by Himalayan glaciers are melting rapidly, but a new report showed that a surprising phenomenon in the world’s highest mountain range could be helping to curb the effects of the global climate crisis.
When warming temperatures hit certain high-altitude ice masses, a surprising reaction is triggered that pushes strong cold winds down the slopes, according to the study published December 4 in the journal Nature Geoscience.
The warming climate creates a greater temperature difference between the surrounding air above the Himalayan glaciers and the colder air that is directly in contact with the surface of the ice masses, explained Francesca Pellicciotti, professor of glaciology at the Institute of Science and Technology of Austria and lead author of the study. .
“This leads to an increase in turbulent heat exchange at the glacier surface and a stronger cooling of the surface air mass,” he said in a press release.
As the cool, dry air at the surface becomes colder and denser, it sinks. The air mass flows down the slopes towards the valleys, causing a cooling effect in the lower areas of the glaciers and in neighboring ecosystems.
Since ice and snow from the mountain range feed 12 rivers that provide fresh water to nearly 2 billion people in 16 countries, it is important to discover whether Himalayan glaciers can maintain this self-preserving cooling effect as the region faces a likely increase. . in temperatures over the next few decades.
Glacier melting
A June report previously covered by CNN showed that glaciers in the Himalayas melted 65% faster in the 2010s compared to the previous decade, suggesting that rising temperatures are already having an impact on the area.
“The main impact of rising temperatures on glaciers is an increase in ice losses, due to increased melting,” said Fanny Brun, a research scientist at the Institut des Géosciences de l’Environnement in Grenoble, France. She did not participate in the study.
“The main mechanisms are the lengthening and intensification of the melting season. They cause glaciers to thin and retreat, giving rise to deglaciated landscapes that tend to further increase air temperatures due to greater energy absorption by the surface,” Brun said.
That energy absorption at the surface is determined by something called the albedo effect. Light or “white” surfaces, such as clean snow and ice, will reflect more sunlight (high albedo) compared to “dark” surfaces, such as land exposed as glaciers retreat, soil and oceans (low albedo). Generally, Brun said this phenomenon is interpreted as a positive feedback loop, or a process that improves a change, but it is generally understudied and difficult to quantify.
However, at the base of Mount Everest, measurements of overall temperature averages seemed curiously stable rather than increasing. A close analysis of the data revealed what was really happening.
“While minimum temperatures have steadily increased, maximum summer surface temperatures have steadily decreased,” said Franco Salerno, co-author of the report and researcher at the Italian National Research Council (CNR).
However, even the presence of these cooling winds is not enough to completely counteract rising temperatures and melting glaciers due to climate change. Thomas Shaw, who is part of the ISTA research group with Pellicciotti, said the reason these glaciers are melting rapidly is complex.
“The cooling is local, but it may not yet be enough to overcome the larger impact of climate warming and fully preserve glaciers,” Shaw said.
Pellicciotti explained that the general scarcity of data in high elevation areas around the world is what led the study team to focus on using the unique Earth observation records at a station in the Himalayas.
“The process we highlight in the paper is potentially of global relevance and can occur on any glacier in the world where the conditions are met,” he said.
The new study provides compelling motivation to collect more high-altitude, long-term data that is much needed to test the new findings and their broader impacts, Pellicciotti said.
A treasure trove of data
Located at a glacial elevation of 5,050 meters (16,568 ft), the Pyramid International Observatory and Laboratory climate station lies along the southern slope of Mount Everest. The observatory has recorded detailed weather data for almost 30 years.
It’s those granular weather observations that Pellicciotti, Salerno and a team of researchers used to conclude that rising temperatures are triggering what are called katabatic winds.
Cold winds, created by air flowing downhill, typically occur in mountainous regions, including the Himalayas.
“Katabatic winds are a common feature of Himalayan glaciers and their valleys, and have probably always occurred,” Pellicciotti said. “However, what we observe is a significant increase in the intensity and duration of katabatic winds, and this is due to the fact that surrounding air temperatures have increased in a warming world.”
Another thing the team observed was higher ground-level ozone concentrations relative to lower temperatures. This evidence demonstrates that katabatic winds function as a pump capable of transporting cold air from higher elevations and atmospheric layers to the valley, Pellicciotti explained.
“According to the current state of knowledge, Himalayan glaciers are evolving slightly better than average glaciers in terms of mass loss,” Brun said.
Loss of glaciers in Asia compared to Europe
Brun explained that in the central Himalayas, on average, glaciers have thinned about 9 meters (29.5 feet) over the past two decades.
“This is much lower than glaciers in Europe, which have thinned of about 20 meters (65.6 feet) during the same time period, but this is larger than other regions in Asia (for example, in the Karakoram region) or in the Arctic region,” Brun said.
Understanding how long these glaciers are able to locally counteract the impacts of global warming could be crucial to effectively addressing our changing world.
“We believe that katabatic winds are the response of healthy glaciers to rising global temperatures and that this phenomenon could help preserve permafrost and surrounding vegetation,” said study co-author Nicolas Guyennon, a researcher at the National Research Council of Italy.
However, more analysis is needed. The study team’s next goal is to identify the glacial features that favor the cooling effect. Pellicciotti said there are virtually no more long-term ground stations to test this hypothesis elsewhere.
“Even if glaciers cannot preserve themselves forever, they could still preserve the environment around them for some time,” he said. “Therefore, we call for more multidisciplinary research approaches to converge efforts toward explaining the effects of global warming.”
A separate 2019 report found that even in the most optimistic case, in which average global warming was limited to just 1.5 degrees Celsius (2.7 degrees Fahrenheit) above pre-industrial temperatures, the Himalayan region would lose the least a third of its glaciers.
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