Antarctica froze because the mantle pushed it uphill, a new Science paper argues

The mechanism is unglamorous and that is the point. Mantle waves, identified recently by the same group, travel beneath continents after plates begin to pull apart, and have already been invoked to explain diamond volcanoes and otherwise unexplained episodes of continental uplift ^[8]. Applied to East Antarctica, they raise a plateau capped by the Gamburtsev Mountains ^[9]. The paper's load-bearing number is the elevation threshold: about 2 km, the height at which mountain glaciers can form and grow, crossed across large parts of East Antarctica by roughly 45 million years ago ^[6]. That is about 11 million years before the ice sheet itself, which the source dates to around 34 million years ago ^{[4] [11]}.

The argument against a purely atmospheric account is one of symmetry rather than magnitude. Falling CO2 is widely accepted as an important trigger for Antarctic glaciation ^[12], but Gernon's objection is that a global forcing should have produced a roughly global response, and the Northern Hemisphere did not build large ice sheets until about the last five million years ^{[5] [13]}. That is a gap of roughly 29 million years between the two poles under, broadly, the same atmosphere ^[14]. Topography is the asymmetry available.

What the work actually delivers is a modelled surface history, not a measurement. The team reconstructed East Antarctica's surface evolution across 100 million years computationally ^[7], and the claim of success is that the models reproduce the three features that exist today: a two-kilometre coastal escarpment, the elevated plateau, and the inland mountains, in the words of co-lead Thea Hincks ^[10]. Reproducing present-day morphology from a chosen mechanism is a consistency test, not a discriminating one, and the paper is honest enough to be judged on whether independent elevation constraints agree with the 45-million-year crossing.

The consequence that reaches beyond palaeoclimate is about the bed. The East Antarctic Ice Sheet is the largest on Earth and holds enough water for roughly 52 metres of sea level rise ^[3]. If its origin depended on land standing above a threshold, then the height and shape of that land is a first-order control on the ice, and one that took more than 100 million years of deep-Earth work to build after Antarctica and Africa began separating in the Jurassic ^{[2] [1]}. Nothing in the paper says the ice needs the mantle to persist. It says the ice needed the mountains to start.

The uncomfortable read is the other direction. An ice sheet that owes its existence to elevation is an ice sheet whose stability argument cannot be made from CO2 alone, in either direction. The paper's own feedback loop makes the same point: once glaciers took hold, their bright surfaces reflected sunlight and cooled the region further ^[15]. A threshold crossed by slow uplift can be recrossed by other means, and the geology is not coming back to help on any timescale that matters.