by frances mack

global temperature has risen at an unprecedented rate since the mid-1800s, and it’s clear humans, not natural forces, are responsible for this change. 

scientists are turning to clues found in ancient ice and rocks to understand how the planet’s climate system has responded to rising temperatures in the past.

a team of researchers led by university of maine climate scientist aaron putnam has uncovered evidence in norway suggesting atmospheric climate trends are globally synchronous. this research gives scientists insight into how the earth could respond to human actions, like the burning of fossil fuels, and it can help society strategize next moves.

“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,” said tricia hall collins, a member of putnam’s team and ph.d. student at the school of earth and climate sciences at the university of maine.

putnam, collins and graduate student katie westbrook, spent a month in the field near forsand, norway, in summer 2023. they collected samples of rocks deposited on well-preserved moraines and have been calculating their ages to construct a timeline of climate system responses.

moraines are piles of rocks ripped off the sides of mountains by passing glaciers, that are then dumped into large piles when the glaciers recede during warming spells.  

glaciers respond to changes in climate: they advance as the atmosphere cools and retreat tens of thousands of years later as it warms. this means the placement of a moraine and its age can indicate when and how fast the glaciers moved away as they melted. this gives researchers insights into climate history.

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, from the samples. 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. 

using the data they collected, collins tracked climate trends in norway, and compared 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 roughly the same time in the northern and southern hemispheres. 

this suggests that climate changes were not isolated occurrences, which is a pattern reflected in modern climate trends.

there’s just one problem, ice cores, which are another climate indicator, show warming and cooling patterns in greenland that oppose the team’s moraine data.

“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.”

collins said during the antarctic cold reversal, a period between 14,600 and 12,780 years ago, antarctic ice cores and the moraine records she collected in norway, both showed cooling trends.

ice core records in greenland showed evidence of warming at this time.

however, collins said this relative warming in greenland was a regional response to global conditions, and not a global climate signal. 

“what’s happening in your backyard isn’t what’s happening in the entire state,” collins said.

according to collins, despite the greenland anomaly, climate change occurred on a global scale, and likely will in the future.

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, conflicting proxy records and several hypotheses that explain global climate trends of the past.

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.”