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A full-spectrum characterization of past interglacial climate is a necessary prerequisite for the detection and attribution of climate changes during the current interglacial. Here we present a speleothem record of Asian summer monsoon (ASM) during Marine Isotope Stage (MIS) 11 interglacial (MIS 11c), from Yongxing cave, China. The record's unprecedented chronologic constraints and decadal-scale temporal resolution allow a precise and direct comparison of ASM between the MIS 11c and the Holocene. Our data suggest that orbital-centennial patterns of ASM were remarkably similar during both interglacial, including their pacing and structure. Notably, a multi-millennial stronger monsoon late in MIS 11c, the "Late-MIS 11c shift," is similar to the Late Holocene strengthening of the ASM, the "2-Kyr shift." Thus, the multicentennial ASM weakening at the end of the Late-MIS 11c shift could imply that the current century-long ASM waning trend may persist into the future, if only natural forcings are considered.

Plain Language Summary The interglacial of Marine Isotope Stage 11 (MIS 11c) is generally considered to be an appropriate natural climate analog to the current interglacial, the Holocene. A new speleothem oxygen-isotope (delta O-18) record is reconstructed to characterize Asian summer monsoon (ASM) variability across MIS 11c on a wide range of timescales. This new record has an unprecedented high resolution (similar to 11 years) and precise chronology constrained by(230) Th dating and annual band counting. It thus allows for the first time a precise comparison of ASM variability between MIS 11c and the Holocene. We find that the observed pattern of decreasing ASM strength during the late portion of MIS 11c was interrupted by a multi-millennial period of stronger monsoon (the "Late-MIS 11c shift"), which is similar to the Late Holocene increase in ASM strength (the "2-Kyr shift"), which also occurred against a backdrop of long-term decline in Northern Hemisphere summer insolation. Notably, the Late-MIS 11c shift was terminated by a multicentennial ASM weakening trend, thus suggesting that the current century-long ASM waning trend could persist into the future, provided that the anthropogenic forcing does not supersede the natural variability.