A new ice core drilled from a tropical glacier in Peru is forcing scientists to rethink the history of atmospheric methane. The record, published in Nature, shows that methane levels in the tropics were far higher in the past than previously assumed, suggesting that current global estimates may be missing a major piece of the puzzle.
A frozen archive from the Andes
Researchers extracted the ice core from a high-altitude glacier in the Peruvian Andes, a region where ice accumulation is rare and difficult to access. The core contains trapped air bubbles that preserve samples of the atmosphere from the past 1,000 years. By analyzing the gas in these bubbles, the team reconstructed a continuous record of methane concentrations, a powerful greenhouse gas.
The scientists, led by Kara A. Lamantia and Lonnie G. Thompson, found that methane levels in the tropical atmosphere were consistently higher than those recorded in polar ice cores from the same periods. This discrepancy is significant because polar cores have long been the standard reference for global methane trends. The new data suggest that tropical sources, such as wetlands and fires, may have played a much larger role in the methane cycle than previously recognized.
Why the tropics matter
Local researchers and communities in Peru have long known that the glaciers are vital for water supply, but the ice also holds clues to global climate. The glacier sits in the tropics, a region that is both a major source and a major sink for methane. Tropical wetlands, for example, produce large amounts of methane naturally, while atmospheric chemistry in the tropics can destroy it. The new record shows that these processes have varied significantly over centuries, likely in response to changes in temperature and rainfall.
The findings are important for climate models, which rely on accurate historical data to predict future changes. If tropical methane emissions were higher in the past, models may need to adjust their assumptions about how sensitive these sources are to climate shifts. The study also highlights the value of tropical ice cores, which are disappearing as glaciers retreat due to warming.
A new window on the past
The Peruvian ice core is one of the few tropical records of its kind, and it offers a rare glimpse into a region that is often underrepresented in climate research. The team compared their data with existing records from Greenland and Antarctica, revealing that the tropics do not always follow the same trends as the poles. This suggests that methane emissions are not uniform across the globe, and that regional differences matter.
The study does not resolve all questions about methane's history, but it opens a new avenue for investigation. As tropical glaciers continue to melt, the opportunity to collect such cores is shrinking. The researchers urge that more efforts be made to preserve these natural archives before they are lost.
In the broader context of climate science, this work underscores the complexity of the methane cycle. It shows that even well-studied gases can hold surprises when examined from a new perspective. The tropical ice core record is a reminder that the Earth's atmosphere has a dynamic and varied past, and that understanding it requires looking beyond the poles.
