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[[File:OCP07 Fig-6.jpg|thumb|320|Topographic map of the Nordic Seas and subpolar basins with surface currents (solid curves) and deep currents (dashed curves) that form a portion of the Atlantic meridional overturning circulation. Colors of curves indicate approximate temperatures.]]
[[File:OCP07 Fig-6.jpg|thumb|320|Topographic map of the Nordic Seas and subpolar basins with surface currents (solid curves) and deep currents (dashed curves) that form a portion of the Atlantic meridional overturning circulation. Colors of curves indicate approximate temperatures.]]
The Atlantic meridional overturning circulation (AMOC) is part of a global thermohaline circulation in the oceans and is the zonally integrated component of surface and deep currents in the Atlantic Ocean. It is characterized by a northward flow of warm, salty water in the upper layers of the Atlantic, and a southward flow of colder, deep waters. These "limbs" are linked by regions of overturning in the Nordic and Labrador Seas and the Southern Ocean, although the extent of overturning in the Labrador Sea is disputed.<ref>Buckley, Martha W.; Marshall, John (2016) [https://doi.org/10.1002%2F2015RG000493 Observations, inferences, and mechanisms of the Atlantic Meridional Overturning Circulation: A review] Reviews of Geophysics</ref><ref>M. S. Lozier et al. (2019) [https://www.science.org/doi/10.1126/science.aau6592 A sea change in our view of overturning in the subpolar North Atlantic] Science</ref> The AMOC is an important component of the Earth's climate system, and is a result of both atmospheric and thermohaline drivers.
The '''Atlantic meridional overturning circulation''' (AMOC) is part of a global thermohaline circulation in the oceans and is the zonally integrated component of surface and deep currents in the Atlantic Ocean. It is characterized by a northward flow of warm, salty water in the upper layers of the Atlantic, and a southward flow of colder, deep waters. These "limbs" are linked by regions of overturning in the Nordic and Labrador Seas and the Southern Ocean, although the extent of overturning in the Labrador Sea is disputed.<ref>Buckley, Martha W.; Marshall, John (2016) [https://doi.org/10.1002%2F2015RG000493 Observations, inferences, and mechanisms of the Atlantic Meridional Overturning Circulation: A review] Reviews of Geophysics</ref><ref>M. S. Lozier et al. (2019) [https://www.science.org/doi/10.1126/science.aau6592 A sea change in our view of overturning in the subpolar North Atlantic] Science</ref> The AMOC is an important component of the Earth's climate system, and is a result of both atmospheric and thermohaline drivers.


