Study of Ice Cores Shows Low CO2 Levels During 3 Million-Year-Old Warm Period

Researchers have used ancient air bubbles trapped in a 3-million-year-old ice core to analyze atmospheric gases from the late Pliocene for the first time. This era, when global temperatures were approximately 1°C higher than today, and sea levels were 25 meters elevated, serves as a crucial reference for current climate discussions.

The results indicated that carbon dioxide and methane concentrations from this period were significantly lower than today’s levels, suggesting that Earth’s climate might be more susceptible to minor changes in atmospheric conditions than previously believed.

In various regions of Antarctica, annual snow accumulation compresses layers into ice that entraps air bubbles, allowing scientists to construct a historical atmospheric record. Last year, the Beyond EPICA team successfully extracted the oldest continuous ice record, dating back over a million years. Learn more about this significant breakthrough.

Furthermore, scientists obtained even older ice in areas where prevailing winds eroded younger layers, bringing older “blue” ice closer to the surface.

Julia Marks Peterson, a professor at Oregon State University, and her colleagues utilized this ancient ice from Allan Hills to make direct measurements of carbon dioxide and methane levels in the Pliocene atmosphere. They discovered that, around 3 million years ago, carbon dioxide was at 250 ppm and methane at 507 ppb—much lower than previously estimated. The higher temperatures of that era went hand-in-hand with a cooling phase where carbon dioxide decreased slightly, while methane remained stable.

These findings starkly contrast earlier indirect measurements, which suggested carbon dioxide levels were nearly equal to today’s 400 ppm. Direct measurements of past methane levels are not feasible, but current standards show it hovering just below the 2000 billionth mark. Explore more about methane trends.

“The results were a bit surprising,” says Marks Peterson. If validated, these findings imply that even slight variations in greenhouse gas concentrations can dramatically affect climate systems. “This could indicate that the Earth is more sensitive to changes in CO2 than we currently understand. That’s a concerning thought,” she adds, “and one that remains unanswered given our existing records.”

New evidence suggesting lower-than-expected Pliocene carbon dioxide levels raises concerns about the potential severity of future climate change, according to Christian Proistosescu from the University of Illinois at Urbana-Champaign, who was not involved in the study.

However, additional research is essential to leverage these findings in climate modeling. Tim Naish from Victoria University of Wellington emphasizes the need for caution. He remains optimistic about uncovering data that could reveal an era of even warmer Pliocene temperatures.

Thomas Chalk from the European Center for Environmental and Geoscience Research and Education asserts the accuracy of the study’s lower CO2 measurements. Yet, he cautions that ancient ice distortions complicate interpretations regarding whether these low values reflect specific climatic periods or an overall average. “It’s essential to understand what these figures truly represent, as they don’t inherently provide a temperature estimate,” he clarifies.

The research team aims to enhance the credibility of their findings by cross-referencing their results with records from the Beyond EPICA group. “This collaborative effort will deepen our understanding of climate history,” states Marks Peterson. “We eagerly anticipate the new insights they will uncover.”