Worldwide, the Earth’s ice sheets melt about 750 billion tons each year. This enormous amount of water is the main reason for the 20 cm rise in sea level since 1900. In addition, glaciers are shrinking due to their front breaking – this loss of ice corresponds to about a tenth of the melting of ice. Researchers have now examined the evolution of such ruptures in more detail on about 1,500 glaciers in the Northern Hemisphere. As they report in the journal “Nature Communications,” vast amounts of ice have found their way into the ocean as a result of glacial collapse in recent years—a good even 52 billion tons per year over the past decade.
The researchers, led by William Kochitzky of the University of Ottawa in Canada, focused on glaciers with direct access to the ocean. With each break-off, such a glacier cuts a more or less large iceberg, which then floats freely in the ocean. If this ice was previously on land, when it breaks into the ocean as an iceberg, it raises the sea level simply by displacing the water—even if the ice doesn’t melt directly. Using position data from glacier tongues and multiple satellite images, scientists have now estimated which frozen portions of a total of 1496 glaciers in the Northern Hemisphere reached the ocean over the past two decades.
Kochtitzky and his colleagues determined that between 2000 and 2010 about 45 billion tons of ice caused glaciers to break into the ocean. In the second decade, this value increased even more – about 52 billion tons. However, he recognized major regional differences. Glaciers in Alaska, along the Russian Arctic coast and in particular at Spitsbergen, shrank severely. In contrast, there were fewer accidents along the coasts of Iceland and Greenland and Canada. Future analysis may reveal the exact reason.
According to the researchers’ calculations, glacial fall in the Northern Hemisphere alone raised sea levels by 2.1 millimeters in the first 20 years of this century. Compared to the increase due to meltwater, this value is small. However, in order to be able to more accurately predict how sea levels will develop in the future, the contribution of breaking glaciers must be taken into account. This is where the current study makes a fundamental contribution and should also help to better understand the global retreat of glaciers – especially if similar detailed studies are conducted for glaciers in the Southern Hemisphere.
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