Zhongshi Zhang

Sea Surface Temperature of the mid-Piacenzian Ocean: A Data-Model Comparison

The mid-Piacenzian climate represents the most geologically recent interval of long-term average warmth relative to the last million years, and shares similarities with the climate projected for the end of the 21st century. As such, it represents a natural experiment from which we can gain insight into potential climate change impacts, enabling more informed policy decisions for mitigation and adaptation. Here, we present the first systematic comparison of Pliocene sea surface temperature (SST) between an ensemble of eight climate model simulations produced as part of PlioMIP (Pliocene Model Intercomparison Project) with the PRISM (Pliocene Research, Interpretation and Synoptic Mapping) Project mean annual SST field. Our results highlight key regional and dynamic situations where there is discord between the palaeoenvironmental reconstruction and the climate model simulations. These differences have led to improved strategies for both experimental design and temporal refinement of the palaeoenvironmental reconstruction.

Arctic sea ice and Eurasian climate: A review

The Arctic plays a fundamental role in the climate system and has shown significant climate change in recent decades, including the Arctic warming and decline of Arctic sea-ice extent and thickness. In contrast to the Arctic warming and reduction of Arctic sea ice, Europe, East Asia and North America have experienced anomalously cold conditions, with record snowfall during recent years. In this paper, we review current understanding of the sea-ice impacts on the Eurasian climate. Paleo, observational and modelling studies are covered to summarize several major themes, including: the variability of Arctic sea ice and its controls; the likely causes and apparent impacts of the Arctic sea-ice decline during the satellite era, as well as past and projected future impacts and trends; the links and feedback mechanisms between the Arctic sea ice and the Arctic Oscillation/North Atlantic Oscillation, the recent Eurasian cooling, winter atmospheric circulation, summer precipitation in East Asia, spring snowfall over Eurasia, East Asian winter monsoon, and midlatitude extreme weather; and the remote climate response (e.g., atmospheric circulation, air temperature) to changes in Arctic sea ice. We conclude with a brief summary and suggestions for future research.

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.

Greenland ice sheet contribution to future global sea level rise based on CMIP5 models

Sea level rise (SLR) is one of the major socioeconomic risks associated with global warming. Mass losses from the Greenland ice sheet (GrIS) will be partially responsible for future SLR, although there are large uncertainties in modeled climate and ice sheet behavior. We used the ice sheet model SICOPOLIS (SImulation COde for POLythermal Ice Sheets) driven by climate projections from 20 models in the fifth phase of the Coupled Model Intercomparison Project (CMIP5) to estimate the GrIS contribution to global SLR. Based on the outputs of the 20 models, it is estimated that the GrIS will contribute 0–16 (0–27) cm to global SLR by 2100 under the Representative Concentration Pathways (RCP) 4.5 (RCP 8.5) scenarios. The projected SLR increases further to 7–22 (7–33) cm with 2×basal sliding included. In response to the results of the multimodel ensemble mean, the ice sheet model projects a global SLR of 3 cm and 7 cm (10 cm and 13 cm with 2×basal sliding) under the RCP 4.5 and RCP 8.5 scenarios, respectively. In addition, our results suggest that the uncertainty in future sea level projection caused by the large spread in climate projections could be reduced with model-evaluation and the selective use of model outputs.

Simulated warm periods of climate over China during the last two millennia: The Sui-Tang warm period versus the Song-Yuan warm period

