The Evolving Role of the Ocean and the Atmosphere in Decadal to Multidecadal Modes of Climate Variability

海洋和大气在十年至多年气候变化模式中的演变作用

• 批准号: 2241752
• 负责人: Amy Clement
• 金额: $ 118.56万
• 依托单位: University of Miami
• 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: 2023-03-01 至 2026-02-28
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2241752&HistoricalAwards=false
• 关键词: Evolving; Role; Ocean; Atmosphere; Decadal

Efforts to address climate change impacts are complicated by the difficulty of distinguishing between the effects of external forcing, predominantly caused by human activities, and the natural internal variability of the climate system. Decade-to-decade variations are typically characterized by a set of climate modes such as the Atlantic Multidecadal Oscillation (AMO), in which the Atlantic north of the equator has alternating episodes of warming and cooling that last 20 to 40 years. The climate modes are generally regarded as natural variability because they can be found in observations from the 1800s and earlier, before the rise of industrial emissions. For this reason regional climate change is often viewed as the superposition of natural variability in the form of climate modes and externally forced change which is distinct from the modes, with a different spatial pattern and involving different physical mechanisms.Here the Principal Investigators (PIs) question this assumption and pose a more challenging hypothesis: prior to 1950 climate modes are largely natural variability arising from atmosphere-ocean coupling, but after 1950 the modes are largely externally forced, and the relationship between the ocean and atmosphere is altered by the external forcing. The hypothesis is motivated by the PIs' recent work with simulations of 20th century climate which include forcing by the radiative effects of aerosol pollution. The dominant sources of aerosol emissions have shifted from western Europe and the eastern US to China and southern Asia, thus the response to shifting aerosol radiative forcing could cause regional climate change on the decadal timescale. The hypothesis is also predicated on the idea that the climate system responds to external forcing through the dynamics that generate the internal variability modes, so that the response to external forcing amounts to an excitation of the natural internal modes.The research is conducted with a variety of climate model simulations including large ensembles (LEs) of simulations performed with the Community Earth System Model (CESM). These include LEs of simulations with no external forcing and single-forcing simulations which isolate the response to aerosol forcing. The work also takes advantage of the hierarchy of simpler configurations developed for CESM, including the "pencil ocean" configuration developed under AGS-2040073, which represents turbulent vertical heat transfer in the ocean but does not simulate the lateral movement of water in ocean currents.The work has societal relevance given the need to address climate change impacts at the regional level. If the PIs' hypothesis is correct it will require some revision of uncertainty estimates for regional climate projections, which do not currently take into account uncertainty in the future evolution of aerosol emissions. The work also has implications for climate prediction efforts, in which it is commonly assumed that climate modes can be predicted from the current state of the atmosphere and oceans and a sufficiently accurate representation of the coupling between the two (see for example AGS-2231237). The work is also directly relevant to climate impacts on coastal communities, particularly given that the AMO has a substantial effect on Atlantic hurricane activity. The researchers work with the Miami Climate Resilience Committee and the Resilient305 Research Collaborative provides a direct application of research results to community-based decision making. The project also provides support and training to a postdoctoral associate, a graduate student and an undergraduate, and the PIs perform a number of outreach activities including the University of Miami Women in Science day, an annual event for girls in the 6th and 7th grade.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.

由于很难区分主要由人类活动引起的外部强迫的影响和气候系统的自然内部变率，因此解决气候变化影响的努力变得更加复杂。 十年到十年的变化通常以一系列气候模式为特征，例如大西洋多年代际振荡 (AMO)，其中赤道以北的大西洋交替出现持续 20 至 40 年的变暖和变冷现象。气候模式通常被视为自然变率，因为它们可以在 1800 年代或更早、工业排放增加之前的观测中发现。 因此，区域气候变化通常被视为气候模式形式的自然变率和外部强迫变化的叠加，这种变化与模式不同，具有不同的空间格局并涉及不同的物理机制。这里的主要研究者（PI）质疑这一假设并提出更具挑战性的假设：1950年之前的气候模式很大程度上是大气-海洋耦合引起的自然变率，但1950年之后这些模式很大程度上是外部强迫的，海洋和大气之间的关系被外部因素改变了。强迫。这一假设的灵感来自于 PI 最近对 20 世纪气候的模拟工作，其中包括气溶胶污染的辐射效应的强迫。 气溶胶排放的主要来源已从西欧和美国东部转移到中国和南亚，因此对气溶胶辐射强迫变化的响应可能会导致十年时间尺度的区域气候变化。 该假说还基于以下观点：气候系统通过产生内部变率模式的动力学对外部强迫做出反应，因此对外部强迫的响应相当于对自然内部模式的激发。该研究是通过多种方法进行的。气候模型模拟，包括使用社区地球系统模型 (CESM) 进行的大型集合 (LE) 模拟。 其中包括无外部强迫的模拟 LE 和隔离对气溶胶强迫响应的单强迫模拟。 这项工作还利用了为 CESM 开发的更简单配置的层次结构，包括根据 AGS-2040073 开发的“铅笔海洋”配置，它代表海洋中的湍流垂直传热，但不模拟洋流中水的横向运动。鉴于需要在区域层面解决气候变化影响，这项工作具有社会意义。 如果PI的假设正确，则需要对区域气候预测的不确定性估计进行一些修改，目前该预测并未考虑气溶胶排放未来演变的不确定性。 这项工作还对气候预测工作产生影响，其中通常假设气候模式可以根据大气和海洋的当前状态以及两者之间耦合的足够准确的表示来预测（例如参见 AGS-2231237） 。 这项工作还与气候对沿海社区的影响直接相关，特别是考虑到 AMO 对大西洋飓风活动有重大影响。 研究人员与迈阿密气候复原力委员会和 Resilient305 研究合作组织合作，将研究成果直接应用于基于社区的决策。 该项目还为一名博士后、一名研究生和一名本科生提供支持和培训，PI 开展了一系列外展活动，包括迈阿密大学女性科学日，这是一项为六年级和七年级女生举办的年度活动。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。

项目成果

Tropical Atlantic multidecadal variability is dominated by external forcing

热带大西洋的数十年变率主要受外力影响

• DOI: 10.1038/s41586-023-06489-4
• 发表时间: 2023-09-13
• 期刊: Nature
• 影响因子: 64.8
• 作者: C. He;A. Clement;Sydney M Kramer;M. Cane;J. Klavans;Tyler M. Fenske;L. Murphy
• 通讯作者: L. Murphy