Understanding the relationship between greenhouse gas emissions, rising temperatures (climate change) and the evolution of the Greenland ice sheet "is crucial to predicting sea level rise" on a global scale, he recalls and warns a new climate modeling study carried out by six experts from the Climate Research Institute in Potsdam, Germany.
One of the main conclusions of this study is that, even if the objective of the Paris Agreement of not exceeding the increase of 1.5ºC is met, Greenland can reach a warming point of "no return" in the progressive disappearance of the ice. The results of this study on Multistability and Transient Response of the Greenland Ice Sheet to Anthropogenic CO₂ Emissions have been published in the journal Geophysical Research Letters.
The Greenland ice sheet covers 1.7 million square kilometers in the Arctic. If it melts completely, the global sea level would rise by about 7 meters. At the moment, scientists aren't sure how fast the ice sheet could melt. To advance this knowledge, various teams are working on what is called "tipping point modeling," which are critical thresholds at which a system's behavior changes irreversibly, helping researchers discover when that meltdown might occur. , as explained by the Potsdam Climate Research Institute.
Based in part on carbon emissions, a new study using simulations identified two tipping points for the Greenland ice sheet: releasing 1,000 gigatonnes of carbon into the atmosphere will cause the southern part of the ice sheet to melt ; about 2,500 gigatonnes of carbon means the permanent loss of almost the entire ice sheet.
The study authors stress that now, "having emitted about 500 gigatons of carbon, we are halfway to the first tipping point."
"The first tipping point is not far from current climate conditions, so we are in danger of crossing it," said Dennis Höning, a climate scientist at the Potsdam Institute for Climate Impact Research who led the study. "Once we start sliding, we'll fall off this cliff and we won't be able to get back up."
Greenland's ice sheet is already melting; between 2003 and 2016, it lost about 255 gigatons (billion tons) of ice each year. Much of the melting to date has occurred in the southern part of the ice sheet. Air and water temperatures, ocean currents, precipitation, and other factors determine how quickly the ice sheet melts and where it loses ice.
The complexity of how those factors influence each other, along with the long time frames scientists must consider to melt an ice sheet of this size, make it difficult to predict how the ice sheet will respond to different climate and carbon emission scenarios.
Previous research identified global warming of between 1 degree and 3 degrees Celsius (1.8 to 5.4 degrees Fahrenheit) as the threshold beyond which the Greenland ice sheet will melt irreversibly.
To more fully model how the ice sheet response to climate might evolve over time, Höning's new study used for the first time a complex model of the entire Earth system, including all key feedback processes. climate, along with a model of ice sheet behavior. . They first used constant-temperature simulations to find ice sheet equilibrium states, or points where ice loss equaled ice gain. They then ran a set of 20,000-year-long simulations with carbon emissions ranging from 0 to 4,000 gigatons of carbon.
From those simulations, the researchers derived the 1,000-gigaton carbon tipping point for the melting of the southern part of the ice sheet and the even more dangerous 2,500-gigaton carbon tipping point for the disappearance of nearly all of it. the ice cap.
As the ice sheet melts, its surface will be at lower and lower elevations, exposed to warmer air temperatures. Warmer air temperatures accelerate melting, causing it to drop and get even hotter. Global air temperatures must remain elevated for hundreds of years or even longer for this feedback loop to be effective; a quick flash of 2 degrees Celsius (3.6 degrees Fahrenheit) wouldn't trigger it, Höning said. But once the ice crosses the threshold, it will inevitably continue to melt. Even if atmospheric carbon dioxide were reduced to pre-industrial levels, it would not 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 tipping points," Höning said. "Most of the melting of the ice sheet won't happen in the next decade, but it won't be long before we can no longer work against it."
