The Greenland ice sheet experienced a tumultuous year of loss in 2021, losing more ice than it gained for the 25th consecutive year. Greenland’s net ice loss from Sept. 2020 to Aug. 2021 is relatively consistent with annual losses over recent decades, but the major swings from intense melting to heavy snowfall — all concurrent with the highest levels of ice loss and calving since satellite records began in 1986 — augur danger.

“When we see instability like this, this switch from a lot of accumulation to a lot of melting to a lot of accumulation to a lot of melting, it’s really a signal of the system that is looking for a way to be stable again,” Marco Tedesco, an adjunct scientist at the NASA Goddard Institute for Space Studies, told the Washington Post. “The message of instability that Greenland is sending is terrible.” (Washington Post $, The Hill; Climate Signals background: Glacier and ice sheet melt)