The amount of sea ice circling Antarctica has suddenly plunged from a record high to record lows, and scientists are baffled by the turn of events.
Floating ice off the coast of the southern continent steadily increased from 1979 and hit a record high in 2014. But three years later, the annual average extent of Antarctic sea ice hit its lowest mark, wiping out three-and-a-half decades of gains — and then some, according to a NASA study of satellite data.
In recent years, "things have been crazy," said Mark Serreze, director of the National Snow and Ice Data Center at the University of Colorado in Boulder. He called the plummeting ice levels "a white-knuckle ride."
Serreze and other experts who weren't involved in the study said they didn't know whether the abrupt change is a natural blip that will smooth out over time or whether it's a sign that long-term global warming is finally catching up with the South Pole. Antarctica hasn't showed as much consistent warming as has been seen in the Arctic.
"But the fact that a change this big can happen in such a short time should be viewed as an indication that the Earth has the potential for significant and rapid change," University of Colorado ice scientist Waleed Abdalati said in an email.
In the polar regions, ice levels grow during the winter and shrink in the summer. Around Antarctica, sea ice averaged 4.9 million square miles (12.8 million square kilometers) in 2014. By 2017, that average fell to a record low of 4.1 million square miles (10.7 million square kilometers), according to the study published Monday in the Proceedings of the National Academy of Sciences.
The difference covers an area larger than Mexico. Losing that much in just three years "is pretty incredible" and faster than anything scientists have seen before, said study author Claire Parkinson, a climate scientist at NASA's Goddard Space Flight Center in Greenbelt, Md.
Antarctic sea ice increased slightly in 2018, but still was the second-lowest since 1979. Even though ice is growing this time of year in Antarctica, levels in the last two months were the lowest on record for May and June, even eclipsing 2017, according to the ice data center.
The melting of ice on the ocean surface doesn't change sea level.
Non-scientists who reject mainstream climate science had sought to deny or downplay the loss of Arctic sea ice by pointing to the increase in Antarctic sea ice. Scientists say that argument is flawed.
While the Arctic has shown consistent and generally steady warming and ice melt — with some slight year-to-year variation — Antarctica has had more ups and downs while sea ice extent has generally trended upward. That is probably in part due to geography, Parkinson and Serreze said.
The Arctic is a floating ice cap on an ocean penned in by continents. Antarctica is just the opposite — land surrounded by open ocean. That allows the ice to grow much farther out, Parkinson said.
When Antarctic sea ice was steadily rising, scientists pointed to shifts in wind and pressure patterns, ocean circulation changes or natural but regular climate changes like El Niño-Southern Oscillation.
Now, some of those explanations may not quite fit, making what happens next a mystery, Parkinson said.