Synchronous Strengthening of the Indian and East Asian Monsoons in Response to Global Warming Since the Last Deglaciation

• Published in: Geophysical research letters 2019-04, Vol.46 (7), p.3944-3952
• Main Authors: Jiang, Wenying, Leroy, Suzanne A.G., Yang, Shiling, Zhang, Enlou, Wang, Luo, Yang, Xiaoxiao, Rioual, Patrick
• Format: Article
• Language: English
• Subjects: Annual temperatures; Area; Asian summer monsoon; Climate change; Climatology; Convergence; Convergence zones; Deciduous trees; Deglaciation; Earth Sciences; East Asian monsoon; Environmental Sciences; Future climates; Global Changes; Global warming; Habitat loss; Holocene; Ice melting; Insolation; Intertropical convergence zone; lake sediments; Lakes; last deglaciation; Latitude; Melting; Meltwater; Monsoons; Northern Hemisphere; Paleovegetation; Pollen; pollen records; Precipitation; Sciences of the Universe; Summer; Summer monsoon; Temperature; Trees; Tsuga dumosa; Wind
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2019GL082084

The responses of the Indian and East Asian summer monsoons (ISM and EASM) to warming since the last deglaciation are controversial. Pollen results from a subalpine lake in the ISM area show that the Tsuga dumosa forest zone migrated at least 650 m upward during 18.6–7.1 kyr BP, indicating a gradual rise in mean annual temperature exceeding 3.9 °C. In response, grasses and deciduous and evergreen broad‐leaved trees successively colonized the mountainous environment. By contrast, the area around a lake in the EASM area was gradually occupied by temperate deciduous trees. In both areas, the maximum monsoonal precipitation occurred during 7.1–6.4 kyr BP, coinciding with peak Holocene warmth, but lagging the peak in Northern Hemisphere summer insolation by 3.9–4.6 kyr, due to delayed ice melting in northern high latitudes. Our results indicate the synchronous strengthening of the ISM and EASM in response to warming‐induced northward shifts in the Intertropical Convergence Zone. Plain Language Summary The responses of the Indian summer monsoon (ISM) and East Asian summer monsoon to past global warming provide valuable insights into future climate scenarios. A paleovegetation reconstruction from the ISM area shows a gradual warming of over 3.9 °C in mean annual temperature from 18.6 to 7.1 kyr BP. The ISM and East Asian summer monsoon strengthened synchronously in response to warming‐induced shifts in the Intertropical Convergence Zone and reached their peak at 7.1–6.4 kyr BP, lagging the summer insolation maximum by 3.9–4.6 kyr, due to delayed ice melting in northern high latitudes. As future warming continues, the loss of habitat for Tsuga dumosa and other alpine species will accelerate in the ISM area, and the abundance of deciduous trees will increase in northern China. Key Points Pollen data show a minimum 650‐m upward migration of the Tsuga dumosa forest zone in the Hengduan Mountains from 18.6 to 7.1 kyr BP Our data and a synthesis of 37 additional paleovegetation records show the peak of the Holocene Climate Optimum occurring around 7 kyr BP The Indian and East Asian summer monsoons strengthened synchronously in response to past global warming