Hai Cheng has over the past three decades been at the leading edge in the technical developments of U-series and other techniques to address many fundamental questions in paleoclimatology and global climate change research. As one of world-leading experts, he has focused largely on studies of cave records worldwide, and produced an incredible body of work, which has led to a clearer understanding of the Earth’s climate history on a wide range of timescales. The broad international significance of his contributions is attested by >620 peer-reviewed papers, including 29 in Nature and Science, >70 in Nature and Science Sub-Journals and PNAS (Google Scholar: H-index: 114 and citations: >81000,). He is a ‘Highly Cited Researches’ (continuously from 2014 to 2023, Thomson Reuters/Clarivate Analytics) and his current world citation rank is ~19^th in the geoscience field (up to the top five, ESI, Web of Science).

U-series dating systematics. Cheng’s most widely recognized technical achievement is his role in the persistent improvement of U-series dating techniques in U-Th, U-Pa and U-Pb dating systematics, including significant improvements in precision in age, large reductions in sample-size requirements, doubling of the time range appropriate for U/Th dating extending to older times, ²³¹Pa and ²³⁰Th dating systematics, and re-determinations of ²³⁰Th and ²³⁴U half-lives that have been widely accepted and used by the U-series community (e.g., Cheng et al., 1998, 2000, 2013a; Wang (his student) et al., 2022). These improvements impact a whole set of fields including geology, oceanography, atmospheric science, anthropology, archeology, and art history. During the last decade, for example, his group has provided innumerable U-series dates for his team and collaborators who have made groundbreaking discoveries on paleoclimatic changes globally, as well as anchoring archeological records of human evolution in Asia, Europe and elsewhere.

Cave records in numerous climate systems. On the basis of state-of-the-art U-series dating techniques, he has played a key role in the reconstruction of the longest climate history in numerous climate domains using cave records, including the longest East Asian (640 ka, Cheng et al., 2016) and longest Indian (280 ka, Kathayat (his student) et al., 2016) monsoon records, the longest Westerly climate record from West China (500 ka, Cheng et al., 2012), central Asia (150 ka, Cheng et al., 2016) and North America (335 ka, Cheng et al., 2019), and the longest record from the Amazon Basin (250 ka, Cheng at al., 2013b). These records are milestones in the paleoclimate reconstruction in these climate systems and have played an important role in understanding, correlating and calibrating global climate variability on various timescales. Before his and his colleagues’ work, the main long (tens to hundreds of thousands of years) climate records were largely dominated by marine and ice core records. Today, cave records have become the strong third leg of this paleoclimate triumvirate.

Global Monsoon and orbital theory of climate. Cheng and his colleagues have established a large number of cave records that characterize global monsoon variations on orbital-decadal timescales, particularly the Asian (Cheng et al., 2016) and South American (Cheng et al., 2013b) monsoon records. On the basis of new correlation strategies (Cheng et al., 2006, 2009, 2016, 2020, 2021a), he correlated the monsoon records to ice core and marine sediment records, thereby transferring precise cave chronologies to other archives with their own rich proxies of hydroclimate. As one of results, the cave data suggested that the Greenland and Antarctic ice-core chronologies require +320- and +400-year adjustments around the time of Heinrich Stadial 2, respectively (Dong (his student) et al., 2022), which is supported by extant volcanic evidence and radiocarbon ages. The correlations also provided the timing and sequence of events surrounding ice age terminations, proving new insights into the causes and mechanisms involved, especially the positive feedback mechanisms caused by perturbation of the ocean-atmosphere carbon and heat cycles by the initial melting of the ice sheets (Cheng et al., 2009, 2016). Because of the absolutely dated chronology of cave records, the comparison with Earth’s insolation kept clear of circular reasoning, which attests that the ice age terminations are separated by four or five precession cycles, supporting the idea that the 100-ka ice age cycle is an average of 4 or 5 discrete precession cycles (Cheng et al., 2016). Taking the advantage of cave records, he has coined two long-standing problems concerning orbital-scale variations of the Asian monsoon ever since 30 years ago as the “Chinese 100 kyr problem” and the “sea-land precession-phase paradox”, respectively regarding (1) discrepancies between the donminant 100-ka periodicity in Chinese loess magnetic susceptibility records and almost pure precession periodicity (20-ka) in Chinese cave δ¹⁸O records, and (2) the nearly opposite precession phases between Asian continental cave records and marine sediment records from oceans surrounding the Asian continent especially the Arabian Sea (Cheng et al., 2021b). He has well reconciled the discripencies with a new interpretation framework, the “monsoon system science”, and showed that the loess, marine, and cave records are complementary, rather than incompatible, with each record preferentially describing a certain aspect of Asian monsoon dynamics/thermodynamics (Cheng et al., 2021b, 2022). From the point of view of orbital dynamic and thermodynamic forcings and climate dual responses in low- and high-latitudes, he proposed blending the global monsoon with Milankovitch orbital theory of climate to formulate a new orbital hypothesis, which explains the observed dual nature of orbital hydrodynamics of the ice sheet and monsoon systems (Cheng et al., 2021b, 2022).

