Insolation Gradients and Eastern Mediterranean Aridity: Impacts on Winter Storms and Implications for Climate Projections

日照梯度和东地中海干旱：对冬季风暴的影响以及对气候预测的影响

• 批准号: 2317159
• 负责人: Michela Biasutti
• 金额: $ 83.1万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-09-01 至 2026-08-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2317159&HistoricalAwards=false
• 关键词: Insolation; Gradients; Eastern; Mediterranean; Aridity

Simulations of the climatic effect of greenhouse gas increases are in remarkable agreement that the Mediterranean Basin will dry out substantially over the 21st century. The projected future drying is consistent with precipitation declines since the mid-20th century, which have already caused hardship in the region. A prime example is the 2007-2010 Syrian drought, which was a contributing factor in the civil war and refugee crisis that began the following year. The multiple lines of evidence pointing to future drying, together with its potential for severe societal disruptions, motivate a concerted effort to understand the dynamics of Mediterranean rainfall change. An overarching question in this effort is how radiative forcing acting on the planetary scale, in this case from greenhouse gas increases, produces such a strong precipitation response over this particular region.Work performed here considers the insights to be gained from the Mediterranean precipitation response to another kind of planetary-scale forcing: the change in sunlight received by the earth over the orbital cycles that produce the ice ages. The project takes advantage of sediment cores and speleothems from the Eastern Mediterranean (EM) that record wet and dry periods during the Last Interglacial (LIG, also called the Eemian), from 135 to 110 thousand years ago (kya), and the Holocene, from 15kya to the present. The changes in aridity during these periods are thought to be due to changes in the seasonality of insolation, with wetter conditions when summer insolation is at its peak and dry periods when fall insolation peaks. The Principal Investigators (PIs) argue that stronger fall insolation leads to a stronger latitudinal surface temperature contrast over the North Atlantic during winter, which leads to a northward shift of the Atlantic jet stream and the paths of winter weather systems that move along it. The northward shift in weather systems causes substantial annual rainfall reductions as the Mediterranean Basin receives most of its rainfall in winter. The insolation changes due to orbital cycles are of course quite distinct from greenhouse warming, but the PIs note that greenhouse gas increases cause a similar latitudinal temperature contrast since the West African landmass heats up more than the adjacent Atlantic Ocean, and the northern North Atlantic features a "warming hole" which further enhances the north-south temperature contrast.The work involves a combination of analysis of the present-day observational record, paleoclimate proxy data, and model simulations of past, present, and projected future climate. One issue to be addressed is the conflation in the proxy record between the effects of the temperature contrast, which are relevant to current climate change, and incursions of the North African monsoon, which are not. A further issue is the abruptness of the aridity changes in the paleoclimate record compared to the orbital forcing, which suggests a role for the dynamics of oceans and ice sheets. These issues are examined using specialized simulations performed with the Community Atmosphere Model, the atmospheric component of the Community Earth System Model (CESM).The work is of societal as well as scientific interest given the profound impacts of aridification in the EM as noted above. The PIs enhance the real-world impact of their work through organizations in the region including the Columbia University Global Center in Amman, Jordan, the Eco-Peace Middle East non-governmental organization, the Weizmann Institute, and Hebrew University. The PIs also participate in outreach activities at their home institution, including the Lamont Open House and visits to local high schools. The project also provides support and training to a postdoc, thereby providing for the future workforce in this research area.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.

对温室气体增加对气候影响的模拟结果非常一致，即地中海盆地将在 21 世纪大幅干旱。 预计未来的干旱与 20 世纪中叶以来的降水量减少是一致的，这已经给该地区带来了困难。 一个典型的例子是 2007 年至 2010 年的叙利亚干旱，这是次年开始的内战和难民危机的一个促成因素。 多种证据表明未来的干旱及其可能造成严重的社会破坏，促使人们共同努力了解地中海降雨变化的动态。 这项工作的一个首要问题是，作用在行星尺度上的辐射强迫（在这种情况下是温室气体增加）如何在这个特定区域产生如此强烈的降水响应。这里进行的工作考虑了从地中海降水对另一种行星尺度强迫的响应中获得的见解：地球在产生冰河时代的轨道周期中接收到的阳光的变化。 该项目利用了东地中海 (EM) 的沉积物岩心和洞穴，记录了 135 至 11 万年前 (kya) 的末次间冰期 (LIG，也称为埃米安) 和 15 年前至今的全新世期间的潮湿和干燥时期。这些时期干旱的变化被认为是由于日照季节性的变化造成的，夏季日照达到高峰时气候湿润，秋季日照达到高峰时气候干燥。首席研究员 (PI) 认为，较强的秋季日照会导致冬季北大西洋纬度表面温度对比更强，从而导致大西洋急流和沿其移动的冬季天气系统的路径向北移动。 天气系统北移导致年降雨量大幅减少，因为地中海盆地大部分降雨是在冬季接收的。 轨道周期引起的日照变化当然与温室变暖截然不同，但 PI 指出，温室气体增加会导致类似的纬度温度对比，因为西非大陆比邻近的大西洋升温更多，而北大西洋北部有一个“变暖洞”，进一步增强了南北温度对比。这项工作包括对当今观测记录、古气候的分析相结合。 过去、现在和预测的未来气候的代理数据和模型模拟。 需要解决的一个问题是代理记录中将与当前气候变化相关的温度对比的影响与与当前气候变化无关的北非季风入侵的影响混为一谈。 另一个问题是，与轨道强迫相比，古气候记录中的干旱变化非常突然，这表明海洋和冰盖的动力学发挥了作用。 这些问题是通过使用社区大气模型（社区地球系统模型（CESM）的大气组成部分）进行的专门模拟来检查的。鉴于如上所述的欧洲大陆干旱化的深远影响，这项工作具有社会和科学意义。 PI 通过该地区的组织（包括位于约旦安曼的哥伦比亚大学全球中心、中东生态和平非政府组织、魏茨曼研究所和希伯来大学）增强其工作在现实世界的影响力。 PI 还参加其所在机构的外展活动，包括拉蒙特开放日和参观当地高中。 该项目还为博士后提供支持和培训，从而为该研究领域的未来劳动力提供支持。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。