Cooling threshold: The end of each interglacial period over the past 800,000 years was characterized by large, abrupt cooling episodes that were distinct from the gradual decrease in insolation that was occurring. Why did these sudden coolings occur? Yin et al . used a suite of climate models to show that an insolation threshold exists, beneath which the slow decrease of energy from the sun leads to rapid climate cooling. This effect results from weakening of the Atlantic meridional overturning circulation involving sea ice feedbacks in the Nordic and Labrador Seas. —HJS

The dominant modes of variability of precipitation for the whole of China over the past millennium and the mechanism governing their spatial structure remain unclear. This is mainly due to insufficient high-resolution proxy records of precipitation in western China. Numerous tree-ring chronologies have recently been archived in publicly available databases through PAGES2k activities, and these provide an opportunity to refine precipitation field reconstructions for China. Based on 479 proxy records, including 371 tree-ring width chronologies, a tree-ring isotope chronology, and 107 drought/flood indices, we reconstruct the precipitation field for China for the past half millennium using the optimal information extraction method. A total of 3631 of 4189 grid points in the reconstruction field passed the cross-validation process, accounting for 86.68 % of the total number of grid points. The first leading mode of variability of the reconstruction shows coherent variations over most of China. The second mode is a north–south dipole in eastern China characterized by variations of the same sign in western China and northern China (except for Xinjiang province). It is likely controlled by the El Niño–Southern Oscillation (ENSO) variability. The third mode is a sandwich triple mode in eastern China including variations of the same sign in western China and central China. The last two modes are reproduced by most of the six coupled climate models' last millennium simulations performed in the framework of the Paleoclimate Modelling Intercomparison Project Phase III (PMIP3). In particular, the link of the second mode with ENSO is confirmed by the models. However, there is a mismatch between models and proxy reconstructions in the time development of different modes. This mismatch suggests the important role of internal variability in the reconstructed precipitation mode variations of the past 500 years.

The relative influence of insolation, CO₂, and ice sheets on the East Asian summer monsoon (EASM) is not well understood especially at regional scale. Here a Gaussian emulator based on simulations with HadCM3 is used to quantitatively assess how astronomical forcing, CO₂, and northern hemisphere ice sheets affect the variation of the summer precipitation over the last 800 ky. Our results show that in the EASM domain north of 25°N, the variation of the summer precipitation is dominated by precession, leading to strong 23‐ky cycles, while the ice sheets only modulate the effect of insolation by influencing the land‐sea pressure gradient. In the southern part, ice sheets play a more important role, generating 100‐ky cycles, through influencing the latitude of the Intertropical Convergence Zone and the Hadley cell. Obliquity and CO₂ have little effect on the summer precipitation as compared to precession and ice sheets.

Identifying the position of the Current Warm Period (CWP) in the context of the long‐term climatic trend is vital for understanding the impact of human activity on climate change. Reconstructions of summer temperature and precipitation in eight sub‐regions of China over the past 22,000 years show that the CWP summer temperature and precipitation in these sub‐regions are all lower than in the Early to Middle Holocene. The timing of the Holocene temperature and precipitation peaks in northern China (including Northwest China, North China, and Northeast China) is mainly determined by orbital forcing. Greenhouse gas forcing and the land ice‐sheet help to fine‐tune the timing of the climate maxima. These findings show that the climate since the Last Glacial Maximum in northern China is more sensitive to non‐anthropogenic external forcings, whereas the summer precipitation in Southwest China since the early 20^th century is controlled more by anthropogenically forced changes.