By Frances Mack
Medill News Service, Dec. 16, 2024
As the three field researchers scaled boulders left by the retreats of Norwegian glaciers thousands of years ago, they could hardly see 10 feet in front of them, let alone the rock samples they were searching for.
Much like the conditions these researchers experienced while climbing the remains of the Scandinavian Ice sheet, Earth’s climate history can be foggy.
“Given modern climate, warming is of concern to us, (but) there are still uncertainties,” said Tricia Hall Collins, a Ph.D. candidate at the School of Earth and Climate Sciences at the University of Maine. “By studying the times when climate has done this before, naturally, without humans’ help, we can start to get an idea of how the climate system responds when you crank up the temperature.”
By observing clues in ice and rocks from the past, we can tell the global temperature is rising now at a faster rate than ever. It is clear humans, not natural forces, are responsible for this change.
Collins, with her Ph.D. advisor, University of Maine climate scientist Aaron Putnam, and her field partner, Katie Westbrook, spent a month in the field near Forsand, Norway, in summer 2023. They collected samples from well-preserved moraines and have been calculating their ages to construct a timeline of climate system responses.
Putnam compares how glaciers act to conveyor belts. They rip off chunks of rock from mountains as they pass, and dump debris into large piles as they recede during warming spells. These piles the glaciers leave behind are called moraines.
Glaciers respond to changes in climate: they advance as the atmosphere cools and retreat tens of thousands years later as it warms.
The team collected pieces of rock from the moraines they found. Then, they extracted atoms of beryllium-10, an isotope found in the quartz minerals of rocks exposed to cosmic rays from the sun. The beryllium-10 collects at predictable rates after the rocks are free of ice.
The number of beryllium-10 atoms tells us how long ago the retreating glacier pushed the rock moraines aside. The age and location of the moraine can be used as a scientific indicator, or proxy, for when and how fast the glaciers moved away as they melted.
Using this proxy, Collins was able to track climate trends in Norway, and compare them to trends across the world.
She presented her findings at the annual Comer Climate Conference in southwestern Wisconsin in October. Collins’ dates showed that cooling and warming events occurred at the same time in the Northern and Southern hemispheres. This could mean climate change in the past was a a global phenomenon, which is consistent with what scientists are observing now.
Collins’ research helps scientists learn the rules of the climate game. Knowing these rules gives
insight into how the Earth could respond to human actions, like the burning of fossil fuels, and it can help society strategize next moves.
There’s just one problem: ice cores in Greenland aren’t playing by those rules.
“You’re seeing (the ice core records in Greenland) behaving opposite.” Collins said. “But the problem is, half the time you have this wonky relationship; then (the other) half the time, Antarctica and Greenland agree with each other.”
According to Collins, Greenland’s ice cores, which act as a more sensitive proxy, show warming between 14,600 and 12,780 years ago. This period was named the Antarctic Cold Reversal due to dramatic cooling in the Southern hemisphere. Additionally, there was a mini-ice age in the Northern Hemisphere from about 12,900 to 11,700 years ago called the Younger Dryas, which also caused cooling.
After the presentation, Roger Creel, a postdoctoral scholar at Woods Hole Oceanographic Institution, brought up another variable, glacial moisture.
“There are a lot of settings where an ice sheet gets big enough (that) it’s moisture starved in the center, and that kind of limits how big it can get.” Creel said. “So as it warms up, you could actually expect that it would get bigger, and that may or may not have happened in Norway.”
There are many environmental variables to consider, and several hypotheses that explain the relationship between hemispheres. According to Collins, the Greenland anomaly doesn’t change the global synchrony of atmospheric climate trends.
The Comer conference brings together top climate scientists and their students to brainstorm and report on their latest research. Together, they cut through the fog of confusion surrounding the climate crisis.
“We’re gonna get better, we’re gonna make our models better,” Collins said, “Because, again, the climate dynamics that we’re saying are in play in the paleo world, are probably at play [now and] going forward.”
Photo at top: Tricia Hall Collins took beryllium-10 samples to date moraines in Norway in August 2023. The samples allowed her to form a paleo-geologic chronology of global climate synchronized during the Antarctic Cold Reversal. (Courtesy of Tricia Collins)
