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.

化石证据显示，过去的气候比人类历史上经历过的任何气候都要温暖得多，而我们对这些气候的了解相当有限。一个特殊的挑战是北极高纬度埃尔斯米尔岛的化石所证明的高纬度地区的极端温暖，其中包括鳄鱼、巨龟、蛇、蕨类植物和开花植物的物种，这些植物不能忍受低于冰点的温度。相比之下，今天埃尔斯米尔岛的冬季气温通常降至 -40C。埃尔斯米尔化石可以追溯到大约 5000 万年前的始新世，当时二氧化碳 (CO2) 浓度较高，可能为百万分之 1,000 (ppm)，而今天的浓度约为 400 ppm。但以始新世二氧化碳水平为依据的气候模型并未成功重现北极化石记录所表明的高于冰点的最低温度。上新世是两到五百万年前的一个温暖时期，低纬度和高纬度之间的温度差异也急剧减小。上新世之所以令人感兴趣，是因为当时的二氧化碳水平与今天大致相同，但全球气温却高了 2-3 摄氏度，海平面也高得多，可能高了 25 米。造成上新世温暖和小温差的动力机制尚不清楚，气候模型也未能成功模拟上新世条件。该奖项的工作旨在了解在温暖气候中产生高极地温度和低纬度温度对比的基本机制。这项工作还研究了向这种状态的转变，特别是从赤道到极地温度对比从高到低的突然转变的可能性。该研究特别关注高纬度云反馈和全球海洋热传输在高纬度地区变暖中的作用。一种云反馈过程涉及从今天在北极上空发现的低云到深对流云的转变，当变暖用开阔的海洋取代海冰时，可能会发生这种情况。用深对流云取代低云可能会对地表产生变暖效应，这可能导致海冰进一步减少和对流云进一步增强的循环。陆地上的云也可能在降低寒冷的大陆温度方面发挥作用，因为海洋温度升高会导致向大陆输送的水分增加，从而导致云阻碍陆地表面的冷却。海洋热传输研究涉及大幅降低赤道与极地温差所需的热传输量、可增强热传输的海洋翻转环流的变化以及最有效的海洋热传输路径。使高纬度陆地变暖。还研究了海洋热传输和云反馈的综合影响。这项工作主要通过数值实验进行，其中大部分是通过 Isca 进行的，Isca 是由一位 PI 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意义，因为世界正在变暖，二氧化碳浓度已经上升到上新世的水平。在过去的三十年里，夏季北极海冰急剧减少，这里考虑的云反馈在当今的气候下可能是可能的。更广泛的影响是伊斯卡模型的开发和传播，该模型可以作为广大气候研究人员的研究工具。 PI 通过公开讲座和一项为波士顿地区高中生提供暑期研究机会的计划来进行教育和推广。此外，该项目还支持两名研究生，从而促进该研究领域的未来劳动力。该项目由美国国家科学基金会地球科学理事会（NSF/GEO）和美国国家环境研究委员会（NERC）共同资助王国（英国）通过 NSF/GEO-NERC 牵头机构协议。该协议允许美国/英国的单一联合提案由其调查人员拥有最大预算比例的机构提交并进行同行评审。成功联合确定奖项后，每个机构将资助与其本国相关的预算和研究人员的比例。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力优点和更广泛的影响审查标准进行评估，被认为值得支持。