Global InformationAtlantic meridional overturning circulation information
The Atlantic meridional overturning circulation (AMOC) is the "main current system in the South and North Atlantic Oceans".[1]: 2238 As such, it is a component of Earth's oceanic circulation system and plays an important role in the climate system. The AMOC includes currents at the surface as well as at great depths in the Atlantic Ocean. These currents are driven by changes in the atmospheric weather as well as by changes in temperature and salinity. They collectively make up one half of the global thermohaline circulation that encompasses the flow of major ocean currents. The other half is the Southern Ocean overturning circulation.[2]
The AMOC is characterized by a northward flow of warmer, fresher water in the upper layers of the Atlantic, and a southward flow of colder, saltier and deeper waters. These limbs are linked by regions of overturning in the Nordic Seas and the Southern Ocean. Overturning sites are associated with the intense exchange of heat, dissolved oxygen, carbon and other nutrients. They are very important for the ocean's ecosystems and for its functioning as a carbon sink.[3][4] Thus, if the strength of the AMOC changes, multiple elements of the climate system would be affected.[1]: 2238
Climate change has the potential to weaken the AMOC through increases in ocean heat content and elevated freshwater flows from the melting ice sheets. Studies using oceanographic reconstructions suggest that the AMOC is now already weaker than it was before the Industrial Revolution.[5][6] However, there is debate over the relative contributions of different factors. It is unclear how much of it is due to either climate change or due to the circulation's natural variability over hundreds or thousands of years.[7][8] Climate models predict that the AMOC will weaken further over the 21st century.[9]: 19 This would affect average temperature over Scandinavia and Great Britain because these regions are warmed by the North Atlantic drift.[10] Weakening of the AMOC would also accelerate sea level rise around North America and reduce primary production in the North Atlantic.[11]
Severe weakening of the AMOC may lead to an outright collapse of the circulation, which would not be easily reversible and thus constitute one of the tipping points in the climate system.[12] A collapse would substantially lower the average temperature and amount of rain and snowfall in Europe.[13][14] It would also potentially raise the frequency of extreme weather events and have other severe effects.[15][16] Gold-standard Earth system models indicate that a collapse is unlikely, and would only become plausible if high levels of warming are sustained well after the year 2100.[17][18][19] Some paleoceanographic research seems to support this idea.[20][21] However, some researchers fear that the complex models are too stable,[22] and lower-complexity projections pointing to an earlier collapse are more accurate.[23][24] One of those projections suggests that AMOC collapse could happen around 2057,[25] but many scientists are skeptical of the claim.[26] Some research also suggests that the Southern Ocean overturning circulation may be more prone to collapse.[27][15]
- ^ a b IPCC, 2021: Annex VII: Glossary [Matthews, J.B.R., V. Möller, R. van Diemen, J.S. Fuglestvedt, V. Masson-Delmotte, C. Méndez, S. Semenov, A. Reisinger (eds.)]. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 2215–2256, doi:10.1017/9781009157896.022.
- ^ "NOAA Scientists Detect a Reshaping of the Meridional Overturning Circulation in the Southern Ocean". NOAA. 29 March 2023.
- ^ Buckley, Martha W.; Marshall, John (2016). "Observations, inferences, and mechanisms of the Atlantic Meridional Overturning Circulation: A review". Reviews of Geophysics. 54 (1): 5–63. Bibcode:2016RvGeo..54....5B. doi:10.1002/2015RG000493. hdl:1721.1/108249. ISSN 8755-1209. S2CID 54013534.
- ^ Lozier, M. S.; Li, F.; Bacon, S.; Bahr, F.; Bower, A. S.; Cunningham, S. A.; de Jong, M. F.; de Steur, L.; deYoung, B.; Fischer, J.; Gary, S. F. (2019). "A sea change in our view of overturning in the subpolar North Atlantic". Science. 363 (6426): 516–521. Bibcode:2019Sci...363..516L. doi:10.1126/science.aau6592. ISSN 0036-8075. PMID 30705189. S2CID 59567598.
- ^ Cite error: The named reference
Rahmstorf2015was invoked but never defined (see the help page). - ^ Caesar, L.; McCarthy, G.D.; Thornalley, D. J. R.; Cahill, N.; Rahmstorf, S. (25 February 2021). "Current Atlantic Meridional Overturning Circulation weakest in last millennium" (PDF). Nature Geoscience. 14 (3): 118–120. Bibcode:2021NatGe..14..118C. doi:10.1038/s41561-021-00699-z. S2CID 232052381.
- ^ Latif, Mojib; Sun, Jing; Visbeck, Martin; Bordbar (25 April 2022). "Natural variability has dominated Atlantic Meridional Overturning Circulation since 1900". Nature Climate Change. 12 (5): 455–460. Bibcode:2022NatCC..12..455L. doi:10.1038/s41558-022-01342-4. S2CID 248385988.
- ^ Kilbourne, Kelly Halimeda; et, al. (17 February 2022). "Atlantic circulation change still uncertain". Nature Geoscience. 15 (3): 165–167. Bibcode:2022NatGe..15..165K. doi:10.1038/s41561-022-00896-4. hdl:2117/363518. S2CID 246901665.
- ^ IPCC, 2019: Summary for Policymakers. In: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate [H.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, A. Alegría, M. Nicolai, A. Okem, J. Petzold, B. Rama, N.M. Weyer (eds.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA. doi:10.1017/9781009157964.001.
- ^ Lenton, T. M.; Held, H.; Kriegler, E.; Hall, J. W.; Lucht, W.; Rahmstorf, S.; Schellnhuber, H. J. (2008). "Inaugural Article: Tipping elements in the Earth's climate system". Proceedings of the National Academy of Sciences. 105 (6): 1786–1793. Bibcode:2008PNAS..105.1786L. doi:10.1073/pnas.0705414105. PMC 2538841. PMID 18258748.
- ^ Cite error: The named reference
Schmittner2005was invoked but never defined (see the help page). - ^ Cite error: The named reference
CarbonBriefwas invoked but never defined (see the help page). - ^ Cite error: The named reference
ArmstrongMcKay2022was invoked but never defined (see the help page). - ^ Cite error: The named reference
Phys2020was invoked but never defined (see the help page). - ^ a b Lenton, T. M.; Armstrong McKay, D.I.; Loriani, S.; Abrams, J.F.; Lade, S.J.; Donges, J.F.; Milkoreit, M.; Powell, T.; Smith, S.R.; Zimm, C.; Buxton, J.E.; Daube, Bruce C.; Krummel, Paul B.; Loh, Zoë; Luijkx, Ingrid T. (2023). The Global Tipping Points Report 2023 (Report). University of Exeter.
- ^ Cite error: The named reference
Hansen2015was invoked but never defined (see the help page). - ^ Cite error: The named reference
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SMC2023was invoked but never defined (see the help page). - ^ Liu, Y.; Moore, J. K.; Primeau, F.; Wang, W. L. (22 December 2022). "Reduced CO2 uptake and growing nutrient sequestration from slowing overturning circulation". Nature Climate Change. 13: 83–90. doi:10.1038/s41558-022-01555-7. OSTI 2242376. S2CID 255028552.