This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A new analysis of ice cores collected from the Andes in Peru has produced the first global record of historical tropical methane, filling a critical gap in our understanding of the origins of Earth's greenhouse gases. By examining small air bubbles trapped in ancient ice, scientists studied a 2,000-year-old record of how atmospheric methane evolved over time.
They discovered that the concentrations found in Nevado Huascarán, the world's highest tropical mountain, broadly agree with global fluctuations recorded in polar regions—but are slightly higher. These results support the longstanding hypothesis that methane emissions from tropical sources like the Amazon rainforest likely dominated Earth during the preindustrial period, while a rise in human-driven agricultural and industrial emissions contributed to methane increases in later periods. The study was published today in Nature.
"Huascarán is a Goldilocks spot for capturing global methane, partly because of its high elevation to capture gases and location close to the equator," said Kara Lamantia, lead author of the study and a former graduate student at the Byrd Polar and Research Climate Center at The Ohio State University. "While past studies hypothesized the tropical dominance of past methane sources, with this new core we can confidently confirm that the region was likely responsible for more of these emissions than we assumed before." The second-most abundant greenhouse gas after carbon dioxide, methane traps about 28 times as much heat, meaning it contributes greatly to the planet's warming. This study was the first to sample ice cores from Huascarán to identify the historic sources of these powerful gases.
After collection, five ice core samples were selected from different depths in the core to correspond to key periods in time. Lamantia's colleagues then tested them for the presence of specific isotopes, chemical signatures that are used to determine the origins of the greenhouse gases. "Depending on the source signature, it is possible to differentiate where the methane originated, letting us separate natural sources from fossil fuels," said Lamantia, now a Royal Society Newton International Fellow at the University of Bristol.
"Our sample revealed a globally well-mixed signature, but methane emissions lean slightly toward a more biogenic source, potentially from the wetlands in South America or Asia." Researchers also found that more recent measurements from the ice matched well with observations from the Mauna Loa base station in Hawaii, the global center for monitoring greenhouse gases. According to the study, previous reconstructions of historical methane records point to the same trends shown in this paper, but because those were built solely around polar ice cores—collected from Greenland and Antarctica—they may have underestimated the importance of tropical emissions. The researchers noticed spikes in their tropical methane record that could be attributed to events like the rise and fall of the Inca Empire, as well as the Little Ice Age, which could be helpful markers for assessing their data against other models.
Overall, the data from this work strengthen historical climate records and further solidify the significant role the tropics play in both monitoring and understanding the distribution of global greenhouse gas emissions, said Lamantia. Learning more about global sources of greenhouse gases can help researchers propose steps to mitigate increased warming, but opportunities to extend the analysis to more targeted ice core sampling in the tropics are rare due to rapid glacier melt. Still, these findings open up new pathways to help resolve other pressing environmental uncertainties, said Lamantia.
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