Though the ISM was relatively weak for much of the Late Holocene, significant glacial accumulation in the Himalayas still occurred due to cold temperatures brought by westerlies from the west. The Indian Summer Monsoon (ISM) underwent several intensifications during the warming following the Last Glacial Maximum, specifically during the time intervals corresponding to 16,100–14,600 BP, 13,600–13,000 BP, and 12,400–10,400 BP as indicated by vegetation changes in the Tibetan Plateau displaying increases in humidity brought by an intensifying ISM. In 2018, a study of the SAM's variability over the past million years found that precipitation resulting from the monsoon was significantly reduced during glacial periods compared to interglacial periods like the present day. It is believed that the resulting increase in sea surface temperatures in the Indian Ocean increased the intensity of monsoons. When this happened, cold waters in the Pacific were impeded from flowing into the Indian Ocean. Then, during ice periods, the sea level fell and the Indonesian Seaway closed. Ī study of marine plankton suggested that the South Asian Monsoon (SAM) strengthened around 5 million years ago.
A study of Asian monsoonal climate cycles from 123,200 to 121,210 years BP, during the Eemian interglacial, suggests that they had an average duration of around 64 years, with the minimum duration being around 50 years and the maximum approximately 80 years, similar to today. The monsoon has varied significantly in strength since this time, largely linked to global climate change, especially the cycle of the Pleistocene ice ages. Testing of this hypothesis awaits deep ocean sampling by the Integrated Ocean Drilling Program. More recently, studies of plant fossils in China and new long-duration sediment records from the South China Sea led to a timing of the monsoon beginning 15–20 million years ago and linked to early Tibetan uplift. Because of studies of records from the Arabian Sea and that of the wind-blown dust in the Loess Plateau of China, many geologists believe the monsoon first became strong around 8 million years ago. Strengthening of the Asian monsoon has been linked to the uplift of the Tibetan Plateau after the collision of the Indian subcontinent and Asia around 50 million years ago. The English monsoon came from Portuguese monção ultimately from Arabic موسم ( mawsim, "season"), "perhaps partly via early modern Dutch monson". The etymology of the word monsoon is not wholly certain. Monsoon clouds over Lucknow, Uttar Pradesh, India
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