CAREER: Understanding Cloud Feedback and Natural Aerosol Fingerprints to Interpret Past Warm Climate Forcing and Constrain Tropical Climate Sensitivity

平衡气候敏感性是指一旦气候系统达到平衡状态，由于外部强迫（例如大气CO2浓度加倍）的变化而引起的地球表面平均温度的变化。平衡气候敏感性是气候科学中的一个核心概念，用于利用气候模式估算大气CO2浓度持续增加情景下的未来温度，因为气候总变暖的很大一部分来自气候系统中响应人为温室气体排放引起的辐射强迫的其他变化，如云、大气湿度和冰雪覆盖。这项研究具有更广泛的社会影响，因为这项研究的中心目标是了解控制热带气候的基本物理机制以及它如何对变暖做出反应。这对于建立气候模式在未来变暖条件下捕捉热带反馈能力的信心具有重要的实用价值。该奖项将支持PI（早期职业女性科学家），研究生和博士后的职业和培训。PI将与地质学研究生合作，通过夏季研究访问和开发一个网站，供全国各地的学生/研究人员访问和分析古气候模型数据。她将通过乔治梅森大学的“有抱负的科学家暑期实习计划”指导当地的本科生和高中生，并在乔治梅森大学为科学、技术、工程和数学领域中代表性不足的女性设计的夏令营中讲授“天气和气候”模块。在过去三十年建立的气候敏感性估计范围之外限制气候敏感性估计已被证明是气候科学的重大挑战之一。由于仪器记录的时间跨度有限，很难从对温室气体引起的变暖作出反应的云反馈中梳理出自然的、十年以上的变化，而20世纪气溶胶的强迫作用使信号更加复杂。这个项目将采用一种新的方法，通过检查过去古气候记录的温暖时期的气候敏感性，来限制变暖下云反馈的性质。目前的气候模式由于受到大尺度地表温度和水循环重建的限制，在上新世、中新世和始新世三个温暖气候期重建的经向地表温度梯度的还原能力不足。PI将寻求气候敏感性所需强度的答案，特别是从热带云辐射反馈中，以供气候模式模拟这三个非常不同的过去暖期。这种多暖气候方法将有助于确定强大的热带云反馈机制在多大程度上能够一致地解释整个20世纪、上新世、中新世和始新世的变暖模式和水文循环响应。该研究项目将整合气候模拟和古气候重建领域的最新科学进展，以：1)解决我们对模拟不同的过去温暖气候所需的热带反馈及其在温暖时期的一致程度的理解的基本空白；2)测试古气候社区提出的气候机制的稳健性，以帮助解释和设计气候重建。该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。

Equilibrium climate sensitivity refers to as the average surface temperature change of the planet in response to a change in external forcing (e.g., the doubling of the atmospheric CO2 concentration) once the climate system has reached a balanced state. Equilibrium climate sensitivity is a central concept in climate science for estimating the future temperature under the scenario of a continuous increase of atmospheric CO2 concentration using climate models, as a large portion of the total climate warming results from other changes in the climate system in response to the radiative forcing due to anthropogenic greenhouse gas emissions, such as clouds, atmospheric moisture, and snow/ice coverage. The research has broader societal impacts as the central goal of this study is to understand the fundamental physical mechanisms that have controlled tropical climate and how it responds to warming. This is of significant practical value in establishing confidence in the ability of climate models to capture tropical feedbacks under future warming. This award will support the careers and training of the PI (an early career female scientist), a graduate student, and a postdoctoral fellow. The PI will work with Geology graduate students through summer research visits and development of a website for students/researchers from across the country to access and analyze paleoclimate model data. She will mentor local undergraduate and high school students through George Mason's Aspiring Scientists Summer Internship Program and present a "weather and climate" module at a George Mason summer camp designed for females underrepresented in fields of science, technology, engineering, and mathematics. Constraining the range of climate sensitivity estimates beyond those established over the last three decades has proven to be one of the grand challenges in climate science. The limited timespan of the instrumental record makes it difficult to tease out natural, decadal-plus variability from cloud feedbacks in response to greenhouse gas induced warming, with signals further complicated by 20th century aerosol forcing. This project will take a new approach towards constraining the nature of cloud feedbacks under warming by examining climate sensitivities in past warm periods of paleo climate records. The current climate models lack ability to adequately reproduce the reduced meridional surface temperature gradients reconstructed for the past three warm climates, namely, the Pliocene, Miocene and Eocene, as constrained by large-scale surface temperature and hydrological cycle reconstructions. The PI will seek answer about the required strength of the climate sensitivity, particularly from tropical cloud radiative feedback, for climate models to simulate these three very different past warm periods. This multi-warm-climate approach will help establish the extent to which robust tropical cloud feedback mechanisms can consistently explain the patterns of warming, and the hydrological cycle response, seen across the 20th century, Pliocene, Miocene and Eocene. The research project will integrate the latest scientific advances within both the climate modeling and paleoclimate reconstruction communities to: 1) address a fundamental gap in our understanding of the tropical feedbacks needed to simulate distinct past warm climates and the extent to which they are consistent across warm periods, and 2) test the robustness of climate mechanisms put forth within the paleoclimate community to aid in the interpretation and design of climate reconstructions.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.