Polar ice holds the key to our future on Earth

Au mois de septembre, où la banquise arctique atteint son minimum, elle était à son cinquième niveau le plus bas jamais enregistré, décrit Julia Schmale © iStock

Au mois de septembre, où la banquise arctique atteint son minimum, elle était à son cinquième niveau le plus bas jamais enregistré, décrit Julia Schmale © iStock

The world’s ice shelves, glaciers and ice caps are melting at an alarming rate. The extent of polar sea ice in both the Arctic and the Antarctic is unusually low this year. Protecting the cryosphere is essential to life on Earth – which is why scientists are pulling out all the stops to understand the complex dynamics

The snow- and ice-covered polar regions might seem like a world away, but they play a crucial role in maintaining global climate stability. Billions of people and animals depend on the frozen parts of our planet for survival. But as the ice melts and sea levels rise, our shared future on Earth is under threat. If the Greenland ice sheet were to melt completely, the global sea level would rise by 6 meters. The loss of all Antarctic ice would cause the oceans to swell by a further 60 meters, fundamentally altering the map of the world as we know it.

Of course, these processes would occur over hundreds or even thousands of years. But one thing is for certain: the cryosphere – which encompasses all of the Earth’s glaciers, ice shelves, polar ice caps and permafrost – is receding, and the pace of this melting is accelerating. This trend is all too clear in satellite images of polar sea ice dating back to 1979, which reveal that the Arctic ice field has shrunk by almost 50% in the space of four decades. And there’s been no letup in this trend in 2023.

“This year, the sea ice minimum, which happens in September, was at its fifth-lowest level ever recorded,” says Julia Schmale, who heads EPFL’s Extreme Environments Research Laboratory – Ingvar Kamprad Chair. “Sea-ice cover varies naturally from year to year, but it’s highly likely that by the middle of the century, the Arctic will be completely ice-free at this time of year.”

Maintaining climate stability

Things on the other side of the planet are even more worrying. After decades of records showing that the extent of Antarctic sea ice had been increasing year after year, the trend now seems to be reversing: significant retreat was recorded in the past two years, and in 2023, the mid-September sea-ice maximum was the lowest on record. “The extent of sea ice at both poles has been unusually low this year,” says Schmale. “The changes in the Arctic are clearly the result of global warming. But in the Antarctic, the dynamics are more counterintuitive, so further research is needed to get a clear picture of what’s going on. In any case, there’s real cause for concern!”

Why is it so important to protect our cryosphere? “First of all, because of the laws of physics,” says Schmale. “Ice and snow reflect the sun’s rays back into space, whereas dark-colored ground absorbs the rays and heats up. This is what’s called the albedo effect. As the ice melts, more heat will be absorbed, which in turn will speed up climate change.”

The vast majority of the world’s freshwater reserves are locked away in land ice (the Antarctic ice sheet alone holds 70% of all fresh water on Earth). Communities across the globe depend on snow that accumulates in the mountains during the winter and provides a source of fresh water in the summer. The cryosphere also hosts precious ecosystems that help maintain a natural ecological balance. Aside from iconic species such as the Arctic polar bear and the Antarctic penguin, the polar regions are home to specially adapted microbes. The loss of these species could lead to a collapse of the food chain.

The extent of sea ice at both poles has been unusually low this year. The changes in the Arctic are clearly the result of global warming

Julia Schmale, Director of EPFL’s Extreme Environments Research Laboratory

Not all ice is made equal

The effects of polar melting are also being felt at lower latitudes. “The Arctic is heating four times as fast as the global average, and the Antarctic twice as fast,” explains Schmale. “The temperature gradient between the poles and the mid-latitudes is decreasing. This gradient affects the movement of air masses and, in turn, the volume, frequency and location of precipitation. So what happens at the poles influences the weather elsewhere on the planet, including in Europe.” Schmale also notes that the loss of polar ice is affecting indigenous Arctic communities, who face fundamental threats to their traditional lifestyles and practices.

To the uninitiated, all ice may look the same. But to scientists, ice is not a uniform medium – which makes studying it a complex endeavor. Sea ice, for instance, expands and contracts as the seasons change, reaching a maximum during the cold winter nights before retreating during the months when the sun never sets. “Think of it like the ice shelf breathing in and out over the course of a year,” says Schmale. At both poles, the frozen seawater is naturally saline and serves as a habitat for numerous microorganisms, meaning it plays a vital role in the food chain.

Land ice, meanwhile, operates under a different set of rules. Glaciers and ice caps are freshwater bodies formed by the accumulation of snow. They move like slow rivers, as the weight of the ice on top pushes the layers underneath outward toward the edges and downward toward the tongue. And they’re formed over long periods of time: the ice is old and thick – up to 3 km in Greenland and 4 km in Antarctica. As temperatures rise, the ice at the summit tends to melt first, creating rivers of water below that accelerate glacier retreat.

The importance of snow

“We can’t understand the processes at work in the cryosphere without studying snow,” says Michael Lehning, head of EPFL’s Laboratory of Cryospheric Sciences. Snow is the main driver of the albedo effect, and the way snow interacts with other components – ice, water, wind, temperature and land – can have major implications. “Bodies of pure ice, like a frozen lake, tend to be quite dark in color,” explains Lehning. “They absorb solar radiation, eventually causing the ice to melt. But when a thin layer of snow accumulates on the ice, the solar radiation is reflected. That means the surface stays cold, allowing the ice to thicken.”

Snow thickness is another important factor: its weight can force part of an ice floe downward, allowing water to seep in through the sides and soak the snow, which then re-freezes. This process plays a key role in sea-ice formation in the Antarctic. If the underlying layer of ice is thin, however, the snow acts like an insulating blanket, preventing the sea ice from thickening. This is what tends to happen in the Arctic.

In short, the various mechanisms taking place are incredibly complex. “Snow is the key to understanding all these processes,” says Lehning. “But existing studies and models often overlook it as a crucial factor.” While gaining further insight into these phenomena is essential, we also need to act on what we learn. Both Schmale and Lehning agree that unless we drastically reduce global CO₂ emissions, there’s no way we could realistically protect the cryosphere and mitigate the effects of climate change.

Author: Sarah Perrin

Source: Extreme Environments Research Laboratory

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