The Earth is not a flawless sphere. Due to centrifugal force generated by its rotation, the planet is slightly flattened at the poles and bulges around the equator. However, recent research reveals that this shape is undergoing subtle transformations driven by the climate crisis.

A study led by Prof. Christophoros Kokkakis from the Department of Geodesy and Surveying at Aristotle University of Thessaloniki in Greece was published on September 9 in the international journal Journal of Geophysical Research (DOI: 10.1029/2026JB034224).

Traditionally, shifts in Earth’s flattening have been tracked via satellite gravimetry, which measures Earth’s gravitational field. Yet, this approach captures both land deformation and mass redistribution simultaneously—mixing up the rebound of landmasses where ice has vanished with the shifting weight of melted water flowing into the oceans. Consequently, isolating pure physical changes to the Earth's surface geometry has proven challenging.

To overcome this, Prof. Kokkakis utilized Global Navigation Satellite Systems (GNSS) data. By measuring the travel time of radio signals from multiple satellites to ground-based stations, GNSS directly tracks the geometric shifts of the Earth's surface—recording precisely how much the ground rises or sinks.

The analysis revealed two contrasting ongoing trends.

First, the uplift rate of polar land surfaces accelerated from an annual average of about 0.5 mm between 1997 and 2000 to approximately 1 mm between 2011 and 2015. This significantly exceeds the sub-0.3 mm per year rate typically explained by "glacial isostatic adjustment"—the slow rebound of the Earth’s crust following the last ice age.

Prof. Kokkakis attributed this phenomenon to the shrinking ice sheets of Greenland and Antarctica, which have lifted a massive weight off the Earth's crust. Released from this heavy burden, the land is rebounding upward.

Simultaneously, land surfaces around the equator are subsiding at a comparable rate as melted water migrates toward lower-latitude oceans, pressing down on the seafloor. As the polar radius increases and the equatorial radius decreases, the physical flattening of the solid Earth is gradually reducing, making the planet slightly rounder than before.

However, a paradoxical picture emerges when examining the Earth through its gravitational field. Because melted polar ice flows toward the equator as ocean water, the planet's mass distribution has shifted more heavily toward low latitudes. Measured by its gravitational field, the Earth has actually become more bulging at the center.

Commenting on these findings, Prof. Kokkakis explained in the paper that while it may seem contradictory for the gravitational flattening to increase while the physical land flattening decreases, both effects are physically compatible and occur simultaneously.

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