Tree-ring oxygen isotopes from the western Kunlun and Karakoram Mountains provide valuable insights into past climate variability in High Asia. Our analysis reveals frequency-dependent climate signals encoded in tree-ring oxygen isotopes. In the western Kunlun Mountains, tree-ring oxygen isotopes primarily reflect summer precipitation and evapotranspiration at lower frequencies, while at higher frequencies, it is strongly correlated with vapor pressure deficit, indicating atmospheric aridity. A similar frequency-dependent pattern emerges in the Karakoram tree-ring oxygen isotopes chronologies, where winter-spring temperatures dominate the low-frequency signals, while summer precipitation drives the higher-frequency variations. Notably, our reconstruction of the low-frequency winter-spring temperature signal reveals unexpectedly warmer conditions during the Little Ice Age (1647–1746) compared to the 20th century. This finding is supported by ice core oxygen isotopes from High Asia and northern North America. We propose that these anomalous conditions may be linked to an eastward shift in the Polar Vortex and strengthened mid-latitude Westerlies over Eurasia.