Development of new high-resolution pCO2 records for quantifying Earth system climate sensitivity

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Determination of Earth system climate sensitivity, the amount that global temperatures increase in response to a doubling of atmospheric carbon dioxide levels, is critical towards predicting the increase in global temperatures from rising carbon dioxide levels in the atmosphere. Much of our knowledge of this value is based on data from periods with atmospheric carbon dioxide levels no higher than today. This project will develop new high-resolution atmospheric carbon dioxide records for comparison with existing temperature data in order to better quantify the response between temperature and atmospheric carbon dioxide levels across the last 65 million years of Earth history. This approach will allow for improved quantification of climate sensitivity across a wide range of atmospheric carbon dioxide levels and climate states, including both icehouse and greenhouse conditions, and will provide better information for understanding how temperatures could increase as a result of future increases in atmospheric carbon dioxide from fossil fuel burning.This research will use the large number of published carbon isotope measurements on fossil terrestrial organic matter and the known effects of pCO2 on C3-plant carbon isotope fractionation in order to provide a new, high-resolution pCO2 reconstruction using a Monte Carlo uncertainty analysis. Expansion of the available pCO2 proxy data to significantly higher resolution using the abundance of terrestrial carbon isotope data available in the literature will allow for improved estimates of Earth system climate sensitivity across different climate states. This work will focus on: 1) the late Cenozoic (30-0 Ma), which is characterized by relatively low pCO2, Antarctic ice sheets, and well-constrained estimates of the carbon isotope composition of atmospheric CO2, and 2) the early Cenozoic (66-50 Ma), which is characterized by elevated temperatures, moderate to high pCO2, a lack of polar ice sheets, and a series of geologically brief global warming events known as hyperthermals.