India is at risk of declining monsoon due to warming of the Indian Ocean

A new study indicates that under the current global warming conditions, the congested Indian subcontinent is likely to experience a sharp reduction in critical monsoon rainfall.

Paleoclimate data recovered from marine sediments 130,000 years ago suggest that prolonged warming in the Indian Ocean during the last glacier increased tropical rainfall over the ocean, but weakened in the Indian summer monsoon land.

The South Asian monsoon, also known as the Indian Summer Rainfall (ISM), is critical to the food security and socio-economic well-being of 40% of the world’s population. Historically, monsoon fluctuations have been linked to the rise and fall of civilizations in the Indian subcontinent.

Now, researchers are increasingly concerned that global warming could threaten the stability of the monsoon system, but accurate forecasts are hampered by the lack of long-term climate data for the Indian subcontinent.

A team of researchers from the Max Blank Institute for the Science of Human History, the University of Kiel and the Alfred Wegener Institute of the Helmholtz Center are seeking to reinforce a new study, PNAS Magazine. To reconstruct the changes of summer monsoon in the Indian subcontinent over the last 130,000 years.

Study reports for the first time that the Indian summer monsoon weakened during the last glacier due to high sea surface temperatures in the equator and tropical Indian Ocean, indicating that modern sea temperature rise may exacerbate drought in South Asia.

Solar radiation is often considered to be the main factor influencing the intensity of Indian summer rainfall, with high solar radiation increasing humidity, air circulation and eventually rainfall. Therefore, higher levels of solar radiation during the last glacier may have led to an increase in monsoon intensity, but this effect has not been verified by paleo-proxy data.

To restore the Indian monsoon rains of last summer, researchers have explored a 10-meter-long marine sediment recovered from the Bay of Bengal about 200 km south of the mouth of the Ganges-Brahmaputra-Magna rivers.

By analyzing the stable isotopes of hydrogen and carbon in the sedimentary leaf wax biomarks, researchers were able to observe changes in rainfall during the planet’s last two warmer climates: the last glacier, which occurred 130 000-115,000 years ago. , And the current warmest climate, the Holocene, which began 11,600 years ago.

Although sunlight penetration was high during the last interclacial, isotopic analysis of leaf wax revealed that the Indian summer monsoon was actually less intense than the Holocene. “This unexpected discovery not only contradicts the simulations of the paleoclimate model, says Yiming Wang, lead author of the paleoglomatologist at the Max Blank Institute for Human History on Human History, but also challenges the general assumptions that the tropics are a very important factor in incoming sunlight.”

To identify the main driver of monsoon during warmer climates, researchers compared available reconstructions of past Indian Ocean surface temperatures and found that the equator and tropics were 1.5–2.5 C warmer during the last glacial period than during the Holocene.

In addition, researchers are using paleoglimeter simulations, which show that when the surface temperature of the Indian Ocean increased in the past, the monsoon decreased on land and increased in the sea off the Bay of Bengal.

“Our mission confirms that sea surface temperature plays an important role in shaping the variation of the Indian summer monsoon in South Asia,” Wang said, adding that “high surface temperatures in the Indian Ocean during the last glacial period can reduce the intensity of ISM.”

The results of the panel indicate that the intensity of the Indian summer monsoon is less likely to increase as sea surface temperatures rise in the Indian Ocean. The extent to which sea surface temperature affects the intensity of monsoon in other tropical regions remains an open question.