In the Arctic, the Greenland Ice Sheet covers an area of 1.7 million square kilometers (660,200 square miles). Global sea level would rise by about 7 meters (23 feet) if the ice sheet completely melted, but scientists are unsure of how quickly it could melt. Researchers are able to determine when that melt might occur by modeling tipping points, which are critical thresholds at which the behavior of a system changes in an irreversible way.
A new simulation-based study found two tipping points for the Greenland Ice Sheet, partly based on carbon emissions: The southern portion of the ice sheet will melt if 1,000 gigatons of carbon are released into the atmosphere; the loss of nearly the entire ice sheet would be permanent if 2500 gigatons of carbon were released.
We are approximately halfway to the first tipping point, having released approximately 500 gigatons of carbon.
“We run the risk of passing the first tipping point given the current state of the environment. We can’t climb back up if we start sliding off this cliff.”
Dennis Höning, a climate scientist at the Potsdam Institute for Climate Impact Research.
Dennis Höning, a climate scientist at the Potsdam Institute for Climate Impact Research who was in charge of the study, stated, “The first tipping point is not far from today’s climate conditions, so we’re in danger of crossing it.” When we begin sliding, we will tumble off this bluff and can’t move back up.”
Geophysical Research Letters is the journal that published the study.
Already, the Greenland Ice Sheet is melting. It lost about 255 gigatons (billions of tons) of ice annually between 2003 and 2016. The southern portion of the ice sheet has seen the majority of the melt thus far. The speed at which the ice sheet melts and where it loses ice are all determined by the temperature of the air and water, ocean currents, precipitation, and other factors.
The intricacy of how those elements impact one another, along with the long timescales researchers need to consider for dissolving an ice sheet of this size, make it challenging to foresee how the ice sheet will respond to different environmental and fossil fuel byproduct situations.
The Greenland Ice Sheet will melt irreversibly if global warming exceeds a threshold of 1 to 3 degrees Celsius (1.8 to 5.4 degrees Fahrenheit), according to previous research.
For the first time, Höning’s new study combined a model of the behavior of the ice sheet with a complex model of the entire Earth system, which includes all of the key climate feedback processes, to more fully model how the ice sheet’s response to climate could change over time. To begin, they used simulations at constant temperatures to locate the ice sheet’s equilibrium states, or points at which ice gain equals ice loss. Then they ran a bunch of 20,000-drawn out recreations with fossil fuel byproducts going from 0 to 4,000 gigatons of carbon.
The researchers calculated the 1,000-gigaton carbon tipping point for the melting of the southern portion of the ice sheet and the 2,500-gigaton carbon tipping point for the disappearance of nearly the entire ice sheet from those simulations.
The ice sheet’s surface will become increasingly exposed to warmer air temperatures as it melts. Melting accelerates as air temperatures rise, causing them to drop and warm even more. For this feedback loop to work, global air temperatures must remain high for hundreds of years or longer; according to Höning, a brief temperature change of 3.6 degrees Fahrenheit would not cause it. However, when the ice passes the boundary, it will unavoidably keep on softening. The ice sheet would not be able to grow significantly even if atmospheric carbon dioxide levels were returned to pre-industrial levels.
Höning stated, “We cannot continue to emit carbon at the same rate for much longer without running the risk of crossing the tipping points.” Although the majority of the ice sheet’s melting won’t occur for another ten years, we won’t be able to fight it for long.
More information: Dennis Höning et al, Multistability and Transient Response of the Greenland Ice Sheet to Anthropogenic CO2 Emissions, Geophysical Research Letters (2023). DOI: 10.1029/2022GL101827
