A stretch of frozen Arctic on the edge of Alaska is melting way ahead of schedule

The Beaufort Sea is melting way ahead of schedule. 

The sea, which borders Alaska to the north, typically melts during the summer and re-freezes in the winter. But this year, pieces of it began detaching in April, a time when it has historically remained frozen. 

Here's what it looked like on April 1, as captured by satellite:

Suomi NPP satellite/NOAA

And then on April 24:

Suomi NPP satellite/NOAA

The ice's expected summer melt typically happens later on in May.

NASA attributed this decline in part to a record-low maximum ice extent. The maximum refers to the period during the year when there's the most sea-ice. The amount of sea ice this winter peaked at just 5.607 million square miles.

For comparison, here's what the same area looked like April 24, 2015, the year with the second-lowest maximum ice extent:

NOAA

Looking even farther back, here's what the same area looked like on April 24, 2014. 

NOAA

Since 1979, when satellites started collecting data on when sea ice hit a maximum, it has declined by about 10%.