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The responses of the Indian and East Asian summer monsoons (ISM and EASM) to warming since the last deglaciation are controversial. Pollen results from a subalpine lake in the ISM area show that the Tsuga dumosa forest zone migrated at least 650 m upward during 18.6-7.1 kyr BP, indicating a gradual rise in mean annual temperature exceeding 3.9 degrees C. In response, grasses and deciduous and evergreen broad-leaved trees successively colonized the mountainous environment. By contrast, the area around a lake in the EASM area was gradually occupied by temperate deciduous trees. In both areas, the maximum monsoonal precipitation occurred during 7.1-6.4 kyr BP, coinciding with peak Holocene warmth, but lagging the peak in Northern Hemisphere summer insolation by 3.9-4.6 kyr, due to delayed ice melting in northern high latitudes. Our results indicate the synchronous strengthening of the ISM and EASM in response to warming-induced northward shifts in the Intertropical Convergence Zone.