Giant icebergs detaching from the front of Zachariæ Isstrøm, whose floating ice tongue collapsed in 2003. The ice discharge into the ocean from this glacier has dramatically increased since then. ANDERS BJØRK, AUGUST 2016

Scientists have long thought that the glaciers in North Greenland have been stable — a vital condition, as they contain enough ice to raise the sea level by nearly 7 feet. But a new study published on Tuesday found that ice shelves in the region have lost more than a third of their volume in the last half-century because of rising temperatures — and if it continues, scientists say there could be "dramatic consequences" for glaciers, and the planet.

Using thousands of satellite images and climate modeling, the study, published in Nature Communications, found that North Greenland's ice shelves "have lost more than 35% of their total volume" since 1978.

Ice shelves are the part of ice sheets — a form of glacier — that float over water. Three of those shelves in North Greenland have "completely" collapsed, researchers said, and of the five main shelves that remain, they said they have seen a "widespread increase" in how much mass they have lost, mostly due to the warming of the ocean.

One of the shelves, called Steenbsy, shrank to just 34% of its previous area between 2000 and 2013. Along with the loss of overall ice shelf volume, scientists said the area of floating ice decreased by more than a third of its original extent since 1978.

This observation could pose a major problem, as the Greenland ice sheet is the second-largest contributor to sea level rise. From 2006 to 2018, scientists noted that the single sheet was responsible for more than 17% of sea level rise in that period.

"The observed increase in melting coincides with a distinct rise in ocean potential temperature, suggesting a strong oceanic control on ice shelves changes," the study authors said. "...We are able to identify a widespread ongoing phase of weakening for the last remaining ice shelves of this sector."

Basal melting — the melting of ice from underneath — could also "be playing a complex and crucial role in thinning the ice shelf from below," study's authors said. And when that ice becomes too thin, it makes the structure more "prone to enhanced fracturing."

"This makes them extremely vulnerable to unstable retreat and ice shelf collapse if ocean thermal forcing continues to rise, which is likely to be the case in the coming century," they wrote, adding that the resulting discharge "could have dramatic consequences in terms of sea level rise."

Glaciers and ice sheets melt faster than they can gather new snow and ice as global temperatures increase — particularly in the oceans, which absorb 90% of warming on the planet. Having both warmer air and warmer ocean water amplifies the loss of ice.

Earlier this year, the World Meteorological Organization projected that Earth will have its hottest year ever recorded for at least one of the next five years, pushing the planet past 1.5 degrees Celsius of warming compared to pre-industrial times. In September, the European Union's Copernicus Climate Change Service reported that this summer was Earth's hottest three months on record.

Source