A global atmospheric methane record from a tropical ice core

A new study has unveiled the first continuous record of atmospheric methane concentrations from a tropical ice core, offering critical insights into how methane levels have changed over the past two millennia. The research, based on ice cores extracted from the Nevado Huascarán in the Peruvian Andes, provides a detailed look at methane variations in the tropics, a region previously underrepresented in global climate studies. Methane levels in the atmosphere reached 1,935 parts per billion (ppb) by 2025, marking a 160% increase since pre-industrial times, according to the findings published in Nature News. The study highlights the importance of tropical regions in shaping global methane dynamics. Until recently, most atmospheric methane records came from polar ice cores, which tend to reflect conditions more accurately in the Northern Hemisphere. However, these records offer limited insight into the tropics, where much of Earth's methane emissions originate. The new data from the Huascarán ice core fills this gap, revealing that methane concentrations in the tropics have historically been distinct from those recorded in the Arctic and Antarctica. The research team, led by the Byrd Polar and Climate Research Center (BPCRC), drilled two ice cores to bedrock on the summit of the South Peak of Nevado Huascarán, which lies at an elevation of 6,768 meters above sea level. These cores, collected in 2019, enabled scientists to measure methane concentrations in discrete samples. The resulting record marks the first comprehensive methane concentration data from a tropical location, providing a crucial baseline for understanding regional and global methane behavior. Comparisons between the Huascarán data and other ice core records, such as those from Greenland (GISP2) and Antarctica (WAIS Divide), reveal interesting patterns. Over the past 2,000 years, particularly during the Preindustrial (PI) period (from 0 CE to 1850 CE), the average methane concentration in the Northern Hemisphere was consistently higher than in the Southern Hemisphere. This suggests that emissions from the Northern Hemisphere have played a dominant role in shaping global methane levels. The study notes that while the GISP2 record showed an average methane concentration 48 ppb higher than the WAIS Divide record, other polar records, such as the NEEM core in Greenland, showed even smaller differences. The data also underscores the challenges of interpreting methane records from ice cores. For instance, some existing records, such as those from the Sajama ice cap in Bolivia and the Dasuopu glacier in the Himalayas, suffer from issues like high variability due to melting or contamination by dust particles. These problems highlight the need for more reliable tropical records to refine models of methane sources and sinks. The latest findings suggest that methane levels have continued to rise sharply after the PI period, with the most pronounced increases occurring during the Industrial Revolution. The study compares the Huascarán data with the Mauna Loa Observatory’s long-term methane measurements, emphasizing the dramatic acceleration in methane concentrations since the mid-18th century. This trend aligns with growing human activities, including fossil fuel extraction and agricultural practices, which have significantly contributed to methane emissions. As researchers continue to analyze the Huascarán ice core data, they aim to further clarify the complex interactions between natural and anthropogenic sources of methane. The study sets the stage for future investigations into how tropical regions influence global climate change, offering valuable context for policymakers seeking to mitigate greenhouse gas emissions.