Image: NASA Scientific Visualization Studio

What’s happening to Arctic sea ice is pretty straightforward: Earth is getting warmer, and everything’s melting. But on the other side of the planet, things are more complicated, as evidenced by the latest Antarctic sea ice slump that has scientists scratching their heads.

Antarctica rang in the new year with record-low levels of sea ice, according to an update released Thursday by the National Snow and Ice Data Center (NSDIC). On January 1, sea ice covered a paltry 2.11 million square miles of water in the Southern Ocean rimming the continent, which is 726,000 square miles below the long-term average for that date. This bizarre start to 2019 followed the most rapid December surge of sea ice loss on record, causing the Antarctic to eclipse record lows set just two years back, in the austral summer of 2016—2017.

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“Notably, the November to December 2016 period was considered an extreme excursion of Antarctic sea ice at the time,” the NSDIC wrote.

You might think: Duh, this is climate change. And that could be part of it! But an analysis conducted after the 2016-2017 sea ice crash—which culminated in a record seasonal sea ice minimum in March 2017—concluded that a spate of freak weather coinciding with an extremely negative phase of the Southern Annular Mode, where the westerly winds circling the continent migrate north, was to blame.

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In short, scientists pinned the last sea ice nosedive on natural variability. But it’s currently unclear what’s behind this year’s ice crash. Notably, University of Washington sea ice researcher Cecilia Bitz told Earther that the Southern Annular Mode is not strongly negative at the moment. Nor are we still nursing the hangover of a monster El Niño, as we were at the end of 2016.

“I think we have to go back to the drawing board a little bit,” Bitz told Earther.

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Sea ice concentration and anomaly maps for December 31, 2018
Image: NSIDC | Phil Reid, Australian Bureau of Meteorology

Bitz was reluctant to speculate as to whether the near back-to-back sea ice slumps are part of a new trend associated with climate change. While parts of Antarctica are definitely feeling the heat, until recently, Antarctic sea ice was growing slightly, reaching a record high in 2014. That doesn’t negate the warming trend, it simply speaks to the complexity of sea ice behavior in an environment impacted by both ocean currents and a giant continent.

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Son Ngheim, a senior research scientist at NASA’s Jet Propulsion Laboratory, told Earther that everything from winds driven by Antarctic continental topography to currents controlled by the shape of the Southern Ocean’s seafloor influences Antarctic sea ice. Bitz pointed to ice melting on the edges of the continent as a factor that could, paradoxically, help new sea ice form by preventing warmer deep waters from rising to the surface. Snowfall might also influence year to year variability in ice, according to NASA.

“Another point of low sea ice extent in the Antarctic this year still cannot be considered as a climatic trend,” Ngheim wrote Earther in an email, noting that spates of record lows occurred in the early part of the satellite record, as well.

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If nothing else, the icy weirdness is sure to spur additional research. NASA’s recently-launched ice-tracking satellite, ICESat-2, might be able to lend a hand, given its ability to measure sea ice thickness, a key indicator of ice age and health.

Meanwhile, global sea ice cover continues to decline, with rapid losses in the Arctic far eclipsing what’s happening around the southern continent.

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