Results after investigations of 21 Swedish lakes show that the ice thickness over the last five decades has decreased by an average of 0.22 centimeters per year. But also the quality and thus the bearing capacity of the ice cover has deteriorated. This is shown by a study from the University of Gothenburg, published in the scientific journal Ambio.
"The structure of lake ice is changing rapidly in a warmer world. In 2023, nine of the investigated lakes had become unsafe for ice skaters and winter fishermen. This is mainly due to the fact that air temperature is fluctuating more than before," says Mark Peternell, lecturer in structural geology at the Department of Earth Sciences at the University of Gothenburg, in a press release.
Climate changes have contributed to freeze-thaw cycles becoming more frequent. A rule of thumb from the Ice Safety Council and the Swedish Snowmobile Association is that a safe core ice for walking or ice skating should be at least 10 cm thick, and at least 15 cm for snowmobiles.
But it's not enough to just measure the thickness of the ice.
"For those who venture out onto lake ice, it's crucial to assess the quality of the ice. Core ice is strong and dark, while layered ice is cloudy and much weaker. Moreover, the ice is not the same across an entire lake," says Mark Peternell.
Core ice: Strong and dark. The safest type of ice that forms when the water in the lake freezes to ice under prolonged cold.
Layered ice: Lighter and cloudy. A weaker ice that forms when snow, slush, or meltwater freezes together to form ice. Contains air bubbles and impurities.
