Expert Explains | Why the collapse of the AMOC ocean ‘conveyor belt’ could disrupt the Indian monsoon

Scientists and climate researchers have highlighted growing evidence that the Atlantic Meridional Overturning Circulation (AMOC) — often described as the oce...

What Happened

Scientists and climate researchers have highlighted growing evidence that the Atlantic Meridional Overturning Circulation (AMOC) — often described as the ocean's "conveyor belt" — is slowing down, raising alarm about its potential impacts on global weather systems, including the Indian summer monsoon.
Studies indicate the AMOC is already approximately 15% weaker than it was in the mid-20th century, primarily due to freshwater input from melting Greenland glaciers driven by anthropogenic climate change.
Research modelling AMOC collapse scenarios suggests the Indian monsoon could weaken by up to 20%, with severe consequences for agriculture, food security, and the broader economy of South Asia.
The findings are drawing increasing attention as El Niño cycles interact with the AMOC slowdown to compound monsoon variability.

Static Topic Bridges

Atlantic Meridional Overturning Circulation (AMOC)

The AMOC is a large system of ocean currents in the Atlantic Ocean that circulates warm surface water northward and cold deep water southward, acting as a critical heat transport mechanism across the globe. It is a component of the broader thermohaline circulation (THC) — ocean currents driven by differences in water temperature (thermos) and salinity (haline). As warm tropical water flows northward, it cools and becomes denser; in the Arctic and North Atlantic, this dense, cold water sinks to the ocean floor and flows southward as North Atlantic Deep Water (NADW). This vertical overturning keeps the cycle going and moderates the climate of Western Europe and influences weather patterns globally.

AMOC transports approximately 18–20 million cubic metres of water per second (sverdrups)
It is responsible for keeping northwest Europe 5–10°C warmer than equivalent latitudes would otherwise be
AMOC is now ~15% weaker than in the mid-20th century
The primary driver of weakening: accelerated Greenland ice melt (from global warming) adds fresh, less-dense water that suppresses the sinking mechanism
Some models suggest a complete collapse could occur as early as 2100 under high-emission scenarios, though estimates carry large uncertainty

Connection to this news: AMOC slowdown is not a localised Atlantic phenomenon — its cascading effects on atmospheric and ocean circulation reach as far as the Indian subcontinent, making it directly relevant to India's monsoon dependability.

Intertropical Convergence Zone (ITCZ) and the Indian Summer Monsoon

The Intertropical Convergence Zone (ITCZ) is a belt of low pressure near the equator where the trade winds from the Northern and Southern Hemispheres converge, causing intense convection, cloud formation, and rainfall. The Indian summer monsoon (June–September) is fundamentally driven by the seasonal northward migration of the ITCZ over the Indian subcontinent, creating the pressure gradient that draws moisture-laden southwest winds from the Arabian Sea and Bay of Bengal. The ITCZ's position is influenced by the cross-equatorial energy balance in the ocean-atmosphere system — a balance that AMOC helps regulate.

The Indian summer monsoon contributes approximately 70–90% of India's total annual rainfall
Agriculture dependent on monsoon rainfall: over 50% of India's net sown area is rain-fed
A 10% reduction in monsoon rainfall in a year is classified as a drought year in India
ITCZ shifts: a weaker AMOC reduces northward heat transport, potentially shifting the ITCZ southward and weakening the monsoon's northern penetration
Modelling studies project up to 20% reduction in monsoon rainfall under AMOC collapse scenarios

Connection to this news: Since the AMOC helps drive the northward energy flow that positions the ITCZ over India, a weakening AMOC could shift the ITCZ equatorward, reducing the intensity and geographic reach of the Indian monsoon.

Thermohaline Circulation and Global Climate Teleconnections

Thermohaline circulation (THC), also called the Global Ocean Conveyor Belt, is the planet-wide system of ocean currents driven by density differences arising from temperature and salinity variations. It redistributes heat absorbed by the tropics to polar regions and moderates global temperatures. Disruptions to THC propagate through complex atmospheric teleconnections — remote climate linkages through which changes in one region's ocean or atmosphere influence weather thousands of kilometres away. The Indian monsoon is one of the most teleconnected climate systems on Earth, sensitive to sea surface temperature anomalies in the Pacific (El Niño/La Niña), Indian Ocean, and Atlantic.

Teleconnection mechanisms linking AMOC to Indian monsoon include: southward shift of subtropical jet stream, Matsuno-Gill-type atmospheric response to Atlantic SST anomalies, and weakening of the cross-equatorial pressure gradient
A weaker AMOC cools the sub-polar North Atlantic, altering westerly wind patterns and interfering with the southwest monsoon flow
El Niño (warm phase of ENSO in the Pacific) independently suppresses the Indian monsoon; combined with AMOC weakening, the compounding effect could be severe
The 2015 North Atlantic Climate Impact Assessment showed interconnections between AMOC state and South Asian monsoon strength

Connection to this news: Understanding AMOC as part of the global thermohaline system explains why a slowdown thousands of kilometres from India can materially affect the reliability of a monsoon on which 1.4 billion people depend.

Key Facts & Data

AMOC current weakness: approximately 15% weaker than mid-20th century baseline
Primary cause of weakening: freshwater influx from Greenland ice melt (climate change)
Potential monsoon rainfall reduction under AMOC collapse: up to 20% (model projections)
Indian summer monsoon season: June to September
Share of India's annual rainfall from summer monsoon: 70–90%
Rain-fed agriculture share of India's net sown area: over 50%
Drought threshold in India: 10% or more below normal monsoon rainfall in a season
ITCZ position determines monsoon northward advance; AMOC influences ITCZ latitude
El Niño's independent monsoon suppression effect: typically 10–15% rainfall deficit in India
Greenland ice sheet: losing approximately 280 billion tonnes of ice per year (accelerating)
AMOC volume transport: ~18–20 million cubic metres per second (sverdrups)
AMOC collapse risk window: models project possible tipping point between 2025–2095 under high-emission pathways (wide uncertainty range)