As levels of the greenhouse gas carbon dioxide rise and warm the globe, Antarctica’s ice will become more vulnerable to cycles on an astronomical scale, particularly the tilt of our planet is as it spins around its axis.

New research finds that over 30 million years of history, Antarctica’s ice sheets responded most strongly to the angle of Earth’s tilt on its axis when the ice extends into the oceans, interacting with currents that can bring warm water lapping at their margins and leading to increased melting. The effect of the tilt peaked when carbon dioxide levels were similar to what scientists predict for the next century, if humans don’t get emissions under control. [Collapsing Beauty: Image of Antarctica’s Larsen Ice Shelf]

As carbon dioxide levels push past 400 parts per million, the climate will become more sensitive to the Earth’s tilt, or obliquity, researchers reported Jan. 14 in the journal Nature Geoscience.

“Really critical is the amount of carbon dioxide in the atmosphere,” said study co-author Stephen Meyers, a paleoclimatologist at the University of Wisconsin, Madison.

A scenario of high carbon dioxide and high tilt angle could be particularly devastating to the the miles-thick ice covering Antarctica.

Reconstructing the past

Over about 40,000 years, the Earth’s axis tilts back and forth “like a rocking chair,” Meyers said. Currently this obliquity is about 23.4 degrees, but it can be as little as 22.1 degrees or as much as 24.5 degrees.

The tilt matters for when and where sunlight hits the globe, and can thus influence climate.

To reconstruct a history of how Antarctica’s ice has responded to this tilt, Meyers and his co-authors used a few sources of information on the Earth’s climate past. One source was calcium carbonate from the ocean bottom, left behind by single-celled organisms called benthic foraminifera. These organisms excrete a calcium carbonate shell around themselves, locking in a global, continuous record of the chemistry of the oceans and atmosphere.

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