In a recent international collaboration, researchers at The Ohio State University's Byrd Polar and Climate Research Center analyzed ice samples from high tropical mountains to gain a unique perspective on the planet's past climate. The research revealed that temperature changes observed in the Huascarán mountains in the Peruvian Andes mirror global mean temperature changes.

The study primarily examined oxygen-stable isotope records within tropical mountain glacier ice cores, offering a distinct paleoclimate history of the Earth's middle and upper troposphere. The researchers made a noteworthy discovery by combining ice core proxy data, paleoclimate simulations, and modern satellite observations and comparing the results to those from previous climate models. During Earth's glacial period, the temperature in this region of the atmosphere cooled significantly by approximately 7.35 degrees Celsius, which, for many researchers, has illuminated new theories about climate dynamics throughout the ages. 

The lead author of the study, Max Thomas Professor of Climate Dynamics, and Atmospheric Sciences Program Director in the Department of Geography and Byrd Center Principal Investigator, Zhengyu Liu, highlighted the importance of this finding, as it provided a remarkably consistent single data source for global mean temperature reconstruction in the tropical region under investigation, consistent with many other independent constructions available, which rely primarily on sea surface temperature proxies. 

The ice cores from Nevado Huascarán in Peru are in a region separated from the oceans, making the samples unique "Goldilocks-type" indicators of global mean temperature changes. Unlike polar ice, tropical ice cores offered an ideal balance and contained evidence suitable for tracking Earth's mean temperature over time. Additionally, this study presented the first land-based estimate of global-stage cooling during the last glacial period.

Published in Science Advances and presented at the annual meeting of the American Geophysical Union this month, the research revealed that surface temperatures during Earth's glacial cooling stages decreased by as much as 5.9 degrees Celsius. 

Due to their unique elevation and location, these high tropical ice records are not affected by regional features of the warming environment. Liu likened this ice core to a weather tower, quietly recording atmospheric history; this is why insights obtained from just one tropical ice core have the potential to improve scientists' comprehension of various aspects of climate, including temperature responses during periods of rapid climate change similar to those occurring today as well those likely to happen in the future, according to co-author and Byrd Center Senior Research Scientist Lonnie Thompson, Distinguished University Professor at the School of Earth Sciences.

Furthermore, these ice cores preserve crucial greenhouse gases. Tropical wetlands are a significant source of methane, a very potent gas preserved in the bubbles in these very high-elevation ice cores where temperatures are frigid and no melting occurs. Methane can warm the atmosphere at alarming rates, so scientists can retrieve methane from these ice cores, enabling them to reconstruct a historical record of its atmospheric concentration. Integrating tropical records with polar data provides a comprehensive global perspective on Earth's climate.

The study's findings also provide insight into a long-standing scientific dispute that has spanned decades concerning using oxygen-stable isotopes in tropical ice cores for deciphering climate fluctuations over time. Previous research has been divided over whether tropical ice core samples can effectively serve as proxies for assessing atmospheric variations driven by temperature or precipitation processes. However, this study proposes that tropical ice cores act as record keepers of air temperature in the mid-upper troposphere across tropical regions. Notably, they also serve as a record keeper of the global mean surface temperature during Earth's last glacial period. 

The study aims to enhance researchers' comprehension of paleoclimatology to bolster our insight into Earth's climatic patterns. Such enhanced knowledge can refine both future climate models and extreme weather predictions.

Collaboration among experts from various fields was crucial in this study, as noted by geography Ph.D. student and co-author Yuntao Bao.

Additional co-authors included Byrd Center Senior Research Scientist and Department of Geography's Atmospheric Sciences Distinguished University Professor Ellen Mosley-Thompson, Clay Tabor from the University of Connecticut, Guang J. Zhang from the University of California, San Diego, Mi Yan from Nanjing Normal University, Marcus Lofverstrom from the University of Arizona, Isabel Montanez from the University of California, Davis, and Jessica Oster from Vanderbilt University. 

The National Science Foundation supported this work.  

Visit Ohio State News or Science Advance to learn more, or download the PDF.

Image: The Col drill site on Huascarán mountain in 2019. Image provided by the expedition team.