An area of West Antarctica more than twice the size of California partially melted in 2016 when warm winds forced by an especially strong El Niño blew over the continent, a group of researchers report in the June 15 issue of the journal Nature Communications. The study was led by Julien Nicolas, a research associate at the Byrd Polar and Climate Research Center (BPCRC) at The Ohio State University.

The warm spell persisted for more than two weeks in January 2016. Satellite data revealed the presence of liquid water over most of the Ross Ice Shelf—a thick platform of floating ice that channels about a third of the ice flowing from the West Antarctic Ice Sheet into the ocean. While researchers have been gathering evidence for years that warm ocean water is melting West Antarctic ice shelves from beneath, this is one of the first times they’ve been able to document how warm air could also cause widespread melting from above.

What makes this event particularly interesting to scientists is that it took place during one of the strongest El Niño events on record. “This conjunction of events was no coincidence,” Nicolas said. Indeed, El Niños favor weather patterns that often steer warm air towards West Antarctica. However, strong westerly winds blowing over the ocean to the north of the continent usually keep the warmer air at bay.

BPCRC senior research associate Aaron Wilson, also a coauthor on the study, used climate models to show that melt events in West Antarctica are more likely to occur during El Niño conditions, especially when westerly winds are weak. What makes this January 2016 event unique, he explained, is that the warming occurred despite strong westerly winds. “Without the strong westerlies, it’s likely there would have been much more melting,” Wilson said.

Coauthor David Bromwich, a senior research scientist at BPCRC and professor with OSU Department of Geography, explained it this way, “In West Antarctica, we have a tug-of-war going on between the influence of El Niños and the westerly winds, and it looks like the El Niños are winning,” he said. “It’s a pattern that is emerging. And because we expect stronger, more frequent El Niños in the future with a warming climate, we can expect more major surface melt events in West Antarctica.”

Co-authors on the paper include former OSU master’s student and BPCRC member Jonathan Wille, who served as a weather observer in West Antarctica in January 2016, in addition to researchers at Brookhaven National Laboratory, Scripps Institution of Oceanography, Argonne National Laboratory, The Pennsylvania State University, Australian Bureau of Meteorology, and Los Alamos National Laboratory.

Read the complete article by Pam Frost Gorder. Additional coverage was provided by the Washington Post and CNN.