The rocky highway to correct sea-level predictions

The 20 km-wide Petermann Fjord with the ice shelf within the far distance. Credit score: Martin Jakobsson

The kind of materials current below glaciers has a big effect on how briskly they slide in the direction of the ocean. Scientists face a difficult job to accumulate knowledge of this under-ice panorama, not to mention find out how to symbolize it precisely in fashions of future sea-level rise.

“Selecting the fallacious equations for the under-ice panorama can have the identical impact on the anticipated contribution to sea-level rise as a warming of a number of levels,” says Henning Åkesson, who led a brand new revealed examine on Petermann Glacier in Greenland.

Glaciers and ice sheets around the globe at present lose greater than 700,000 Olympic swimming swimming pools of water each day. Glaciers type by the transformation of snow into ice, which is later melted by the ambiance in summer season, or slides all the way in which into the ocean. With local weather change, glaciers are breaking apart and drop icebergs into the ocean at an accelerating tempo. Precisely how briskly relies upon to a big extent on the mattress under all of the ice. Glaciers conceal a panorama below the ice lined by rocks, sediments and water. A brand new examine reveals that the way in which we symbolize this under-ice panorama in laptop fashions means an ideal deal for our predictions of future sea-level rise. Extra particularly, how we incorporate the friction between the bottom and the ice sliding over it in glacier fashions is what impacts our predictions. This was discovered by a crew of Swedish and American scientists, once they simulated the way forward for Petermann Glacier, the biggest and quickest glacier in northern Greenland.

Petermann is likely one of the few glaciers within the northern hemisphere with a remaining ice tongue, a kind of floating glacier extension in any other case primarily present in Antarctica, the place they’re known as ice cabinets. These floating extensions have been discovered to be uncovered to heat subsurface water flowing from the open ocean in the direction of the glaciers. This occurs each in Antarctica and in lots of fjords round Greenland, together with the Petermann Fjord.

The rocky road to accurate sea-level predictions
Swedish icebreaker Oden on the entrance of Petermann Ice Shelf in 2019. The brand new examine reveals that this ice shelf might break up if ocean warming continues. Credit score: Martin Jakobsson

“Peterman misplaced 40% of its floating ice tongue during the last decade. It nonetheless has a forty five km tongue, however we discovered {that a} barely hotter ocean than as we speak would result in its break up, and set off a retreat of the glacier,” says Henning Åkesson, a postdoctoral researcher at Stockholm College who led the examine.

Many glaciers in Greenland and Antarctica circulation in the direction of the ocean a lot quicker than they did a number of many years in the past, and due to this fact contribute extra to international sea-level rise. Scientists have due to this fact mobilized nice efforts into studying what’s going on in these environments. This has spurred new insights into the panorama below glaciers and the form of the seafloor the place they drain. We now additionally know way more about what occurs to the ice when glaciers meet the ocean.

Nonetheless, the distant polar areas are notoriously troublesome to review due to sea ice, icebergs, and infrequently harsh climate. The under-ice panorama is a selected problem as a result of, frankly, it’s laborious to measure one thing lined by a kilometer of ice on prime. Even in areas of recognized under-ice topography, describing its bodily properties utilizing mathematical equations is troublesome. Pc fashions are due to this fact nonetheless considerably at the hours of darkness in the case of find out how to symbolize issues like sediments, rocks, ponds and rivers below glaciers within the equations that describe ice circulation. These equations are in the end the muse of the fashions utilized by the IPCC to estimate how briskly glaciers circulation and the way a lot sea ranges will rise below future local weather warming.

“As we stated, selecting the fallacious equations for the under-ice panorama can have the identical impact on the contribution to sea-level rise as a warming of a number of levels,” Åkesson says.

“Actually, predicted sea-level rise for this Greenland glacier can quadruple relying on how we symbolize friction below the ice. We nonetheless do not know which means is one of the best, however our examine illustrates that ice-sheet fashions nonetheless have to progress on this respect, with a view to enhance our estimates of mass loss from Earth’s polar ice sheets.”


New examine: Thick sea-ice warms Greenland fjords


Extra info:
Henning Åkesson et al, Future projections of Petermann Glacier below ocean warming rely strongly on friction regulation, Journal of Geophysical Analysis: Earth Floor (2021). DOI: 10.1029/2020JF005921

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