A recent study published in Proceedings of the National Academy of Sciences (PNAS) by researchers from the Institute of Earth Environment, Chinese Academy of Sciences, reveals that the East Asian summer monsoon experienced frequent and rapid shifts even during past warm periods once thought to be climatically stable.

From a 512-meter sediment core from the Weihe Basin in central China, the research team reconstructed a 2-million-year climate history. Their findings indicate that millennial-scale monsoon fluctuations were common during interglacial periods, not driven by high-latitude ice sheet dynamics, but by low-latitude solar insolation forcing. "Our results challenge the notion of climatic stability during warm periods," said Prof. SUN Youbin, first author of the study. “They highlight the role of precession-paced solar forcing, independent of large ice sheet presence, in triggering abrupt hydrological shifts.”

Spectral analysis of paleolake sediment proxies revealed strong 11,000- and 5,500-year patterns—signatures of hemispheric solar radiation peaks—which likely drove alternating megadroughts and wet intervals across East Asia. The study also suggests that under current orbital configurations, East Asian monsoon strength may decline in the coming millennia, raising the risk of prolonged droughts. By revealing new aspects of interglacial climate dynamics, this research demonstrates that low-latitude mechanisms are critical for robust hydroclimatic projections.

This work is supported by the National Natural Science Foundation of China, the Strategic Priority Research Program of CAS, and the Second Tibetan Plateau Scientific Expedition and Research Program.

Fig. Abrupt climate changes over the last 2 Ma. (a) Clay content of HX core; (b) Strong (red) and weak (blue) monsoon events inferred from high-frequency component of HX clay content; (c) Benthic δ¹⁸O stack. (Image by SUN, et al)