AGS-PRF: Assessing Causes of the Divergence between Past and Projected Responses of Global Aridity to Greenhouse Warming

AGS-PRF：评估全球干旱对温室变暖的过去和预测反应之间差异的原因

• 批准号: 1433551
• 负责人: Jacob Scheff
• 金额: $ 8.6万
• 依托单位: Scheff Jacob
• 依托单位国家: 美国
• 项目类别: Fellowship Award
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-01-01 至 2016-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1433551&HistoricalAwards=false
• 关键词: AGS; PRF; Assessing; Causes; Divergence

This award provides funds for a 2-year Postdoctoral Research Fellowship for the PI, who will work under the mentorship of Professor Richard Seager at Columbia University. The goal of the project is to reconcile an apparent discrepancy between expected changes in hydroclimate due to global warming with paleoclimate proxy data from past climates. Global warming simulations typically suggest that water will become more scarce over the continents as temperatures rise, due to increases in evaporative demand that outpace increases in precipitation. But if drying accompanies warming then the same logic would suggest that colder climates, including ice age climates, should be wetter. This argument is apparently in conflict with the geological evidence, which suggests that the ice ages were in fact dryer than today's climate. Moreover, there is evidence that the warm climate of the early Cenozoic (about 55 million years ago) was wetter than today's world despite the higher temperatures.Three avenues of research are pursued to address this discrepancy, the first of which is a careful examination of modern-day climate simulations from climate models participating in the Coupled Model Intercomparison Project version 5 (CMIP5). The premise is that the drying produced in climate change simulations from these models could be associated with biases in the present-day simulations, thus models may overestimate future drying if they are consistently biased dry in their control simulations. The second activity is a diagnostic examination of continental hydroclimate in model simulations of the last glacial maximum (LGM, roughly 20 to 25 thousand years ago), taken from the Paleoclimate Model Intercomparison Project version 3 (PMIP3). While changes in precipitation and potential evapotranspiration have been examined in detail for future climate simulations, comparable diagnoses have not been performed for LGM simulations.The third is a reexamination of the paleo-proxy record to make sure that the evidence for LGM drying has not been misinterpreted. Much of this evidence is based on vegetation, and it is possible that the vegetation is responding to lower values of carbon dioxide (CO2) and a reduction in CO2 fertilization, rather than a reduction in available water. The PI proposes to address this possibility by looking at proxy data which is not related to vegetation, for example lake levels and evaporite deposits. If the non-vegetation proxies do not show the same aridity signal found in vegetation-based proxies (pollen, fossils, carbon isotope ratios), a role for CO2 fertilization would seem likely.The work has inherent broader impacts due to the profound consequences of water shortages for human well-being and natural ecosystems. The work specifically addresses the potential for climate change to produce water shortages and the question of how well we can anticipate such shortages based on climate model simulations. In addition, the postdoctoral research fellowship, under the mentorship of an established scientist, will help to build the career of the PI, thereby providing support for the future workforce in this scientific discipline.

该奖项为PI提供为期2年的博士后研究奖学金，PI将在哥伦比亚大学的Richard Seager教授的指导下工作。该项目的目标是调和由于全球变暖引起的水文气候预期变化与过去气候的古气候代用数据之间的明显差异。全球变暖模拟通常表明，随着气温上升，由于蒸发需求的增加超过了降水量的增加，各大洲的水资源将变得更加稀缺。但如果干燥伴随着变暖，那么同样的逻辑也表明，包括冰河时代气候在内的寒冷气候应该更加潮湿。 这一论点显然与地质学证据相冲突，地质学证据表明冰河时代实际上比今天的气候干燥。此外，有证据表明，新生代早期（约5500万年前）的温暖气候比今天的世界更潮湿，尽管温度更高。为了解决这一差异，我们进行了三种研究，第一种是仔细检查参与耦合模式相互比较项目第5版（CMIP 5）的气候模式的现代气候模拟。其前提是，从这些模型中产生的气候变化模拟干燥可能与偏见在当今的模拟，因此，模型可能高估未来的干燥，如果他们一直偏干在他们的控制模拟。第二项活动是对末次盛冰期（LGM，大约20至25万年前）的模型模拟中的大陆水文气候进行诊断检查，来自古气候模型相互比较项目第3版（PMIP 3）。虽然降水量和潜在蒸散量的变化已经详细研究了未来的气候模拟，可比的诊断还没有进行LGM模拟。第三个是重新检查的古代理记录，以确保LGM干燥的证据没有被误解。这些证据大部分是基于植被，植被可能是对二氧化碳（CO2）值降低和CO2施肥量减少做出反应，而不是对可用水减少做出反应。PI建议通过查看与植被无关的替代数据来解决这种可能性，例如湖泊水位和蒸发岩沉积。如果非植被替代物没有显示出与植被替代物（花粉、化石、碳同位素比）相同的干旱信号，那么CO2施肥似乎可能发挥作用。由于水资源短缺对人类福祉和自然生态系统的深远影响，这项工作具有内在的广泛影响。 这项工作专门解决了气候变化导致水资源短缺的可能性，以及我们如何根据气候模型模拟预测这种短缺的问题。 此外，博士后研究奖学金，在一个既定的科学家的指导下，将有助于建立PI的职业生涯，从而为这一科学学科的未来劳动力提供支持。