Arctic sea ice cover was at its lowest extent on record this winter, scientists are reporting.

Scientists at the National Snow and Ice Data Centre (NSIDC) released a statement on Monday, March 28, saying that the maximum extent of sea ice cover was 14.52 million sq km (5.607 million sq miles). That is the lowest recorded winter maximum, with records dating back to 1979.

March marks the third month in a row of record lows in sea ice cover. Extreme temperatures in January and February produced record lows for their monthly extents. When combined with the data from March, scientists determined that sea ice cover for the whole winter was below that of previously recorded years.

“I’ve never seen such a warm, crazy winter in the Arctic,” NSIDC director Mark Serreze told the Guardian. “The heat was relentless.”

This low is even less than the maximum of 14.54 million sq km (5.612 million sq miles) from 2015, the previous record.

Scientists are concerned that this trend of declining ice extent is an indicator that the Arctic is locked into a course of continually shrinking ice.

The winter season is the time of year when the Arctic is in complete darkness, due to Earth’s rotation and tilt along its axis. This darkness leads to extreme cold, allowing sea ice to freeze and accumulate. Warmer global temperatures, however, prevented the usual amount of ice accumulation, leading to the lower sea ice extent.

With spring and warmer temperatures around the corner, the sea ice will begin its yearly melt. With less ice cover than usual, more ice could melt, setting the ice back for next year.

“If we are starting out very low that gives a jump on the melt season,” said Rick Thoman, climate science manager for the National Weather Service’s Alaska region. “For the last few years, we have had extremely low ice cover in the summer. That means a lot more solar energy absorbed by the darker open water. That heat tends to carry over from year to year.”

If the trend continues, some scientists expect the Arctic to be ice-free during the summer within the next 20 or 25 years. Already, continuous ice cover is down from just 40 years ago. Ships can now move from Barrow to Prudhoe Bay off the north coast of Alaska for months during the year; in 1975, that window was only a few days.

Dr. John Walsh, chief scientist of the International Arctic Research Centre, told the Guardian, “Sometime in the 2030s or 2040s time frame, at least for a few days, you won’t have ice out there in the dead of summer.”

The change in the sea ice cover has implications for the conditions of the lower latitudes as well. Bright white, snow-covered ice reflects around 85 percent of sunlight back to the atmosphere, while the dark surfaces of open water absorbs the sun’s rays. With less ice cover, more water absorbs the sun’s rays, warming the rest of the planet as well.

“Basically the polar regions are the refrigerator for the Earth,” Dr. Donald Perovich, a researcher at Dartmouth University, told the Guardian. “They are extremely important for being able to keep the Arctic colder, and in turn help keep the rest of the planet colder.”

Summer sea ice cover over the Arctic has seen a drastic decline since 1980, when it was 7.8 million sq km, reaching 4.4 million sq km in 2012 before rebounding a little.

“It would be as if the entire United States east of the Mississippi melted away, plus the states from Minnesota down to Louisiana, past North Dakota, South Dakota, Nebraska, Kansas and Oklahoma. It’s huge,” Perovich told the Guardian.