Climate change has the potential to weaken the AMOC through increases in ocean heat content and elevated freshwater flows from the melting ice sheets. Oceanographic reconstructions generally suggest that the AMOC is already weaker than it was before the Industrial Revolution,<ref>Rahmstorf, S., Box, J., Feulner, G. et al. (2015) [https://www.nature.com/articles/nclimate2554 Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation] Nature</ref><ref>Caesar, L., McCarthy, G.D., Thornalley, D.J.R. et al. (2021) [https://www.nature.com/articles/s41561-021-00699-z Current Atlantic Meridional Overturning Circulation weakest in last millennium] Nat. Geosci.</ref> although there is a robust debate over the role of climate change versus the circulation's century-scale and millennial-scale variability.<ref>Latif, M., Sun, J., Visbeck, M. et al. (2022) [https://www.nature.com/articles/s41558-022-01342-4 Natural variability has dominated Atlantic Meridional Overturning Circulation since 1900] Nat. Clim. Chang.</ref><ref>Kilbourne, K.H., Wanamaker, A.D., Moffa-Sanchez, P. et al. (2022) [Atlantic circulation change still uncertain https://www.nature.com/articles/s41561-022-00896-4] Nat. Geosci.</ref> Climate models consistently project that the AMOC would weaken further over the 21st century,[7]: 19  which would affect average temperature over areas like Scandinavia and Britain that are warmed by the North Atlantic drift,<ref>Lenton TM, Held H, Kriegler E, Hall JW, Lucht W, Rahmstorf S, Schellnhuber HJ. (2008) [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2538841/ Tipping elements in the Earth's climate system] Proc Natl Acad Sci</ref> as well as accelerate sea level rise around North America and reduce primary production in the North Atlantic.<ref>Osman, M.B., Das, S.B., Trusel, L.D. et al. (2009) [https://www.nature.com/articles/s41586-019-1181-8 Industrial-era decline in subarctic Atlantic productivity] Nature</ref>
Climate change has the potential to weaken the AMOC through increases in ocean heat content and elevated freshwater flows from the melting ice sheets. Oceanographic reconstructions generally suggest that the AMOC is already weaker than it was before the Industrial Revolution,<ref>Rahmstorf, S., Box, J., Feulner, G. et al. (2015) [https://www.nature.com/articles/nclimate2554 Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation] Nature</ref><ref>Caesar, L., McCarthy, G.D., Thornalley, D.J.R. et al. (2021) [https://www.nature.com/articles/s41561-021-00699-z Current Atlantic Meridional Overturning Circulation weakest in last millennium] Nat. Geosci.</ref> although there is a robust debate over the role of climate change versus the circulation's century-scale and millennial-scale variability.<ref>Latif, M., Sun, J., Visbeck, M. et al. (2022) [https://www.nature.com/articles/s41558-022-01342-4 Natural variability has dominated Atlantic Meridional Overturning Circulation since 1900] Nat. Clim. Chang.</ref><ref>Kilbourne, K.H., Wanamaker, A.D., Moffa-Sanchez, P. et al. (2022) [Atlantic circulation change still uncertain https://www.nature.com/articles/s41561-022-00896-4] Nat. Geosci.</ref> Climate models consistently project that the AMOC would weaken further over the 21st century,[7]: 19  which would affect average temperature over areas like Scandinavia and Britain that are warmed by the North Atlantic drift,<ref>Lenton TM, Held H, Kriegler E, Hall JW, Lucht W, Rahmstorf S, Schellnhuber HJ. (2008) [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2538841/ Tipping elements in the Earth's climate system] Proc Natl Acad Sci</ref> as well as accelerate sea level rise around North America and reduce primary production in the North Atlantic.<ref>Osman, M.B., Das, S.B., Trusel, L.D. et al. (2009) [https://www.nature.com/articles/s41586-019-1181-8 Industrial-era decline in subarctic Atlantic productivity] Nature</ref>

Revision as of 07:41, 11 May 2023

Topographic map of the Nordic Seas and subpolar basins with surface currents (solid curves) and deep currents (dashed curves) that form a portion of the Atlantic meridional overturning circulation. Colors of curves indicate approximate temperatures.

The Atlantic meridional overturning circulation (AMOC) is part of a global thermohaline circulation in the oceans and is the zonally integrated component of surface and deep currents in the Atlantic Ocean. It is characterized by a northward flow of warm, salty water in the upper layers of the Atlantic, and a southward flow of colder, deep waters. These "limbs" are linked by regions of overturning in the Nordic and Labrador Seas and the Southern Ocean, although the extent of overturning in the Labrador Sea is disputed.[1][2] The AMOC is an important component of the Earth's climate system, and is a result of both atmospheric and thermohaline drivers.

Climate change has the potential to weaken the AMOC through increases in ocean heat content and elevated freshwater flows from the melting ice sheets. Oceanographic reconstructions generally suggest that the AMOC is already weaker than it was before the Industrial Revolution,[3][4] although there is a robust debate over the role of climate change versus the circulation's century-scale and millennial-scale variability.[5][6] Climate models consistently project that the AMOC would weaken further over the 21st century,[7]: 19  which would affect average temperature over areas like Scandinavia and Britain that are warmed by the North Atlantic drift,[7] as well as accelerate sea level rise around North America and reduce primary production in the North Atlantic.[8]

