Editing Intertropical Convergence Zone (section)

== Effects of climate change ==
{{see also|Effects of climate change on the water cycle}}
[[File:Cariaco basin titanium 2000 300 BP 1.svg|thumb|[[Titanium]] concentrations in sediment within the [[Cariaco Basin]] have been used as a paleoclimate proxy to infer shifts in the ITCZ.<ref name="Haug et al. 2001">{{cite journal |last1=Haug |first1=Gerald H. |last2=Hughen |first2=Konrad A. |last3=Sigman |first3=Daniel M. |last4=Peterson |first4=Larry C. |last5=Röhl |first5=Ursula |author1-link=Gerald Haug |author3-link=Daniel Sigman |title=Southward Migration of the Intertropical Convergence Zone Through the Holocene |journal=Science |date=17 August 2001 |volume=293 |issue=5533 |pages=1304–1308 |doi=10.1126/science.1059725|publisher=[[American Association for the Advancement of Science]]|pmid=11509727 |bibcode=2001Sci...293.1304H |s2cid=24591761 }}</ref>|alt=Line graph showing titanium concentrations over time within Cariaco Basin sediment]] 
Based on [[paleoclimate proxies]], the position and intensity of the ITCZ varied in prehistoric times along with [[climate change|changes in global climate]]. During [[Heinrich event]]s within the last 100&nbsp;ka, a southward shift of the ITCZ coincided with the intensification of the Northern Hemisphere Hadley cell coincident with weakening of the Southern Hemisphere Hadley cell. The ITCZ shifted north during the [[Holocene|mid-Holocene]] but migrated south following changes in [[insolation]] during the late-Holocene towards its current position. The ITCZ has also undergone periods of contraction and expansion within the last millennium.<ref name="AR6.1.2">{{cite book |last1=Gulev |first1=Sergey K. |last2=Thorne |first2=Peter W. |display-authors=etal |author1-link=Sergey Gulev |author2-link=Peter Thorne (climatologist) |editor1-last=Masson-Delmotte |editor1-first=Valerie |editor2-last=Zhai |editor2-first=Panmao |editor1-link=Valerie Masson-Delmotte |editor2-link=Panmao Zhai |display-editors=etal|title=Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change |date=2021 |publisher=Cambridge University Press |location=Cambridge, United Kingdom |pages=287&ndash;422 |url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter02.pdf |access-date=18 January 2023 |language=en |chapter=Changing State of the Climate System}}</ref> A southward shift of the ITCZ commencing after the 1950s and continuing into the 1980s may have been associated with [[particulates#Aerosol radiative|cooling induced]] by [[aerosol]]s in the Northern Hemisphere based on results from [[climate model]]s; a northward rebound began subsequently following [[climate forcing|forced changes]] in the gradient in temperature between the Northern and Southern hemispheres. These fluctuations in ITCZ positioning had robust effects on climate; for instance, displacement of the ITCZ may have led to [[Sahel drought|drought in the Sahel]] in the 1980s.<ref name="AR6.1.3">{{cite book |last1=Eyring |first1=Veronika |last2=Gillett |first2=Nathan P. |display-authors=etal |editor1-last=Masson-Delmotte |editor1-first=Valerie |editor2-last=Zhai |editor2-first=Panmao |title=Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change |date=2021 |publisher=Cambridge University Press |location=Cambridge, United Kingdom |pages=423&ndash;551 |url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter03.pdf |access-date=18 January 2023 |language=en |chapter=Human Influence on the Climate System}}</ref><ref name="AR6.1.8" />

[[Atmospheric convection]] may become stronger and more concentrated at the center of the ITCZ in response to a globally warming climate, resulting in sharpened contrasts in precipitation between the ITCZ core (where precipitation would be amplified) and its edges (where precipitation would be suppressed). [[Atmospheric reanalysis|Atmospheric reanalyses]] suggest that the ITCZ over the Pacific has narrowed and intensified since at least 1979, in agreement with data collected by satellites and in-situ precipitation measurements. The drier ITCZ fringes are also associated with an increase in [[outgoing longwave radiation]] outward of those areas, particularly over land within the mid-latitudes and the [[subtropics]]. This change in the ITCZ is also reflected by increasing salinity within the Atlantic and Pacific underlying the ITCZ fringes and decreasing salinity underlying central belt of the ITCZ. The [[IPCC Sixth Assessment Report]] indicated "medium agreement" from studies regarding the strengthening and tightening of the ITCZ due to anthropogenic climate change.<ref name="AR6.1.8" />

Less certain are the regional and global shifts in ITCZ position as a result of climate change, with paleoclimate data and model simulations highlighting contrasts stemming from asymmetries in forcing from aerosols, volcanic activity, and [[Milankovitch cycles|orbital variations]], as well as uncertainties associated with changes in [[monsoon]]s and the [[Atlantic meridional overturning circulation]]. The climate simulations run as part of [[Coupled Model Intercomparison Project|Coupled Model Intercomparison Project Phase 5]] (CMIP5) did not show a consistent global displacement of the ITCZ under anthropogenic climate change. In contrast, most of the same simulations show narrowing and intensification under the same prescribed conditions. However, simulations in [[Coupled Model Intercomparison Project|Coupled Model Intercomparison Project Phase 6]] (CMIP6) have shown greater agreement over some regional shifts of the ITCZ in response to anthropogenic climate change, including a northward displacement over the Indian Ocean and eastern Africa and a southward displacement over the eastern Pacific and Atlantic oceans.<ref name="AR6.1.8">{{cite book |last1=Douville |first1=Hervé |last2=Raghavan |first2=Krishnan |last3=Renwick |first3=James |author3-link=James Renwick (climate scientist) |display-authors=etal |editor1-last=Masson-Delmotte |editor1-first=Valerie |editor2-last=Zhai |editor2-first=Panmao |title=Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change |date=2021 |publisher=Cambridge University Press |location=Cambridge, United Kingdom |pages=1055&ndash;1210 |url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter08.pdf |access-date=18 January 2023 |language=en |chapter=Human Influence on the Climate System}}</ref>