GREENLAND SEES MASSIVE ICE LOSS FROM CALVING ICEBERGS, OCEAN MELT
Ice sheet loses more than it gains for 25th consecutive year
Greenland had a quite a year. For the first time in its history, rain fell at its summit. In August, it experienced one of the latest-occurring melt events in recent memory. This also became the third year with major melting events in the past decade.
By the end of the melt season, the ice sheet lost more ice than it gained — for the 25th year in a row.
“The long-term past two decades have shown us the incredible wrongness in calling ‘glacial pace’ something slow,” said Marco Tedesco, a research professor at the Lamont-Doherty Earth Observatory at Columbia University.
Greenland lost a net total of 166 gigatons of ice from September 2020 through August 2021. Overall, this loss is on par with recent decades — but how it arrived at that final number is not.
“2020/21 was a comparably ‘normal’ year. The new normal, that is,” wrote Martin Stendel, a polar researcher at the Danish Meteorological Institute, in an email. “But that does not mean it was good in this sense.”
The island experienced anomalous swings from intense melting to unusual snowfall from a former hurricane. While the annual snowfall accumulation was healthy, ice loss from iceberg calving and ocean melt was the highest since at least satellite
records began in 1986.
This year’s activity over Greenland has many researchers concerned for a not-too-distant future.
Scientists calculate Greenland’s total mass losses and gains by accounting for several factors. For one, they look at the net accumulation of snow on the ice sheet’s surface, known as surface mass balance, from when the first snowflakes fall (typically September) through the end of the melt season (the following August).
Winter snowfall was close to average this year, according to a summary by Stendel and his colleagues. Then in late June, a near-record amount of snow fell. Not only did the snow add mass to the ice sheet, but it also helped reflect
sunlight back into the atmosphere and helped delay the first melt of summer.
But starting in July, Greenland experienced three notable melting events. Researchers reported that one episode triggered an impressive loss of eight to 12 gigatons per day. Another episode in August also caused widespread melting, but it was perhaps more noteworthy because it occurred unusually late in the melt season while rain fell on the ice sheet’s summit for the first time on record.
Overall, the ice sheet managed to gain 396 gigatons of mass due to snow from September 2020 to August 2021 — average for recent decades, although still significantly lower than in the 1990s.
However, mass increases
from snow on the ice sheet’s surface are only part of the story.
During the year, a large portion of ice is lost through the calving, or breaking off, of icebergs. Ice is also lost from relatively warmer seawater coming into contact and melting glacier tongues. (A much smaller proportion of ice is also lost through “basal melting,” which accounts for the heat flux from under the ice sheet as ice slides over the ground.)
This year, scientists calculated that around 500 gigatons were lost from iceberg calving and ocean melt — the highest in 35 years of satellite records.