What was behind the seismic boom that wrapped Earth for 9 days?

It was a warning shot picked up by seismometers around the world. Last September, a melting glacier collapsed, sending the mountaintop it propped up careening into the Dickson Fjord in East Greenland. The impact created a 650-foot tall tsunami — twice as tall as the Statue of Liberty — which crashed back and forth between the steep, narrow walls of the channel, booming so loud that the vibrations wrapped the globe in a 90-second interval pulse for 9-straight days.

“It’s like a climate change alarm,” said Stephen Hicks, a seismologist at University College London. Hicks is part of an international team of researchers who finally sleuthed out the source of the vibrations that had been a source of bafflement ever since earthquake monitoring stations recorded the signal. Unraveling the mystery and mapping out the tsunami took the team of 68 scientists, from a wide range of disciplines, a full year.

The resulting paper, recently published in Science, blames man-made global warming for the collapse. A century of greenhouse gasses heating up the atmosphere have eroded swaths of the Greenland ice sheet — frozen freshwater that holds back 23 feet of potential sea level rise. Hicks said this kind of landslide-tsunami has never been seen in East Greenland, an area that tends to experience less melt than the country’s Western perimeter. It could be a one-off, random event, or a sign of spreading instability. “We can maybe expect more of these events in the future,” Hicks said. 

Another group of researchers, from the University of Barcelona, recently confirmed the ice sheet’s trajectory. Their study, published in the Journal of Climate by the American Meteorological Society, found that days of extreme melt, linked to periods of hot, stagnant air in the summer, have doubled in frequency and also intensified since 1950. Roughly 40 percent of the ice Greenland loses in a year occurs during these extreme melting events.

“Each episode of melting is becoming more intense and frequent than in the past,” said Josep Bonsoms, a geography researcher at the University of Barcelona and the study’s lead author. For instance, an extreme melting event in 2012 led to the loss of 610 gigatons of ice, enough to fill Lake Eerie, and then some. 

According to the University of Barcelona researchers, even days of average melt, often influenced by the same weather conditions as extreme days, contribute to worsening melt in the future. Although their study did not make predictions, Bonsoms says the pattern will likely continue to accelerate as the planet heats up.

Take this summer. Greenland experienced above average melt, according to the National Snow and Ice Data Center, but not enough to be considered extreme. In July, two heatwaves ate away at the snowfall in the Western area of the ice sheet, depleting its ability to reflect sunlight, known as albedo. When the darker, glacial ice beneath it became exposed, the land absorbed more heat, intensifying the melt. 

On a bigger scale, this type of feedback loop is one of the reasons that the region is warming four times faster than the rest of the planet, a phenomenon known as Arctic amplification. Tyler Jones, an arctic researcher at the University of Colorado, Boulder, said that among the many catalysts driving Arctic amplification, “the most important is the loss of sea ice.” Unlike Greenland’s land-bound ice, these floating patches of sea ice don’t directly contribute to sea level rise when they melt, but their albedo acts like a giant mirror reflecting the sun’s heat. 

“If you remove that giant mirror, all of a sudden that incoming solar energy gets absorbed by the ocean,” Jones said. Because the ocean can trap and store so much heat, this means the entire region becomes warmer even in the winter. The amount of sea ice remaining in September, the end of the annual melt season, has almost halved since the 1980s — with hardly any older than 4 years surviving. This year, global sea ice levels neared record lows. 

“We’re in a new climate regime. We are seeing extremes that just weren’t in our records of climate ever, just now appearing before us,” Jones said. Because the melting is self-perpetuating, he says, the ice sheet will continue to destabilize until the damage is irreversible. And as sea levels continue to rise, coastal communities around the world will have to adapt to a new world of extremes their cities weren’t built for.

This story was originally published by Grist with the headline What was behind the seismic boom that wrapped Earth for 9 days? on Sep 25, 2024.