With ongoing carbon dioxide emissions from the burning of fossil fuels, the atmosphere of Earth heats up, which has dramatic consequences for the ice sheets. In a new study, researchers focused on the Greenland Ice Sheet, which holds so much ice that a complete melting would cause the global sea level to rise by 7 m (23 feet).
A large stream of meltwater (about 5 to 10 m in width) emerges from an upstream supraglacial lake in the Greenlandic ice on July, 21 2012. The darker shapes are minor streams covered by cryoconite (a mix of dust particles, soot, meteorite dust and organic material) which covers the ice sheet. Cracks cutting through the streams are visible. Along these cracks water can flow through, enlarging them and, eventually, generating moulins that can deliver meltwater through the ice. Image credit: M. Tedesco / CCNY / NASA ICE.
The Greenland Ice Sheet (GIS) covers 1.7 million km2 (660,200 square miles) in the Arctic.
Mass loss of the GIS is one of the main contributors to sea level rise. Between 2003 and 2016, it has lost mass at a rate of 255 gigatons (billions of tons) per year, with increasing atmospheric carbon dioxide from anthropogenic emissions expected to lead to further mass loss.
If the GIS melts entirely, global sea level would rise about 7 m, but scientists aren’t sure how quickly the ice sheet could melt.
Air and water temperature, ocean currents, precipitation and other factors all determine how quickly the GIS melts and where it loses ice.
The complexity of how those factors influence each other, along with the long timescales scientists need to consider for melting an ice sheet of this size, make it difficult to predict how the ice sheet will respond to different climate and carbon emissions scenarios.
Previous research identified global warming of between 1 and 3 degrees Celsius as the threshold beyond which the GIS will melt irreversibly.
To more comprehensively model how the ice sheet’s response to climate could evolve over time, Potsdam Institute for Climate Impact Research’s Dr. Dennis Höning and colleagues used a complex model of the whole Earth system, which includes all the key climate feedback processes, paired with a model of ice sheet behavior.
They first used simulations with constant temperatures to find equilibrium states of the ice sheet, or points where ice loss equaled ice gain.
Then they ran a set of 20,000-year-long simulations with carbon emissions ranging from 0 to 4,000 gigatons of carbon.
From among those simulations, the researchers derived the 1,000-gigaton carbon tipping point for the melting of the southern portion of the ice sheet and the even more perilous 2,500-gigaton carbon tipping point for the disappearance of nearly the entire ice sheet.
As the ice sheet melts, its surface will be at ever-lower elevations, exposed to warmer air temperatures.
Warmer air temperatures accelerate melt, making it drop and warm further.
“Global air temperatures have to remain elevated for hundreds of years or even longer for this feedback loop to become effective; a quick blip of 2 degrees Celsius (3.6 degrees Fahrenheit) wouldn’t trigger it,” Dr. Höning said.
“But once the ice crosses the threshold, it would inevitably continue to melt. Even if atmospheric carbon dioxide were reduced to pre-industrial levels, it wouldn’t be enough to allow the ice sheet to regrow substantially.”
“We cannot continue carbon emissions at the same rate for much longer without risking crossing the tipping points.”
“Most of the ice sheet melting won’t occur in the next decade, but it won’t be too long before we will not be able to work against it anymore.”
The study was published in the journal Geophysical Research Letters.
Dennis Höning et al. 2023. Multistability and Transient Response of the Greenland Ice Sheet to Anthropogenic CO2 Emissions. Geophysical Research Letters 50 (6): e2022GL101827; doi: 10.1029/2022GL101827
Source : Breaking Science News