Paleoatmospheric Carbon Dioxide Dynamics

Atmospheric carbon dioxide (CO2) has fluctuated markedly over geological time, exerting a primary control on Earth’s long-term climate. Variations in pCO2 arise from a balance between volcanic outgassing, weathering of silicate rocks, organic carbon sequestration and biotic feedbacks such as the evolution of land plants. Elevated CO2 intervals, including the Eocene climatic optimum, correspond with warmer global temperatures and intensified hydrological cycles, while declines in pCO2 have been linked to major climatic transitions such as the onset of Antarctic glaciation. Reconstructions rely on diverse proxies—leaf stomatal traits, stable carbon isotopes, boron isotopes in marine carbonates and ice-core records—that collectively inform estimates of palaeo-CO2 and climate sensitivity. These reconstructions underpin climate models, guide assessments of carbon cycle feedbacks and furnish analogues for future greenhouse gas trajectories, offering crucial insights into the resilience of Earth’s systems under rapid CO2 perturbations.

Research from Nature Portfolio

Recent studies have quantified the long-term decline in atmospheric carbon dioxide over the past 420 million years, attributing this trend to the interplay between silicate weathering and the expansion of land flora. These analyses demonstrate that, while solar irradiance has increased, the decline in CO2 maintained Earth’s habitability and highlight that current fossil-fuel emissions may propel atmospheric CO2 to levels not seen since the early Eocene. Other work has refined the interpretation of terrestrial stable carbon isotope records, revealing that variations in plant δ13C reflect both changes in pCO2 and environmental factors such as precipitation. This research emphasises that isotopic signatures in gymnosperm and angiosperm fossils must be corrected for atmospheric effects to reconstruct ancient climates accurately.

Research from all publishers

Critical appraisal of a novel C3 proxy based on carbon isotope discrimination (Δ13C) in model plants has shown that Δ13C–CO2 relationships are poorly constrained under varying water regimes, limiting the proxy’s reliability for deep-time reconstructions. Advances in leaf gas-exchange modelling have provided a mechanistic framework for stomatal proxies, yielding median error rates near 28 % and demonstrating robustness across diverse taxa and fossil preservation states. Empirical leaf gas-exchange reconstructions from early Miocene fossil floras indicate pCO2 levels of approximately 450–550 ppm, aligning with projected twenty-first-century concentrations and revealing enhanced intrinsic water-use efficiency and productivity under elevated CO2, thereby offering analogues for future ecosystem responses.

Paleoatmospheric Carbon Dioxide Dynamics publication trend

The graph below shows the total number of articles in paleoatmospheric carbon dioxide dynamics across all publications each year (not limited to Nature Index journals).

Technical terms

pCO2: Partial pressure of CO2 in the atmosphere, used as a measure of its concentration in palaeoclimate studies.

Stomatal density: Number of microscopic pores per unit leaf area; inversely related to atmospheric CO2 concentration in many plants.

Stable carbon isotope ratio (δ13C): The ratio of 13C to 12C in a sample relative to a standard, employed to infer past carbon cycle dynamics.

Carbon isotope discrimination (Δ13C): Difference between δ13C of atmospheric CO2 and plant tissue, reflecting photosynthetic gas exchange and environmental conditions.

Silicate weathering: Chemical breakdown of silicate minerals, serving as a long-term sink for atmospheric CO2 and regulator of Earth’s climate.

References

1. Future climate forcing potentially without precedent in the last 420 million years. Nature Communications (2017).
2. Atmospheric CO2 effect on stable carbon isotope composition of terrestrial fossil archives. Nature Communications (2018).
3. An experimental evaluation of the use of Δ13C as a proxy for palaeoatmospheric CO2. Geochimica et Cosmochimica Acta (2019).
4. Sensitivity of a leaf gas-exchange model for estimating paleoatmospheric CO2 concentration. Climate of the Past (2019).
5. Elevated CO2, increased leaf-level productivity, and water-use efficiency during the early Miocene. Climate of the Past (2020).