Andes to Amazon climate change. Cheng and his colleagues have carried out a series of work for more than ten years in the South American monsoon domain. His work precisely characterized the timing and nature of pluvial events of South American monsoon that broadly correlate with Heinrich Stadials in the North Atlantic and weak Asian monsoon events (Cheng et al., 2013b, 2020, 2021b). The cave records revealed a quasi-dipole pattern of orbital-scale precipitation between western and eastern Amazonia, and a modest increase in precipitation amount in western Amazonia but a significant drying in eastern Amazonia during the last glacial period. He then suggested that higher biodiversity in western Amazonia, contrary to ‘Refugia Hypothesis’, is maintained under relatively stable climatic conditions. In contrast, the glacial–interglacial climatic perturbations might have been instances of loss rather than gain in biodiversity in eastern Amazonia (Cheng et al., 2013b). He also showed that while the initial onset in the North Atlantic was essentially synchronous with Amazon rainfall increase, the initial termination of Heinrich Stadial 4 commenced significantly earlier in the South American monsoon, resulting in a large reduction in the Amazon River runoff hundres of years prior the termination of Heinrich Stadial 4. He thus hypothesized a new mechanism that the runoff reduction may contribute to the resumption of the Atlantic meridional ocean circulation, eventually triggering the Heinrich Stadial 4 termination (Cheng et al., 2021a).

Cultural changes and last stages of hominid evolution. In the research forefront of cultural changes and last stages of hominid evolution, cave work from Cheng and choleagues have shown links between rainfall changes and the rise and fall of Chinese dynasties/Neolithic cultures, for example, summer monsoon rainfall was plentiful during the Northern Song Dynasty when rice became the staple of the Chinese diet and the Chinese population tripled (Zhang, Cheng* et al., 2008); a plausible role of climate change in shaping the important chapters of the history of human civilization in the Indian subcontinent (Kathayat (his student), Cheng* et al., 2017, 2022); and chronological framework of the earliest known parietal art in the form of children’s hand- and footprints in Tibet (Zhang*, Bennett*, Cheng* et al., 2021); evidence that the Liangzhu culture in the Yangtze River Delta, one of the world’s most advanced Neolithic cultures, collapsed within a short and anomalously wet period around 4300 years ago (Zhang*, Cheng* et al., 2021); an important role of climate in the rise and fall of the Neo-Assyrian Empire (Sinha et al., 2019); and many others.

¹⁴C calibration and radiocarbon changes in the atmosphere. Cheng had played a leading role in the ¹⁴C calibration using speleothems, which provided a critical ¹⁴C dataset for reconstruction of atmospheric ¹⁴C back to the ¹⁴C dating limit of around 54,000 years ago (Cheng et al., 2018). A precise and accurate ¹⁴C calibration has been considered the Holy Grail of radiocarbon dating ever since Nobel Laureate Willard Libby originally developed the method about 70 years ago. The older half of the timescale lacked precision and accuracy for a long time. In collaboration with R.L. Edwards & J. Southon and Chinese colleagues, he completed the full calibration of the radiocarbon timescale with reasonable precision and accuracy via paired measurements of U-Th and ¹⁴C ages of two stalagmites from the now iconic Hulu cave (Cheng et al., 2018). The new calibration adjusts calibrated ages for much of the older half of the ¹⁴C timescale, therefore affecting a whole set of ages, such as estimated length of overlap between Neaderthals and Homo sapiens in Europe. The new dataset also allows us to link the ¹⁴C changes with the oceanic carbon cycle and in the geomagnetic field, for instance, the high atmospheric ¹⁴C associated with the Laschamps magnetic excursion as well as Heinrich Stadial 4.

