Posted for Quirin Schiermeier

Two papers in Nature today shed light on the possible future behaviour of the West Antarctic ice sheet (WAIS), complete loss of which would produce a worldwide rise in sea level of around 5 metres.

The two teams – one using a high-resolution ice sheet model, the other looking at glacial records contained in seafloor sediment – independently arrive at similar conclusions: The WAIS has intermittently melted during the past five million years or so, and its oscillations follow a 40,000 year cycle in the Earth’s axial tilt. Small variations in tilt – called the obliquity of the ecliptic – result in reduced or increased amounts of sunlight reaching the poles, thus pacing the succession of ice ages and warm periods.

During the warmest interglacial phases the WAIS has in the past episodically collapsed entirely, the studies suggest (Editor’s Summary). Global temperatures around 3 degrees Celsius warmer than today seem to have sufficed to initiate the transition from grounded ice to open waters in the Ross Bay, reports the team led by Tim Naish of Victoria University in Wellington, New Zealand, who analysed a sediment core recovered from beneath the Ross ice shelf by the ANDRILL programme. Model simulations suggest the transition from full glacial to intermediate state (such as today’s) to nearly ice-free conditions can proceed rapidly. In the warmest ‘super-interglacials’, such as one around 1.07 million years ago, it took only around thousand years for the WAIS to collapse, report David Pollard and Robert DeConto of Pennsylvania State University in the second study.

Continue reading “Antarctica: Memento melting” on Nature’s Climate Feedback blog»