Why Did Earth Experience Climate Swings Without Ice Sheets? Scientists Identify Orbital Wobbles as the Driver

New findings explain abrupt climate swings in ancient ice-free worlds and inform future warming scenarios

BEIJING, Jan. 22, 2026 /PRNewswire/ -- Earth's slow axial wobbles—known as precession cycles—do not just shape long-term climate trends. A new study led by researchers from China, Belgium, and Austria shows that these orbital motions can also spark climate swings on thousand-year timescales, even in ancient ice-free greenhouse worlds. The findings suggest that rapid climate variability may be an intrinsic feature of Earth's climate system and could recur under future warming.

Abrupt climate shifts are well documented in Earth's history and are commonly associated with ice-sheet dynamics during past ice ages. However, how similar millennial-scale climate variability could occur during warm "greenhouse" periods—when large ice sheets were absent—has remained a long-standing puzzle.

Now, an international research team led by Professor Chengshan Wang at the China University of Geosciences (Beijing) provides a compelling new clue. Working with collaborators from Belgium, Austria, and China, the team shows that Earth's precession cycles—slow wobbles in its rotational axis—can naturally generate abrupt millennial-scale climate fluctuations even under ice-free conditions. Their findings were published in the Nature Communications journal on November 27, 2025.

The study is based on sediment cores recovered from China's Songliao Basin, deposited about 83 million years ago during the Late Cretaceous—a classic greenhouse interval marked by high atmospheric CO₂ levels and an absence of ice sheets. The cores were obtained through the Cretaceous Continental Scientific Drilling Project, an international initiative launched in 2006.

Earth's axial precession alters how solar radiation is distributed between the hemispheres. The researchers show that interactions between precession-related solar forcing and Earth's orbital geometry can amplify climate variability, generating recurring humid–arid climate oscillations every few thousand years even without ice sheets.

Geochemical and sedimentological evidence from the Songliao Basin reveals pronounced climate oscillations with periodicities of about 4–5 thousand years, consistent with theoretical predictions of precession-driven insolation changes. These results demonstrate that even under warm, ice-free conditions, Earth's climate repeatedly fluctuated between arid and humid states.

"During the Late Cretaceous, atmospheric CO₂ levels reached about 1,000 parts per million—comparable to projections for the end of this century," says Prof. Michael Wagreich, a paleoclimatologist at the University of Vienna. "This makes the Cretaceous greenhouse climate a meaningful analogue for understanding Earth's future."

"Because Earth's orbital configuration will remain stable for billions of years, similar high-frequency climate oscillations could also emerge under future warming scenarios," first author Zhifeng Zhang concludes.

For a visual overview of the findings: https://www.youtube.com/watch?v=6Vjl3YOa0Lg

Reference
DOI: https://doi.org/10.1038/s41467-025-66219-4
Title of original paper: Precession-induced millennial climate cycles in greenhouse Cretaceous
Journal: Nature Communications

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SOURCE China University of Geosciences