Abstract
Abstract. Previous studies based on multiple paleoclimate archives suggested a prominent intensification of the South Asian Monsoon (SAM) during the mid-Holocene (MH, ∼6000 years before present). The main forcing that contributed to this intensification is related to changes in the Earth's orbital parameters. Nonetheless, other key factors likely played important roles, including remote changes in vegetation cover and airborne dust emission. In particular, northern Africa also experienced much wetter conditions and a more mesic landscape than today during the MH (the so-called African Humid Period), leading to a large decrease in airborne dust globally. However, most modeling studies investigating the SAM changes during the Holocene overlooked the potential impacts of the vegetation and dust emission changes that took place over northern Africa. Here, we use a set of simulations for the MH climate, in which vegetation over the Sahara and reduced dust concentrations are considered. Our results show that SAM rainfall is strongly affected by Saharan vegetation and dust concentrations, with a large increase in particular over northwestern India and a lengthening of the monsoon season. We propose that this remote influence is mediated by anomalies in Indian Ocean sea surface temperatures and may have shaped the evolution of the SAM during the termination of the African Humid Period.
Highlights
The South Asian Monsoon (SAM) directly affects the climate of the Indian subcontinent and indirectly influences farafield regions through atmospheric and oceanic teleconnections (e.g., Lau, 1992; Liu et al, 2004)
The reduced Saharan dust (MHRD) leads to a pattern that is very similar – albeit with weaker anomalies – to the orbital-only forcing (MHPMIP; Fig. A3b); the precipitation increase over southern India is confined to east of the Western Ghats, while a small decrease in rainfall is simulated along the western coast of the Indian subcontinent
The reduced precipitation over the Western Ghats is further enhanced in the MHGS+RD, while the increase over the Himalayan foothills is reduced compared to the MHGS, which is due to the effect of the dust reduction
Summary
The South Asian Monsoon (SAM) directly affects the climate of the Indian subcontinent and indirectly influences farafield regions through atmospheric and oceanic teleconnections (e.g., Lau, 1992; Liu et al, 2004). Due to its key role for regional and global hydrological cycles, much attention has been devoted to better understand and predict its variability on multiple timescales, including its long-term future changes (e.g., Huo and Peltier, 2020; Swapna et al, 2018). SAM future projections are highly uncertain (e.g., Huang et al, 2020), and even representing recent trends and identifying their drivers has been challenging (e.g., Mishra et al, 2018) due to the relatively short modern observational record that spans roughly a century. R. Pausata et al.: SAM remote response to Sahara greening
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