Greenland had quite a year. For the first time in its history, it rained on its summit. In August, it experienced one of the latest molten events in recent memory. It also became the third year with major melting events in the past decade.
By the end of the melting season, the ice sheet had lost more snow than it gained – the 25th year in a row.
“The long period of the past two decades has shown us an incredible inaccuracy in calling ‘glacial speed’ something slow,” says Marco Tedesco, a research professor at the Lamont-Doherty Earth Observatory at Columbia University.
Greenland lost a total of 166 gigatons of ice from September 2020 to August 2021. Overall, this loss is on par with that of recent decades – but how it arrived at that final number is not.
“2020/21 was a comparatively ‘normal’ year. The new normal, that is, “but that doesn’t mean it was good in that sense,” wrote Martin Stendel, a polar researcher at the Danish Meteorological Institute, in an email.
The island experienced odd swings from a prior storm, from intense melting to unusual snowfall. While annual snow accumulation was healthy, ice loss from iceberg calving and ocean melting was the highest since satellite records began in 1986.
“When we see this kind of instability, it switches from very high accumulation to very high melting, it is really a sign of the system that is looking for a way to stabilize again,” Tedesco, who also serves as an assistant scientist at NASA’s Goddard Institute for Space Studies. “The message of instability that Greenland is sending is terrifying.”
This year’s activity over Greenland has many researchers concerned for the not-too-distant future.
Scientists calculate Greenland’s total mass loss and gain by taking into account a number of factors. For one, they look at the net accumulation of ice at the surface of the ice sheet, known as surface mass equilibrium, from the time the first snowflakes fall (usually September) to the melting season (next August). till the end.
According to a summary by Stendhal and his colleagues, winter snowfall this year was close to average. Then in late June, there was an almost record amount of snow. The ice not only added mass to the ice sheet, but it also helped reflect sunlight back into the atmosphere and helped delay the first melting of the summer.
But starting in July, Greenland experienced three notable melting events. The researchers reported that a single episode caused a significant loss of eight to 12 gigatonnes per day. Another episode in August also caused widespread melting, but this was perhaps more notable because it occurred unusually late in the melting season as it rained on the summit of the ice sheet for the first time on record.
Overall, the ice sheet managed to gain 396 gigatons of mass due to ice from September 2020 to August 2021 – the average for recent decades, though still significantly lower than in the 1990s.
However, the mass increase from ice on the surface of the ice sheet is only part of the story.
During the year, a large part of the ice is destroyed by the calving or breaking of icebergs. Ice is also eroded by exposure to relatively warm seawater and melting glacier tongues. (A very small proportion of ice is also lost through “basal melting,” which is attributed to the flow of heat from the bottom of the ice sheet as the ice slid across the ground.)
This year, scientists calculated that iceberg calving and ocean melting destroyed nearly 500 gigatons—the most in 35 years of satellite records.
Notably, the Jakobshavn Glacier (also known as the Ilulissat Glacier) on West Greenland, the world’s fastest-moving glacier, shed about 45 gigatons in the past year – especially considering that this recent Was just growing up. This calving accounts for about 10% of the total calf and ocean melt loss this year.
Ocean scientist Josh Willis writes in an email, “The warmer ocean – melting along with the surface – is what actually creates a glacier like that retreat and maybe Jacobshavn got a double whammy this year.” Willis leads NASA’s Ocean Melting Greenland Project, and he conducted field research in Greenland this summer.
Finally, the high amount of ice loss from calf and submarine melts significantly affected the mass balance of the ice sheet for this year. But it could have been worse if the surface mass accumulation wasn’t that high. In 2019, less winter snowfall and a warmer summer resulted in a net ice loss of 329 gigatons.
The 2020-21 period “wasn’t close to a record that I’m very grateful for, but it was another year where we were losing ice overall and not gaining it on the ice sheet,” says Twyla Moon , a researcher with the National Snow and Ice Data Center.
From September 1968 to August 2021, the Greenland ice sheet has lost about 5,500 gigatons of ice – the equivalent of 1.5 cm of global mean sea level rise.
Climate change is a double-edged sword for Greenland. On the one hand, as global temperatures rise, the moisture content in the air will increase and there may be more precipitation – including more snowfall.
“You have an accumulation that’s helping to mute the melt and helping Greenland’s mass gain a little bit,” Tedesco says. “But at the same time, it’s something that we think is very much connected to what’s going to happen as part of global warming.”
Global temperatures will also induce more surface melting and melting from the ocean, with losses from increased ice accumulation as in this year.
“What we have seen, if we look at long-term trends, is that the loss of mass from Greenland from increased melt and runoff from heat will more than offset the increased accumulation that we will see.” ,” says Tom Motte. A climate scientist at the University of Georgia.
Another concern is that increased snowfall could turn into rain as the climate warms. Tedesco says that in recent decades, dark, wetter clouds over Greenland have increased rapidly. This year the snow cover was dominated by rain. Kakortok, a city in southern Greenland, recorded a summer daily rainfall of 5.7 inches. The city of Kanak in north-western Greenland also experienced flooding. Then, it rained on the summit.
“When we look at the events we saw in mid-August, where we see precipitation at the highest elevations of the ice sheet, I think it portrays what we might see in future weather,” Motte says. Huh.
Rain negatively affects the health of the ice sheet in many ways. The Moon says it could change the shape of the ice grains and cause them to darken, allowing more sunlight to be absorbed and melt at the surface. Rain can also form ice lenses, which prevent meltwater from seeping into older layers of ice in the ground and freezing. Instead, meltwater will flow through the ice sheet.
Rain would also make life difficult for researchers visiting the ice sheet for field research. The sector will affect everything from technology, aircraft runways, underground food storage and even sewage.
“Breaking records is the new normal, with each decade being warmer than the previous one. The ice sheet is in for a wild ride,” writes Willis. “And so are we.”
© Washington Post
Credit: www.independent.co.uk /