Melting permafrost 304 million years ago may have released vast amounts of carbon into the atmosphere.
A warming episode 304 million years ago may show how a relatively small climate shift can trigger much larger changes. Researchers studying the event found evidence that thawing permafrost released methane into the atmosphere, helping drive a dramatic rise in global temperatures during an ancient ice age.
University of Cincinnati Professor Thomas Algeo joined an international team led by Le Yao of the Nanjing Institute of Geology and Paleontology to investigate this rapid warming during the Late Paleozoic Ice Age, the second most recent ice age in Earth’s history.
Their analysis suggests that an initial increase in global sea surface temperature was followed by much stronger warming as melting permafrost released additional methane. Sea surface temperatures ultimately increased by more than 7 degrees Celsius, or 12 degrees Fahrenheit.
The findings were published in the Proceedings of the National Academy of Sciences. The research received support from Peking University and the National Natural Science Foundation of China.
A modest warming crossed a threshold
According to Algeo, the warming unfolded over tens of thousands of years, with temperatures rising by roughly one tenth of a degree Celsius every 1,000 years. Modern warming has proceeded much faster. Researchers have measured an increase of nearly 1 degree Celsius in sea surface temperature over only the past century.
The ancient episode may have begun with volcanic activity and been reinforced by cyclical changes in the shape of Earth’s orbit, which alter how solar energy is distributed across the planet. The resulting carbon release appears to have crossed a “climatic tipping point that led to massive carbon release and transient global warming.”
Melting permafrost could amplify warming
The findings raise concerns about a similar feedback process today. As temperatures rise, thawing permafrost can release stored carbon into the atmosphere, potentially accelerating warming and causing even more permafrost to melt.
Episodes of rapid global warming are more commonly associated with what scientists call greenhouse conditions, when large concentrations of heat-trapping gases such as methane and carbon dioxide accumulate in the atmosphere.
Ancient warming offers a rare comparison
Algeo noted that recorded human history has also unfolded during an ice age. The most recent glacial maximum occurred about 20,000 years ago, when woolly mammoths, cave bears, and giant ground sloths still inhabited Earth.
“We’re technically in an ice age because there are two continent-scale ice masses in Greenland and Antarctica,” he said. “What makes this warming event 304 million years ago unique is that it occurred during an ice age. That’s what makes this event important as an analog for modern-day climate warming.”
Reference: “A transient global warming event during Earth’s penultimate icehouse” by Le Yao, Thomas J. Algeo, Qiulai Wang, Wang Zheng, Qiang Wei, Yu-ping Qi, Guzel M. Sungatullina, Genming Luo, Ganqing Jiang, Guoqiang Tang, Jian Zhang, Hui Wang, Yaqiu Zhao, Xing Huang, Qiu-Li Li, Xiang-dong Wang, Shucheng Xie and Xian-Hua Li, 10 August 2026, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2601643123
This work was supported by the National Natural Science Foundation of China (grant nos. 42293290, 42372038, 41630101, 42293280, 42405055, 42525302, and 42421003), the Youth Innovation Promotion Association of the CAS (grant no. 2022311), and the State Key Laboratory of Paleobiology and Stratigraphy of Nanjing Institute of Geology and Paleontology, CAS (grant no. 20232101).
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