Temperature and CO2 Causality Across Different Climate Regimes

This study examines which comes first-changes in Earth's temperature or changes in atmospheric CO 2 levels-during three key periods of Earth's recent climate history. We analyze the relationship during the period before 1.2 million years ago (when ice ages occurred roughly every 40,000 years), during the transition period (1.2-0.8 million years ago), and during the most recent period (when ice ages occur roughly every 100,000 years). Using computer models based on Antarctic ice core data, where trapped air bubbles and isotope ratios provide records of ancient CO 2 levels and temperatures, we test whether temperature changes typically preceded CO 2 changes or vice versa. Our initial analysis using F-statistic ratios suggested a possible shift over time, with temperature changes appearing to more strongly predict CO 2 in older periods, while CO 2 showed stronger predictive power for temperature in the more recent period. However, our bootstrap analysis revealed considerable uncertainty in these patterns, with nearly equal support for both causal directions in all climate regimes. Although none of the relationships reached statistical significance, this uncertainty itself is informative, highlighting the intrinsic limitations of paleoclimate time series-such as short record lengths, proxy noise, and autocorrelation-which challenge traditional significance testing. Rather than dismissing these patterns, we interpret them as testable hypotheses and emphasize the importance of effect sizes and directional consistency. These findings underscore the need for cautious interpretation of lead-lag relationships in paleoclimate research and advocate for more nuanced approaches that go beyond binary significance thresholds.