Researchers startled by a sudden nosedive in Antarctic sea ice since 2014—at a rate that makes current Arctic melting look slow by comparison—are pointing to the likelihood of further accelerated melting at both poles as yet another reason to limit average global warming to 1.5ºC.

A study of satellite data just published in the Proceedings of the National Academy of Sciences found that Antarctic ice cover has shrunk precipitously over the last half-decade, losing “as much sea ice in four years as the Arctic lost in 34” and reaching a record low in 2017, reports the Guardian.

While the loss of sea ice alone does not contribute to sea level rise, a shrinking Antarctica is still very bad news for the global climate, as the loss of a bright, reflective surface further contributes to rising temperatures.

Just what is driving the sudden Antarctic melt remains something of a mystery, The Guardian states. While there is a clear correlation between global warming and the Arctic’s melting, such is not the case with its southern cousin which, rather than being an ocean encircled by warming continents, is a fearsomely cold continent insulated from warming air by strong westerly winds.

Contributing to the puzzle is the fact that the sharp drop in Antarctic sea ice since 2014 comes on the heels of a 40-year increase. One likely contributing factor, said study author Claire Parkinson of NASA’s Goddard Space Flight Center, was the 2016 El Niño, which gave an added boost to anthropogenic global warming.

While “the Arctic has become a poster child for global warming,” she added, the sudden Antarctic melt has researchers wondering if “some huge acceleration in the rate of decrease in the Arctic” is looming.

A separate assessment of the Antarctic Peninsula conducted by the London, UK-based Grantham Institute reinforces the urgency of setting 1.5ºC as the upper limit on average warming. While that threshold will still “likely result in a 50 to 150% increase in the number of days a year the frozen peninsula spends above zero,” reports the BBC, that outcome pales compared to an overshoot scenario.

Critically, keeping below 1.5ºC “should allow the peninsula to hang on to its remaining ice shelves,” which in turn would keep the continent’s massive glaciers from collapsing into the ocean, an event that would trigger considerably more sea level rise.