Published on 25 October 2024
Around 12,000 years ago, the most recent ice age had ended, Earth’s climate warmed, and glaciers shrank back. Since then, glaciers have advanced and retreated many times, driven in part by changes in the climate. Today, many alpine glaciers are in rapid retreat, but it’s not because of ice age cycles. This round of melting is likely being caused by human activities.
On a warm morning in August 2024, glaciologist Mauri Pelto stood below the Easton Glacier on the flanks of Mount Baker in northern Washington. This spot was covered by ice in 1990, down to about the orange tent in the photo below, but now the glacier sits well uphill, glimmering brightly in the distance. “These glaciers have advanced and retreated quite a few times in the past 5,000 years,” he said. “It’s not just one progression backwards.”
Alpine glaciers around the world were advancing as recently as 1990. Now they’re melting fast.
The most recent peak extent of the Easton Glacier was around 1850 during a period of regional cooling that caused glaciers in North America and Europe to grow. This event is often called the “Little Ice Age,” though it was not a true ice age because it wasn’t a global occurrence; it involved episodes of both warming and cooling, and it was comparatively short. Since then, the Easton Glacier has acted somewhat like a yo-yo, advancing down the valley during cooler periods, then melting back to higher elevations during warmer times. Even a relatively short-term climate swing on the order of tens of years can cause the glacier to change its size.
August 2024
Shifting glaciers leave behind abundant evidence of their movement. As glaciers advance, they push rocks and sediments in front of them, much like a snowplow on a dirt road. The resulting rockpile is called a terminal moraine. As glaciers shrink, then grow again, a smaller pile of rocks, called a recessional moraine, marks each phase of advancing ice. Amid the rocks, vegetation slowly gains a foothold.
Scientists use this evidence to weave together a timeline of a glacier’s advance and retreat. “There are features you can see, trees you can date, and volcanic tephra layers that tell you how old those moraines are,” said Pelto.
The raw landscape downslope of Easton Glacier is hummocky and treacherously uneven, with loose piles of rock that have only recently been exposed by melting ice. The valley is rimmed on both sides with steep slopes that rise to a crisp edge. These are a third type of moraine, lateral moraines, marking where the sides of the glacier would have been 175 years ago during the Little Ice Age. One such moraine is visible as the sharp ridgeline on the right side of the photo above.
Pelto ticked through the comings and goings of the Easton Glacier since then. “By 1924, this glacier was much larger than today and retreating fairly rapidly,” he explained. By 1950, it had retreated significantly, but then it reversed course. “Around the world, many glaciers—and in some regions, most glaciers—were advancing from 1950 to 1980.”
August 28, 1990 - August 17, 2024
Things began to change by 1990, in the North Cascades and elsewhere in the world. Glaciers melted slowly at first, but then more quickly. And now, the melt is accelerating well beyond anything Pelto has seen. “It’s in the last three years that it’s really roared backwards,” he said, as he motioned to a jumble of bare rock where glacial ice stood not long ago.
The pair of images above shows Mount Baker during the summer in 1990 and 2024. They were acquired with the Thematic Mapper on Landsat 5 and the OLI-2 (Operational Land Imager-2) on Landsat 9, respectively.
Today’s Accelerating Melt
Scientists are tracking the behavior of the world’s alpine glaciers, 45 of which are part of a network of reference glaciers across the planet. Each of these glaciers has over 30 years of continuous measurements. The Easton Glacier is one of seven reference glaciers in the United States.
Pelto and his team have been studying many of the major glaciers in the North Cascades since 1983, using both field measurements and Landsat satellite imagery. His 41 years of firsthand observations for the North Cascade Glacier Climate Project have instilled a deep sense of familiarity with this rapidly changing landscape. As global temperatures rise, the glaciers are melting at an increasingly fast pace.
Hiking up toward the glacier, Pelto pointed out where the ice had been in recent years. He paused at a large boulder, and he motioned toward it with his ice axe (below-left). “I sat on that rock and put my crampons on, with one foot on the ice, in 1990.” Today, in 2024, the ice was 2,000 feet (600 meters) uphill from that spot (below-right).
August 8, 2024
The retreat of the glacier started off relatively slowly, around 30 to 40 feet (10 to 12 meters) per year from 1990 to 2015. “In the last decade, it’s really accelerated,” Pelto said. It’s averaging about 100 feet (30 meters) per year now. But even that rate has been eclipsed in the past few summers.
Hiking closer to the ice, Pelto got his first up-close look at the glacier this year. He then reached the point where ice had been just two years earlier. “In 2022, we stepped onto the glacier here,” Pelto said. “Now this whole flat area, more than 100 meters across, is all free of ice.”
Just in the past two years, Easton Glacier has retreated 450 feet (140 meters). “That’s the fastest retreat rate, by far, that we’ve seen,” said Pelto. At the same time, the glacier has lost around 6 feet (2 meters) of ice thickness each summer since 2021.
This accelerated retreat isn’t a localized occurrence. The glaciologist continued, “2023 was the first year that every reference glacier in the world lost mass. We couldn’t find a single glacier in the network that was gaining mass.” Furthermore, the loss of ice among the reference glaciers is accelerating, just as it is at Easton Glacier.
“It doesn’t matter if you’re in New Zealand or Tibet, or in the North Cascades; glaciers are melting at close to the same rate, all over the place. I’ve worked on 250 glaciers around the world, and 25 of them are gone now.” Pelto continued, sounding resolute, “The glaciers are telling us—they’re struggling with the temperatures they’re experiencing, and they’re disappearing.”
Source:
NASA. (2024, October 24). Today’s Glacial Retreat is a Recent Phenomenon. Earth Observatory.