Researchers have reconstructed a dramatic 7.5-degree Celsius global warming event that occurred around 300 million years ago during a major ice age. Published in PNAS by an international team from China, the study reveals how volcanic activity and orbital cycles pushed Earth past a critical carbon-release tipping point, serving as a warning for modern climate change.
Reconstructing a Deep-Time Thermal Maximum During an Ice Age
Scientists have pieced together a dramatic warming event that shook Earth approximately 300 million years ago, providing a stark look at how vulnerable planetary systems are to sudden climatic shifts. Known as the Kasimovian-Gzhelian Thermal Maximum, this ancient hot spell was investigated by an international team of researchers led by scientists from the Nanjing Institute of Geology and Palaeontology (NIGPAS) and Institute of Tibetan Plateau Research of the Chinese Academy of Sciences.
The findings, published in the journal Proceedings of the National Academy of Sciences (PNAS), detail an era when Earth was already locked in a major ice age with massive ice sheets blanketing vast areas of land. Despite these frozen conditions, the planet warmed by an average of about 7.5 degrees Celsius, while atmospheric carbon dioxide levels roughly doubled.
By analyzing fossil teeth and rocks sourced from China and Russia, the research team successfully reconstructed shifts in sea-surface temperatures. The unfolding of this ancient warming happened in two distinct phases. The first phase lasted about 60,000 years, pushing sea-surface temperatures up by roughly 2 degrees Celsius. A much shorter second phase lasting only about 35,000 years added another 3.5 degrees Celsius.
The ancient Earth has shown us that once a climatic tipping point is crossed, the system can change far faster than we might expect,
Yao Le, a professor at NIGPAS, added that the event serves as a cautionary tale for our own time, noting that even modest warming events during an icehouse climate require serious attention because thawing permafrost and melting ice sheets could unleash massive carbon stores.
Volcanic Triggers, Orbital Cycles, and Permafrost Feedback Loops
Unraveling the mechanics behind the ancient warming revealed a surprising sequence of natural drivers. According to the study, volcanic eruptions initiated the preliminary warming phase. However, volcanic activity had already ceased before the main warming phase began.
Instead, natural orbital cycles stepped in to amplify the effect, pushing the global climate past a critical threshold. Once that tipping point was breached, the planet itself began releasing additional carbon—likely sourced from melting permafrost—which drove much more intense and abrupt warming. Researchers noted that the change unfolded over tens of thousands of years at a rate of roughly a tenth of a degree Celsius every 1,000 years.
To put that deep-time rate into perspective, researchers today have observed a nearly 1 degree Celsius increase of sea surface temperature in just the past 100 years.
Algeo emphasized that what makes this 304-million-year-old warming event unique is that it occurred during an ice age, making it a critical baseline analog for modern-day climate warming.
Marine Ecosystem Collapses and the Stakes for Modern Biodiversity
The ecological fallout from the Kasimovian-Gzhelian Thermal Maximum was swift and severe. As oceans warmed and lost vital oxygen reserves, marine ecosystems suffered widespread collapse. Fossil evidence demonstrates that tiny marine animals known as conodonts shrank in size and dropped in diversity, while metazoan reefs were replaced by simple macroalgal reefs.
The findings emphasize that crossing climatic tipping points can destabilize oceanic health and marine life on a massive scale. By observing how ancient systems reacted when pushed beyond environmental limits, geoscientists gain a clearer window into the potential consequences facing modern oceans, where warming pressures continue to mount.