A 2000 year simulation forced by the external forcings of the last two millennia is carried out with the Community Earth System Model. We compare climate changes over China between the peak Sui-Tang warm period (Sui-TangWP; 650–700 A.D.) and Song-Yuan warm period (Song-YuanWP; 950–1000 A.D.), which were two key culturally, economically, and educationally prosperous eras in Chinese history. The simulation indicates warm conditions in both periods, but the warmth is mainly seen in East China in the peak Sui-TangWP, and over the whole of China in the peak Song-YuanWP. The warming in the peak Sui-TangWP is attributed to the localized increase of atmospheric net energy with favorable heat transport, whereas the peak Song-YuanWP results from the increase of global solar radiation. The annual mean precipitation anomalies in the peak Sui-TangWP exhibit a meridional dipole pattern over East China, with enhanced precipitation in the region south of the Yangtze River and decreased precipitation to the north. In the peak Song-YuanWP, the precipitation enhances over most parts of China. The precipitation anomalies are largely attributed to the water vapor transport anomalies associated with monsoon circulation changes. The simulated climate changes are broadly consistent with reconstructions, but the magnitude is greatly underestimated. Based on the simulation and reconstructions, we suggest that the Sui-TangWP may have been a regional phenomenon in China, while the Song-YuanWP was a reflection of global/hemispheric-scale warm events that took place at the same time.

Tropical Cyclone Genesis Factors in a Simulation of the Last Two Millennia: Results from the Community Earth System Model

AbstractUsing a coupled global climate model, Community Earth System Model (CESM), the authors investigate the response of tropical cyclone (TC) genesis factors (i.e., potential intensity, vertical wind shear, midtropospheric moisture content, and absolute vorticity) to external forcings in the last two millennia (L2M). They then examine how the large-scale conditions that favor TC activity varied using a genesis potential index (GPI). These large-scale genesis factors generally exhibit no long-term trend in the simulation of the L2M prior to the industrial revolution, and the spread in the interannual variability lies within a small window. The estimated TC activity is highly variable from region to region on multidecadal time scales. Conditions appear to be more favorable for TC genesis in the twentieth century in the Northern Hemisphere relative to earlier centuries of the L2M. Additionally, conditions in this simulation are not more favorable for TC formation during the Medieval Climate Anomaly (AD 10...

Causes of mid-Pliocene strengthened summer and weakened winter monsoons over East Asia

The mid-Pliocene warm period was the most recent geological period in Earth’s history that featured long-term warming. Both geological evidence and model results indicate that East Asian summer winds (EASWs) strengthened in monsoonal China, and that East Asian winter winds (EAWWs) weakened in northern monsoonal China during this period, as compared to the pre-industrial period. However, the corresponding mechanisms are still unclear. In this paper, the results of a set of numerical simulations are reported to analyze the effects of changed boundary conditions on the mid-Pliocene East Asian monsoon climate, based on PRISM3 (Pliocene Research Interpretation and Synoptic Mapping) palaeoenvironmental reconstruction. The model results showed that the combined changes of sea surface temperatures, atmospheric CO2 concentration, and ice sheet extent were necessary to generate an overall warm climate on a large scale, and that these factors exerted the greatest effects on the strengthening of EASWs in monsoonal China. The orographic change produced significant local warming and had the greatest effect on the weakening of EAWWs in northern monsoonal China in the mid-Pliocene. Thus, these two factors both had important but different effects on the monsoon change. In comparison, the effects of vegetational change on the strengthened EASWs and weakened EAWWs were relatively weak. The changed monsoon winds can be explained by a reorganization of the meridional temperature gradient and zonal thermal contrast. Moreover, the effect of orbital parameters cannot be ignored. Results showed that changes in orbital parameters could have markedly affected the EASWs and EAWWs, and caused significant short-term oscillations in the mid-Pliocene monsoon climate in East Asia.

