Why is it in the News?

The circulation of the Atlantic Ocean, a key component in global climate regulation, is “on route” to a tipping point, according to a new study, which describes the findings as “bad news for the climate system and humanity.”

What is Atlantic Meridional Overturning Circulation (AMOC)?

• The ocean’s water is constantly circulated by currents.
  • Tidal currents occur close to shore and are influenced by the sun and moon and the surface currents are influenced by the wind.
• However, other, much slower currents that occur from the surface to the seafloor are driven by changes in the saltiness and ocean temperature, a process called thermohaline circulation.
  • These currents are carried in a large "global conveyor belt," which includes the AMOC.
• AMOC stands for Atlantic Meridional Overturning Circulation.
• The AMOC circulates water from north to south and back in a long cycle within the Atlantic Ocean.
  • This circulation brings warmth to various parts of the globe and also carries nutrients necessary to sustain ocean life.
• The circulation process begins as warm water near the surface moves toward the poles (such as the Gulf Stream in the North Atlantic), where it cools and forms sea ice.
• As this ice forms, salt is left behind in the ocean water.
• Due to the large amount of salt in the water, it becomes denser, sinks down, and is carried southwards in the depths below.
• Eventually, the water gets pulled back up towards the surface and warms up in a process called upwelling, completing the cycle.
• The entire circulation cycle of the AMOC, and the global conveyor belt, is quite slow.
• It takes an estimated 1,000 years for a parcel (any given cubic meter) of water to complete its journey along the belt.
• Even though the whole process is slow on its own, there is some evidence that the AMOC is slowing down further.

Is the AMOC Slowing Down?

• As our climate continues to change, there is a possibility that the AMOC will slow down, or come to a complete stop.
• While research shows it is weakening over the past century, whether or not it will continue to slow or stop circulating completely remains uncertain.
• If the AMOC does continue to slow down, however, it could have far-reaching climate impacts.
  • For example, if the planet continues to warm, freshwater from melting ice at the poles would shift the rain belt in South Africa, causing droughts for millions of people.

What Would Happen if AMOC Failed?

• AMOC acts as a sort of "switch" for the climate, particularly in Europe and the northern hemisphere.
• It would result in less precipitation in regions like Europe, North America, China, and certain regions of Russia in Asia, as well as widespread cooling throughout the northern hemisphere.
• The Amazon rainforest might become dry and drought-prone as a result of the extra heat brought on by a collapsing AMOC, and it might even become a savannah state.
• In certain areas, monsoon development and rainfall might be impeded by a slowing in AMOC.
• There might be less rainfall in the Sahel (the West African monsoon area), less summer monsoon circulation in South Asia and India, and more winter storms in Europe.
• The summer monsoon circulation over the Indian subcontinent and the sea level pressure gradient are both weakened by a weakening of the land-sea heat gradient.