Ocean Heat Uptake of the Last Twenty Thousand Years

当地球接收的能量与释放到太空的能量之间不平衡时，全球变冷或变暖就会发生。由于在任何给定的时间都有大量的能量来来去去，因此很难检测到这种预算的不平衡。海洋温度是地球能量收支变化的最可靠指标，因为地球主要将多余的能量储存在海洋中。此外，储存能量的增加导致海洋温度上升。海洋储存更多热量的速率是海洋热吸收，这是衡量气候变化的一个关键指标。在过去的几十年里，海洋的热量吸收正在加速，但目前还不清楚地球过去是否有任何先例。这项研究将重建过去两万年来的海洋热量吸收，以便将持续的变化纳入背景。在过去的两万年里，气候发生了巨大的变化，包括向南延伸到现在美国大部分地区的大冰盖的解体。这一时期也有大的变暖事件与海洋热吸收，可以媲美今天。海洋热量吸收的重建可能会通过提高我们对气候如何响应大气二氧化碳变化的理解而造福社会。此外，该项目还将量化深海和冰盖影响21世纪气候的潜力。该项目包括通过支持博士后研究人员和将方法纳入麻省理工学院/世界卫生组织联合方案研究生课程来培训下一代海洋科学家的计划。所有研究成果都将通过国家环境信息中心和GitHub的档案公开免费获取。该项目旨在通过将古海洋学温度数据同化到海洋环流模型中来重建过去20，000年的全球海洋热吸收，该模型描述了十年，百年和千年的气候变化时间尺度。关键的方法问题是，如何以及古温度观测反演海洋热吸收？该方法将利用已知的气候功率定律，该定律规定低频温度变化比高频包含更多的能量。这些幂律允许填补古数据中的空白，并进行严格的不确定性分析。改进海洋热吸收的重建将解决由于观测系统的组成随时间变化、1955年之前观测的稀疏性以及深海的预期变化而隐藏的系统误差。由此产生的海洋热吸收的演变通过代理和仪器数据，包括最后一次冰消期，全新世中期气候最佳，中世纪气候异常，小冰期和工业时代，这有利于过去和现在的海洋条件之间的比较。对末次冰盛期（20 000年前）以来海洋热吸收的研究将使人们对变暖率有一个广泛的认识，新的观测证据表明，在某些时间间隔内，冰消期海洋热吸收与当今相当。该项目通过对过去20，000年海洋热吸收的动态重建，包括不确定性估计，使更广泛的科学界受益。海洋热吸收是诊断平衡和瞬态气候敏感性所需的量，这是预测表面温度的两个关键气候指标。量化不确定性是对未来气候情景进行更准确风险评估的必要步骤，并与政策决策相关。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

Global cooling or warming occurs when Earth has an imbalance between the energy received versus that released to space. Imbalances in this budget are difficult to detect due to the large amounts of energy that come and go at any given time. Ocean temperature is the most reliable indicator of changes in the planet’s energy budget because Earth primarily stores excess energy in the ocean. Furthermore, increases in stored energy cause ocean temperature to rise. The rate that the ocean stores more heat is the ocean heat uptake, a key measure of climate variability. Ocean heat uptake is accelerating over the last few decades, but it is unknown whether there is any precedent in Earth’s past. This study will reconstruct ocean heat uptake for the last twenty thousand years in order to put ongoing changes into context. The last twenty thousand years included enormous changes in climate, including the disintegration of large ice sheets that extended southward into much of the current United States. This time period also had large warming events with ocean heat uptake that could have rivaled the present day. The reconstruction of ocean heat uptake may benefit society by improving our understanding of how climate responds to changes in atmospheric carbon dioxide. In addition, this project will quantify the potential for the deep ocean and ice sheets to affect the climate of the 21st century. The project includes plans to train the next generation of ocean scientists through support for a postdoctoral researcher and integration of methods into a MIT/WHOI Joint Program graduatecourse. All research products will be publicly and freely accessible through archives at the National Centers for Environmental Information and GitHub.This project aims to reconstruct global ocean heat uptake for the last 20,000 years by assimilating paleoceanographic temperature data into an ocean circulation model that describes decadal, centennial, and millennial timescales of climate variability. The key methodological question is, how well can paleo-temperature observations be inverted for ocean heat uptake? The method will utilize known climate power laws that dictate that low-frequency temperature variations contain more energy than high frequencies. These power laws permit the infilling of gaps in paleo-data and a statistically-rigorous uncertainty analysis. Improved reconstructions of ocean heat uptake will address the hidden systematic errors due to the time-evolving composition of the observing system, the sparsity of observations before 1955, and the expected variability of the deep ocean. The resulting ocean heat uptake evolution connects through periods with both proxy and instrumental data, including the last deglaciation, the mid-Holocene climate optimum, the Medieval Climate Anomaly, the Little Ice Age, and the industrial era, which facilitates comparison between past and present ocean conditions. Examination of ocean heat uptake since the Last Glacial Maximum (20,000 years ago) will allow a wide perspective on warming rates, and new observational evidence suggests that deglacial ocean heat uptake rivaled the present day during some time intervals. This project benefits the broader science community by producing dynamically-informed reconstructions of ocean heat uptake for the last 20,000 years, including uncertainty estimates. Ocean heat uptake is a required quantity to diagnose equilibrium and transient climate sensitivity, two key climate metrics for predicting surface temperature. Quantification of uncertainties is a necessary step toward more accurate risk assessments of future climate scenarios and has relevance to policy decisions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.