Liya Jin

A Test of Climate, Sun, and Culture Relationships from an 1810-Year Chinese Cave Record

A record from Wanxiang Cave, China, characterizes Asian Monsoon (AM) history over the past 1810 years. The summer monsoon correlates with solar variability, Northern Hemisphere and Chinese temperature, Alpine glacial retreat, and Chinese cultural changes. It was generally strong during Europes Medieval Warm Period and weak during Europes Little Ice Age, as well as during the final decades of the Tang, Yuan, and Ming Dynasties, all times that were characterized by popular unrest. It was strong during the first several decades of the Northern Song Dynasty, a period of increased rice cultivation and dramatic population increase. The sign of the correlation between the AM and temperature switches around 1960, suggesting that anthropogenic forcing superseded natural forcing as the major driver of AM changes in the late 20th century.

East Asian summer monsoon precipitation variability since the last deglaciation

The lack of a precisely-dated, unequivocal climate proxy from northern China, where precipitation variability is traditionally considered as an East Asian summer monsoon (EASM) indicator, impedes our understanding of the behaviour and dynamics of the EASM. Here we present a well-dated, pollen-based, ~20-yr-resolution quantitative precipitation reconstruction (derived using a transfer function) from an alpine lake in North China, which provides for the first time a direct record of EASM evolution since 14.7 ka (ka = thousands of years before present, where the “present” is defined as the year AD 1950). Our record reveals a gradually intensifying monsoon from 14.7–7.0 ka, a maximum monsoon (30% higher precipitation than present) from ~7.8–5.3 ka, and a rapid decline since ~3.3 ka. These insolation-driven EASM trends were punctuated by two millennial-scale weakening events which occurred synchronously to the cold Younger Dryas and at ~9.5–8.5 ka, and by two centennial-scale intervals of enhanced (weakened) monsoon during the Medieval Warm Period (Little Ice Age). Our precipitation reconstruction, consistent with temperature changes but quite different from the prevailing view of EASM evolution, points to strong internal feedback processes driving the EASM, and may aid our understanding of future monsoon behaviour under ongoing anthropogenic climate change.

Variation of East Asian monsoon precipitation during the past 21 k.y. and potential CO2 forcing

Paleoclimatic research can provide critical insight on causes of change in the East Asian monsoon, which influences the lives of 1.6 billion people today. In this study, we use paleoclimatic indexes from Chinese loess deposits, which have clear climatic implications and are independently dated, to reconstruct the monsoon precipitation since 21 ka. Our results show that monsoon precipitation persistently decreased from 21 ka to ca. 8 ka, and increased after ca. 8 ka, with a precipitation peak at 8–3 ka. These changes in East Asian summer monsoon precipitation are synchronous with changes in high-northern-latitude ice volume/ice cover and atmospheric CO2. These new data suggest that variation of the monsoon precipitation was probably driven by CO2-forced high-northern-latitude temperature changes, shifting the location of the intertropical convergence zone that dominates monsoon precipitation. Our TraCE-21000 modeling experiment supports this interpretation.

Response of East Asian climate to Dansgaard/Oeschger and Heinrich events in a coupled model of intermediate complexity

[1] Terrestrial records of loess-paleosol sequences from across the Asian interior (Chinese Loess Plateau) have been used to reconstruct climatic conditions through the Quaternary and they correlate, in general, with oxygen isotope records from deep sea cores (e.g., the grain-size maxima from Chinese loess with ages that match well those of the last six Heinrich events evidenced in the North Atlantic marine sediments during the last glacial period). Possible reasons for this teleconnection of the similar climate signal of the North Atlantic and China are investigated by using an Earth system model of intermediate complexity (CLIMBER-2) forthe typicalperiod oflastglacial age(during60– 20 kyr BP). By using the CLIMBER-2 model, we have studied the response of East Asian climate during the typical glacial age (60–20 kyr BP) to Dansgaard/Oeschger (D/O) and Heinrichevents.TotriggerD/OandHeinricheventsinthemodel,transientforcingsinaddition tochangesininsolationcausedbyvariationsintheEarthorbitareprescribedinthemodeling experiment. These additional forcings include changes in inland-ice volume over North America, infreshwater flux intothenorthern NorthAtlantic. Themodeling resultsshowthat the variations of the annual-mean near-surface air temperature over Eurasia closely follow climate changes inNorth Atlantic. Thestronger intensity ofwesterly windinthe midlatitude of northern hemisphere versus the weaker Asian summer monsoon as well as the slightly weaker Asian winter monsoon (north easterly flow near surface) corresponds well with the (prescribed) Heinrich events during 60–20 kyr BP. This suggests that the climate signals foundinChineseloess(grain-sizemaximawithagesthatmatchthoseofthelastsixHeinrich events) during the last glaciation are likely related to the relatively stronger westerly winds over Eurasia in boreal winter and a relatively weaker Asian summer monsoon that intensified the aridity of northern China which lead to expansion of the northern deserts during the Heinrich events.

