Weekly Science Talk丨How do ancient ice cores tell the story of the ancient Earth’s climate evolution?

When archaeologists want to learn about ancient civilizations, they look for artifacts to help them do so. Paleoclimatologists take a similar approach, looking for clues to Earth's climate history by studying coral reefs, digging up ocean and lake sediments, and glaciers and ice sheets.

Like organisms trapped in amber, airborne remnants of Earth's early climate, such as dust, air bubbles, sea salt, volcanic ash and soot from forest fires, can also be trapped in glaciers for hundreds of millions of years. For climate scientists, these relics tell the story of how Earth's climate and atmosphere have changed over thousands of years.

Ice cores are cylindrical snow and ice samples drilled from glaciers. Ice cores taken from glacier accumulation areas contain snowfall and dry and wet sediments that have accumulated year by year, which preserve information about the climate and environment at the time of their deposition. Ice cores obtained from glaciers have the characteristics of high resolution, strong continuity, and good fidelity.

Each layer of ice tells a story about past climates, what the Earth looked like when a layer of snow fell. The ice also contains particles from the atmosphere at the time, such as dust, ash, pollen, trace elements, and aerosols like sea salt. These particles remain in the ice thousands of years later, providing physical evidence of past global events. In addition, as the ice compresses over time, tiny bubbles of air from the atmosphere—including greenhouse gases like carbon dioxide and methane—are pressed into the ice.

In order to explore the changes in the global climate environment in different geological periods, scientists around the world have conducted extensive research on the ice cores of the Arctic and Antarctic, and gradually clarified the characteristics of climate change in the Arctic and Antarctic over the past hundreds of thousands of years. However, this is only a study of the polar regions. The ice core research in the mid-latitude regions, as the "bridge and link" of the ice core research in the polar regions, should not be ignored. The Qinghai-Tibet Plateau, known as the "Asian Water Tower", is the source of water for several major rivers in Asia (such as the Yangtze River, the Yellow River, the Yarlung Zangbo River, the Indus River, etc.). The Qinghai-Tibet Plateau is also the most extensive glacier distribution area in the mid-latitude region, so ice core research in this area is particularly important. Thanks to the natural geographical advantages, the research on climate and environmental records of ice cores conducted by Chinese researchers in the Qinghai-Tibet Plateau region has gradually received attention. The "Research on High-Resolution Climate and Environmental Records of Ice Cores in the Qinghai-Tibet Plateau" jointly carried out by the Qinghai-Tibet Plateau Institute of the Chinese Academy of Sciences and other units won the second prize of the National Natural Science Award in 2014.

Based on the monitoring of the climatic significance of modern precipitation on the Qinghai-Tibet Plateau, the project carried out the reconstruction of the paleoclimate significance and environmental changes of 12 ice cores, and studied the climate and environmental changes of the Qinghai-Tibet Plateau since the last interglacial period and its relationship with surrounding areas. The Qinghai-Tibet Plateau has shown a clear warming trend over the past half century, with a greater warming than areas at the same latitude, and a unique altitude-dependent warming phenomenon. By studying the relationship between a variety of proxy indicators in the ice cores of the Qinghai-Tibet Plateau and climate and environmental changes, the researchers reconstructed and analyzed high-resolution climate and environmental records at different time scales over the past 100,000 years, and found that under the influence of global changes, the Qinghai-Tibet Plateau is more sensitive than other regions, with more dramatic changes and more regional differences.

It was not until the middle of the 19th century that humans began to observe temperature and other variables on a global scale. Due to the short recording period, it is impossible to fully and objectively understand and recognize climate change by relying solely on short-term observations. Therefore, it is very necessary to conduct simultaneous research on climate change in historical and geological periods (i.e., paleoclimate change). Ice cores are one of the means to study paleoclimate characteristics, providing a comprehensive perspective for understanding the laws of long-term climate change. On the other hand, they also provide extremely valuable reference information for predicting future climate change and identifying the impact of human activities on the climate.

(Text: Zhu Yehua, deputy editor of Science and Technology Herald; review expert: Zou Zhen, associate researcher of China Science Popularization Research Institute)

China Association for Science and Technology Department of Science Popularization

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