The prevailing mid-latitude westerly winds, known as the westerlies, are a fundamental component of the climate system because they have a crucial role in driving surface ocean circulation¹ and modulating air–sea heat, momentum and carbon exchange^1,2,3. Recent work suggests that westerly wind belts are migrating polewards in response to anthropogenic forcing^4,5. Reconstructing the westerlies during past warm periods such as the Pliocene epoch, in which atmospheric carbon dioxide (CO₂) was about 350 to 450 parts per million⁶ and temperatures were about 2 to 4 degrees Celsius higher than today⁷, can improve our understanding of changes in the position and strength of these wind systems as the climate continues to warm. Here we show that the westerlies were weaker and more poleward during the warm Pliocene than during glacial periods after the intensification of Northern Hemisphere glaciation (iNHG), which occurred around 2.73 million years ago⁸. Our results, which are based on dust and export productivity reconstructions, indicate that major ice sheet development during the iNHG was accompanied by substantial increases in dust fluxes in the mid-latitude North Pacific Ocean, especially compared to those in the subarctic North Pacific. Following this shift, changes in dust and productivity largely track the glacial–interglacial cycles of the late Pliocene and early Pleistocene epochs. On the basis of this pattern, we infer that shifts in the westerlies were primarily driven by variations in Plio-Pleistocene thermal gradients and ice volume. By combining this relationship with other dust records^9,10,11 and climate modelling results¹², we find that the proposed changes in the westerlies were globally synchronous. If the Pliocene is predictive of future warming, we posit that continued poleward movement and weakening of the present-day westerlies in both hemispheres can be expected.

盛行的中纬度西风，被称为西风，是气候系统的基本组成部分，因为它们在推动地表海洋环流¹和调节海气热、动量和碳交换^1、2、3方面发挥着至关重要的作用。最近的工作表明，西风带正在向极地迁移以响应人为强迫^4,5。在过去的温暖时期（例如上新世）重建西风带，其中大气中的二氧化碳 (CO ₂ ) 约为百万分之 350 至 450 ⁶，温度比今天高约 2 至 4 摄氏度⁷，可以提高我们对随着气候继续变暖这些风系统的位置和强度变化的理解。在这里，我们表明，在大约 273 万年前发生的北半球冰期 (iNHG) 强化后，暖上新世西风带比冰期更弱且更偏向极地⁸. 我们基于尘埃和出口生产力重建的结果表明，iNHG 期间的主要冰盖发展伴随着北太平洋中纬度地区尘埃通量的大幅增加，特别是与亚北极北太平洋相比。在这种转变之后，尘埃和生产力的变化在很大程度上追踪了晚上新世和早更新世时期的冰期-间冰期循环。基于这种模式，我们推断西风带的变化主要是由上更新世热梯度和冰量的变化驱动的。通过将此关系与其他尘埃记录^9、10、11和气候模拟结果^12相结合，我们发现西风带的拟议变化是全球同步的。如果上新世预示着未来的变暖，我们假设可以预期两个半球持续的极地运动和现今西风带的减弱。