Scientists have known for years that the Arctic is warming faster than the rest of the world—nearly four times faster, according to a recent study. Tracking that warming is critical to understanding climate change not just in the Arctic but around the world. New data and analysis are crucial.

Now, an international team of scientists has compiled data from 2001 to 2018 to explore both surface and basal freezing/thaw cycles and uncover the mechanisms behind them. These findings could improve our understanding of changes in the atmosphere–ice–ocean system and the balance of sea ice in the Arctic.

The new study was published in November in the European Geosciences Union publication The Cryosphere, helping scientists understand when Arctic ice might disappear altogether in the summer. 

The study looks at both the surface ice, which is measured primarily by satellites, and the ice underneath, which is measured by sonar and by acoustic doppler profilers, which use sound waves to measure the speed of currents around the water column and other data. Cables extended from surface buoys into the below-ice water feed sonar data to the buoys and reveal important information about the freeze-thaw cycle, including timing. 

“Timing is really critical, and this shows that the timing is changing,” said Dartmouth Professor Donald K. Perovich, one of the study’s five authors.

“The study looked at the buoy results in the context of the satellite results, which agree really well. That’s a really powerful finding,” said Perovich.

And, as it turns out, the surface and under-ice measurements are different. The surface ice forms earlier than the ice underneath because the water’s temperature, which is warmer than the atmosphere, freezes later in the season.

“That’s something that’s been known, but it’s nice to see it put together in the data set,” said Walter Meier, senior research scientist at the National Snow and Ice Data Center.

“The real value of the study is that it’s giving us a reasonably comprehensive look at the basal melt, and tells us when the melt is starting and when it’s ending. This is something we really didn’t have before.”

According to Meier, the study gives scientists a picture of how the melt season is evolving and how it might evolve in the future, and when Arctic ice might disappear in the summer. Current predictions suggest that this may occur by 2040 or 2050, although it’s a complicated calculus affected by many variables. One variable, of course, is whether the countries of the world drastically cut emissions of CO2, methane and other greenhouse gases.

“The Arctic Ocean is roughly the same size as the lower 48 states, and it used to be mostly ice covered, like 90 percent ice covered,” said Meier. “Now it’s down to 40-50 percent ice covered at the end of summer, and getting lower. That’s a big change.”

The consequences will include a wetter Arctic with more storms with large waves eroding coastlines. That’s already happening to communities in Alaska. In Hooper Bay, a coastal community facing the Bering Sea, a stretch of rolling sand dunes is now a floodplain. Once there were five rows of dunes, but erosion has reduced that to one row. Those dunes once formed a natural sea wall for the town, but now the town is much more exposed.

Newtok, a small Yup’ik village in western Alaska, is losing 70 feet of coastline each year through erosion caused by waves and storm surges. The community is currently moving to a new village called Mertarvik, making Newtok residents the first Americans to be relocated due to climate change.

Dozens of coastal communities in Alaska—most of them populated by Indigenous peoples—are likewise threatened with flooding and erosion.

Polar bears have become the iconic symbol of threats to the Arctic from climate change. For millennia, the bears lived on the ice and preyed on seals, primarily. With reduced ice cover, the bears are increasingly restricted to land, with severe consequences on their diet and health. Some scientists believe that confined to land, polar bears may mate with brown bears, and their offspring will lose the characteristics that make polar bears uniquely suited for life on the ice.

The researchers say future research should focus on upper ocean water characteristics along with ice mass balance observations, to advance our understanding of the Arctic ice-ocean system.