Mid-Holocene climate at mid-latitudes: assessing the impact of Saharan greening

IF 3.8 2区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY
Marco Gaetani, Gabriele Messori, Francesco S. R. Pausata, Shivangi Tiwari, M. Carmen Alvarez Castro, Qiong Zhang
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Abstract

Abstract. During the first half of the Holocene (11 000 to 5000 years ago), the Northern Hemisphere experienced a strengthening of the monsoonal regime, with climate reconstructions robustly suggesting a greening of the Sahara region. Palaeoclimate archives also show that this so-called African humid period (AHP) was accompanied by changes in climate conditions at middle to high latitudes. However, inconsistencies still exist in reconstructions of the mid-Holocene (MH) climate at mid-latitudes, and model simulations provide limited support in reducing these discrepancies. In this paper, a set of simulations performed using a climate model are used to investigate the hitherto unexplored impact of Saharan greening on mid-latitude atmospheric circulation during the MH. Numerical simulations show Saharan greening has a year-round impact on the main circulation features in the Northern Hemisphere, especially during boreal summer (when the African monsoon develops). Key findings include a westward shift in the global Walker Circulation, leading to modifications in the North Atlantic jet stream in summer and the North Pacific jet stream in winter. Furthermore, Saharan greening modifies atmospheric synoptic circulation over the North Atlantic, enhancing the effect of orbital forcing on the transition of the North Atlantic Oscillation phase from predominantly positive to negative in winter and summer. Although the prescription of vegetation in the Sahara does not improve the proxy–model agreement, this study provides the first constraint on the influence of Saharan greening on northern mid-latitudes, opening new opportunities for understanding MH climate anomalies in regions such as North America and Eurasia.
中纬度全新世中期气候:评估撒哈拉绿化的影响
摘要在全新世的前半期(距今 11000 至 5000 年),北半球经历了季风制度的加强,气候重建有力地表明了撒哈拉地区的绿化。古气候档案也显示,所谓的非洲湿润期(AHP)伴随着中高纬度气候条件的变化。然而,对中纬度地区全新世中期(MH)气候的重建仍然存在不一致的地方,而模型模拟在减少这些差异方面提供的支持有限。本文利用气候模式进行了一系列模拟,以研究迄今为止尚未探索过的撒哈拉绿化对中纬度 MH 期间大气环流的影响。数值模拟结果表明,撒哈拉沙漠绿化对北半球的主要环流特征有全年性影响,尤其是在北半球夏季(非洲季风发展时期)。主要发现包括全球沃克环流的西移,导致夏季北大西洋喷流和冬季北太平洋喷流的改变。此外,撒哈拉绿化改变了北大西洋上空的大气同步环流,增强了轨道强迫对北大西洋涛动相位从冬季和夏季的正向为主过渡到负向为主的影响。虽然规定撒哈拉地区的植被并不能改善代用模型与模型之间的一致性,但这项研究首次限制了撒哈拉绿化对北部中纬度地区的影响,为了解北美和欧亚等地区的 MH 气候异常提供了新的机会。
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来源期刊
Climate of The Past
Climate of The Past 地学-气象与大气科学
CiteScore
7.40
自引率
14.00%
发文量
120
审稿时长
4-8 weeks
期刊介绍: Climate of the Past (CP) is a not-for-profit international scientific journal dedicated to the publication and discussion of research articles, short communications, and review papers on the climate history of the Earth. CP covers all temporal scales of climate change and variability, from geological time through to multidecadal studies of the last century. Studies focusing mainly on present and future climate are not within scope. The main subject areas are the following: reconstructions of past climate based on instrumental and historical data as well as proxy data from marine and terrestrial (including ice) archives; development and validation of new proxies, improvements of the precision and accuracy of proxy data; theoretical and empirical studies of processes in and feedback mechanisms between all climate system components in relation to past climate change on all space scales and timescales; simulation of past climate and model-based interpretation of palaeoclimate data for a better understanding of present and future climate variability and climate change.
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