Climate change

Shrinking Greenland glaciers losing ice more rapidly than can be replenished

written by Oceanographic Staff

A new study from Ohio State University, which examined almost 40 years of data, has found that even if the climate cools, Greenland’s glaciers will continue to shrink. The researchers found that the snowfall that replenishes the ice sheet each year cannot keep up with the ice that is flowing into the ocean from glaciers.

The research team analysed monthly satellite data from more than 200 large glaciers draining into the ocean around Greenland. Their findings show how much ice breaks off into icebergs or melts from the glaciers into the ocean. They also show the amount of snowfall each year.

“We’ve been looking at these remote sensing observations to study how ice discharge and accumulation have varied,” said Michalea King, lead author of the study and a researcher at The Ohio State University’s Byrd Polar and Climate Research Center. “And what we’ve found is that the ice that’s discharging into the ocean is far surpassing the snow that’s accumulating on the surface of the ice sheet.”

Greenland glaciers

King and a team of researchers found that, throughout the 1980s and 1990s, snow gained through accumulation and ice melted or calved from glaciers were mostly in balance, keeping the ice sheet intact. Through those decades, the researchers found, the ice sheets generally lost about 450 gigatons (about 450 billion tons) of ice each year from flowing outlet glaciers, which was replaced with snowfall.

“We are measuring the pulse of the ice sheet – how much ice glaciers drain at the edges of the ice sheet – which increases in the summer. And what we see is that it was relatively steady until a big increase in ice discharging to the ocean during a short five- to six-year period,” King said. “Glaciers have been sensitive to seasonal melt for as long as we’ve been able to observe it, with spikes in ice discharge in the summer. But starting in 2000, you start superimposing that seasonal melt on a higher baseline – so you’re going to get even more losses.”

Since 1985, large glaciers across Greenland have retreated approximately three kilometres on average. The glaciers have shrunk back enough that many of them are sitting in deeper water, so there is more ice in contact with water. Warm ocean water melts glacier ice, and also makes it difficult for the glaciers to grow back to their previous positions.

The team’s analysis found that the baseline of that pulse started increasing steadily around 2000, so that the glaciers were losing around 500 gigatons each year. Snowfall did not increase at the same time, and throughout the past ten years, the rate of ice loss from glaciers has stayed about the same. This means that the ice sheet has been losing ice more rapidly than it’s being replenished.

As a result, even if we managed to stop all climate change tomorrow, ice would still drain into the ocean from glaciers and likely still exceed ice gained from snow accumulation. The ice sheet would continue to shrink for some time. Before 2000, the ice sheet would have about the same chance to gain or lose mass each year. In the current climate, the ice sheet will gain mass in only one out of every 100 years.

“Glacier retreat has knocked the dynamics of the whole ice sheet into a constant state of loss,” said Ian Howat, a co-author on the paper, professor of earth sciences and distinguished university scholar at Ohio State. “Even if the climate were to stay the same or even get a little colder, the ice sheet would still be losing mass.”

Ice from Greenland’s glaciers is a leading contributor to sea level rise. Last year, enough ice melted or broke off from the Greenland ice sheet to cause the global oceans to rise by 2.2mm in just two months.

“It’s always a positive thing to learn more about glacier environments, because we can only improve our predictions for how rapidly things will change in the future,” said King. “And that can only help us with adaptation and mitigation strategies. The more we know, the better we can prepare.”

Photography by Michalea King.

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