It’s not just the extent of the sea ice that has changed, it’s also the character. Arctic sea ice has become dramatically younger. As NOAA explains, when it comes to ice, age refers to thickness and durability. Young ice it is thinner and more likely to melt in the summer. The oldest ice – which is usually four years old or more – is the ice that survives all year and continues to thicken over time. Per National Snow and Ice Data Center, old ice can reach between 1.8 and 7.6 meters in thickness.
As you can see in the graph, the oldest Arctic ice is a slice of what it once was. In 1985, 33% of the ice in the Arctic was very old ice; in March 2020, only 4.4% of sea ice was old.
According NOAA, 20 to 30 years ago, sea ice in the Arctic was dominated by ancient sea ice. Over time, however, the ancient ice left the Arctic across the Fram Strait, where it melted in the relatively warmer Atlantic waters. At the time, this was not a problem, as new batches of old ice were created at Giro Beaufort, which NOAA describes as a “nursery” for young ice to get thicker and stronger as it wanders for many years. Today, summers in the southern arm of the Giro Beaufort are often too hot for the ice to survive, the agency said.
To use a phrase from NSIDC, this “Benjamin Button ice” is an element of the dangerous cycle, in which rising air and ocean temperatures more easily destroy first-year ice and weaken older ice. If this cycle continues and the oldest ice disappears from the Arctic Ocean, the world could see ice-free summers in the Arctic as early as 2030.