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一个公认的驱动因素，也是进入大气中的𝐶𝑂2通量的最大强海洋源，其对温室气体（GHG）上升的反应将影响未来的全球气候平均值和极端情况以及碳循环。模型模拟了过去几十年该地区的变暖情况，这在观测记录中没有看到。对于这种差异或它对未来预测的意义，目前还没有明确的解释。这项工作将是一项独特的详细分析。热带太平洋对温室气体驱动的热力学和动力强迫的响应与观测和重新分析的海洋环流和温度变化的比较虽然许多研究都集中在热带大气对温室气体上升的响应上，但对热带海洋的研究却少得多。因此，在辐射强迫气候变化的背景下，该项目将在了解热带大气-海洋耦合系统的海洋一侧方面取得重要的知识进展，从而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的气候碳反馈至关重要。这项工作将推进对气候变化减缓和适应重要的知识。这项工作将为两名早期职业研究人员（博士后和研究生）和一名女教员提供支持。在理解气候系统的一个关键组成部分如何响应人为强迫方面取得根本性进展，首席研究员很好地融入了研究北美不断变化的干旱风险的社区，其中赤道太平洋是一个关键驱动因素。其社会影响将在那里传达，以识别温室气体引起的变化下近期水文气候预测的不确定性。自大约 1960 年以来，全球变暖伴随着温室气体急剧上升，观测显示赤道太平洋寒冷几乎没有变暖甚至变冷。相比之下，连续的耦合模型比较项目（CMIP）中的模型模拟了冷舌头的变暖。有人认为这种差异是由于舌头的强烈内部变化造成的。然而，各种研究都表明，CMIP 模型不太可能与观察结果相符，尽管它们在可能性上存在差异。另一方面，人们利用了温室气体上升导致区域强化的现象。有人认为，由于模拟热带太平洋大气-海洋系统的偏差，海温梯度、沃克环流和贸易、动态浅滩温跃层和上升流增强冷却模型的反应基本上相反。该项目将解决热带太平洋上层的温度、海流和热结构如何应对温室气体上升的问题。这是一项针对迄今为止可评估模型的观测和模型的深入调查。解决以下问题：1）热力学和动力过程在确定热带太平洋对温室气体上升的反应方面的相对作用是什么？2）气候模型是否存在偏差（过度寒冷的舌头、过度发达的南部辐合带、过于温暖的东部副热带）层云和上升流区域）导致上升流和俯冲区域的海温响应存在偏差，以及进入赤道暗流的传输路径存在偏差？ 3）模型偏差是否会影响热带太平洋海温对温室气体强迫的响应？自然海洋在应对温室气体排放上升中的作用 模型是这项调查的主要工具。为了应对温室气体排放上升，这项工作将研究：表面增加的热量如何混合并在海洋中传输。亚热带俯冲后的内部；风应力的变化如何影响洋流、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流的水温。响应将通过使用欧洲中期天气预报中心重新分析的海洋模型实验进行分解以进行验证。这些实验将以各种组合、建模和观测场、温室气体引起的加热和影响进行分析。重新分析的和 CMIP6 平均和异常风应力、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，这如何取决于平均海洋状态受到扰动，以及被动和动态海洋过程在确定热带太平洋海表温度趋势中的相对作用。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查进行评估，被认为值得支持标准。