Photo: Martin Truffer. NASA ICE.
If greenhouse gas emissions continue apace, Greenland and Antarctica’s ice sheets could together contribute about 40 centimeters of global sea level rise – and that’s beyond the amount that has already been set in motion by Earth’s warming climate. An international effort that brought together more than 60 ice, ocean and atmosphere scientists from three dozen international institutions has generated new estimates on how much of an impact Earth’s melting ice sheets could have on global sea levels by 2100.
These new results, published this week in a special issue of the journal The Cryosphere, come from the Ice Sheet Model Intercomparison Project (ISMIP6) led by NASA. The study is one of many efforts scientists are involved in projecting the impact of a warming climate on melting ice sheets, understand its causes and track sea level rise.
Results from this effort are in line with projections presented in the Intergovernmental Panel on Climate Change’s (IPCC) 2019 Special Report on Oceans and the Cryosphere. Meltwater from ice sheets contribute about a third of the total global sea level rise.
Finnish participants: Artic Centre and CSC
In the Ice Sheet Model Intercomparison Project, the participants from Finland are Rupert Gladstone at the Arctic Centre, University of Lapland, and Thomas Zwinger at CSC – the IT Center for Science. Their work was funded by the Academy of Finland.
– Our contribution, together with colleagues from Australia, was to simulate the future evolution of the Antarctic ice sheet until the end of the 21st century. We contributed to the ISMIP6 project which brings together many different ice sheet models to provide input for the upcoming IPPC assessment report, said Rupert Gladstone at the Arctic Centre. These results are documented in the article of Seroussi et al. (2020) ISMIP6 Antarctica: a multi-model ensemble of the Antarctic ice sheet evolution over the 21st century.
The simulation code used is Elmer/Ice, an Open Source Software for Ice Sheet, Glaciers and Ice Flow Modelling. Elmer/Ice is an add-on package to Elmer, which is a multi-physics Finite Element Model suite mainly developed in Finland by CSC – IT Center for Science.
– Ice creeps along an inclined surface like a very viscous drop of honey. Elmer/Ice is one of the few ice flow models that does not apply simplification to the governing equations of highly viscous fluid flow and hence is a highly accurate but computationally expensive tool to perform simulations as given in this study, explains Thomas Zwinger.
The affect of Greenland and Antarctic ice sheets
– One of the biggest uncertainties when it comes to how much sea level will rise in the future is how much the ice sheets will contribute,” said project leader and ice scientist Sophie Nowicki, now at the University at Buffalo, and formerly at NASA Goddard.
– And how much the ice sheets contribute is really dependent on what the climate will do.
Greenland’s ice sheet is a significant contributor to sea level rise. The ISMIP6 team investigated two different scenarios the IPCC has set for future climate to predict sea level rise between 2015 and 2100: one with carbon emissions increasing rapidly and another with lower emissions.
In the high emissions scenario, they found that the Greenland ice sheet would lead to an additional global sea level rise of about 9 cm by 2100. In the lower emissions scenario, the loss from the ice sheet would raise global sea level by about 3 cm. This is beyond what is already destined to be lost from the ice sheet due to warming temperatures between pre-industrial times and now.
The ISMIP6 team also analyzed the Antarctic ice sheet to understand how much ice melt from future climate change would add to sea level rise, beyond what recent warming temperatures have already put in motion. Ice loss from the Antarctic ice sheet is more difficult to predict: In the west, warm ocean currents erode the bottom of large floating ice shelves, causing loss; while the vast East Antarctic ice sheet can gain mass, as warmer temperatures cause increased snowfall.
The results point to a greater range of possibilities, from ice sheet change that decreases sea level by 7.8 cm, to increasing it by 30 cm by 2100, with different climate scenarios and climate model inputs. The regional projections show the greatest loss in West Antarctica, responsible for up to 18 cm of sea level rise by 2100 in the warmest conditions, according to the research.
– The Amundsen Sea region in West Antarctica and Wilkes Land in East Antarctica are the two regions most sensitive to warming ocean temperatures and changing currents, and will continue to lose large amounts of ice, said Hélène Seroussi, an ice scientist at NASA. Seroussi led the Antarctic ice sheet modeling in the ISMIP6 effort.
The new results will help inform the Sixth IPCC report scheduled for release in 2022.
Digital Elevation Model (DEM) of the bedrock of the Antarctic Ice Sheet. The current sea-level is indicated by the yellow line and the bedrock below sea level is shown with light blue. Areas below sea level can have the risk of showing unstable ice sheet retreat. Visualization CSC.
Measured ice flow velocities imposed on the Digital Elevation Model (DEM) of the upper surface of the Antarctic Ice Sheet. Fastest flow velocities are in the range of several kilometres per year. Visualization CSC.
NASA press release: Emissions Could Add 15 Inches to 2100 Sea Level Rise, NASA-Led Study Finds
Rupert Gladstone, Arctic Centre, University of Lapland
+49 152 5878 4656
Thomas Zwinger, CSC – IT Center for Science