The polar ice sheets store 99% of Earth’s freshwater ice on land
A quarter of sea-level rise comes from melting ice sheets of Greenland and Antarctica, a new study found.
The melting polar ice sheets raised the global mean sea level by roughly 21 millimetres (mm) during 1992-2020, the study published in the journal Earth System Science Data stated.
“This corresponds to a loss of 7,560 billion tonnes of ice, which is enough ice to fill an ice cube of 20 km in height,” Inès Otosaka from the University of Leeds and lead author of the study told Down To Earth.
This, she added, has important consequences for coastal communities around the world as it indicates a higher risk of flooding.
The sea level has risen by approximately 97 mm since 1993, according to the National Aeronautics and Space Administration of the United States.
The rate at which the ice sheets are losing mass increased to 372 Gt per year during 2016-2020 from 105 gigatonnes (Gt) per year during 1992-1996.
Further, the past decade has seen the seven worst years for polar ice sheets melting and ice loss.
The Antarctic and Greenland ice sheets store 99 per cent of Earth’s freshwater ice on land.
In the last three decades, researchers have recorded a six-fold increase in ice losses from Antarctica and Greenland.
Some 60 polar scientists from 41 international organisations compared and analysed measurements from 50 satellite surveys of Antarctica and Greenland to determine their rate of ice melting.
They analysed the ice sheet mass balance, which is the net balance between the mass gained by snowfall and mass loss due to melting.
In the early 1990s, ice sheet melting was responsible for 5.6 per cent of sea-level rise, compared to the current 25.6 per cent.
The rate of Greenland’s ice sheet mass change from 1992-2020 was estimated to be 169 Gt per year, the paper highlighted.
For Antarctica, it was 92 Gt per year during the same period. Within the south pole, West Antarctica and the Antarctic Peninsula lost ice at the rate of roughly 82 Gt per year and 13 Gt per year respectively.
West Antarctica showed large variability. For example, the ice loss was 86 Gt in 2017 and 444 in 2019, according to the experts.
East Antarctica, on the other hand, gained 3 Gt annually in these years. The researchers noted that this is the most uncertain component of Antarctica's mass balance.
This is because East Antarctica, which covers around two-thirds of the Antarctic continent, is harder to monitor due to its large area, Otosaka explained.
“In addition, there are large snowfall fluctuations in East Antarctica, which are hard to monitor from space,” she added.
Further, the experts noted, ice losses and the rate of ice loss are currently five times higher in Greenland and 25 per cent higher in Antarctica compared to the early 1990s.
The losses in Antarctica were primarily due to the ocean-driven melting of ice shelves and their collapse, they added.
In Greenland, increasing air temperatures and decreasing cloud cover have intensified surface melting in the summer.
Another contributor is the retreating of outlet glaciers due to a warming ocean.
If ice sheets continue to lose mass at this pace, they will add around 148-272 mm to the global mean sea-level rise by 2100, according to the Intergovernmental Panel on Climate Change.
“Continuously monitoring the ice sheets is critical to predict their future behaviour in a warming world and adapt for the associated risks that coastal communities around the world will face,” Otosaka added.
The researchers plan to expand their assessment to cover more recent years and also include data going back to the 1970s.
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