Recent developments. Cheng and his students/postdocs have developed triple-oxygen-isotope analytical technique for carbonate, and obtained for the first time a number of novel ¹⁷O_excess datasets from cave and marine samples, which provided new insights (additional to δ¹⁸O) into hydroclimate changes and underlying dynamics in many climate systems (Sha (his student) et al., 2020, 2021, 2022, 2024). In the past a few years, Cheng and his students extended cave climate records substantially beyond the U-Th dating upper limit (~650 ka) to the Late Pliocene (~3.6 Ma ago) using U-Pb dating techniques (Wang (his student) et al., 2022), leading to potential breakthroughs in the research forefront of the Earth’s long-term climate evolution (Niu (his student) et al., 2024).

程海教授在过去三十年里一直处于铀系技术发展的前沿。他发展了国际领先水平的U系质谱测量技术，提供了许多重要和精确的晚第四纪气候变化绝对年代尺标、以及精确测量海水等地质样品中一些极微量元素及其同位素的技术方法，这些技术被广泛应用于古气候学、古海洋学和全球气候变化研究中的许多基本问题的研究。他最广为人知的技术成就是在²³¹Pa和²³⁰Th测年系统学中对U系测年技术的改进，包括重新测定²³⁰Th和²³⁴U半衰期，该成果已被铀系测年领域广泛接受和使用。 

程海教授还是国际领先的石笋古气候研究专家之一，取得了许多突破性的科学发现。基于最先进的U系测年技术，他在利用石笋记录重建不同区域不同时间尺度的气候历史方面发挥了重要作用，其中包括最长的东亚（640 ka）和印度（280 ka）季风石笋记录，最长的西风带气候记录包括中国西部（500 ka）、中亚（350 ka）和北美（335 ka）的石笋记录，最长的亚马逊流域石笋记录（250ka）。这些记录是重建不同气候系统古气候变化的里程碑，在理解、关联和校准全球气候变化方面发挥了重要作用。同时，他在利用石笋进行¹⁴C校准中发挥了主导作用，为大气¹⁴C的重建提供了一个关键的¹⁴C数据集，并将校正极限扩展到¹⁴C的定年极限（约54000年）。最近，由他引导的西安交通大学同位素实验室建立了高精度石笋三氧同位素（¹⁶O-¹⁷O-¹⁸O）分析技术，并首次获得了一组石笋¹⁷O_excess数据，将新的¹⁷O_excess指标与δ¹⁸O指标结合，用以研究洞穴石笋古气候变化，为水文气候变化及潜在动力学提供了新的见解。

他为众多合作单位提供了大量的²³⁰Th测年数据，这些精确的年代数据被应用于亚洲、南美洲、阿拉伯、非洲、北美、中美洲、欧洲、热带太平洋等区域的不同时间尺度的古气候变化的突破性研究中，同时为中国、印度及其他区域的古人类进化等考古研究提供了“金钉子”年代。

程海教授的贡献在国际上具有广泛的意义，他在国际期刊上发表论文620余篇,含29篇Science、Nature和70余篇PNAS及Nature和Science子刊文章。论文被引用8.1万余次(H-因子114，Google Scholar)。他在2014-2023年连续入选汤森路透/科睿唯安（Thomson Reuters/Clarivate Analytics）全球高被引科学家和爱思唯尔（Elsevier）中国高被引学者,在地球科学领域（ESI，科学网）的世界引文排名是第20位(最高前5），2022年当选奥地利科学院外籍院士，获欧洲地球科学联合会（EGU）米兰科维奇奖章等国际荣誉，得到国际学术界的高度认可。