Recent research from leading European institutions has uncovered a startling effect of human-induced climate change: it's literally making our days longer. Scientists at the University of Vienna and ETH Zurich have demonstrated that the melting of polar ice sheets and glaciers is slowing Earth's rotation at a rate not seen in over 3.6 million years. This unprecedented slowdown, driven by rising sea levels redistributing mass toward the equator, is lengthening the length of day (LOD) by approximately 1.33 milliseconds per century—a subtle but profound shift with far-reaching implications.

The study, published in the Journal of Geophysical Research: Solid Earth, bridges paleoclimate records with modern observations, highlighting how anthropogenic forces are altering fundamental planetary dynamics. For academics and researchers in geophysics, climatology, and Earth sciences, this work underscores the urgency of interdisciplinary collaboration in understanding—and mitigating—climate impacts.

Behind the Research: Key Players from Vienna and Zurich

At the heart of this discovery is Mostafa Kiani Shahvandi, a climate scientist and geophysicist from the University of Vienna's Department of Meteorology and Geophysics. Shahvandi led the effort, building on his prior work showing climate's dominant role in 21st-century LOD changes. Collaborating closely is Benedikt Soja, Professor of Space Geodesy at ETH Zurich's Department of Civil, Environmental and Geomatic Engineering. Their partnership exemplifies the strength of European academic networks, combining Vienna's expertise in paleoclimate modeling with Zurich's precision in space geodesy.

"The accelerated melting of polar ice sheets and mountain glaciers in the 21st century is raising sea levels, which slows Earth's rotation," Shahvandi explained, likening it to a figure skater extending her arms to slow her spin. Soja added, "This rapid increase implies modern climate change is unprecedented since the late Pliocene." Their team's prior publication in PNAS (2024) laid the groundwork, quantifying climate's growing influence on LOD variations.

Both universities are powerhouses in Earth system science. ETH Zurich, consistently ranked among Europe's top technical institutions, hosts advanced geodesy labs monitoring global rotation via satellite data. The University of Vienna excels in meteorology and geophysics, with state-of-the-art facilities for paleoclimate analysis. This collaboration highlights how joint EU-funded projects foster breakthroughs at the intersection of history and futurism.

Innovative Methodology: Fossils Meet Machine Learning

To peer into Earth's rotational past, the team turned to benthic foraminifera—tiny, single-celled marine organisms whose fossilized shells preserve chemical signatures of ancient ocean chemistry. By analyzing these from sediment cores spanning 3.6 million years, they reconstructed past sea-level fluctuations. "From the chemical composition of the foraminifera fossils, we infer sea-level changes and derive day-length variations mathematically," Shahvandi noted.

Handling the inherent uncertainties in paleodata required cutting-edge tools: a physics-informed diffusion model, a probabilistic deep learning algorithm. This AI approach embeds geophysical laws into neural networks, generating robust probabilistic reconstructions while accounting for data gaps. Modern LOD measurements from 2000–2020, sourced from space geodesy, served as benchmarks. The result? A continuous record linking Pleistocene ice ages to today's anthropogenic era.

This fusion of micropaleontology, geodesy, and AI represents a methodological leap, accessible to graduate students in geosciences across Europe. Tools like these are increasingly taught in Vienna's geophysics MSc and ETH's Earth Science programs, training the next generation for climate challenges.

Core Findings: A Rate Unmatched in Millions of Years

The numbers are striking: between 2000 and 2020, LOD increased at 1.33 ms/century, driven mainly by mass shifts from land (melting ice) to ocean via sea-level rise. This eclipses natural variations from the Quaternary (last 2.6 million years), when ice sheet cycles caused swings but at slower rates. Only circa 2 million years ago approached parity, during intense Northern Hemisphere glaciation.

• Current climate signal: Dominant over core-mantle and tidal effects.
• Historical peak: ~2 Ma ago, but brief and natural.
• Unprecedented since late Pliocene (3.6 Ma), signaling human fingerprint.

Projections warn that by 2100, climate-driven LOD changes could outpace lunar tides—the primary long-term driver—necessitating adjustments in global time standards like UTC.

The Physics: Ice Melt as Planetary Brakes

Earth's rotation obeys conservation of angular momentum. Polar ice, near the axis, minimizes moment of inertia for faster spin. Melting transfers mass equatorward via sea-level rise, increasing inertia and slowing rotation—like an ice skater's arms-out maneuver. Glaciers amplify this, as their meltwater flows to oceans.

Quantitatively, glacial isostatic adjustment (GIA)—Earth's rebound from past ice loads—interacts, but modern melt dominates. The team's models disentangle these, isolating climate's signal amid noise from mantle convection and atmospheric winds.

Photo by Limi change on Unsplash

Historical Deep Dive: Lessons from 3.6 Million Years

Extending beyond the ice ages, the study scans the Pliocene-Pleistocene transition. Natural forcings like Milankovitch cycles drove sea-level swings of 100+ meters, yet no era matched today's acceleration. This rarity underscores anthropogenic warming's velocity, outpacing even hyperthermal events like the PETM (though not covered here).

For European paleoclimatologists, this validates benthic δ¹⁸O records as LOD proxies, opening doors for refined GIA models used in IPCC assessments.

Real-World Implications: Beyond the Clock

Though 1.33 ms/century seems trivial (a second every 75,000 years), cumulative effects challenge precision tech. GPS satellites orbit assuming fixed LOD; discrepancies demand corrections, risking navigation errors in aviation, shipping, finance. Telecom, power grids syncing via UTC face disruptions.

Space agencies like ESA note LOD variability complicates missions; Vienna and Zurich's geodesy labs contribute to IERS monitoring. Academically, this spurs demand for experts in rotational dynamics, boosting PhD opportunities in Europe.

Future Outlook: 2100 and Beyond

Under high-emission scenarios, LOD acceleration could reach 2.5 ms/century by century's end, rivaling lunar drag (2.3 ms/century). Mitigating emissions curbs this; net-zero paths limit it to historical norms. Policymakers must integrate rotational impacts into climate models, as urged by Soja.

European Research Excellence in Action

This study shines a light on Europe's higher education prowess. ETH Zurich's geodetic observatories, funded by Swiss National Science Foundation, pair seamlessly with Vienna's paleoclimate archives. EU Horizon programs likely supported data sharing, fostering pan-continental science. Similar collaborations thrive at Max Planck, CNRS—positioning Europe as climate research leader.

For students, programs like Erasmus Mundus in Geophysics offer pathways to such work. AcademicJobs.com lists openings at these unis for postdocs in climate modeling.

Toward Solutions: Mitigating Rotational Impacts

Curbs on emissions via Paris Agreement slow ice loss, stabilizing LOD. Enhanced GIA modeling aids adaptation. Universities ramp up courses in climate geodesy; ETH's MSc in Geodesy trains specialists. Stakeholders—from ESA to IPCC—eye this for updated projections.

Photo by Markus Spiske on Unsplash

Related Research and Broader Context

Builds on 2024 PNAS paper by same team. Complements NASA GRACE data on mass redistribution. Aligns with IPCC AR6 on sea-level rise (0.2m since 1900, accelerating). Future work: Integrate core dynamics, extend to Holocene.