「经济学人」Scientists are getting to grips with ice

Climate change is making water freeze in unexpected ways

Jack Frost is a tricky adversary. As the mercury falls, water’s behaviour becomes erratic, leading to ice and snow with physical properties that can vary enormously depending on environmental factors such as temperature and moisture. That can complicate tasks as varied as developing new ice-repellent materials and predicting the likelihood of an avalanche. New research is suggesting ways to put this slippery field on firmer foundations.

“Ice is a complicated material,” says Jean-Denis Brassard, an anti-icing specialist at the University of Quebec. Although one chunk may look like any other, each is a messy collection of individual crystals formed in ways that are sensitive to the conditions. Everything from the air pressure to the size of water droplets and the type of surface can affect the type of ice that will form and, thereby, its clinginess. To make matters worse, climate change brings with it different types of ice.

This is a problem for those creating materials to protect aircraft, roads, bridges and power lines from dangerous build-ups of ice. At present, such materials are tested in a number of different ways, from checking how easily a layer of ice can be pulled vertically away from a surface, to measuring ice-on-ice friction. Writing in Cold Regions Science and Technology, Dr Brassard and his colleagues argue that such tests do not replicate the way ice is removed from surfaces in the real world, which can lead to inconsistent and misleading results.

Dr Brassard’s team has, therefore, built a tool that mimics the way people scrape their car windscreens. Rather unimaginatively called the human-motion-inspired automated apparatus, it uses compressed air to steadily push an angled blade along an icy surface. By measuring the force applied, it can rate the effectiveness of different de-icing techniques.

Such a device will help ice-clearers tackle the novel forms of ice produced in a warming world. Climate change is increasing the likelihood of mixed-phase precipitation—a weather forecaster’s way of saying one of those wintry spells when you get a bit of everything. As a result, says Dr Brassard, clients are increasingly finding hitherto unseen types of ice with no sense of how best to clear them. “Then they come to see us,” he says.

Based on photographs and a handful of on-the-ground measurements, his team can try to replicate the unusual ice. Their device can then be used to test combinations of coatings and chemicals to see which might be most effective.

Another type of ice test, carried out routinely on ski slopes, seeks to measure the stability of snow packs in order to assess the chances of an avalanche. This is often done by counting how many taps it takes for cracks to appear and propagate in a column of snow. The tests are typically performed in three sets of increasing power, hinging the hand tap from either the wrist, elbow or shoulder.

Havard Toft, then a PhD student at the Centre for Avalanche Research and Education at the Arctic University of Norway in Tromso, was concerned that these avalanche tests were not reliable. Dr Toft and his team therefore persuaded almost 300 avalanche experts to have the strength of their hand taps measured, collecting more than 8,500 data points in total.

In a paper published in Natural Hazards and Earth System Sciences, Dr Toft showed that different individuals delivered taps of the same type with varying degrees of force. Most striking, many experts produced more load with wrist taps than colleagues did with shoulder taps, which the researchers say could lead to some dangerous misclassification of avalanche risk. The field should proceed with caution.

This article appeared in the Science & technology section of the print edition under the headline “Deep freeze” (Apr 16th 2025)

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