A recent study examining ancient methane trapped in Antarctic ice provides evidence that global wildfire activity likely increased during times of rapid climate change throughout the last Ice Age.
Published in the journal Nature, this research highlights heightened wildfire occurrences as a significant aspect of these periods of sudden climate change, which coincided with major alterations in tropical rainfall and temperature patterns worldwide.
“Our study indicates that the Earth underwent brief, intense burning events that coincided with these notable climate shifts,” stated Edward Brook, a paleoclimatologist at Oregon State University and a co-author of the study. “This adds new information to our understanding of historical climate data.”
According to Ben Riddell-Young, the lead author of the study and a doctoral candidate at OSU’s College of Earth, Ocean, and Atmospheric Sciences, these findings could enhance our insights into contemporary abrupt climate change.
“This research suggests that we might not fully appreciate how wildfire activity could evolve as global temperatures rise and rainfall patterns change,” he explained. Riddell-Young is currently a postdoctoral scholar at the Cooperative Institute for Research in Environmental Sciences at the University of Colorado, Boulder.
Antarctic ice, formed over tens of thousands to hundreds of thousands of years, contains ancient air bubbles. Researchers analyze ice samples obtained by drilling into these ice layers to study the gases trapped within them, which helps reconstruct the Earth’s historical climate.
Earlier studies have indicated that atmospheric methane levels, a potent greenhouse gas, rose sharply during periods of abrupt climate change in the last Ice Age, which concluded around 11,000 years ago. These climate change events—referred to as Dansgaard-Oeschger and Heinrich events—were associated with rapid temperature variations and changes in rainfall, along with methane spikes. The study aimed to uncover the reasons behind these methane increases.
“The rapid fluctuations in methane levels during these periods stand out,” noted Riddell-Young.
He utilized samples from the two-mile-long Western Antarctic Ice Sheet Divide Ice Core, along with an additional core collected using a specialized drill that collects more ice without losing the core sample. The data from these cores extend back 67,000 years.
“Although the ice in this region doesn’t date as far back as other ice cores due to higher annual snowfall rates, it provides more ice per year, allowing us to capture greater detail for those specific years,” added Brook, a professor at OSU’s College of Earth, Ocean, and Atmospheric Sciences.
Riddell-Young employed a system of his own design to extract air from the ice samples, followed by using a mass spectrometer to analyze the isotopic makeup of the methane, which can reveal its atmospheric sources.
The observed isotopic changes indicate that the spikes in methane were likely driven by increases in wildfires around the globe, according to Riddell-Young.
“These fire incidents probably contributed to the series of effects triggered by the abrupt climate change,” he explained. “It seems that rapid changes in ocean currents led to quick temperature shifts in the northern hemisphere, which then resulted in sudden changes in tropical rainfall, inducing more drought and fire.”
While earlier studies have associated temperature changes and shifts in tropical rainfall with periods of abrupt climate change, this new study provides compelling evidence that wildfire activity was also a characteristic of these times, according to Brook.
Further research is required to understand better how these burning periods influence climate patterns, Brook mentioned. For example, fires produce atmospheric CO2, another greenhouse gas that contributes to climate change.
“Delving into what these burning patterns imply for the carbon cycle is one of the future research directions,” he added.
This research received support from the National Science Foundation. Other co-authors of the study include James Lee from Los Alamos National Laboratory; Jochen Schmitt and Hubertus Fischer from the University of Bern; Thomas Bauska from the British Antarctic Survey; James A. Menking from the Commonwealth Scientific and Industrial Research Organization in Australia; René Iseli from the University of Fribourg; and Justin Reid Clark from the University of Colorado, Boulder.
