Ancient trees that lived between 115000 and 12000 years ago have revealed surprising clues about how Earth stabilized its climate during the last ice age. Researchers at Pennsylvania State University discovered that these trees struggled to use carbon efficiently when atmospheric carbon dioxide dropped to extremely low levels near 185 parts per million. Their findings are detailed in a paper published on 5 November 2025 in Nature Geoscience.
Ancient Conifers Reveal How Inefficient Photorespiration Helped Stabilize the Climate on Earth During the Last Glacial Period
A surprising inefficiency in ancient tree physiology may have quietly stabilized the atmosphere of the Earth during the last ice age. Research suggests that slow, wasteful photorespiration in these trees helped regulate carbon dioxide levels, thus preventing dramatic climate swings and supporting long-term planetary balance.
Researchers examined subfossil wood preserved across North America. These included pieces recovered from the La Brea Tar Pits. They applied a clumped-isotope technique that measures rare isotope combinations within the wood, allowing them to reconstruct biochemical signals that reveal how ancient trees managed carbon under low atmospheric conditions.
Their measurements showed that trees growing during the last glacial period frequently shifted into photorespiration. Note that this is a process that releases carbon dioxide rather than storing it. Low atmospheric concentrations forced the Rubisco protein to select oxygen more often. This causes metabolic losses that reduce the capacity of trees to capture long-term carbon.
Rubisco is the most abundant protein on Earth and a crucial enzyme in photosynthesis. It is mainly responsible for fixing atmospheric carbon dioxide into organic molecules. This protein specifically catalyzes the initial step of carbon fixation by combining carbon dioxide with a sugar called RuBP or ribulose-1,5-bisphosphate. However, in ancient trees, this process was inefficient.
The researchers further discovered that Trees from warmer glacial regions showed the strongest signs of inefficiency, suggesting that temperature influenced the severity of photorespiration. Several La Brea samples indicated that some trees released carbon dioxide nearly as quickly as they absorbed it, leaving little net carbon stored within their wood or soils.
Nevertheless, because of the metabolic shift, a stabilizing feedback was created during the glacial period. To be particular, as atmospheric carbon dioxide declined, ancient trees became less efficient at retaining carbon, causing them to return more carbon dioxide to the air. This response slowed declines and prevented atmospheric levels from dropping below thresholds.
The aforementioned discovery provides the first direct evidence that plant physiology influenced carbon levels during the last ice age. By demonstrating elevated photorespiration in trees that lived under glacial conditions, the researchers confirmed a hypothesis suggesting that tree or plant inefficiencies helped maintain atmospheric carbon dioxide near its lower boundary.
It is also worth noting that the active role of the biosphere in regulating the atmosphere has also been highlighted. Ancient forests did not respond to environmental stress but altered the global carbon balance through metabolic feedbacks. Such interactions shaped glacial climates and will help scientists refine models that examine climate stability and resilience.
FURTHER READING AND REFERENCE
- Lloyd, M. K., Sprengel, R. S., Wortham, B. E., Dunn, R. E., Ibarra, D. E., Dawson, T. E., and Stolper, D. A. 2025. “Isotopic Evidence for Elevated Photorespiration During the Last Glacial Period.” Nature Geoscience. DOI: 1038/s41561-025-01841-x