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

确定地球系统气候敏感性，即全球温度因大气中二氧化碳水平增加一倍而升高的幅度，对于预测大气中二氧化碳水平上升导致的全球温度升高至关重要。我们对这个值的大部分知识都是基于大气二氧化碳水平不高于今天的时期的数据。该项目将开发新的高分辨率大气二氧化碳记录，以便与现有的温度数据进行比较，以便更好地量化过去6500万年地球历史中温度和大气二氧化碳水平之间的响应。这种方法将允许在大范围的大气二氧化碳水平和气候状态（包括冰窖和温室条件）中改进气候敏感性的量化，并将为理解未来化石燃料燃烧导致的大气二氧化碳增加如何导致温度升高提供更好的信息。本研究将利用大量已发表的陆地化石有机质碳同位素测量结果和已知的二氧化碳分压对c3 -植物碳同位素分异的影响，利用蒙特卡罗不确定性分析提供一种新的、高分辨率的二氧化碳分压重建方法。利用文献中丰富的陆地碳同位素数据，将现有的二氧化碳分压代理数据扩展到更高的分辨率，将有助于改进对不同气候状态下地球系统气候敏感性的估计。这项工作将重点关注：1)晚新生代（30-0 Ma），其特征是相对较低的二氧化碳分压，南极冰盖，以及对大气二氧化碳碳同位素组成的良好约束估计；2)早期新生代（66-50 Ma），其特征是温度升高，二氧化碳分压中高，缺乏极地冰盖，以及一系列地质上短暂的全球变暖事件，称为超热活动。

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.