Jun Cheng

The Younger Dryas (YD, 12,900–11,700 years before present) event offers a key opportunity to investigate climate system responses to abrupt perturbations, yet regional hydroclimate responses in northeastern China remain debated. Here we reconstruct the spatial fingerprint of YD hydroclimate variability using a comprehensive fossil pollen data set. Our results show regionally coherent cooling but strong spatial heterogeneity in precipitation. At YD onset, northern regions became drier, whereas southern areas experienced slight wetting. By YD termination, precipitation increased significantly in most regions, while changes in the interior was limited. Comparison with climate model simulations indicated that these patterns were likely associated with a YD‐related weakening and subsequent recovery of moisture transport, superimposed on a persistent poleward and inland expansion of atmospheric circulation. Previously reported spatially inconsistent proxy signals can be reconciled by the high tolerance of boreal forests to low‐precipitation conditions.

East Asian Summer Monsoon (EASM) varied at orbital and millennial timescales during the Last Deglaciation (∼20–11 ka). The uniform δ ¹⁸ O response in East China is often linked to EASM circulation that drives a precipitation dipole in North and South China on orbital scale. Yet the relationship between stalagmite oxygen isotopes (δ ¹⁸ O _c ) and regional rainfall remains ambiguous at millennial timescales. Combining proxy records with isotope‐enabled transient climate simulations (iTraCE), we demonstrate a decoupling between changes in δ ¹⁸ O _c and regional precipitation in North China during millennial‐scale events. Although δ ¹⁸ O _c responds uniformly across East China to AMOC changes and is correlated with South China rainfall, North China rainfall is instead largely driven by insolation, with negligible millennial‐scale variability. This reflects that East China δ ¹⁸ O _c is driven by AMOC‐induced shifts in moisture source δ ¹⁸ O. Our findings emphasize that δ ¹⁸ O _c records require forcing‐specific interpretation in East Asia across timescales.

The mid-latitude ecological environment is highly vulnerable, and increasing hydroclimate variability poses a significant threat to it. However, the mechanisms driving this variability remain unclear due to short observational records and climate model biases. Here, we present a sub-millennial resolution precipitation record spanning the past ~5.7 million years (Myr), derived from a 300.8-meter fluvio-lacustrine sediment core in mid-latitude East Asia (northern China). Our results reveal a persistent influence of the westerly jet on mid-latitude precipitation since the Pliocene, as well as a marked reduction in mid-latitude precipitation variability alongside amplified low-latitude variability after ~3 million years ago (Ma). Based on idealized sensitivity simulations, we attribute the amplified mid-latitude precipitation variability before ~3 Ma to enhanced westerly jet waviness driven by Arctic warming. Given projected increases in jet waviness under future global warming, we predict more frequent hydroclimate extremes in mid-latitude regions.

Temperature is the key variable in the study of climate changes in the past and future. Most previous studies on past temperature reconstructions, however, have focused on the mean annual temperature (MAT). Here, focusing on the seasonal temperature reconstructions in the Northern Hemisphere extratropics during the Holocene period, we show that the change in seasonal cycle of temperature reconstructions is severely underestimated in comparison with the expectation from present observations. Our study highlights the current uncertainty in seasonal temperature reconstructions in the Holocene, with an implication that the MAT simulation in current climate models may not be much biased.

Extensive research has explored how sweet spot conditions influence climate variability in the nonlinear Earth system. However, their effects throughout deglaciations remain unclear. Based on an annual‐laminated speleothem δ ¹⁸ O record with unprecedented chronology precision, we first identified a two‐step termination of the Asian Heinrich Period‐1 at 15.11 and 14.69 ky BP (thousand years before present, where the present is 1950 CE), each marked by a centennial‐scale strengthening of the Asian summer monsoon (ASM), in contrast to centennial‐scale ASM weakening events observed at 17.8 and 16.09 ky BP. These transitions occurred under intermediate CO ₂ and ice volume conditions, which dynamically paced the Atlantic Meridional Overturning Circulation (AMOC) fluctuations and the subsequent reoccurrence of ASM events. It highlights the role of stochastic resonance in nonlinear climate system. Additionally, these AMOC/ASM events also resonated with abrupt CO ₂ risings across various pervasive modes of variability, which account for half of total CO ₂ rise during last deglaciation. This substantial contribution to CO ₂ increases played a key role in ice termination.

Organic carbon burial (OCB) in lakes, a critical component of the global carbon cycle, surpasses that in oceans, yet its response to global warming and associated feedbacks remains poorly understood. Using a well-dated biomarker sequence from the southern Tibetan Plateau and a comprehensive analysis of Holocene total organic carbon variations in lakes across the region, here we demonstrate that lake OCB significantly declined throughout the Holocene, closely linked to changes in temperature seasonality. Process-based land surface model simulations clarified the key impact of temperature seasonality on OCB in lakes: increased seasonality in the early Holocene saw warmer summers enhancing ecosystem productivity and organic matter deposition, while cooler winters improved organic matter preservation. The Tibetan Plateau’s heightened sensitivity to climate and ecosystem dynamics amplifies these effects. With declining temperature seasonality, we predict a significant slowdown or reduction in OCB across these lake sediments, leading to carbon emissions and amplified global warming.