Concern about Arctic sea ice has been growing as global temperatures increase. The National Oceanic and Atmospheric Administration reported in January that the ice coverage was 9.4 percent below previous averages. That’s the smallest extent recorded in January since scientists began recording in 1979. Last Thursday, the Washington Post reported that Arctic temperatures were 45 degrees above normal, the warmest temperatures in February ever recorded.

This weekend, temperatures at the Cape Morris Jesup weather station—one of the northernmost in the world—remained above freezing for 24 straight hours. Meanwhile, climate change is causing a secret military base in Greenland to melt out of the ice, and scientists have reported open water north of Greenland. This, all in the dead of winter, when the Arctic has constant darkness.

Though there are no temperature recording stations at the North Pole, scientists believe that temperatures there reached 35 degrees Fahrenheit this weekend.

The heat wave and persistent concern about climate change has led a time-lapse video showing Arctic ice melt produced by NASA Goddard to go viral again, moving quickly to the top of the r/videos subreddit.

The video itself was originally posted on YouTube in October 2016, where it has so far garnered 1.1 million views, and offers a look at the progress of sea ice in the Arctic over a 32 year time period.

The time-lapse starts in September 1984 and is narrated by Walt Meier, a research scientist at the National Snow & Ice Data Center. He explains that whiter ice is older and thicker ice, which clearly diminishes over the course of the video. One Reddit commenter described its slow but sure progress as “the slowly withering heartbeat of a dying man.” The difference is the most shocking in the final image, which compares 1984 and 2016 ice cover side by side.

Meier explains that ice cover evolves throughout the year, growing thicker and expanding outwards in the winter and retracting back in the summer. As the ice moves further outwards into warmer waters, it melts, but Meier says that it is replenished each year through the Beaufort Gyre, which traps the ice, allowing it to grow older and thicker.

“But in recent years, we’ve seen less replenishment,” Meier says as the ice cover in the video thins before our eyes. “We’re seeing the Beaufort Sea go from a nursery to a graveyard for older ice.”

Ice that’s older than five years is the thickest, brightest white, and Meier says this has “virtually disappeared” from the Arctic. This tracks with data from the National Oceanic and Atmospheric Administration, which reported in January that the last four years saw the five warmest Januarys on record. No wonder there’s virtually no white ice in the last image of the video.