The Mesozoic Conundrum: Global Albedo Factors Resolve the Lack of Correlation Between Temperatures and CO2 Concentrations.

Ugo Bardi

The "Mesozoic Conundrum" refers to the lack of correlation between CO₂ atmospheric concentration and global mean surface temperatures in Mesozoic climate reconstructions (Judd et al., 2024). Here, I show that Mesozoic forest cover, proxied by carbon burial flux (Nelsen et al., 2016), correlates strongly (R²=0.88, p<0.01) with GMST across the Mesozoic (252–66 Ma before present). The analysis reveals a progression from low forest cover in the Early Triassic (GMST ca. 22°C) to a peak in the Mid Cretaceous (103.2 Ma; GMST ca. 27.5°C), increasing land cover from ~50% to 80%. This correlation indicates that albedo feedbacks from forest expansion amplified warming, resolving the conundrum. These findings highlight vegetation’s role in Mesozoic climate, showing the influence of plate tectonics on Earth’s climate over tens of millions of years.