304-Million-Year-Old Warming Event Shows How a Small Shift Can Trigger a Climate Tipping Point

An international team led by Le Yao of the Nanjing Institute of Geology and Paleontology, including University of Cincinnati Professor Thomas Algeo, studied a rapid warming episode that occurred 304 million years ago during the Late Paleozoic Ice Age, the second most recent ice age in Earth's history. Their analysis, published in the Proceedings of the National Academy of Sciences, found evidence that an initial rise in global sea surface temperature was followed by much stronger warming as thawing permafrost released additional methane, a heat-trapping gas, into the atmosphere.

Sea surface temperatures ultimately rose by more than 7 degrees Celsius (12 degrees Fahrenheit). 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 -- much slower than modern warming, in which sea surface temperature has risen by nearly 1 degree Celsius over just 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 researchers say the resulting carbon release appears to have crossed a "climatic tipping point that led to massive carbon release and transient global warming."

Algeo noted that recorded human history has also unfolded during an ice age, with two continent-scale ice masses still present in Greenland and Antarctica today. "What makes this warming event 304 million years ago unique is that it occurred during an ice age," he said. "That's what makes this event important as an analog for modern-day climate warming," since today's thawing permafrost could similarly release stored carbon and potentially accelerate further warming.