Description: The late Pliocene warm period, approximately 3.0 to 3.3 million years ago, is the most recent geological warm period in the Earth’s history. We used PlioMIP simulations together with proxy evidence to investigate the westerlies and paleomonsoon variation in the late Pliocene warm period. Compared to the pre-industrial period, the simulated westerlies generally shifted poleward with a dipole pattern, and were closely related to the change of the tropospheric meridional temperature gradient as a result of thermal structure adjustment. Convincing geological evidences from the North Pacific deep-sea sites supported the major features of the simulated North Pacific westerlies. The simulated global land monsoon system enhanced in terms of area and monsoon precipitation, mainly over northern Africa, Asia, and northern Australia, and was roughly consistent with the reconstructions. The anomalous inland water vapor transportation together with the variation of vertical moisture advection and evaporation, explains most of the global land monsoon changes. The poleward shift of the westerlies and global land monsoon systems corresponded to the poleward shift of the mean meridional circulation. The sea surface temperatures and sea ice contributed to the model spread of the westerly anomalies and global land monsoon. The poleward shift and intensified Asian monsoon, and/or an overall intensified global land monsoon in the late Pliocene warm period is hypothesized to contribute to the lowering of atmospheric CO〈sub〉2〈/sub〉 concentration and the subsequent onset of the sustained major Northern Hemisphere glaciation, through the impact on and feedback from the terrestrial carbon cycle process.