Transforming our understanding of climate shifts in the North African dust belt and upskilling Earth System Models to simulate them

改变我们对北非沙尘带气候变化的理解，并提高地球系统模型的模拟能力

• 批准号: NE/X000869/1
• 负责人: Paul Wilson
• 金额: $ 73.52万
• 依托单位: University of Southampton
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2022
• 资助国家: 英国
• 起止时间: 2022 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FX000869%2F1
• 关键词: Transforming; our; understanding; climate; shifts

As Earth heats up in the coming decades, global rainfall patterns will shift with uncertain regional outcomes. Nowhere is this problem more acute than in North Africa. The world's largest hot desert and biggest source of atmospheric dust, the Sahara, grew by >10% in the 20th century. In the semi-arid Sahel and Mediterranean borderlands, where annual rainfall amounts are low and inter-annual rainfall variability is high, tens of millions of people live in extreme water stress with sometimes devastating consequences as during the late 20th century Sahel drought. These are major incentives to understand the mechanisms driving past variability in the climate of North Africa. However, the instrumental record is short (~150 yrs) and geological and archaeological data reveal a capacity for far more extreme shifts in North African climate. Paced by Earth's gradually changing orbit around the Sun and millennial-scale variability in the climate system, North Africa's past climate has shifted repeatedly between drier and dustier conditions than today and humid green Sahara periods (GSPs) when the desert was transformed into a well vegetated landscape crosscut by rivers and lakes, populated by hippopotamuses and our early ancestors (most recently during the African Humid Period, AHP, ~14.5 to 5 thousand years ago, ka).What caused these past shifts? What do they imply for the future? We lack convincing answers to these questions because the extreme shifts indicated by the palaeo-data are not reproduced by the computer models used to predict future change. A main weakness of the existing palaeo-data is their limited diagnosis of mechanistic control. North Africa has two latitudinal and seasonally distinct rainfall regimes, the summer monsoon and winter westerly storm track, but we know too little of their temporal and spatial contributions to the profound changes in humidity-aridity and vegetation recorded in the data. A main weakness in the models is that we do not know whether their lack of skill reflects missing processes and feedbacks that dampen the response to climate forcing or whether they adequately represent the key processes but are inadvertently hard-wired for stability because uncertain parameter values are determined solely by evaluation against contemporary observational targets. We propose to transform our understanding of climate shifts in the North African dust belt and to upskill models to successfully simulate them by capitalizing on recent breakthroughs that we have made (see Track Record). We will develop proxy climate records for a bellwether Saharan region to tease apart past variability in summer monsoon and winter storm-track rainfall (see Objectives). And we will configure an IPCC-class Earth System model (ESM) that shows novel power to green the Sahara and is sufficiently computationally inexpensive to permit adequate sampling of parameter space to confront our new proxy records (see Objectives). This will allow us to develop a mechanistic understanding of extreme change and to translate our findings to those scientists who are developing the next generation of ESMs that will be used to predict future change over the coming decades (see Academic Beneficiaries).

随着未来几十年地球变暖，全球降雨模式将发生变化，区域结果也不确定。这个问题在北非最为严重。撒哈拉沙漠是世界上最大的炎热沙漠和最大的大气尘埃来源，其面积在 20 世纪增长了 10% 以上。在半干旱的萨赫勒和地中海边境地区，年降雨量较低，年际降雨量变化较大，数以千万计的人生活在极度缺水的情况下，有时会造成毁灭性的后果，就像 20 世纪末萨赫勒干旱一样。这些是了解推动北非气候过去变化的机制的主要动力。然而，仪器记录很短（约 150 年），地质和考古数据揭示了北非气候发生更极端变化的能力。由于地球绕太阳轨道的逐渐变化和气候系统千禧年尺度的变化，北非过去的气候在比现在更加干燥和多尘的条件和潮湿的绿色撒哈拉时期（GSP）之间反复变化，当时沙漠变成了植被茂密的地区河流和湖泊横切的景观，居住着河马和我们的早期祖先（最近在非洲湿润时期，AHP，约 14.5 至 5 千年前，ka）。造成这些过去的转变？它们对未来意味着什么？我们对这些问题缺乏令人信服的答案，因为用于预测未来变化的计算机模型无法再现古数据所表明的极端变化。现有古数据的一个主要弱点是它们对机械控制的诊断有限。北非有两种纬度和季节性不同的降雨机制，即夏季季风和冬季西风风暴路径，但我们对它们对数据中记录的湿度-干旱和植被的深刻变化的时间和空间贡献知之甚少。这些模型的一个主要弱点是，我们不知道它们缺乏技能是否反映了缺失的过程和反馈，从而抑制了对气候强迫的响应，或者它们是否充分代表了关键过程，但无意中硬连线了稳定性，因为不确定的参数值是仅通过针对当代观察目标的评估来确定。我们建议转变我们对北非沙尘带气候变化的理解，并通过利用我们最近取得的突破来提高模型的技能，以成功地模拟它们（见跟踪记录）。我们将为撒哈拉地区的领头羊开发代理气候记录，以梳理夏季季风和冬季风暴路径降雨过去的变化（见目标）。我们将配置一个 IPCC 级地球系统模型 (ESM)，该模型显示出绿化撒哈拉的新能力，并且计算成本足够低，可以对参数空间进行充分采样，以应对我们的新代理记录（参见目标）。这将使我们能够对极端变化产生机械性的理解，并将我们的发现转化为那些正在开发下一代 ESM 的科学家，这些下一代 ESM 将用于预测未来几十年的未来变化（参见学术受益人）。

项目成果

Monsoon-driven changes in aeolian and fluvial sediment input to the central Red Sea recorded throughout the last 200,000 years

过去 20 万年记录的红海中部风沙和河流沉积物输入的季风驱动变化

• DOI: 10.5194/cp-2023-33
• 发表时间: 2023
• 作者: Ehrmann W