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Atlantic Meridional Overturning Circulation (AMOC)

2024 FEB 16

Mains   > Geography   >   Oceanography   >   Oceanography

Syllabus: GS 1 > Geography   >   Oceanography


  • Recent studies and discussions around the Atlantic Meridional Overturning Circulation (AMOC) have highlighted concerns regarding its stability and the potential for significant climate impacts.
  • A recent study by researchers from the University of Copenhagen, Denmark, published in Nature Communications, indicates that the Atlantic Meridional Overturning Circulation (AMOC) is at risk of collapsing within the period from 2025 to 2095 due to the effects of human-caused emissions. The findings suggest that, given the current trajectory of emissions, the likelihood of this event occurring in the 2050s is high, with the scientists expressing 95 percent confidence in their prediction.If this prediction deems true, AMOC may be the first of the 16 climate tipping elements to be breached.

Tipping elements are large-scale systems that influence the planet’s climate and ecology, which are undergoing changes due to warming and accumulation of greenhouse gases in the atmosphere from anthropogenic emissions. If these elements cross certain thresholds due to rise in temperature, changes in them will become irreversible. 

Description: tipping points climate


  • The Atlantic Meridional Overturning Circulation (AMOC) is the Atlantic branch of the ocean conveyor belt or Thermohaline circulation (THC), and distributes heat and nutrients throughout the world’s ocean basins.

Thermohaline circulation:

  • Thermohaline circulation describes the movement of ocean currents due to differences in temperature and salinity in different regions of water.
  • Temperature and salinity change the density of water, resulting in the water to move accordingly.
  • Cold water is usually denser than warm water (4°C is where water is densest). Water with a high salinity is also denser than less saline water.
  • Deep ocean currents are driven by differences in the water density, which is controlled by temperature (thermo) and salinity (haline), hence the name "thermohaline circulation". This process is also sometimes to referred to as the "ocean's conveyor belt system".
  • Any major change to ocean circulation could have damaging effects on the water cycle and weather patterns
Description: Multimedia Gallery - Ocean currents slowed 950,000 years ago, triggering  colder but less frequent ice ages. | NSF - National Science Foundation



  • AMOC transports warm salty surface waters from the tropics to the northern regions. 
  • The waters then cool down, increase in density and sink in the North Atlantic Ocean, in a phenomenon called downwelling or overturning.
  • Cold, fresh water from the melting ice of the Arctic is added to the cooler ocean that moves towards the equator. This cycle, therefore, acts like a heat conveyor belt, warming the northern latitudes and cooling the southern latitudes.
  • The warm, salty water of the Gulf Stream, as part of the AMOC, travels northward from the Gulf of Mexico, along the eastern coastlines of the United States and Canada, and across the North Atlantic. This water warms the atmosphere above it, contributing to warmer air temperatures in Northern Europe. As the water cools, it becomes denser and sinks in the North Atlantic, driving the deep-water component of the circulation.


  • Climate Regulation: The AMOC helps to regulate the climate of the North Atlantic and Europe. By transporting warm water northwards, it contributes to milder winter temperatures in Western Europe than would otherwise be expected at those latitudes.
  • Heat Exchange: The AMOC is a key mechanism for the global redistribution of heat. It transports heat from the equator towards the poles and cold water from the poles back to the equator, helping to moderate global temperatures.
  • Carbon Dioxide Sequestration: The AMOC plays a role in the global carbon cycle. Deep water formation in the North Atlantic is a process where surface water becomes dense enough to sink, which helps sequester carbon dioxide from the atmosphere into the deep ocean.
  • Influence on Weather Patterns: The AMOC influences weather patterns across the North Atlantic and beyond. Changes in the strength or direction of the AMOC can impact hurricane activity, rainfall patterns, and even droughts in various parts of the world.
  • Potential for Abrupt Climate Change: There is concern among scientists that significant alterations to the AMOC, such as a slowdown or shutdown, could lead to abrupt changes in the climate system. Historical evidence suggests that past changes in the AMOC have been linked to rapid climate shifts.
  • Impact on Marine Ecosystems: The flow of the AMOC affects marine ecosystems by influencing water temperature, salinity, and nutrient distribution across the Atlantic. This can impact fish populations, coral reefs, and the broader biodiversity of the Atlantic Ocean.


