Arctic sea ice forms and expands during the dark, frigid northern winter, reaching its seasonal high point in March. But in recent years, less new ice has formed, and the accumulation of multi-year ice has steadily declined.

The maximum sea ice level for 2025 was likely reached on March 22, measuring 14.33 million square kilometers (5.53 million square miles) -- below the previous low of 14.41 million square kilometers set in 2017.

"This new record low is yet another indicator of how Arctic sea ice has fundamentally changed from earlier decades," said NSIDC senior research scientist Walt Meier in a statement.

"But even more importantly than the record low is that this year adds yet another data point to the continuing long-term loss of Arctic sea ice in all seasons."

The Arctic record follows a near-record-low summer minimum in the Antarctic, where seasons are reversed.

The 2025 Antarctic sea ice minimum, reached on March 1, was just 1.98 million square kilometers, tying for the second-lowest annual minimum in the satellite record, alongside 2022 and 2024.

Combined Arctic and Antarctic sea ice cover -- frozen ocean water that floats on the surface -- plunged to a record low in mid-February, more than a million square miles below the pre-2010 average. That is an area larger than the entire country of Algeria.

"We're going to come into this next summer season with less ice to begin with," said Linette Boisvert, an ice scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "It doesn't bode well for the future."

- A vicious cycle -

US scientists primarily monitor sea ice using satellites from the Defense Meteorological Satellite Program (DMSP), which detect Earth's microwave radiation.

Because open water and sea ice emit microwave energy differently, the contrast allows sea ice to stand out clearly in satellite imagery -- even through cloud cover, which obscures traditional optical sensors.

DMSP data is supplemented with historical records, including early observations from the Nimbus-7 satellite, which operated from 1978 to 1985.

While floating sea ice does not directly raise sea levels, its disappearance sets off a cascade of climate consequences, altering weather patterns, disrupting ocean currents, and threatening ecosystems and human communities.

As reflective ice gives way to the darker ocean, more solar energy is absorbed rather than reflected back into space, accelerating both ice melt and global warming.

Shrinking Arctic ice is also reshaping geopolitics, opening new shipping lanes and drawing geopolitical interest. Since taking office this year, US President Donald Trump has said his country must control Greenland, a Danish autonomous territory rich in mineral resources.

The loss of polar ice spells disaster for numerous species, robbing polar bears, seals, and penguins of crucial habitat used for shelter, hunting, and breeding.

Last year was the hottest on record, and the trend continues: 2025 began with the warmest January ever recorded, followed by the third-warmest February.

NOAA predicts that La Nina weather conditions, which tend to cool global temperatures, are likely to give way to neutral conditions that would persist over the Northern Hemisphere summer.

Polar regions are especially vulnerable to global warming, heating several times faster than the global average.

Since mid-2023, only July 2024 fell below 1.5 degrees Celsius of warming, raising concerns that the Paris Agreement's goal of limiting long-term warming to 1.5C may be slipping out of reach.