How geoscientists in Ireland use Ice Age boulders to forecast climate change
September 17, 2025
The tourists stopped to spread picnic blankets at a scenic point overlooking the picturesque lake of Lough Tay in Ireland’s Wicklow Mountains. But the four scientists trekked on, climbing toward the mountain’s highest reaches in search of promising rocks.
Sam Kelley and Margaret Jackson—the co-principal investigators leading a joint research project for University College Dublin and Trinity College—were gathering samples to date the retreat of the glaciers of the British-Irish Ice Sheet. During the last ice age, 35,000 to 18,000 years ago, that ice sheet covered two-thirds of Britain and Ireland. As a result of warming temperatures and rising sea level, the ice sheet retreated and shrank, completely disappearing 11,300 years ago.
The factors that led to the demise of the British-Irish Ice Sheet are now contributing to the potential collapse of the West Antarctic Ice Sheet. Kelley and Jackson are reconstructing past examples of abrupt climate change to improve existing ice sheet maps and climate models.
“You can’t model the future unless you understand what happened once,” said Kelley, a quaternary geology lecturer at University College Dublin.
Kelley and Jackson’s team chipped pieces of rock laced with quartz from boulders, stowing them in canvas pouches to take back to the lab. The quartz in the samples they collected contains a rare nuclide: beryllium 10. This specific isotope of beryllium is a key ingredient in cosmogenic exposure dating, a technique used to determine the age of a rock’s surface.
There are only two existing ice sheets on Earth, in Antarctica and Greenland. According to imagery from NASA’s satellites, they are melting rapidly, at rates of 136 and 267 billion tons per year, respectively. Climate scientists study the collapse of past ice sheets, like the British-Irish Ice Sheet, to better grasp how much temperature and precipitation fluctuation makes a glacier or ice sheet melt completely. They can then apply this information to the two remaining ice sheets.
Global surface temperature has risen on average 0.11 degrees Fahrenheit every decade since the 1850s. This means Earth is over 2 degrees warmer than before the Industrial Revolution. Rapid warming has already caused dramatic changes in the rates of glacial retreat, ocean acidification, sea level rise, and Arctic ice melt—all of which are unmatched by rates from the last few millennia. According to an annual report from the National Oceanic and Atmospheric Administration, 2024 was the warmest year on record since their climate data collection began.
Data from NASA’s GRACE and GRACE Follow-On satellites show Earth’s temperature has increased over the last century (above), and the land ice sheets in Antarctica (below)and Greenland (bottom) have lost mass since 2002. (NASA)
Data from NASA’s GRACE and GRACE Follow-On satellites show Earth’s temperature has increased over the last century (left), and the land ice sheets in Antarctica (middle) and Greenland (right) have lost mass since 2002. (NASA)
Even if emissions slow or decline, temperatures are projected to rise to between 2.4 and 5.9 degrees Fahrenheit above pre-industrial levels by 2050. At the low end of these projections, there will be deadlier heat waves, heavier rainstorms, and an increase in regional droughts and forest fires. At the higher end of climate projections, the Antarctic and Greenland ice sheets could melt irreversibly, according to the Intergovernmental Panel on Climate Change’s sixth assessment report. If the ice sheets were to melt completely, sea level would rise by up to 70 yards (yes, more than 200 feet), inundating coastal cities and ecosystems and displacing millions of people.
Scientists have been studying the physical legacy of the British-Irish Ice Sheet for over a century, and years of observations and records have been funneled into one place: the BRITICE Glacial Mapping Project. But in spite of the years of work that have gone into collecting and publishing this information, there are still unresolved questions around the timing and melt pattern of the ice sheet’s retreat.
Jackson’s team is working to fill in gaps in the BRITICE dataset about the ice sheet’s sensitivity over time. The dating technique her team uses gives them more accurate and precise locations for glaciers than are outlined on the BRITICE map.
Not just any rock will do when you are searching for time machines.
Jackson marched toward a boulder in the Wicklow Mountains with Apolline Mariotti and Helen Dulfer, two postdoctoral researchers at Trinity College. Once they reached it, the three members of the team knelt to examine the quartz-abundant boulder sitting on cobbles on top of bedrock.
“I don’t think anything could have moved it,” Jackson told the researchers.
The dating process analyzes beryllium 10 to estimate the timing of the rocks’ surface exposure to the atmosphere. By counting how many atoms of beryllium 10 are in a sample, scientists can estimate how old it is using the known accumulation rate for the nuclide.
The team decided it was worth collecting samples from the boulder. Quartz holds the time machine, after all. When the mountain glaciers retreated thousands of years ago, the boulders they left behind were exposed to cosmic rays, high-energy subatomic particles released by supernova explosions of stars. These cosmogenic particles careened through the atmosphere, smashing into stable atoms on a rock’s surface, rearranging the subatomic particles of silicon and oxygen in the quartz and producing a distinct flavor, or isotope, of beryllium—one with two extra neutrons, known as beryllium 10.
These nuclides are usually collected from moraines, which are ridges of dirt and rocks that were carried and left behind as glaciers melted. By dating a series of moraines, the researchers can track the recession of glaciers during a period of abrupt warming at the end of the last ice age.
