Professor Benjamin Horton is Dean of the School of Energy and Environment at City University of Hong Kong (CityUHK) and President’s Chair Professor of Earth Science. He is internationally recognised for pioneering research on sea-level change and coastal flood risk, combining field evidence, geochronology, and quantitative modelling to reconstruct the timing, magnitude, and rates of past sea-level rise and fall, and to strengthen projections of future coastal hazards under a warming climate.
Before joining CityUHK, Professor Horton was Director of the Earth Observatory of Singapore and Chair of the Asian School of the Environment at Nanyang Technological University (NTU), where he held the AXA Chair in Natural Hazards. He previously served as Professor of Marine Science at Rutgers University and Associate Professor at the University of Pennsylvania. He earned a BA (Hons) from the University of Liverpool and a PhD from Durham University.
A hallmark of his work is leadership of large international, interdisciplinary teams developing and testing sea-level models and reconstructions across all seven continents, clarifying links among ice-sheet dynamics, ocean–atmosphere variability, and vertical land motion. His research on coastal wetlands, carbon storage, and ecosystem stability has also strengthened the evidence base for nature-based adaptation.
Professor Horton contributes expertise to global climate and policy processes associated with the IPCC and COP, and regularly advises governments, agencies, and industry, including invited briefings to the Supreme Court Bench and the World Bank. He has published over 300 peer-reviewed articles and 12 books/edited volumes, supervised 28 PhD students and 27 postdoctoral researchers, and has an h-index of 91 with ~24,000 citations.
Sea Level as Earth’s Integrator: Ice Sheets, Earthquakes, Ecosystems, and the Future of Coastal Risk
Sea level is often treated as a single global number, yet it is anything but: it varies across space and time, responding to interacting processes in the cryosphere, ocean–atmosphere system, solid Earth, and biosphere. In this Axford Medal Lecture, I will argue that sea level is best understood as Earth’s integrator—a measurable outcome that links disciplines across AOGS, from paleoclimate and geodesy to coastal ecology, hazards, and societal risk. I will show how reconstructing past sea level—from decades to millennia—provides the long context needed to separate background variability from human-driven change and to test the mechanisms behind regional sea-level patterns.
My work begins with “archives” of former sea level preserved in tidal marshes, mangroves, and coral reefs. By combining these geological records with instrumental observations, advanced statistical analysis, and quantitative models, we can reconstruct how sea level has changed, why it changed, and what that implies for the future.
First, I will discuss efforts to standardize sea-level data collection and analysis across arctic, temperate, and tropical environments—an essential step for comparing sites and building robust syntheses. This approach underpinned the development of multiple regional databases of sea-level change since the Last Glacial Maximum across Africa, Asia, the Caribbean, Europe, North America, the Pacific Islands, Russia, and beyond, culminating in a unified global atlas. These resources have strengthened constraints on key physical processes such as glacial isostatic adjustment, sediment compaction, and tidal range, and they have helped evaluate why projection frameworks can differ and where major knowledge gaps remain. I will also highlight an example of sea level as a bridge to the human sciences: deglacial sea-level rise reshaped Southeast Asian landscapes in ways that influenced prehistoric migration and present-day genetic diversity.
Second, I will focus on the Common Era (last ~2,000 years), where short instrumental records capture only a narrow slice of climate variability. Using quantitative reconstructions from tidal-marsh microfossils, we continuous records that challenged earlier assumptions of near-stable preindustrial sea level. These reconstructions enabled: (i) attribution showing it is extremely likely that, without anthropogenic climate change, 20th-century sea-level rise would have been far smaller than observed; (ii) the first sea-level “budget” beyond the instrumental era for parts of the US Atlantic coast; and (iii) global estimates of when modern rates emerged above background variability. I will also illustrate how the same methods unlock tropical cyclone, earthquake and tsunami histories, revealing vertical land motions and long stratigraphic records of extreme events.
Third, I will connect sea-level rise to the resilience of coastal ecosystems that support fisheries, livelihoods, and blue-carbon storage. Holocene and modern syntheses reveal threshold behavior: tidal marshes and mangroves are far more likely to retreat than expand when sea-level rise approaches ~7 mm/yr, with evidence of growing ecological “deficits” beginning around ~4 mm/yr.
The take-home message for AOGS is clear: by reading sea level’s history quantitatively, we gain one of the strongest cross-disciplinary tools for anticipating coastal hazards, ecosystem tipping points, and adaptation pathways in a rapidly changing world.