Severe weakening of the AMOC has the potential to cause an outright collapse of the circulation, which would not be easily reversible and thus constitute one of the tipping points in the climate system.[9] A shutdown would have far greater impacts than a slowdown on both the marine and some terrestrial ecosystems: it would lower the average temperature and precipitation in Europe, slashing the region's agricultural output,[10] and may have a substantial effect on extreme weather events.[11] Earth system models used in the Coupled Model Intercomparison Project indicate that shutdown is only likely after high levels of warming are sustained well after 2100,[12][13][14] but they have been criticized by some researchers for what they saw as excessive stability,[15] and a number of lower-complexity studies argue that a collapse can happen considerably earlier.[16][17] On the other hand, paleoceanographic research suggests that the AMOC may be even more stable than what is assumed by most models.[18][19]

References

  1. ↑ Buckley, Martha W.; Marshall, John (2016) Observations, inferences, and mechanisms of the Atlantic Meridional Overturning Circulation: A review Reviews of Geophysics
  2. ↑ M. S. Lozier et al. (2019) A sea change in our view of overturning in the subpolar North Atlantic Science
  3. ↑ Rahmstorf, S., Box, J., Feulner, G. et al. (2015) Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation Nature
  4. ↑ Caesar, L., McCarthy, G.D., Thornalley, D.J.R. et al. (2021) Current Atlantic Meridional Overturning Circulation weakest in last millennium Nat. Geosci.
  5. ↑ Latif, M., Sun, J., Visbeck, M. et al. (2022) Natural variability has dominated Atlantic Meridional Overturning Circulation since 1900 Nat. Clim. Chang.
  6. ↑ Kilbourne, K.H., Wanamaker, A.D., Moffa-Sanchez, P. et al. (2022) [Atlantic circulation change still uncertain https://www.nature.com/articles/s41561-022-00896-4] Nat. Geosci.
  7. ↑ Lenton TM, Held H, Kriegler E, Hall JW, Lucht W, Rahmstorf S, Schellnhuber HJ. (2008) Tipping elements in the Earth's climate system Proc Natl Acad Sci
  8. ↑ Osman, M.B., Das, S.B., Trusel, L.D. et al. (2009) Industrial-era decline in subarctic Atlantic productivity Nature
  9. ↑ Rosamund Pearce, Tom Prater (2020) Tipping Points in the Climate System Carbon Brief
  10. ↑ (2020)Atlantic circulation collapse could cut British crop farming University of Exeter
  11. ↑ J. Hansen et al. (2015)Ice melt, sea level rise and superstorms:evidence from paleoclimate data, climatemodeling, and modern observations that2◦C global warming is highly dangerous Atmospheric Chemistry and Physics
  12. ↑ Wei Liu et al. (2017) Overlooked possibility of a collapsed Atlantic Meridional Overturning Circulation in warming climate Science Advances
  13. ↑ P. Bakker et al.(2016) Fate of the Atlantic Meridional Overturning Circulation: Strong decline under continued warming and Greenland melting AGU
  14. ↑ Sigmond, M., Fyfe, J.C., Saenko, O.A. et al. (2020) Ongoing AMOC and related sea-level and temperature changes after achieving the Paris targets Nature
  15. ↑ Valdes, P. (2011) Built for stability nature Geosci.
  16. ↑ Johannes Lohmann and Peter D. Ditlevsen (2021) Risk of tipping the overturning circulation due to increasing rates of ice melt PNAS
  17. ↑ Boers, N. (2021) Observation-based early-warning signals for a collapse of the Atlantic Meridional Overturning Circulation Nat. Clim. Chang.
  18. ↑ He, F., Clark, P.U. (2022) Freshwater forcing of the Atlantic Meridional Overturning Circulation Nat. Clim. Chang.
  19. ↑ Kim, SK., Kim, HJ., Dijkstra, H.A. et al. (2022) Slow and soft passage through tipping point of the Atlantic Meridional Overturning Circulation in a changing climate Clim Atmos Sci
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