Monday, July 14, 2014

Atlantic Meridional Overturning Circulation (AMOC)

The Atlantic Meridional Overturning Circulation (AMOC) is a major current in the Atlantic Ocean, characterized by a northward flow of warm, salty water in the upper layers of the Atlantic, and a southward flow of colder water in the deep Atlantic. The AMOC is an important component of the Earth’s climate system.

This ocean current system transports a substantial amount of heat energy from the tropics and Southern Hemisphere toward the North Atlantic, where the heat is then transferred to the atmosphere. Changes in this ocean circulation could have a profound impact on many aspects of the global climate system.
There is growing evidence that fluctuations in Atlantic sea surface temperatures, hypothesized to be related to fluctuations in the AMOC, have played a prominent role in significant climate fluctuations around the globe on a variety of time scales.

Because the AMOC's heat transport makes a substantial contribution to the moderate climate of maritime and continental Europe, and any slowdown in the overturning circulation would have profound implications for climate change, there have been questions about the likelihood of an "collapse" or an abrupt change. In the a 2008 study on Abrupt Climate Change by the U.S. Climate Change Science Program, the following conclusions were drawn :
  • It is very likely that the strength of the AMOC will decrease over the course of the 21st century in response to increasing greenhouse gases, with a best estimate decrease of 25–30%.
  • Even with the projected moderate AMOC weakening, it is still very likely that on multidecadal to century time scales a warming trend will occur over most of the European region downstream of the North Atlantic Current in response to increasing greenhouse gases, as well as over North America.
  • It is very unlikely that the AMOC will undergo a collapse or an abrupt transition to a weakened state during the 21st century.
  • It is also unlikely that the AMOC will collapse beyond the end of the 21st century because of global warming, although the possibility cannot be entirely excluded.
  • Although it is very unlikely that the AMOC will collapse in the 21st century, the potential consequences of this event could be severe. These might include a southward shift of the tropical rainfall belts, additional sea level rise around the North Atlantic, and disruptions to marine ecosystems.

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