A giant blob of unusually cold water in the North Atlantic Ocean is shifting the Indian summer monsoon, threatening the livelihoods of more than 1 billion people, new research shows.
Scientists say the link between these two systems highlights a previously unknown connection that could inform weather forecasting in South Asia and shed light on climate events elsewhere.
The Indian summer monsoon is a rainfall pattern that lasts from June to September and is induced by the temperature difference between the warm northern Indian Ocean and the cold ocean waters below the equator. Historically, the monsoon caused heavy rainfall along the west coast of India and a vast area of northern India called the Indo-Gangetic Plain. But since 1999, this pattern has changed dramatically, researchers report in a new study.
The team found that northwest India now receives about 25% more rain during the monsoon season than before 1999, while the Indus-Gangetic plain receives about 4% less rain. This is especially devastating for farmers, because their soils and crops are adapted to old rainfall patterns, said the study’s first author. Mahendra NimmakantiA climate scientist at the Center for Atmospheric and Oceanic Sciences of the Indian Institute of Science.
“India is largely dependent on agriculture,” Nimmakanti told Live Science in a joint interview with a co-author of the study. Matthew HuberProfessor in the Department of Earth, Atmospheric and Planetary Sciences at Purdue University in Indiana. Higher than normal rainfall is causing flash floods and crop damage in northwest India, as agriculture in the region is adapted to dry conditions. Meanwhile, the Indo-Gangetic plain has experienced several droughts, leading to crop failure and impacting farmers’ livelihoods, Nimmakanti said.
Previous studies have Related changes in Indian summer monsoon Changes in the Atlantic Meridional Overturning Circulation (AMOC), a vast web of ocean currents in the Atlantic that regulates global climate and transports heat to the Northern Hemisphere. data suggests AMOC is slowing down due to climate change And releasing less heat into the North Atlantic Ocean than before. This may be due to the southward shift of the intertropical convergence zone, a band of low-pressure atmospheric conditions around the equator. drives the tropical monsoonWhich also includes the Indian summer monsoon.
But these studies do not specify how the Indian monsoon might change or explain the underlying mechanisms in detail, Nimmakanti said. “They generally explain that if the AMOC weakens, it suppresses the Indian summer monsoon,” he said.
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Part of the problem is that current climate models do not reflect real-life changes in the Indian monsoon, possibly because they do not fully capture changes in North Atlantic sea surface temperatures. This is especially true for the area southeast of Greenland known as the “cold blob,” where between 1901 and 2021 the water was colder than it was in the 1800s, even as the ocean surrounding it warmed.
Cold blob shows AMOC is weakening Because it indicates a reduction in the amount of heat reaching the North Atlantic.
To find out how and why the Indian monsoon has changed, researchers fed rainfall data, sea surface temperature records and other real-life observations into dozens of climate models. This replicated the changes seen over the past 27 years. However, the results only show a relationship between changes in the North Atlantic and changes in the monsoon, not that the monsoon directly caused the monsoon.
Northwest India now receives 25% more rain during the monsoon season than before 1999, and this change has also increased the risk of floods in Pakistan.
(Image credit: Sabir Mazhar/Anadolu via Getty Images)
To find out whether North Atlantic sea surface temperatures were causing the Indian monsoon to behave strangely, the team added and removed cold blobs in a simulation. The results showed that the cold blob shifted the Indian monsoon by creating a strong temperature gradient over the North Atlantic, which, in turn, influenced jet stream winds and pressure systems in the atmosphere over Eurasia.
In particular, the jet stream over the North Atlantic has intensified, and an “obstructed” system over the Ural Mountains in western Russia has strengthened, Huber said. As a result, weather systems over India have shifted, moving moist air towards the north-west of the country and away from other areas.
“It’s a shifting of high and low pressure systems,” Huber said. “To realize that these two systems were directly connected through this wave train coming from the North Atlantic was new.”
More than 1 billion people in India and other parts of South Asia depend on the monsoon for food security and economic stability. The new results, published April 27 in the journal agu advanceThis may help forecasters to predict extreme rainfall and drought events in neighboring countries like India and Pakistan during the monsoon season.
Some researchers believe the Indian monsoon is a turning point within the global climate, and the findings suggest the system crossed a threshold in 1999. Since then, the cold blob has caused “persistent jet stream reorganization”, leading to sudden changes in the monsoon, according to the study.
It is unclear how the Indian monsoon will develop under intensification Climate changeThat’s because climate models make different predictions of what will happen in the North Atlantic, Huber said, and other factors may also play a role as the world changes.
“What we know now is that this is one of the important building blocks for building a theory for what will happen in the future,” he said.
Mahendra, N., Chilukoti, N., Liu, X., Chaudhary, J.S., Wang, L., and Huber, M. (2026). Lack of summer westerly jet barotropic governor effect explains anomalies in climate model-Indian monsoon trends. agu advance, 7(3). https://doi.org/10.1029/2025av002173