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

• Main Authors: Gaetani, Marco, Messori, Gabriele, Pausata, Francesco S. R., Tiwari, Shivangi, Alvarez Castro, M. Carmen, Zhang, Qiong
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus GmbH 2024
• Subjects: Pacific; North Atlantic; North Atlantic oscillation
• Online Access: https://archimer.ifremer.fr/doc/00876/98751/108361.pdf; https://doi.org/10.5194/egusphere-2024-272; https://archimer.ifremer.fr/doc/00876/98751/

During the first half of the Holocene (11,000 to 5,000 years ago) the Northern Hemisphere experienced a strengthening of the monsoonal regime, with climate reconstructions robustly suggesting a greening of the Sahara region. Paleoclimate archives also show that this so-called African Humid Period (AHP) was accompanied by changes in the climate conditions at mid to high latitudes. However, inconsistencies still exist in reconstructions of the mid-Holocene (MH) climate at mid-latitudes, and model simulations provide limited support to reduce these discrepancies. In this paper, a set of simulations performed with a climate model is used to investigate the hitherto unexplored impact of the Saharan greening on mid-latitude atmospheric circulation during the MH. Numerical simulations show a year-round impact of the Saharan greening on the main circulation features in the Northern Hemisphere, especially during boreal summer when the African monsoon develops. Key findings include a westward shift of the global Walker Circulation, leading to a modification of the North Atlantic jet stream in summer and the North Pacific jet stream in winter. Furthermore, the Saharan greening modifies the atmospheric synoptic circulation over the North Atlantic, transitioning the North Atlantic Oscillation phase from prevailingly positive to neutral-to-negative in winter and summer. This study provides a first constraint on the Saharan greening influence on northern midlatitudes, indicating new opportunities for understanding the MH climate anomalies in regions such as North America and Eurasia.