Paleoclimate Modeling in China: A Review

This paper provides a review of paleoclimate modeling activities in China. Rather than attempt to cover all topics, we have chosen a few climatic intervals and events judged to be particularly informative to the international community. In historical climate simulations, changes in solar radiation and volcanic activity explain most parts of reconstructions over the last millennium prior to the industrial era, while atmospheric greenhouse gas concentrations play the most important role in the 20th century warming over China. There is a considerable model-data mismatch in the annual and boreal winter temperature change over China during the mid-Holocene [6000 years before present (ka BP)], while coupled models with an interactive ocean generally perform better than atmospheric models. For the Last Glacial Maximum (21 ka BP), climate models successfully reproduce the surface cooling trend over China but fail to reproduce its magnitude, with a better performance for coupled models. At that time, reconstructed vegetation and western Pacific sea surface temperatures could have significantly affected the East Asian climate, and environmental conditions on the Qinghai-Tibetan Plateau were most likely very different to the present day. During the late Marine Isotope Stage 3 (30–40 ka BP), orbital forcing and Northern Hemisphere glaciation, as well as vegetation change in China, were likely responsible for East Asian climate change. On the tectonic scale, the Qinghai-Tibetan Plateau uplift, the Tethys Sea retreat, and the South China Sea expansion played important roles in the formation of the East Asian monsoon-dominant environment pattern during the late Cenozoic.

Forcing mechanisms of orbital-scale changes in winter rainfall over northwestern China during the Holocene

The moisture history in arid central Asia (ACA) differs from that in the Asian monsoon region during the Holocene. Much less is known about causes of Holocene moisture changes in ACA than Asian monsoon precipitation changes, hampering our understanding of their spatiotemporal differences. In this study, orbital-scale evolution of winter rainfall in northwestern China (a part of the core zone in ACA) during the Holocene and possible driving mechanisms are investigated using results from a long-term transient simulation performed by an atmosphere–ocean–sea-ice coupled general circulation model, the Kiel Climate Model, forced by orbital variations. Our results reveal a persistent wetting trend in northwestern China in winter throughout the Holocene, which is in response to winter insolation at mid-northern latitudes. Winter insolation can influence the rainfall via three ways. First, increasing latitudinal gradient of the incoming solar insolation at mid-latitudes strengthens the westerly intensity. Second, the evaporation is enhanced because of insolation-induced winter temperature rising, resulting in an increase in the air humidity. Intensified westerly winds and the increased water vapour together are conductive to enhance moisture transport towards northwestern China and thus increase winter precipitation in this area. Third, the increasing trend of winter insolation weakens the East Asian winter monsoon, which is favourable for the formation of rainfall via crippling the Siberian High that is beneficial for atmospheric lifting motion.

Impacts of snow and glaciers over Tibetan Plateau on Holocene climate change: Sensitivity experiments with a coupled model of intermediate complexity

[1] An Earth system model of intermediate complexity has been used to investigate the sensitivity of simulated global climate to gradually increased snow and glacier cover over the Tibetan Plateau for the last 9000 years (9 kyr). The simulations show that in the mid-Holocene at about 6 kyr before present (BP) the imposed ice sheets over the Tibetan Plateau induces summer precipitation decreases strongly in North Africa and South Asia, and increases in Southeast Asia. The response of vegetation cover to the imposed ice sheets over the Tibetan Plateau is not synchronous in South Asia and in North Africa, showing an earlier and, hence, a more rapid decrease in vegetation cover in North Africa from 9 to 6 kyr BP while it has almost no influence on that in south Asia until 5 kyr BP. The simulation results suggest that the snow and glacier environment over the Tibetan Plateau is an important factor for Holocene climate variability in North Africa, South Asia and Southeast Asia.