  • Warming of cold North Atlantic deep water:
    • Warming of cold North Atlantic deep water mass due to global warming has adversely affected the vertical mixing of water and thereby the AMOC.
  • Freshwater influx :
    • The freshwater from the melting of Greenland’s ice sheet reduces the salinity and density of the water
    • As a result the water is unable to sink as it used to and weakens the AMOC flow.
  • Gulf Stream:
    • Studies show that the Gulf Stream, a part of the Atlantic Meridional Overturning Circulation (AMOC) system, has weakened substantially in the past decades.


Impact on Local Climate of Europe and North America:

The AMOC's role in moderating the climate of Europe and North America is significant. A slowdown or collapse would likely lead to:

  • Decreased Temperature and Rainfall: Europe could experience cooler temperatures and reduced rainfall, affecting agriculture, water supply, and general climate comfort.
  • Increase in Sea Ice: The Greenland-Iceland-Norwegian seas could see an increase in sea ice coverage, altering marine habitats and possibly affecting shipping routes.
  • Increased Winter Storms: Europe may face more frequent and intense winter storms, leading to increased damage and climate-related challenges.
  • Stronger Hurricanes in the US: The shift in temperature gradients could lead to more intense hurricanes impacting the eastern coast of the United State


Indirect Impacts:

  • Shrinking of the West Antarctic Ice Sheet: The redistribution of heat could accelerate ice melt in the Antarctic, contributing to sea-level rise.
  • Migration of the ITCZ and Tropical Rain Belt: Shifts in these critical climate zones could alter rainfall patterns, affecting agriculture and water resources in the tropics and subtropics.
  • Warming of the Southern Ocean: This could further contribute to Antarctic ice melt and global sea-level rise.
  • Disruption of Hemispherical Heat Transfer: Affecting atmospheric pressure cells, wind patterns, and long-term climate processes, potentially altering weather patterns globally.
Description: Sources: “South Asian monsoon response to weakening of Atlantic meridional overturning circulation in a warming climate”, Climate Dynamics; “Warning of a forthcoming collapse of the Atlantic meridional 
overturning circulation”, Nature Communications; “Impact of an AMOC weakening on the stability of the southern Amazon rainforest”, The European Physical Journal Special Topics;  Woods Hole Oceanographic Institution, US; National Oceanic and Atmospheric Administration (NOAA); expert comments

Ecological and Broader Climate Impacts:

  • Amazon Rainforest: The collapse of the AMOC could lead to less rainfall over the Amazon, making it drought-prone and potentially transforming it into a savannah-like ecosystem. This would have profound effects on global biodiversity, carbon storage, and local climates.
  • Monsoon Systems: The stability of monsoon systems in South Asia and West Africa could be compromised, impacting water availability and agriculture in regions that are home to billions of people. For example, the weakening of the summer monsoon circulation over the Indian region could alter agricultural productivity and water resource management in South Asia.
  • Global Climate Feedback Loops: The AMOC's collapse could trigger or exacerbate other climate tipping points, leading to cascading effects across various ecosystems and climate systems.


  • Despite these alarming findings from various studies, the Intergovernmental Panel on Climate Change (IPCC) maintains that a halt to the AMOC this century is unlikely. Nevertheless, the recent studies underscore the importance of revising current models and assumptions about the AMOC's stability, highlighting the urgent need for global efforts to reduce greenhouse gas emissions. Only through such measures can we hope to delay or prevent the collapse of this vital climate system, thereby mitigating its cascading effects on global climate stability and ecosystem health.


Q. Explain the mechanism of Atlantic Meridional Overturning Circulation (AMOC). Also discuss the causes and probable impacts of its slowing down. (15 marks, 250 words)