Last Sunday, the record-breaking melt of Arctic sea ice likely stopped for the year, according to scientists at the National Snow and Ice Data Center (NSIDC). It’s unclear what will happen next, because the changes have been so dramatic.

“We are now in uncharted territory,” said NSIDC Director Mark Serreze. “While we’ve long known that as the planet warms up, changes would be seen first and be most pronounced in the Arctic, few of us were prepared for how rapidly the changes would actually occur.”

Arctic sea ice grows in the winter when the sun sets, and shrinks in the summertime. In the past, the ice commonly survived for several years, but in recent years it has become more common for large areas of ice to completely melt away in the summertime. This year, following record retreats in June and July, sea ice fell to the lowest extent ever on record on Aug. 26. That record low — of 4.10 million square kilometers — was broken again on Sept. 4, when the extent of ice fell below 4.00 million square kilometers. On Sept. 16, it fell again to 3.41 million square kilometers.

The changes are unprecedented. It’s very unusual for melting to happen this late in the season, and the researchers note that it’s possible the melting could continue. The fact that melting has occurred in late August and September demonstrates how unusually thin the ice is. The researchers had predicted the ice would refreeze much earlier.

The melting of the ice will itself increase global warming, helping to speed more melting. What’s next? It’s possible it won’t be long before the ice is almost gone.

“Twenty years from now from now in August you might be able to take a ship right across the Arctic Ocean,” said Serreze.

Image of arctic sea ice extent on Sept. 16 by NASA.