The percentage of multi-year sea ice in the Arctic has fallen from 61 to 34% since 1984, the U.S. National Snow & Ice Data Center reported last week, with the oldest sea ice—patches that have been frozen for at least five years—now accounting for only 2% of the total.
The rapid shift is a result of climate change, and “these trends are not to be taken lightly,” Scientific American reports. “When it comes to sea ice, age is far more than just a number—it’s an indicator of the ice thickness, its likelihood of melting away in warm weather, the amount of light it lets through to the ocean below, and other factors that affect the Arctic ecosystem and its resilience to climate change.”
Last month, Arctic sea ice hit a near-record low, second only to April 2016.
“Sea ice freezes from the bottom up, so every additional winter that it persists, it gets a little bit thicker,” the magazine explains. “While first-year ice is often just a few feet thick, multi-year ice can grow to be nearly 15 feet deep. Thicker ice is generally more likely to survive the summer months, while younger, thinner ice is at a greater risk of melting away entirely during the warm season.”
Arctic sea ice has always been subject to “a kind of natural flux” based on seasons, notes reporter Chelsea Harvey. “But as temperatures in the rapidly warming Arctic continue to climb, year after year, the warm season is straining even the oldest, thickest layers of ice. And as multi-year ice disappears, and more of the total ice cover consists of thinner, more vulnerable ice, some experts worry that the Arctic is inching closer to a future in which it all melts away entirely during the summer months.”
Last month, Harvey notes, two separate studies concluded that a failure to meet the stretch targets in the Paris agreement could lead to ice-free Arctic summers by 2100.
“Ice-free summers, in and of themselves, are cause for concern,” she writes. “For one thing, year-round ice cover is important to animals like polar bears, which use it as their hunting grounds. Additionally, the less sea ice covers the surface of the ocean, the more sunlight is absorbed by the water, which scientists warn could accelerate the Arctic’s warming. In fact, experts suggest that long-term sea ice declines are already helping to amplify climate change in the Arctic.”