For decades, the sea ice surrounding Antarctica has been increasing. Now, an analysis of satellite data led by NASA finds that the continent is experiencing a “precipitous decline” bringing total sea ice extent to the lowest it has been in 40 years, wiping out 35 years of overall ice increases in just a few years.

The space agency has been tracking changes in Antarctica’s sea ice since the late 1970s, recording three decades of gradual, albeit uneven, increases in sea ice coverage that reached a high in 2014. These increases were puzzling scientists, particularly in the face of climate change, with explanations ranging from connections with the ozone hole to El Niño trends and basal meltwater from ice shelves – none of which have yielded a consensus as to why Antarctica has seen long-term sea ice increases. Perhaps more puzzling is why the continent has seen such drastic declines in recent years.

New numbers published by the National Snow and Ice Data Center found that at the end of last month, Antarctica sea ice was 160,000 square kilometers (62,000 square miles) below its previous low record set in 2002. Altogether, it’s more than 1.1 million square kilometers (425,000 square miles) below the 1981-2010 average.

“In contrast, it took the Arctic sea ice cover a full 3 decades to register a loss that great in yearly average ice extents,” write the authors in the Proceedings of the National Academy of Sciences. Sea ice spreads over large areas and influences the planet’s climate system by reflecting solar radiation and restricting oceanic and atmospheric changes. Meltwater can also play a role in sea level rise globally.

The changes in sea ice coverage are significant, but the authors note that when considering the 40-year record as a whole, the Antarctic sea ice “continues to have a positive overall trend in yearly average ice extents.”

Patchy satellite data from the 1960s show similar swings in sea ice extent throughout the decade. Scientists note that the recent decline can be attributed in part to a series of intense storms in the region. In general, Antarctica sees large variability in sea ice throughout the year given its open geography and exposure on all sides to the Southern Ocean, notes the National Snow and Ice Data Center.

In fact, four out of five of Antarctica’s sectors have experienced at least one period in the last 20 years where the yearly average decreased for three years or more only to rebound again and eventually exceed the previous three years of decreases.

“This illustrates that the ice decreases since 2014 are no assurance that the 1979-2014 overall positive trend in Southern Ocean ice extents has reversed to a long-term negative trend,” write the authors. “Only time and an extended observational record will reveal whether the small increase in yearly average ice extents from 2017 to 2018 is a blip in a long-term downward trend or the start of a rebound.”

Still, the authors say the decreases are “remarkable”. Together, the data can help researchers understand why such massive fluctuations occur.