Enhanced intensity of global tropical cyclones during the mid-Pliocene warm period

Significance To better understand how tropical cyclones (TCs) may respond to future warming, we explore the behavior of TCs during the mid-Pliocene warm period (∼3 Ma), which shares characteristics of projected warmer climate. Our TC-permitting numerical simulations predict enhanced global-average peak TC intensity, longer duration, increased power dissipation, and a poleward migration of the location of peak intensity during the mid-Pliocene, although there are regional differences in the magnitude and statistical power of the climate/TC relationships. Our results share similarities with global TC changes observed during recent global warming and in most future projections and provide a window into the potential TC activity that may be expected in a warmer world. Given the threats that tropical cyclones (TC) pose to people and infrastructure, there is significant interest in how the climatology of these storms may change with climate. The global historical record has been extensively examined, but it is short and plagued with recurring questions about its homogeneity, limiting its effectiveness at assessing how TCs vary with climate. Past warm intervals provide an opportunity to quantify TC behavior in a warmer-than-present world. Here, we use a TC-resolving (∼25 km) global atmospheric model to investigate TC activity during the mid-Pliocene warm period (3.264−3.025 Ma) that shares similarities with projections of future climate. Two experiments, one driven by the reconstructed sea surface temperatures (SSTs) and the other by the SSTs from an ensemble of mid-Pliocene simulations, consistently predict enhanced global-average peak TC intensity during the mid-Pliocene coupled with longer duration, increased power dissipation, and a poleward migration of the location of peak intensity. The simulations are similar to global TC changes observed during recent global warming, as well as those of many future projections, providing a window into the potential TC activity that may be expected in a warmer world. Changes to power dissipation and TC frequency, especially in the Pacific, are sensitive to the different SST patterns, which could affect the viability of the role of TCs as a factor for maintaining a reduced zonal SST gradient during the Pliocene, as recently hypothesized.

Comparison of the climate effects of surface uplifts from the northern Tibetan Plateau, the Tianshan, and the Mongolian Plateau on the East Asian climate

Surface uplifting from the northern East Asian mountains has had an important effect on the evolution of the East Asian climate since the Late Miocene; however, the uplifting climate effects from each of these mountains remain unclear. This paper compares the climate effects of surface uplifts from the northern Tibetan Plateau (TP), the Tianshan, and the Mongolian Plateau (MP) on the East Asian climate. Our model results indicate that each of these mountains has different climate effects along an uplifting sequence from south to north. Compared to the combined surface uplifts from the northern TP and the Tianshan, the last surface uplift from the MP made a greater contribution to the decreased annual precipitation over inland Asia north of ~45°N and strengthened summer middle tropospheric westerly wind on its north side; furthermore, it made a comparable contribution to the intensified winter low-level (850 hPa) northwesterlies in northern East Asia and intensified winter middle tropospheric westerly wind over the region from East Asia to the northwestern Pacific. However, different uplift scenarios influenced these uplifting climate effects. For example, if the MP rose without the northern TP and the Tianshan, the uplifting climate effects of the MP described above largely weakened. In comparison, the combined further surface uplifts of the northern TP and the Tianshan had a more marked regional climate effect, particularly for the winter monsoon wind, and summer and winter middle tropospheric westerly wind.

Drivers and mechanisms for enhanced summer monsoon precipitation over East Asia during the mid-Pliocene in the IPSL-CM5A

A comparative analysis of East Asian summer monsoon (EASM) precipitation is performed to reveal the drivers and mechanisms controlling the similarities of the mid-Pliocene EASM precipitation changes compared to the corresponding pre-industrial (PI) experiments derived from atmosphere-only (i.e. AGCM) and fully coupled (i.e. CGCM) simulations, as well as the large simulated differences in the mid-Pliocene EASM precipitation between the two simulations. The area-averaged precipitation over the EASM domain is enhanced in the mid-Pliocene compared to the corresponding PI experiments performed by both the AGCM (LMDZ5A) and the CGCM (IPSL-CM5A). Moisture budget analysis reveals that it is the surface warming over East Asia that drives the area-averaged EASM precipitation increase in the mid-Pliocene in both simulations. The surface warming increases the atmospheric moisture content, as revealed by an increase in the thermodynamic component of vertical moisture advection, resulting in enhanced mid-Pliocene EASM precipitation compared to PI in both simulations. Moist static energy diagnosis identifies the combined effect of enhanced zonal thermal contrast and column-integrated meridional stationary eddy velocity