Our review of recently published climatic proxy sequences shows that the most dramatic climate tranistion of the mid Holocene (~8500–~3500 cal. yr BP) occurred at the middle- to late-Holocene transition at ~4000 cal. yr BP. In northern China, an abrupt climatic shift at ~4000 cal. yr BP was recorded in the eastern margin of the Tibetan Plateau, in the western part of the Chinese Loess Plateau and in the vast Inner Mongolian Plateau. In southern China, the ~4000 cal. yr BP event was also abrupt, but it is expressed as one of several quasi-cyclic events in most of the records. We propose that the cumulative effects of insolation-dictated declining trend in tropical SST and the geologically documented increasing trend of ENSO activity were the first-order causes of the cooling and the associated drying during the past 6000 years. Superimposed on the first-order causes were the second-order causes, i.e. the additive effects of the ‘Bond Event 3’-associated lower insolation and the increasingly drying-resulted negative feedback of ‘air–land interactions’. The second-order causes made ~4000 cal. yr BP the tipping point when the resultant drying had destroyed many Chinese Neolithic cultures. Our review of published archaeological literature shows that six of the seven well-documented Chinese Neolithic cultures collapsed at ~4000 cal. yr BP with the exception of the Henan Longshan Culture that evolved to the more advanced Erlitou Culture. The indicators of the cultural collapse include (1) the number of archaeological sites was significantly reduced, (2) the quality of the archaeological artifacts of the succeeding culture is lower than that of the preceding culture, (3) more sophisticated architectures disappeared, and (4) agricultural cultures were replaced by pastoralism or by agro-pastoralism in northern China.

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This paper reviews recently published literature, most of which was published in Chinese, and searches for regional patterns of Holocene changes useful in depicting global patterns. The Holocene in the Xinjiang region can be divided into three stages: a warming and dry early stage (from 11 10 to 8-7 ka BP), a warm and wet middle stage (from 8-7 to 4.5-3 ka BP) and a fluctuating cool and dry late stage (since 4.5-3 ka BP). The Holocene in the northern Tibetan Plateau can also be divided into three stages: a warming and wet stage (from 10.5-10 to 5-4 ka BP), followed by a variable drying and probably warm stage (5-4 to 3 ka BP) and ending with a cool and dry stage (since 3 ka BP). In the Inner Mongolian Plateau, the early Holocene (from 10.5-9.5 to 8-7.5 ka BP) was warming and dry, and a warm and wet climate occurred from 7.5 to 3.5, during which the best time was 6.3-3.8 ka BP; the climate has been variably drying and probably cooling since 3.5 ka BP. In the northwestern part of the Loess Plateau, several Holocene palaeosols have been identified (10-9, 7.5-5, 4-3 and 2.7-2 ka BP) with the 7.5-5 ka BP palaeosol being most strongly expressed. The best-developed palaeosol-equivalent in major valleys is a swamp-wetland facies deposited between 8885 and 3805 14C yr BP under an extremely wet regime. The climate has fluctuated significantly at least three times around a dry and probably cool regime after the swamp-wetland facies-depositional period. Our summary shows that the Holocene Climatic Optimum occurred nearly contemporaneously (8-5 ka BP) at all sites in the Xinjiang region, in the Inner Mongolian Plateau and in the northwestern part of the Loess Plateau. A warming and wet early Holocene (10-8 ka BP) in the northern Tibetan Plateau is most likely related to high effective soil moisture resulting from snow and ice melting. We propose here that the middle Holocene Climatic Optimum (8-5 ka BP) in arid to semi-arid China was primarily a delayed response of the low latitude oceans to high latitude peak insolation (9-8 ka BP).

Aim  This modern pollen‐rain study documents the spatial and quantitative relationships between modern pollen and vegetation in Mongolia, and explores the potential for using this relationship in palaeoclimatic reconstructions. Location  East‐central Mongolia. Methods  We collected 104 pollen surface samples along a south–north transect across five vegetation zones in Mongolia. Discriminant analysis was used to classify the modern pollen spectra into five pollen assemblages corresponding to the five vegetation zones. Hierarchical cluster analysis was used to divide the main pollen taxa into two major groups and seven subgroups representing the dry and moist vegetation types and the main vegetation communities within them. Results  Each vegetation zone along the transect can be characterized by a distinctive modern pollen assemblage as follows: (1) desert zone: Chenopodiaceae–Zygophyllaceae–Nitraria–Poaceae pollen assemblage; (2) desert‐steppe zone: Poaceae–Chenopodiaceae pollen assemblage; (3) steppe zone: Artemisia–Aster‐type–Poaceae–Pinus Haploxylon‐type pollen assemblage; (4) forest‐steppe zone: Pinus Haploxylon‐type–Picea–Artemisia–Betula, montane forb/shrub and pteridophyte pollen assemblage; and (5) mountain taiga zone: Pinus Haploxylon‐type–Picea–Poaceae–Cyperaceae, montane forb/shrub and Pteridophyte pollen assemblage. Main conclusions  Based on the ratio between the major pollen taxon groups and subgroups, we propose two pollen–climate indices that represent the precipitation and temperature conditions in the study region. When plotted along our south–north transect, the moisture indices (M) and temperature indices (T) mimic the regional gradients of precipitation and temperature across Mongolia very closely. These pollen–climate indices can be used for palaeoclimatic reconstruction based on fossil pollen data.

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Thermoelectric modules, consisting of multiple pairs of n- and p-type legs, enable converting heat into electricity and vice versa. However, the thermoelectric performance is often asymmetrical, in that one type outperforms the other. In this paper, we identified the relationship between the asymmetrical thermoelectric performance and the weighted mobility ratio, a correlation that can help predict the thermoelectric performance of unreported materials. Here, a reasonably high ZT for the n-type ZrCoBi-based half-Heuslers is first predicted and then experimentally verified. A high peak ZT of ~1 at 973 K can be realized by ZrCo0.9Ni0.1Bi0.85Sb0.15. The measured heat-to-electricity conversion efficiency for the unicouple of ZrCoBi-based materials can be as high as ~10% at the cold-side temperature of ~303 K and at the hot-side temperature of ~983 K. Our work demonstrates that the ZrCoBi-based half-Heuslers are highly promising for the application of mid- and high-temperature thermoelectric power generation.

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