Glacier geologists search for global climate clues to support urgent action now

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By Poonam Narotam, Dec. 15, 2021 – 
When he’s not teaching earth science classes and analyzing data at the University of Maine, glacier whisperer Aaron Putnam is trekking into the high Himalayas or New Zealand’s Southern Alps to study where glaciers once stood.

The United Nations officials behind the recent global COP26 climate conference urged countries to eliminate carbon emissions by 45% below 2010 levels by 2030 to stabilize global warming driven by fossil fuel use. No definitive commitments were made toward that goal.

Researchers deepen our knowledge of climate systems and models in the hopes of awakening the urgent need for international solutions before global warming hits a tipping point. Putnam asks the big questions vital to modeling future climate patterns: What caused the last global ice age and how did it suddenly end?

“We need this information from the past to help calibrate our understanding of what’s coming in the future,” said Putnam, 40, an associate professor of earth science at the University of Maine.

Putnam is one of many paleoclimate scientists who studied under and worked with George Denton, distinguished professor at the University of Maine’s School of Earth and Climate Sciences and Climate Change Institute. Putnam and Denton spent the better part of a decade developing a new hypothesis published in March introducing how the westerly winds, the earth’s strongest wind system, contribute to climate shifts between glacial (when glaciers grow) and interglacial periods (when glaciers decline). Both scientists discussed their research at the Comer Climate Conference this fall, an annual gathering of international researchers held remotely this year due to the pandemic.

The findings prompted Putnam to look closely at the similarities between modern global warming and the end of the last ice age, the primary difference being that the pace of today’s climate change is escalating due to human-induced carbon emissions. Putnam, along with Denton and other paleoclimate scientists in their group, tested the hypothesis by mapping key glacier sites in both hemispheres. They found this dynamic system could have a dramatic impact on melting ice in the Southern Hemisphere and global sea level rise.

Putnam studies the land and patterns of rocks to identify where glaciers used to be. He draws detailed maps of the ridges and valleys, and collects rock samples. His research teams ship hundreds of pounds of rock to the Maine lab for testing to determine when the ice sheet melted and exposed the rock.


Aaron Putnam's Field Notes
Aaron Putnam takes copious notes in his all-weather geological field book and illustrated a boulder he sampled in New Zealand in 2014. “I don’t know how he gets all that detail in there,” said Lauren Woods, 22. “His ability to draw things is astonishing.” Woods first took Putnam’s Habitable Planet Seminar as a college sophomore and studies glacial geology and geochronology as a master’s student with Putnam at the University of Maine. (Photo Credit: Aaron Putnam/UNIVERSITY OF MAINE)


Using chemical analysis techniques, graduate students measure the amount of the isotope Beryllium-10 in the rock. The isotope forms in exposed rock when cosmic rays collide with quartz. Piecing together hundreds of precise calculations, Putnam’s team develops a chronology of how that glacier grew and shrank.

As the pandemic prevented travel to Southern Hemisphere glacier sites, Putnam led fieldwork in Wyoming in July to study the Laurentide Ice Sheet, the largest ice sheet of the last ice age. The ice sheet covered the upper half of North America during the ice age and its retreat gouged out the Great Lakes we know today, filling them with meltwater. Expanding glacier chronologies in both hemispheres furthers our understanding of global climate systems and the new patterns Putnam and Denton have been studying.

“We were looking at the surface [of a boulder] to see if it would be good to sample,” said Lauren Woods, a master’s student on the Wyoming trip. “He just kind of leans down to the rock and whispers, ‘Tell us your secrets.’”

Reaching remote field sites

Glacier research also requires finding the right combination of flights, boating routes, drives and treks into some of the world’s most remote places. Putnam said it took his team a week to traverse the Lunana Snowman trek on the border of Bhutan and Tibet, a snowy route amongst glaciers along the main spine of the Himalayas

Disconnected from mainstream communications and living among communities that don’t speak English, Putnam’s group relies heavily on local guides to coordinate directions, emergencies, and food.

Putnam’s Ph.D. student Peter Strand said they bought a sheep from a local herder in Mongolia to keep everyone fed.

“It’s not a good place in the world to be a vegetarian,” said Strand, who jumped at the opportunity to sign on as Putnam’s first Ph.D. student.

“He’s always encouraging everyone to think big,” Strand said. He said Putnam prompts them with the question: “What can this really tell us about how the whole earth system works?”

Without much cell phone coverage, Putnam said he feels more present and able to think in the “glacial graveyards,” areas of land marked by bodies of water and ridges of rock, called moraines, lining the landscape where glaciers once discarded them.

The ‘science’ gene

“When you’re young, you think you’re invincible,” said Putnam. Now the father of a 3-year-old, he’s aware of the dangers of exploring remote terrains. “You had to go over a number of very high passes to get to where you’re going,” he said of his many adventures. “It’s not like you just go back downhill.”

When there was Wi-Fi in the Himalayas, Whatsapp was his lifeline to his wife and baby. Nowadays, he looks forward to spending fewer than four months a year in the field in favor of his dad duties.

Putnam’s love of science runs in the family. His father, archaeologist David Putnam, took a college class with George Denton, who later became Putnam’s Ph.D. adviser. Putnam’s wife is a paleoceanographer and led research on a cruise off the Gulf of Maine in August.

“We’re trying to see if we can begin to plan our fieldwork in ways that we can do it together,” Putnam said. The climate science couple is considering Southern California for her research and New Zealand for his.

They haven’t been in the field together since Putnam’s wife visited him in New Zealand several years ago and he proposed on a peak of the Tasman Glacier.

“I was kind of a nervous wreck about the whole thing, like what if she says no?” Putnam said. She said yes, and they helicoptered back down to finish the day’s work.

Growing up in the Arctic Circle

When Putnam was in high school, his family spent a year in Utqiagvik (then called Barrow) in the northern tip of Alaska.

“We could see when the sea ice [or frozen ocean water] would come in and when it would leave,” Putnam said. The deep north first exposed him to how climate impacted people. The Inupiat people native to Alaska travel over sea ice to hunt and fish for food during the winter.

He celebrated his eighteenth birthday with his biology teacher in the Arctic Ocean on an icebreaker, a ship designed to cut through the ice sheets on the water. His mom snuck a birthday cake for him onto a helicopter during a supply run from the mainland.

“She had me thoroughly embarrassed,” Putnam said. “But that [trip] really clinched it for me; I knew somehow I wanted to get involved, I wanted to be a part of the climate science community.”

“There’s just some sort of intrinsic curiosity in trying to figure out how things work,” he said. “That’s what I find fun about it.”

Determined to continue developing glacier chronologies to advance climate research, Putnam is laying plans for next year’s field seasons – hopefully to Patagonia. His and others’ glacier chronologies demonstrate the complexity of dynamic global climate cycles documented across much of the past 1 million years. And yet, scientists agree that human-driven ice melt and climate change is eclipsing the speed at which climates changed in the past.

Photo at top: Glacier geologist and paleoclimate scientist Aaron Putnam, 40, snaps a photo of a boulder in Soda Lake, Wyoming, in July 2021. The Laurentide Ice Sheet covered the northern regions of the continent, including Wyoming, during the last ice age. The retreat of the ice sheet gouged out the Great Lakes we know today and filled them with meltwater. (Lauren Woods/UNIVERITY OF MAINE)

Poonam Narotam is a health, science, and environment reporter at Medill. You can follow her on Twitter at @namsorama.

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