Basal melting of ice shelves in Greenland may lead to a 2-meter rise in sea levels

Nuuk [Greenland], November 8 : Published in 'Nature Communications' on Tuesday, a study into Greenland's huge northern glaciers found that melting of ice shelves may lift the sea levels by 2.1 meters, nearly 7 feet if the glaciers were to break down completely.
The report suggests that since 1978, ice shelves in North Greenland have lost more than 35 per cent of their total volume, with three of them collapsing completely.
The study examines eight ice shelves, which act as floating extensions of Petermann, Steensby, Ryder, Ostenfeld, Hagen Brae, Zachariae Isstrom and Storstrommen/Bistrup Brae glaciers.
The authors of the study used thousands of satellite images, along with climate models and measurements from the field. The study describes the scientist's methods stating, "We document the evolution of basal melting rates, calving fluxes, ice front/grounding line (GL) positions, ice shelf volume, velocity and discharge using a combination of multiple remote sensing datasets and outputs from a regional climate model. Finally, we use Conductivity Temperature Depth (CTD) measurements and an Arctic Ocean Physics Reanalysis (AOPR) to compare the ice shelves' evolution with changes in ocean temperature."
Over the eight main ice shelves, the floating extensions of Zachariae Isstrom, Ostenfeld and Hagen Brae completely collapsed between 2003 and 2010, the study shows.
With the collapse of the Zachariae Isstrom glacier's ice shelf in 2003, the ice discharge into the ocean doubled, according to the study. Millan said when he visited the glacier in 2016 and 2017, the changes were alarming.
The report largely puts basal melting rates at the heart of the issue, which originates from warm ocean currents melting the glaciers from underneath. Between 2000 and 2020, widespread rises in ocean temperature resulted in a "widespread increase of basal melt rate."
Greenland has often been a cause for concern in relation to rising sea levels, the ice sheet in Greenland has contributed to "17.3 per cent of the observed rise in sea level in the period 2006-2018, and has thus become the second largest contributor after ocean thermal expansion."
Thermal expansion is the result of heat-trapping greenhouse gases being absorbed by the oceans, resulting in rising temperatures and water consequently expanding.
The result of thermal expansion is the disruption of Greenland's last remaining ice shelves in northern Greenland. Ice Shelves act as a dam preventing land glaciers from sliding into the ocean. If these ice shelves are weakened or destroyed, more land glaciers will slide into the ocean causing significant rises in the sea level.
In the southern section of the shelf, the study found that measuring basal melting rates, with the combination of strain rates, made the section prone to collapse and thus enabled the entrance of large volumes of glacier ice.
The report stresses that "earlier observations of changes in ice thicknesses and basal melting in 1990-2000 would be needed to further detail the processes and exact timing of events that have led to the collapse of these ice shelves."
Although the glacier runoff increased between 1990 and 2010 basal melting rates continued to increase, hence suggesting that runoff played a minor role in its evolution which further supports the interpretation that changes in runoff had a negligible influence on basal melt rates. Glacier runoff is all melt and rainwater that proceeds to "run off" the glacier without refreezing.
The report calls for further assessments to be enabled in order to further understand basal melting and the impact that it has on sea levels.
"This will ultimately provide insight into the future of these glaciers as well as the fate of larger ice shelves in Antarctica," the report notes. A recent study in Antarctica found that the rapid melting of the continent's ice shelves may now be "unavoidable" due to melting from below.
The degradation of ice shelves from below can have a domino effect and disrupt neighbouring shelves and glaciers, that may not be as affected by basal melting. Greater assessment will have to be undertaken, to assess the effect of greenhouse gas emissions on the ocean, which will lead to basal melting and the consequent collapse of glaciers in Greenland.