This study investigates whether atmospheric CO₂ precedes or lags global temperature changes over the past 2000 yr, using both visual and statistical analyses. A parallel evaluation of Total Solar Irradiance (TSI) and temperature was conducted to assess the influence of solar forcing on climate variability.
Temperature, CO₂, and TSI data were drawn from many well-established publications and international climate data repositories. Original, unsmoothed series were used to identify visual markers such as peak–trough alignments, correlative clusters, and trend concordance, while smoothed series (using 50-yr and 100-yr running averages and Loess filters) were employed to emphasize large-scale patterns and reduce local variability. Correlation analysis, conducted within a statistical validation framework, was applied across all data variants.
Results show that atmospheric CO₂ consistently lags temperature by approximately 150 yr from 1 to 1850 AD. After applying this lag correction (CO₂Lag), Pearson correlation coefficients (rPCC) between CO₂Lag and temperature reached Very Strong values ranging from 0.85 to 0.99. TSI–temperature correlations were generally Strong across the full 2000 yr interval, and Very Strong from 1850 to present. A prominent alignment among CO₂Lag, TSI, and temperature occurs around 1460 AD.
These findings indicate that atmospheric CO₂ does not precede, nor appear to drive, global temperature trends. Rather, CO₂ consistently lags temperature, suggesting it functions as a response variable rather than a primary forcing. In addition, TSI exhibits Strong to Very Strong temporal alignment with temperature, supporting the hypothesis that solar variability plays a significant role in long-term climate change.