Collaborative Research: Response of the upper tropical Pacific Ocean to greenhouse gas forcing in observations and models

合作研究：热带太平洋上层对观测和模型中温室气体强迫的响应

• 批准号: 2219829
• 负责人: Richard Seager
• 金额: $ 70.18万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-08-15 至 2025-07-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2219829&HistoricalAwards=false
• 关键词: Collaborative; Research; Response; upper; tropical

The tropical Pacific Ocean is a well-established driver of global climate anomalies and the largest oceanic source of 𝐶𝑂2 flux into the atmosphere. Its response to rising greenhouse gases (GHGs) will strongly influence future global climate means and extremes and the carbon cycle. Climate models simulate a warming in this region for the last several decades, which is not seen in the observational record. There is not a clear explanation of this difference or what it means for future projections. This work will be a uniquely detailed analysis of the tropical Pacific Ocean response to GHG-driven thermodynamic and dynamic forcing focusing on comparisons to observed and reanalyzed changes in ocean circulation and temperature. While much research has focused on the tropical atmosphere’s response to rising GHGs there has been much less work on the tropical oceans. This project will therefore by an important intellectual advance in understanding, in the context of radiatively-forced climate change, the ocean side of the coupled tropical atmosphere-ocean system. Determining how the tropical Pacific responds to rising GHGs is critical to projecting changes in regional climates worldwide and climate-carbon feedbacks that influence atmospheric 𝐶𝑂2. The work will advance knowledge important to climate change mitigation and adaptation. The work will support two early-career researchers (postdoctoral and graduate) and a female faculty member to make fundamental advances in understanding how a key component of the climate system responds to anthropogenic forcing. The lead PI is well integrated into the community researching evolving drought risk over North America, for which the equatorial Pacific is a key driver, and its societal impacts. Results will be communicated there to identify errors and narrow uncertainties regarding near-term hydroclimate projections under GHG-induced changeAmidst the global warming accompanying the sharp rise in GHGs since circa 1960 observations show little warming or even cooling in the equatorial Pacific cold tongue. In contrast, models within successive Coupled Model Intercomparison Projects (CMIPs) simulate warming of the cold tongue. It has been argued that this discrepancy is due to strong internal variations in nature rather than a response to GHGs. Yet various studies all show it is unlikely that CMIP models can match the observations, though they differ on just how unlikely. On the other hand, it has been hypothesized that rising GHGs lead to strengthening of the zonal SST gradient, Walker circulation and trades, a dynamically-shoaled thermocline and enhanced cooling by upwelling. Models, it is argued, have a largely opposite response due to biases in simulating the tropical Pacific atmosphere-ocean system. This project will address how the temperature, currents and thermal structure of the upper tropical Pacific Ocean respond to rising GHGs. It is a deep investigation with observations and models of the period to date for which models can be evaluated. The work is organized around hypotheses that address the questions: 1) what are the relative roles of thermodynamic and dynamic processes in determining the tropical Pacific Ocean response to rising GHGs? 2) do biases in climate models (excessive cold tongue, overdeveloped southern convergence zone, too-warm eastern subtropical stratus cloud and upwelling regions) lead to biased SST responses in upwelling and subducting regions and biased transport pathways into the Equatorial Undercurrent? 3) do model biases influence the response of tropical Pacific SSTs to GHG forcing? The main goal is to better understand the active role of nature’s ocean in the response to rising GHGs. Models are primary tools for this investigation. In response to rising GHGs the work will examine: how heat added at the surface is mixed down and transported in the interior after subduction in the subtropics; how changes in wind stress impact currents, upwelling, thermal structure and SST; how mean wind stress influences interior pathways between the equator and the subtropics and, hence, the temperature of water upwelling in the cold tongue. The responses will be decomposed with experiments with ocean models using European Center for Medium Range Weather Forecasts reanalyses for validation. The experiments will impose, in various combinations, modeled and observed fields, GHG-induced heating, and reanalyzed and CMIP6 mean and anomalous wind stresses. Heat budgets, tracers, Explanatory Artificial Intelligence methods and causal pathway analysis will reveal the mechanisms of ocean responses to observed and CMIP6 wind stress trends, how this depends on the mean ocean state being perturbed, and the relative roles of passive and dynamical ocean processes in determining trends in tropical Pacific SSTs.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.

