Study warns that glaciers’ ability to cool ambient air faces imminent decline

Glaciers fight climate change by cooling the air that touches their surface. But for how long? The Pellicciotti group at the Institute of Science and Technology Austria (ISTA) has compiled and reanalyzed an unprecedented dataset of glacier observations from around the world. Their findings, published today in Climate changedemonstrate that glaciers will likely reach peak self-cooling power within the next decade before their near-surface temperatures increase and their melting accelerates.

Thomas Shaw has a vivid memory of this special summer day in August 2022. The postdoctoral researcher in Francesca Pellicciotti’s group at the Austrian Institute of Science and Technology (ISTA) was in the Swiss Alps, with blue skies and a pleasant temperature of 17 degrees Celsius. Except that he was at the top of the Corbassière glacier, at an altitude of 2,600 meters, collecting data on the state of the glacier.

While ambient temperatures are steadily rising around the world, near-surface temperatures on glaciers appear to be lagging behind. The immense Himalayan glaciers even blow cold winds down their slopes in an attempt to cool themselves and preserve their ecosystems. Yet this strange effect is far from an indicator of the long-term stability of glaciers.

A new study led by Shaw shows that this glacier response will likely peak in the 2030s. “As the climate warms, glaciers will cool their own microclimate and local environments downstream,” says Shaw. “But this effect will not last long and a change in trend will follow before the middle of the century.” From then on, the melting and fragmentation of glaciers due to human-caused climate change will intensify, and their near-surface temperatures will rise more rapidly, accelerating their decline.

Large glaciers and cold winds

Considerable effort is required to understand the effects of local climate in some of the world’s most remote regions and to map their evolution on a global scale. Often, on-site data is simply lacking. This poses a challenge for the accuracy of computer models that simulate detailed climate change. When Pellicciotti and his collaborators first saw the data collected at a climate station located 5,000 meters above sea level on the slopes of Mount Everest, they couldn’t believe their eyes.

“By carefully examining the data, we understood that glaciers responded to warming air in summer by intensifying their surface temperature exchange,” says Pellicciotti. Due to the size of Himalayan glaciers, this results in the cooling of large air masses in direct contact with the glacier surface. “These vast, dense cold air masses then flow down slopes under the influence of gravity in a phenomenon called ‘katabatic winds.'” Other large glaciers around the world behave in a similar way.

Scientists who go out of their way

Shaw now sought to develop a robust global model that overcomes the limitations of data scarcity. He developed a new method to estimate how long glaciers would continue to absorb climate shock on a global scale.

“We compiled data from our research group’s past and recent projects, grouped it with all published data, and contacted other researchers to ask them to share their unpublished data with us,” says Shaw. “Using this unprecedented dataset, we re-evaluated physical processes to find generalizable aspects and developed a statistical framework that can give us insight into the evolution of glacier cooling around the world.”

Maximum cooling

Shaw and the team compiled an inventory of hourly data from 350 weather stations located on 62 glaciers around the world, representing a total of 169 summer measurement campaigns. They specifically looked at the relationship between near-surface temperature and non-glacial ambient temperature just above each station and analyzed it in space and time.

“We call the temperature difference ‘decoupling,’ because it seems at odds with warming ambient temperatures,” says Shaw. They showed that, on average, the near-surface temperature of mountain glaciers around the world increased by 0.83 degrees Celsius for every degree increase in ambient temperature.

They also studied glacier properties most likely to limit the decoupling effect, such as the presence of a debris mantle on the lower part of a glacier, and refined their model with this information. By modeling future projections, they demonstrated that this cooling effect would peak between the 2020s and 2040s, before steady mass loss from glaciers causes them to retreat on a large scale, reversing the cooling trend.

“By then, worn-out and significantly degraded glaciers will ‘recouple’ with the continued warming of the atmosphere, sealing their fate,” says Shaw.

Accept loss and coordinate future actions

Although these projections depict a bleak future for the world’s majestic water towers, there will be pragmatic consequences if current trends continue. “Knowing that glaciers’ self-cooling will continue for a little longer could buy us additional time to optimize our water management plans over the coming decades,” says Shaw.

However, the team is fully aware that they can neither save nor restore the world’s mountain glaciers. “We must accept committed ice loss and make every effort to limit global warming, rather than resorting to ineffective geoengineering strategies such as cloud seeding and glacier blanketing. It’s like putting an expensive bandage on a gunshot wound. The coming decades are a time for reflection, effective water management and action to change public consciousness about climate change of human origin.”

The researchers further emphasize the need for coordinated global climate policies to significantly reduce emissions and protect human life on Earth from the unpredictable effects of global warming. “Every degree counts,” Shaw says, echoing words scientists have insisted on for decades.