A study found that the Greenland ice sheet is losing an average of 30 million tons of ice per hour due to the climate crisis; This figure is 20% higher than previously thought.
Some scientists worry that this additional supply of freshwater pouring into the North Atlantic could mean that ocean currents called the Atlantic meridional overturning circulation (Amoc) are closer to being triggered, with serious consequences for humanity.
Massive ice loss in Greenland as a result of global warming has been recorded for decades. Techniques used to date, such as measuring the height or weight of the ice sheet with gravity data, are good at determining the losses that reach the ocean and raise sea levels.
But they cannot explain the retreat of the glaciers, which are currently mostly below sea level in the narrow fjords around the island. In the research, scientists analyzed satellite photographs every month from 1985 to 2022 to determine the final location of many glaciers in Greenland. This showed a massive and widespread shortening and amounted to a total loss of one trillion tonnes of ice.
Dr. from NASA’s Jet Propulsion Laboratory in the USA, who conducted the research. “The changes around Greenland are huge and happening everywhere; almost every glacier has retreated in the last few decades,” said Chad Greene. “If you dumped fresh water into the North Atlantic Ocean, there would definitely be a weakening of Amoc, but I have no idea how much it would weaken.”
Amoc was already known to be at its weakest point in 1,600 years, and in 2021 researchers noticed warning signs of a tipping point. A recent study suggested that, in a worst-case scenario, the collapse could occur as soon as 2025. Scientists think a significant portion of the Greenland ice sheet is close to an irreversible melting point; ice is already expected to be equivalent to a 1-2 meter rise in sea level.
The study, published in the journal Nature, used artificial intelligence techniques to map the final positions of more than 235,000 glaciers at 120-meter resolution over a 38-year period. This showed that the Greenland ice sheet had lost around 5,000 square kilometers of area at its edges since 1985, the equivalent of a trillion tonnes of ice.
The latest update from a project that brings together all other measurements of Greenland ice has revealed that 221 billion tonnes of ice have been lost each year since 2003. The new study adds another 43 billion tons per year, bringing the total loss to about 30 million tons per hour. average.
The scientists said: “There is some concern that any small freshwater body could act as a ‘tipping point’ that could trigger a full-scale collapse of the Amoc, disrupting global weather patterns, ecosystems and global food security. But freshwater from retreating glaciers in Greenland is not currently included in oceanographic models.” The flow of less dense freshwater into the sea slows the process by which heavier salt water in the polar region sinks and drives the Amoc.
Prof Tim Lenton of the University of Exeter, UK, who was not part of the study, said: “This additional freshwater input into the North Atlantic is a concern for deep water formation, particularly in the sub-arctic Labrador and Irminger Seas.” “As other evidence has shown, these are the areas most prone to fall into a ‘closed’ or collapsed state.”
“This could be like a partial Amoc collapse, but it will develop more rapidly and have profound impacts on the UK, Western Europe, parts of North America and the Sahel region, where the West African monsoon could be severely disrupted,” he said. “Whether this previously undisclosed resource has enough freshwater to make a difference depends on how close we are to the tipping point of the subpolar vortex. Recent models suggest global warming may already be near its current level.”
But Prof Andrew Shepherd, of Northumbria University in the UK, said: “Although there was a step change in glacier retreat at the turn of the century, it is reassuring to see that the rate of ice loss has remained consistent since then and is still well below the levels needed to disturb the Amoc.” .”
Greene said the discovery of extra ice loss is also important for calculating Earth’s energy imbalance, that is, how much solar heat the Earth retains due to human-caused greenhouse gas emissions. “It takes a lot of energy to melt 1 ton of ice. “So if we want very accurate energy-balanced models for the Earth, this needs to be taken into account.”
Most of the glaciers examined in the study were already below sea level, so the lost ice was replaced by seawater and did not directly affect sea level. But Green said: “It almost certainly has an indirect effect by allowing the glaciers to accelerate. These narrow fjords are bottlenecks, so if you start gouging the edges of the ice, it’s like removing the plug in the drain.”
Chad and his colleagues also analyzed the extent of Antarctic ice shelves over time in a study published in 2022. They found that when the shrinking area coverage of the shelves was taken into account, the total loss of ice shelves since 1997 had doubled, to about 12 tons. added to the thinning of the shelves.