Fifty-six million years ago, Earth underwent a catastrophic global warming event. On July 7, scientists from the Hainan University’s State Key Laboratory of Marine Resource Utilization in South China Sea reported that Professor Jiang Shijun’s team, in collaboration with domestic and international research teams, used high-precision geological records and Earth system models to detect rapid CO2 release event preceding this warming event. This finding sheds light on the mechanism by which rapid carbon release in deep-time triggered global warming, providing valuable insights into today’s extreme climate events. The results were recently published in the international academic journal Nature Communications.
The Paleocene-Eocene Thermal Maximum (PETM) was the most extreme global warming event since the Mesozoic era. It was triggered by the rapid release of large amounts of light carbon, leading to a global temperature increase of 5°C to 6°C, a sharp rise in atmospheric CO2 concentrations, intensified ocean acidification and hypoxia, and the restructuring of ecosystems, making it a climate disaster of unprecedented scale.
Before this warming event, geological records captured a “warning signal”: a shorter-duration, lower-amplitude carbon isotope negative excursion event (POE), akin to the first rumblings of a storm, though the connection between the two phenomena remained unclear.
Professor Jiang’s team focused on the sedimentary strata at the Kuzigongsu section in Xinjiang, China. These strata contain “climate diaries” that span millions of years. By conducting multi-indicator analysis and Earth system model cGENIE dual inverse simulations, the team pioneered sensitivity simulation experiments to reconstruct ocean carbon cycling and environmental changes during the POE, on scales ranging from centuries to millennia. The team confirmed that the POE event was synchronous on a global scale. Results showed that the POE lasted a short time with a negative carbon isotope shift of approximately 1‰ to 2‰, accompanied by slight warming, shallow ocean acidification, increased terrestrial input, microbial community restructuring, and a trend toward deoxygenation in shallow marine environments.
Further analysis revealed that during the POE, carbon was released at a rate of approximately 1 gigatonne per year (Gt/yr), comparable to global fossil fuel emissions during the 1960s. This caused atmospheric CO₂ concentrations to rise by ~40% within 100–1,000 years—a rate of increase mirroring that seen over the past six decades. Both simulation results and geological evidence indicated that the primary source of the POE’s carbon emissions came from early volcanic activity in the North Atlantic Igneous Province. Magma intruding into organic-rich sediment layers triggered instantaneous pyrolysis, which “baked out” vast quantities of CO₂ in a geologically abrupt “carbon explosion”. This pulse of carbon abruptly disrupted the global carbon cycle, priming the Earth system for the subsequent, larger-scale PETM extreme warming event.
56 million years ago, Earth demonstrated the consequences of rapid carbon release through a “natural experiment”. Today, humans are pumping CO2 into the atmosphere at an even faster pace. Professor Jiang Shijun cautioned that studying Earth’s climate history reveals that once carbon emissions exceed a critical threshold, the climate system could collapse like dominoes, triggering even greater crises. “We must reduce emissions before carbon accumulation reaches a tipping point to avoid repeating the PETM-style global climate disaster,” said Professor Jiang.
Translated by Shi Buyue
Proofread by Zhao Yanchun
