NOAA/WDS Paleoclimatology - Paleo-pCO2 Database Early Paleocene Multiproxy CO2 Data

Proxy estimates of atmospheric CO2 are necessary to reconstruct Earth's climate history. Confidence in paleo-CO2 estimates can be increased by comparing results from multiple proxies at a single site, but so far this strategy has been implemented only for marine-based techniques. Here we present CO2 estimates for the well-studied early Paleocene Castle Rock site in Colorado using four paleobotanical proxies. Median estimates range from 470 to 813 ppm, demonstrating fair correspondence. The synthesis yields a median of 616 ppm (352-1110 ppm at 95% confidence), considerably higher than previous early Paleocene CO2 estimates (~300 ppm). Ash bed geochronology by the high-precision U-Pb method places the Castle Rock assemblage at 63.844 ± 0.097 Ma (fully propagated 2sigma error). When these results are placed into the broader context of other Cenozoic CO2 estimates from plant-gas-exchange approaches and coeval estimates of global mean surface temperature, a pattern emerges of an Earth system sensitivity around 3C per CO2 doubling during the Paleocene and Eocene, a time with little land ice, then steepening to >7C after the Eocene once land ice was present on Antarctica.