The Atlantic is at risk of circulation collapse – it would mean even greater climate chaos across Europe

The Atlantic is at risk of circulation collapse – it would mean even greater climate chaos across Europe

Subject: Geography

Section :Physical geography

Context:

• New findings suggest the Atlantic meridional overturning circulation, or AMOC, could collapse within the next few decades — maybe even within the next few years — driving European weather to even greater extremes.

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).
  • THC is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes.
• AMOC distributes heat and nutrients throughout the world’s ocean basins.
• It carries warm surface waters from the tropics towards the Northern Hemisphere, where it cools and sinks.
• Collapse of AMOC:
  • AMOC is also only one part of the wider Gulf Stream system, much of which is driven by winds that will continue to blow even if the AMOC collapses. So part of the Gulf Stream will survive an AMOC collapse.
  • Larger ocean temperature extremes may alter the character of weather systems that are powered by heat and moisture from the sea.
• Implications:
  • 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.
  • A significant southward rain-belt migration over the tropical Atlantic.
• Previous events of slowdown of AMOC:
  • Northern Europe experienced successive severe winters in 2009-10 and 2010-11, subsequently attributed to a brief slowdown of the Amoc. At the same time heat had built up in the tropics, fuelling an unusually active June-November hurricane season in 2010.
  • In the mid 2010s a “cold blob” formed in the North Atlantic, reaching its most extreme in the summer of 2015 when it coincided with heatwaves in central Europe and was one of the only parts of the world cooler than its long-term average.
  • The cold blob suggested the persistence of a week AMOC.

Significance of AMOC for Europe:

• During northern winters, AMOC keeps the temperature of north europe higher than the average temperature of that latitude by as much as 20^oC.
• The northeast Pacific — and therefore western Canada and Alaska — enjoys a more modest 10°C warming from a similar current, while prevailing westerly winds mean the northwest Atlantic and northwest Pacific are much colder, as are the adjacent land masses of eastern Canada and Siberia.

How ocean temperatures are linked to weather:

• Due to increase in sea surface temperature from tropics to arctic regions, temperatures have persisted 1°C-2°C above or below normal levels, for months or even years on end. These patterns appear to exert a strong influence on the atmosphere, even influencing the path and strength of the jet stream.