热带太平洋是全球气候异常的公认驱动力，也是进入大气的𝐶𝑂2通量的最大海洋来源。它对不断上升的温室气体(GHGs)的反应将极大地影响未来全球气候的手段和极端情况以及碳循环。气候模型模拟了过去几十年该地区的气候变暖，这在观测记录中是看不到的。对于这种差异或它对未来预测意味着什么，目前还没有一个明确的解释。这项工作将是对热带太平洋对温室气体驱动的热力和动力强迫的反应的独特的详细分析，重点是比较观察和重新分析海洋环流和温度的变化。虽然许多研究都集中在热带大气对温室气体上升的反应上，但对热带海洋的研究要少得多。因此，该项目将在理解辐射强迫气候变化背景下热带大气-海洋耦合系统的海洋方面取得重要的智力进步。确定热带太平洋如何应对不断上升的温室气体，对于预测全球区域气候变化和影响大气𝐶𝑂2的气候碳反馈至关重要。这项工作将促进对气候变化缓解和适应至关重要的知识的发展。这项工作将支持两名职业生涯早期的研究人员(博士后和研究生)和一名女性教员在理解气候系统的一个关键组成部分如何应对人为强迫方面取得根本性进展。带头的非政府组织很好地融入了研究北美干旱风险演变及其社会影响的社区，赤道太平洋是这一风险的关键驱动因素。结果将在那里传达，以确定在温室气体诱导的变化下关于近期水文气候预测的误差和狭义不确定性。自1960年左右以来，全球变暖伴随着温室气体的急剧上升，观测显示赤道太平洋冷舌几乎没有变暖甚至变冷。相比之下，连续耦合模式比较项目(CMIP)中的模式模拟了寒冷舌头的变暖。有人争辩说，这种差异是由于大自然的强烈内部变化，而不是对温室气体的反应。然而，各种研究都表明，CMIP模型不太可能与观测结果相匹配，尽管它们在可能性有多大上存在分歧。另一方面，假设温室气体增加导致纬向海温梯度增强、Walker环流和贸易、动态浅滩温跃层和上升流加强冷却。有人认为，由于在模拟热带太平洋大气-海洋系统时存在偏差，模型的反应在很大程度上是相反的。该项目将探讨热带太平洋上层海洋的温度、洋流和热结构如何应对温室气体上升。这是对这一时期的观测和模型进行的深入调查，可以对哪些模型进行评估。这项工作围绕以下假设展开：1)热力和动力过程在确定热带太平洋对温室气体上升的响应中的相对作用是什么？2)气候模式中的偏差(过度寒冷的舌头、过度发展的南部辐合带、过热的东部副热带层云和上升区)是否会导致上升和俯冲地区的SST响应偏差以及进入赤道潜流的偏差输送路径？3)模式偏差是否影响热带太平洋SST对温室气体强迫的响应？主要目标是更好地了解自然界海洋在应对温室气体上升方面的积极作用。模型是本次调查的主要工具。为了应对不断上升的温室气体，这项工作将研究：在亚热带俯冲后，增加在地表的热量如何混合并在内部输送；风应力的变化如何影响气流、上升流、热结构和海温；平均风应力如何影响赤道和亚热带之间的内部路径，从而影响冷舌中上升的水的温度。这些响应将通过使用欧洲中期天气预报再分析中心的海洋模型实验进行分解，以进行验证。这些实验将在不同的组合中施加模拟和观测场，温室气体诱导的加热，并重新分析和CMIP6平均和异常风应力。热量预算、示踪剂、解释性人工智能方法和因果路径分析将揭示海洋对观测到的和CMIP6风应力趋势的响应机制，这如何依赖于被扰动的平均海洋状态，以及被动和动力海洋过程在确定热带太平洋SST趋势中的相对作用。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。