East Asian summer monsoon precipitation variations in China over the last 9500 years: A comparison of pollen-based reconstructions and model simulations

To better understand the long-term changes of the East Asian summer monsoon precipitation (Pjja), quantitative reconstructions and model simulations are needed. Here, we develop continental-scale pollen-based transfer functions for Pjja with weighted averaging–partial least squares (WA-PLS) regression and a Bayesian multinomial regression method. We apply these transfer functions to a set of fossil pollen data from monsoonal China for quantitatively reconstructing the Pjja changes over the last 9500 years. We compare the reconstructions with Pjja simulations from a coupled atmosphere–ocean–sea ice general circulation model (the Kiel Climate Model, KCM). The results of cross-validation tests for the transfer functions show that both the WA-PLS model (r2 = 0.83, root mean square error of prediction (RMSEP) = 112.11 mm) and the Bayesian model (r2 = 0.86, RMSEP = 107.67 mm) exhibit good predictive performance. We stack all Pjja reconstructions from northern China to a summary curve. The stacked record reveals that Pjja increased since 9500 cal. yr BP, attained its highest level during the Holocene summer monsoon maximum (HSMM) at ~7000–4000 cal. yr BP and declined to present. The KCM output and the reconstructions differ in the early-Holocene (~9500–7000 cal. yr BP) where the model suggests higher Pjja than the reconstructions. Moreover, during the HSMM, the amplitude of the Pjja changes (~20–60 mm above present) in simulations is lower than the reconstructed changes (~70–110 mm above present). The rising (declining) Pjja patterns in reconstructions before (after) the HSMM are more pronounced and fluctuating than in simulations. Other palaeohydrological data such as lake-level reconstructions indicate substantial monsoon precipitation changes throughout the Holocene. Our results therefore show that the KCM underestimates the overall amplitude of the Holocene monsoon precipitation changes.

Asynchronous variation in the East Asian winter monsoon during the Holocene

The East Asian winter monsoon (EAWM) is one of the most active components of the global climate system. Climate anomalies associated with the EAWM differ between extratropical and tropical regions due to the EAWMs meridional extent. Spatial differences in the EAWM variability on centennial and millennial time scales during the Holocene have not been well understood. This study describes Holocene spatiotemporal features of the EAWM based on comparisons of proxy records and climate simulations. The analysis specifically compared four proxy records located throughout China to assess the EAWMs spatial variability during the Holocene. These records indicate a stronger EAWM during the early Holocene than that during the late Holocene. The EAWM also shows a rapid, asynchronous decline from northwestern to southeastern China. The EAWM declined in northwestern China from 10 to 7.5 ka B.P., whereas the decline did not occur in southern China and the eastern Tibetan Plateau until 6–4.5 ka B.P. Coupled equilibrium and transient simulations of climate evolution during the Holocene indicate that the decline of the EAWM from 10 to 7.5 ka B.P. was probably caused by melting of Northern Hemisphere (NH) ice sheets and enhanced Atlantic meridional overturning circulation (AMOC). The decline of the EAWM from 6 to 4.5 ka B.P. over the eastern Tibetan Plateau and southern China is related to an abrupt increase in sea surface temperatures (SSTs) of the tropical western Indian Ocean. We therefore argue that the regional shift in EAWM intensity was probably related to a distinguishing response to high-latitude (NH ice sheets and AMOC) and low-latitude (tropical SSTs) forcings.

Association of the Northern Hemisphere circumglobal teleconnection with the Asian summer monsoon during the Holocene in a transient simulation

This paper provides another look at the response of the Asian summer monsoon (ASM) to insolation forcing and oceanic feedback during the Holocene, using a fully coupled general circulation ocean–atmosphere model forced by Earth’s orbital variations. The model results revealed a recurrent circumglobal teleconnection (CGT) pattern in the summertime (June–July–August) mid-latitude circulation of the Northern Hemisphere during the Holocene. The CGT index showed a decreasing trend before ~5 ka BP and a slight increasing trend afterwards, affected by the combined effects of summer insolation, Indian summer monsoon (ISM), North Atlantic and Indian Ocean–western Pacific Ocean sea surface temperature (SST). The CGT showed a close relationship with ASM precipitation and surface air temperature during the Holocene and, therefore, could act as a bridge linking the ASM to insolation, high-latitude forcing (North Atlantic SST), and low-latitude forcing (tropical Ocean SST). We emphasize that the mid-latitude atmospheric circulation has been a key factor for the evolution of the ASM during the Holocene. In addition, the CGT provides a viable explanation for the out-of-phase relationship in the moisture evolution but an in-phase relationship in the speleothem δ18O between arid central Asia and the ISM region during the Holocene.