NSFGEO-NERC: Dynamics of Warm Past and Future Climates

NSFGEO-NERC：过去和未来温暖气候的动态

基本信息

批准号：
1924538
负责人：
Eli Tziperman
金额：
$ 48.02万
依托单位：
Harvard University
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2019
资助国家：
美国
起止时间：
2019-10-01 至 2024-09-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1924538&HistoricalAwards=false
关键词：
NSFGEO NERC Dynamics Warm Past

项目摘要

Fossil evidence reveals past climates that were dramatically warmer than any experienced in human history, and our understanding of these climates is quite limited. A particular challenge is the extreme warmth of the high latitudes demonstrated by the fossils of Ellesmere Island in the high Arctic, which include species of alligators, giant tortoises, snakes, ferns, and flowering plants that do not tolerate below-freezing temperatures. By comparison, winter temperatures on Ellesmere Island today commonly drop to -40C. The Ellesmere fossils date from the Eocene, roughly 50 million years ago, at a time when carbon dioxide (CO2) concentration was higher, perhaps 1,000 parts per million (ppm) compared to about 400ppm today. But climate models forced with Eocene levels of CO2 have not successfully reproduced the above-freezing minimum temperatures indicated by the Arctic fossil record. A dramatically reduced temperature contrast between low and high latitudes also occurred during the Pliocene, a warm period from two to five million years ago. The Pliocene is of interest because its CO2 level was about the same as today yet global temperature was 2-3C higher and sea level was considerably higher, perhaps by 25 meters. The dynamical mechanisms responsible for the warmth and small temperature contrast of the Pliocene are not known, and climate models have not succeeded in simulating Pliocene conditions. Work under this award seeks to understand the fundamental mechanisms which give rise to the high polar temperatures and low latitudinal temperature contrasts found in warm climates. The work also examines the transition to such states, in particular the possibility of an abrupt transition from high to low equator-to-pole temperature contrast. The research focuses specifically on the roles of high latitude cloud feedbacks and global ocean heat transport in warming the high latitudes. One cloud feedback process involves a transition from the low clouds found today over the Arctic to deep convective clouds, which could happen when warming replaces sea ice with open ocean. The replacement of low clouds with deep convective clouds would likely have a warming effect on the surface, which could lead to a cycle of further sea ice reduction and further enhancement of convective clouds. Clouds over land could also play a role in reducing cold continental temperatures, as warmer sea temperatures cause increased moisture transport onto the continents, resulting in clouds that block cooling of the land surface. Research on ocean heat transport involves an examination of the amount of heat transport required to substantially reduce the equator-to-pole temperature difference, changes in the ocean overturning circulation that could enhance heat transport, and pathways of ocean heat transport that would be most effective for warming the high latitude landmasses. The combined effect of ocean heat transport and cloud feedbacks is also examined. The work is conducted primarily through numerical experimentation, much of it with Isca, a simplified and highly configurable climate model developed by one of the PIs.The research is of societal as well as scientific interest as the world is warming and CO2 has already risen to the level of the Pliocene. Summer Arctic sea ice has declined dramatically over the last three decades and the cloud feedbacks considered here may be possible in the present-day climate. A further broader impact is the development and dissemination of the Isca model, which could serve as a research tool for a broad community of climate researchers. Education and outreach is conducted by the PIs through public lectures and a program connecting Boston-area high school students with summer research opportunities. In addition, the project supports two graduate students, thereby promoting the future workforce in this research area.This project is jointly funded by the National Science Foundation's Directorate of Geosciences (NSF/GEO) and the National Environment Research Council (NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award, each Agency funds the proportion of the budget and the investigators associated with its own country.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.

化石证据揭示了过去的气候比人类历史上经历的任何人都要温暖，我们对这些气候的理解非常有限。一个特殊的挑战是高北极地区埃勒斯米尔岛化石所证明的高纬度的极端温暖，其中包括鳄鱼的种类，巨型乌龟，蛇，蕨类植物和开花植物，这些植物不耐受温度低于冰点的温度。相比之下，埃尔斯米尔岛（Ellesmere Island）的冬季温度通常下降到-40c。 Ellesmere化石可以追溯到始新世，大约5000万年前，当时二氧化碳（CO2）浓度更高，大概为每百万（ppm）约为400ppm。但是用始新世二氧化碳水平强迫的气候模型并未成功再现北极化石记录所指示的上述最低温度。在上新世期间，低纬度和高纬度之间的温度对比度大大降低，温暖的时期从200万年前到500万年前。上新世引起了人们的关注，因为它的二氧化碳水平与今天的二氧化碳水平相同，但全球温度高2-3c，海平面高得多，也许高25米。尚不清楚造成上新世温度对比度温度对比的动力学机制，气候模型尚未成功模拟上新世条件。该奖项下的工作旨在了解基本机制，这些机制引起高极温度和低纬度温度对比，在温暖的气候中发现。这项工作还检查了向这种状态的过渡，特别是从高到低赤道到极端温度对比的突然过渡的可能性。该研究专门介绍了高纬度云反馈和全球海洋热运输在变暖高纬度方面的作用。一个云反馈过程涉及从今天在北极上发现的低云到深云的过渡，当变暖用开阔的海洋代替海冰时，这种情况可能会发生。用深云的替换为低云，可能会对表面产生变暖的影响，这可能导致进一步的海冰还原并进一步增强对流云的循环。土地上的云也可能在降低寒冷的大陆温度中发挥作用，因为较高的海温导致水分传输到大陆上的增加，从而导致云层阻止了陆地表面的冷却。对海洋热传输的研究涉及对大大降低赤道到极端差异所需的热传输量的检查，可以增强热传输的海洋循环的变化以及海洋热传输的途径，这对于加热高纬度地质量最有效。还检查了海洋热传输和云反馈的综合作用。这项工作主要是通过数值实验进行的，其中大部分是由PIS之一开发的简化且高度可配置的气候模型。这项研究具有社会和科学兴趣，因为世界正在变暖，二氧化碳已经提高到了上新世的水平。在过去的三十年中，夏季北极海冰急剧下降，在当今的气候中可能会有可能的云反馈。更广泛的影响是ISCA模型的发展和传播，它可以作为广泛的气候研究人员社区的研究工具。 PIS是通过公开讲座和将波士顿地区高中学生与夏季研究机会联系起来的计划。此外，该项目支持两名研究生，从而在该研究领域促进了未来的劳动力。该项目由国家科学基金会的地球科学局（NSF/GEO）共同资助，并通过NSF/GEO-GEO-GEO-NERC-NERC LEADNC LEADNC LEADNC LEADNC LEADNC LEADNC LEADNC LEADNC LEADNC LEADERC LEADERC LEAD CONDER INDERAME INTICE ANCENATE（NSF/GEO）和国家环境研究委员会（NERC）（NERC）共同资助。该协议允许该机构提交和同行评审的一项联合提案，其调查员的预算比例最大。成功确定裁决后，每个机构都为预算的比例和与其自己的国家相关的调查人员提供了资金。该奖项反映了NSF的法定任务，并且使用基金会的知识分子优点和更广泛的审查标准，被认为值得通过评估来获得支持。