Because beryllium 10 does not naturally occur in quartz, and is primarily formed by exposure to cosmic rays, Earth scientists look for granite or sandstone boulders that contain large quantities of gray-colored quartz at the surface. The general rule of thumb is to look for boulders that clearly sunbathe and do not sit in mountain shadows. But there are exceptions to this rule, according to Kelley.
“Cosmic rays are coming from every direction at once,” Jackson said. “It’s how much of the actual horizon the rock surface can ‘see.’”
While hiking up Ireland’s mountains, the geoscientists try to locate the appropriate boulders at higher altitudes because cosmic rays hit the rocks with greater intensity where the magnetic field weakens and is less capable of “protecting” the rocks from radiation.
At each boulder location, Jackson withdrew a small metal instrument, not unlike a vertical compass or protractor. The tool, called a clinometer, measures the precise angle between the horizon and surrounding landforms to calculate how much of a boulder would be shielded from descending cosmic rays.
Once the team has decided a boulder is worth examining, they collect about one kilogram of the sample to bring back to the lab.
Video by Frances Mack
In a small, ivy-shrouded shed on the edge of the University College Dublin campus, Jackson and Dulfer prepared to pulverize the rocks they spent so long collecting. Jackson adjusted her N95 respirator and put her safety glasses on. She wove between the commercial vacuums hanging from the ceiling, switched on the ventilation system to collect dust, and sat down next to the “jawbreaker.”
Jackson dropped rocks into the machine, which rattled as it crushed them into bits. She then took the pieces of rock and poured them into a second machine that ground them even smaller, before passing them off to Dulfer to shake through a series of sieves. They will go through this process three times for each of Dulfer’s 30 samples.
They do this because they need to separate the beryllium 10 from the rest of the rock. According to Dulfer, most of the samples are conglomerates, or rocks made of different sediments and minerals clumped together. It’s easier to separate the beryllium 10 from rocks that have been ground into sand-like granules, she added. And there’s more than one “recipe” for stripping the sample down to what they need. The scientists soak their samples in what Jackson referred to as “nasty” baths: a series of nitric, hydrochloric, and hydrofluoric acids. Afterward, they use other techniques, like density separation and heating, to make sure the samples are as pure as possible.
“Once we have just that pure quartz left, then we dissolve that totally,” Jackson said, “and from that dissolved pool of quartz and acids, we do a few different things to remove all of the different minerals and atoms that are not (beryllium 10).” In the end, they’re left with samples barely larger than “a few flakes of dandruff,” Kelley said. The miniscule samples are sent across the Atlantic Ocean to a facility in California for dating.
Returning to the field, Dulfer sat cross-legged on top of a large, mossy boulder in the middle of a valley in the Comeragh Mountains, near Ireland’s southern coast. She pulled out her yellow field notebook and started to sketch the landscape, trying to visualize how the glaciers carved through the rocky slopes. Through her postdoctoral project, Dulfer is trying to find the last little mountain glaciers that existed in Ireland at the end of the most recent ice age.
According to Kelley, small glaciers are very sensitive to shifts in climate. During periods of cooling, the glaciers would grow and advance onto the land enough to form moraines, and during warming spells, they would melt and retreat. Dating these moraines tells Dulfer how the glaciers were moving and interacting with the landscape, which reflects when there were rapid shifts in climate in the greater North Atlantic.
“Helen had three or four samples that show the glaciers were retreating during the Last Glacial period,” Kelley said.
The next step for Dulfer’s project will be mapping the movement of these glaciers. The team will be working with a modeler to create a visualization of her findings.
Dulfer previously worked with the team at Sheffield that developed the BRITICE map. Though she didn’t work on the mapping project directly in her time there, the boulder locations and dates she finds now build on their work. “These kinds of maps are really great because they highlight what’s missing,” Dulfer said.
Dulfer’s colleague Mariotti is investigating how and at what speed ice sheets break down. It’s difficult to model large ice sheets, since they cover large areas and change slowly over long periods of time. But by looking at the small signs of ice sheet movement in the mountains, Mariotti will build on and refine past projects, like the BRITICE map.
Understanding how the ice sheet that covered Ireland broke down will help climate modelers paint a more accurate picture of how the Greenland and West Antarctic ice sheets will collapse if global temperatures continue to rise. Scientists can use these models to make predictions about things like how much sea level will rise as the ice sheets melt or where devastating tropical storms might hit. This will inform decision-making and disaster management, as society will be better able to prepare for intense natural disasters caused by climate change.
“Whenever we make a model of either the Greenland ice sheet or one of the Antarctic ice sheets, we always have to test it on the past to see how well it can reconstruct what we know happened,” Kelley said.
This article was produced in partnership with Northwestern University’s Medill School of Journalism, Media, Integrated Marketing Communications.
Frances Mack is a freelance multimedia journalist specializing in scientific and environmental reporting. She is an editorial intern for the Bulletin... Read More
Cathy Ching is a freelance journalist focused on stories that explore climate, justice, and accountability. She aims to interpret complex issues in... Read More
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Keywords: Ireland, climate change, climate science, glacial geology, glaciers, ice ages
Topics: Climate Change
