Climate change pushes Greenland over the edge

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Matthew Osman sits atop an ice cap in West Greenland and overlooks the Nuussuaq Peninsula. In the distance and more than 2,000 meters below, the village of Ilulissat is just a tiny speck in the vast expanse of snow and ice. As Osman sinks into the snow, he sinks into a crevasse up to his thigh. As he walks away cautiously, he is reminded of the dangers of working on the ice. Like others who have ventured to drill into the ice of Greenland, Osman and his colleagues brave the dangers to search for clues about how the climate has changed in the past and, by extension, how it might change in the future. to come up. What they discovered is an unexpected sign of the true scale of ongoing climate change.

The research team led by Osman, a geoscientist from the University of Arizona, came to Greenland to extract a 140-meter-long ice core. This core extends almost to bedrock and, in the gases and chemicals it contains, contains evidence of climate change over the past 2,000 years. Their kernel analysis shows that at this location during the Medieval Warm Period, a roughly 400-year phase of higher global temperatures around 1,000 years ago, the ice was getting thicker and advancing, the opposite of what it does today.

Previously, scientists assumed that advancing ice during the Medieval Warm Era was evidence that the west coast of Greenland was subject to paradoxically colder conditions during the otherwise Warm Era. But the results of Osman and his teams show that the ice sheet was growing because it was warmer. Higher temperatures, Osman says, caused more evaporation which led to more snowfall. “It’s really surprising and it’s not like you would expect an ice cap to react during a warmer period,” he says.

Rising temperatures during the Medieval Warm Period would have caused the wind to pick up more moisture from the ocean and bring more snowfall along the coast. But whether the ice thickens and progresses also depends on how much ice melts due to warmer weather. During the Medieval Warm Period, summer melt increased, Osman says, but increased snowfall eventually won out and the ice grew larger.

The study shows the complexity of a warming climate system, says Anais Orsi, a polar scientist at the University of British Columbia who was not involved in the study. With the right conditions, “you can have warming and advancing ice at the same time.”

Today, however, driven by anthropogenic climate change, the ice caps and glaciers along the west coast of Greenland, like in most other places, are retreating rapidly.

The contrast makes the implication easy to see: “Our summer warming is unprecedented,” says Orsi. “Our summer warming is greater than during the medieval warm period.”

“We are definitely going into climate change surprise mode,” she adds.

“It’s an alarming sign that we’ve tipped the scales on how this aspect of the climate system fundamentally responds to warming,” Osman says.

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