winter precipitation over the Northeastern Pacific and Western North America (NPWNA) is irreversible even if global warming is reversed back to 2 °C level. This asymmetric change features a tripolar pattern and is tied to Aleutian Low intensification, which is driven by both zonal and meridional gradients of sea surface temperature (SST) anomalies in the tropical central-eastern Pacific. Distinct from the zonal SST gradient—explained by different timescales of surface and subsurface warming and ocean dynamical processes, amplified through the Bjerknes feedback—the meridional SST gradient originates from the southward shift of the intertropical convergence zone, maintained by the wind-evaporation-SST feedback. Our findings suggest that the regional hydrological risks over the NPWNA induced by CO₂ ramp-up cannot be fully eliminated by CO₂ removal even if the global warming level is restored back.

了解区域水文气候对 CO₂ 去除的适应能力对于指导未来的缓解和适应战略至关重要。使用理想化的 CO₂ 上升后下降的一组模型模拟，我们在这里表明，即使全球变暖逆转回 2 °C 的水平，东北太平洋和北美西部 （NPWNA） 的冬季降水也是不可逆的。这种不对称变化具有三极模式，与阿留申低压增强有关，阿留申低压增强是由热带中东部太平洋海面温度 （SST） 异常的纬向和经向梯度驱动的。与纬向 SST 梯度不同——由地表和地下变暖以及海洋动力学过程的不同时间尺度解释，通过 Bjerknes 反馈放大——经向 SST 梯度起源于热带辐合带的南移，由风-蒸发-SST 反馈维持。我们的研究结果表明，即使全球变暖水平恢复，也无法通过去除 CO₂ 来完全消除 CO₂ 增加引起的 NPWNA 区域水文风险。