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Atlantic Meridional Overturning Circulation (AMOC)

Atlantic Meridional Overturning Circulation (AMOC)

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According to the IPCC’s Report (AR6) released on August 9, it is very likely that Atlantic Meridional Overturning Circulation (AMOC) will weaken over the 21st century.

Findings of the report

  • Critical Threshold: AMOC decline is not just a fluctuation or a linear response to increasing temperatures but likely means the approaching of a critical threshold beyond which the circulation system could collapse.
  • Changes in Weather patterns: If such a collapse were to occur, it would very likely cause abrupt shifts in regional weather patterns and water cycle, such as
  • A southward shift in the tropical rain belt, weakening of the African and Asian monsoons and strengthening of Southern Hemisphere monsoons, and drying in Europe.
  • A prominent cooling over the northern North Atlantic and neighbouring areas, sea ice increases over the Greenland-Iceland-Norwegian seas and to the south of Greenland.

 

 

What is Atlantic Meridional Overturning Circulation (AMOC)?

  • The AMOC is a large system of ocean currents. It is the Atlantic branch of the ocean conveyor belt or Thermohaline circulation (THC). It distributes heat and nutrients throughout the world’s ocean basins.
  • AMOC carries warm surface waters from the tropics towards the Northern Hemisphere, where it cools and sinks. It then returns to the tropics and then to the South Atlantic as a bottom current. From there it is distributed to all ocean basins via the Antarctic circumpolar current.

Reason for weakening of AMOC

  • Global warming and Melting glaciers: The freshwater from the melting ice reduces the salinity and density of the water. As this water is unable to sink as it used to, it weakens the AMOC flow.
  • Increasing precipitation in the Indian Ocean: As the Indian Ocean is warming at a faster rate, it generates additional precipitation. This draws more air from other parts of the world to the Indian Ocean, including the Atlantic. High precipitation in the Indian Ocean, thus leads to less precipitation in the Atlantic Ocean. This causes higher salinity in the waters of the tropical portion of the Atlantic. This saltier water in the Atlantic, as it comes north via AMOC, will gets cold much quicker than usual and sinks faster.

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