Ancient Antarctic Ice Uncovers Spike in Wildfires During Past Climate Changes

Microscopic bubbles preserved in ancient Antarctic ice have uncovered periods of increased global wildfires that align with abrupt climate changes.

Although climate shifts are typically marked by temperature fluctuations, alterations in tropical rainfall, and methane spikes, the role of wildfires had remained unrecognized until now.

“We weren’t specifically searching for evidence of wildfires,” explained lead author and climate scientist Ben Riddell-Young in an interview with ScienceAlert.

“Our primary objective was to identify the cause of the small but sudden methane increases that occurred during recurring intervals of abrupt climate change in the last glacial period.”

The ice core samples analyzed by Riddell-Young’s team provide a 67,000-year record of ice and trapped air. Using mass spectrometry, they deciphered this geological archive by examining methane isotopes.

“Each measurement takes roughly four hours, and we only had a handful of samples representing these abrupt methane increases,” Riddell-Young recalled. “I vividly remember the excitement of observing a significant shift in the isotopic composition in those samples for the first time.”

From Atmosphere to Antarctic Ice

Methane released into the atmosphere typically remains for about nine years before being broken down or removed. During that time, it disperses across the globe and becomes trapped in tiny air pockets within ice layers, such as those found in the Western Antarctic Ice Sheet.

The number of neutrons in the carbon and hydrogen atoms of a methane molecule reveals clues about its origin. Methane from biological sources, like decomposing algae or animal emissions, would show a decrease in isotopic composition as methane levels rise. Conversely, methane released from geological sources, such as volcanic activity, would result in an increase in isotopic composition alongside atmospheric methane levels.

Wildfire Evidence Hidden in Ice

Riddell-Young’s team identified moments in the ice core record where the isotopic composition of methane spiked far beyond levels explainable by geological sources, pointing to the presence of wildfire emissions. Notably, these spikes coincided with known periods of abrupt climate change, suggesting a strong link between the two.

“This study demonstrates that significant shifts in rainfall patterns associated with abrupt climate change can trigger dramatic increases in wildfire activity,” Riddell-Young stated. “It’s a feature of this type of climate change that we hadn’t recognized before.”

These past climate shifts include Heinrich events, where massive icebergs calved off a now-extinct North American ice sheet, and Dansgaard–Oeschger events, characterized by rapid regional warming over decades followed by a few hundred years of cooling.

“The warming and cooling in these events caused rainfall patterns to shift, leading to droughts and, as our study shows, increased wildfire activity,” Riddell-Young explained. “A similar ‘reorganization’ could be triggered by today’s warming, potentially resulting in comparable increases in fire activity. However, modern and past abrupt climate changes are distinct phenomena.”

Today’s warming presents a more sustained and global challenge compared to the episodic Heinrich and Dansgaard–Oeschger events. With wildfires growing in frequency and intensity due to rising greenhouse gas emissions, understanding the complex interplay between fire and climate will be crucial for addressing future risks.

Read the original article on: Science Alert

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