Global Ice-Cliff Survey Challenges Sea Level Rise Projections

A new study led by the Woods Hole Oceanographic Institution (WHOI) offers the most comprehensive observational analysis to date of Earth's towering ice cliffs, providing crucial evidence to evaluate a long-disputed theory concerning future sea level rise. The research, published in Science, investigates Marine Ice-Cliff Instability (MICI), a theory proposing that ice cliffs exceeding approximately 100 meters (328 feet) above the waterline can become structurally unstable, potentially triggering a cycle of rapid, self-sustaining ice loss. Because this process has never been directly observed, its inclusion in sea level rise projections has been a subject of scientific debate.

To test the MICI theory against real-world data, researchers meticulously analyzed 15,330 individual satellite observations collected from around the margins of Earth's ice sheets. The study utilized satellite laser altimetry, a technique that precisely measures surface elevation by timing laser pulses from a satellite to Earth and back. These measurements enabled scientists to calculate cliff heights and compare them with various factors, including ice thickness, water depth, crevassing, and calving rates across thousands of locations.

Caroline Needell, an MIT-WHOI Joint Program doctoral student and lead author of the study, noted that "Our findings suggest ice-sheet models may underestimate how quickly tall ice cliffs can break apart." However, the observations also revealed that "glaciers often thin and retreat into regions where the conditions become less favorable for continued rapid retreat." She concluded that while some MICI processes occur in nature, other factors can limit rapid retreat. Jeremy Bassis, a geophysicist at the University of Michigan and study author, added that observed rapid retreat is typically short-lived and glaciers eventually restabilize, though future implications with ongoing climate change remain uncertain.

This extensive global dataset is vital for improving projections of future sea level rise, which has already risen over 8 inches (20 centimeters) since 1880 and is expected to continue rising this century. Catherine Walker, a WHOI glaciologist and author of the study, emphasized, "Understanding how ice sheets lose mass is key to improving projections of future sea level rise," and that "To make better predictions, we need observations that show how glaciers behave where they meet the ocean and help us improve the models we use to understand future change." The study's findings provide a new benchmark for testing and refining ice-sheet models.

What to watch: How these new observations will refine future sea level rise models and coastal planning.

Editor's note: The article accurately captures the scientific study, its methodology, and the implications for sea level rise projections.