By Sara Cooper
Medill News Service, Dec. 18, 2024
Nearly 19,000 years ago the Cordillera Darwin mountain range was changing. Fast. The mass of glacial ice that blanketed the region, previously sustained by the cool conditions of the Last Glacial Maximum, was under attack by a warming climate.
Glaciers receded but they did so conspicuously. As they melted, the rocks and other debris held within their ice were released. These deposits, called moraines, are the footprints of glaciers, capturing their movement over time and space.
Under a stable climate this movement is slow, occurring on a geologic timescale. When the climate changes, however, glaciers can be quick to respond. According to recent data on Cordillera Darwin glaciers, their melting can take a rapid pace even in the absence of human-driven climate change.
Field researcher Brenda Hall, a professor at the University of Maine’s School of Earth and Climate Sciences, is chronicling the geologic history of Cordillera Darwin glaciers through moraines, ridges of boulders tossed out of the ice as massive glaciers melt and retreat away. Hall shared her newest findings with fellow climatologists at the Comer Climate Conference in southwestern Wisconsin this fall. Their collective mission: decipher the mechanisms that underlie our climate’s past and future.
“We’re really interested in understanding how it was that the earth, when it was in the depths of its coldest climate, suddenly switched to the climate we have today,” said Hall.
This is difficult work. It takes Hall and her research partner Tom Lowell, a glacial geologist at the University of Cincinnati, to the tip of South America, scouring rocky fields to gather the dozens of moraine samples necessary to build a biography of the Cordillera Darwin glaciers. For these researchers, however, there’s no better place to be.
This is because the Cordillera Darwin mountains sit at the heart of multiple climate mechanisms that may determine whether the global thermostat is set to warm or cool. From this position, the glaciers of Cordillera Darwin are on the front lines of global warming and their inflections over time capture the pattern of climate change.
Hall’s recent findings indicate that the Cordillera Darwin glaciers began to melt sometime before 18,200 years ago, while the final gasps of the Last Glacial Maximum, the ice age preceding our current, warm interglacial climate, may have only occurred several hundred years prior.
“There is a perception that climate change can be slow,” said Hall. “I think with these results I really gain appreciation of how fast things can change.”
This revelation has also surfaced in the work of Hall’s colleagues.
Aaron Putnam is a climatologist at the University of Maine. He presented his own field research from New Zealand moraines at the Comer Conference. Putnam observed similar periods of rapid glacial recession, with some sites retreating as much as 70 meters per year during the Last Glacial Maximum.
“Maybe what that’s trying to tell us is that this is how the earth’s climate system works,” Putnam said, “that it jumps in between stable modes.”
Hall added that this theory of shifting climate modes holds major implications for our current circumstance. “If that is indeed how climate really works, and our results are consistent with that, then that means that it could do so again.”
This suggests that the Earth’s climate is a sensitive creature, vulnerable to dramatic shifts when disrupted. And humans are disrupting it in a profound way.
More than anything, this research is a reminder of the power humans hold over the environment. While our influence has largely been seen in the scarring of earth, this also means that we are far from helpless to reverse course.
Roger Creel, a researcher with the Woods Hole Oceanographic Institute who studies Antarctic ice melt, views this silver lining with optimism: “As soon as we muster up the collective action to start cooling the planet off, the ice sheets are going to respond fast. It’s a great incentive for us to work towards that goal.”
Image at top: The view of Isla Hoste as Hall’s team left the Bahia Penhoat region in the Cordillera Darwin mountains early in the morning of March 2024. Exposure ages indicate ice filled the head of this fjord system about 13,000 years ago. (Photo/Brenda Hall)
