Carbon emissions could add 40 cm to 2100 sea level rise

17.09.2020

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.