Someday, I would like to write a happy story about ice. Today is not that day.
Using historical photos and modern satellites, scientists have taken an unprecedented dive into understanding some of Greenland’s most imperiled glaciers. The findings show the at-risk ice has undergone a major retreat over the the past century-plus, indicating that our future projections of ice loss may be underestimating the massive scale of melt that awaits this century if carbon emissions are allowed to rise unchecked.
The study, published in Nature Communications on Tuesday, looks at Jakobshavn, Kangerlussuaq, and Helheim glaciers, all of which tumble from the heights of the ice sheet down to sea. The first is Greenland’s fastest-moving glacier and has been the source of massive iceberg calving events in recent years. Kangerlussuaq Glacier is equally struggling, while Helheim Glacier drains a large swath of Greenland and is the fastest ice conveyor belt on Greenland’s east side that’s also popped off some big ‘bergs.
Researchers have generally relied on the satellite record to monitor changes to these and other glaciers. But the new study also uses old photographs taken during aerial surveys from the mid-20th century, as well as records from the early 20th century kept by Danish explorer Lauge Koch (I know, I know). Together, the historical data allowed researchers to identify the “trimlines”—basically, bathtub rings where the ice once reached—and track where the glaciers’ fronts once stood and how thick they were.
The results show absolutely staggering ice loss from the late 19th century to present at both Jakobshavn and Kangerlussuaq glaciers. The former has shed over 1.5 trillion tons. Helheim has seen “just” 31 billion tons of ice slip into the sea. The reason for the massive loss at Jakobshavn and Kangerlussuaq glaciers is that the bedrock beneath them slopes downward, allowing increasingly warm water to undercut them, similar to processes playing out in West Antarctica. Kangerlussuaq had what the researchers lovingly call a “bedrock bump” that protected it from that process in the late 19th century, but once the glacier front receded, warm water came pouring over the bump.
Though Helheim Glacier was relatively more stable, the study shows that its recently increasing speed of retreat is more likely to be the norm, since the oceans continue to warm. All told, ice from these three glaciers alone is responsible for about a tenth of an inch (8.1 millimeters) of sea level rise over the past decade.
That may not sound like a big amount, but the findings raise concerns about the future of the ice, and thus the coasts. We already know Greenland is losing ice at a quickening pace over the satellite era, and the trend is likely to continue. Climate models factor in that quickening, but they don’t necessarily get the mechanisms quite right. The widespread, sustained ice loss over the past century happened as the world has warmed just 1.8 degrees Fahrenheit (1 degree Celsius). Future warming will likely be much more intense as emissions rise, particularly in the Arctic, which is warming three times as fast as the rest of the world.
“To look at more than a hundred years gives us confidence that our measurements are correct, and not caused by short-term weather fluctuations,” Anders Bjørk, a University of Copenhagen ice researcher who co-authored the study, said in an email. “This study tells us that it is likely that the best models we have at the moment are very likely underestimating what will happen in the future.
“What the models are missing is higher-resolution input data and the ability to be coupled with other models,” Bjørk said, noting that ice loss is affected by a variety of factors and feedbacks, and climate models need to better capture them to more closely mirror reality.
Indeed, the threats to Greenland’s ice sheet and glaciers are myriad. Byond temperature, recent findings show increasingly sunny skies could melt ice as could more soot from wildfires driven by climate change. To understand the climate system really requires a birds eye view, and unfortunately the higher we get to take it in, the worst things look.