Editing Climate variability and change (section)

==== Oscillations and cycles {{anchor|Oscillations|Cycles}} ====
[[File:20210827 Global surface temperature bar chart - bars color-coded by El Niño and La Niña intensity.svg|thumb| upright=1.25|Colored bars show how El Niño years (red, regional warming) and La Niña years (blue, regional cooling) relate to overall [[global surface temperature|global warming]]. The [[El Niño–Southern Oscillation]] has been linked to variability in longer-term global average temperature increase.]]
A ''climate oscillation'' or ''climate cycle'' is any recurring cyclical [[oscillation]] within global or regional [[climate]]. They are [[quasiperiodic]] (not perfectly periodic), so a [[Fourier analysis]] of the data does not have sharp peaks in the [[spectral density estimation|spectrum]]. Many oscillations on different time-scales have been found or hypothesized:<ref>{{Cite web|url=https://www.whoi.edu/main/topic/el-nino-other-oscillations|title=El Niño & Other Oscillations|website=Woods Hole Oceanographic Institution|access-date=6 April 2019|archive-date=6 April 2019|archive-url=https://web.archive.org/web/20190406082544/https://www.whoi.edu/main/topic/el-nino-other-oscillations|url-status=live}}</ref>

* the [[El Niño–Southern Oscillation]] (ENSO) – A large scale pattern of warmer ([[El Niño]]) and colder ([[La Niña]]) tropical [[sea surface temperature]]s in the Pacific Ocean with worldwide effects. It is a self-sustaining oscillation, whose mechanisms are well-studied.<ref>{{Cite journal|last=Wang|first=Chunzai|date=2018|title=A review of ENSO theories|journal=National Science Review|volume=5|issue=6|pages=813–825|doi=10.1093/nsr/nwy104|issn=2095-5138|doi-access=free}}</ref> ENSO is the most prominent known source of inter-annual variability in weather and climate around the world. The cycle occurs every two to seven years, with El Niño lasting nine months to two years within the longer term cycle.<ref>{{cite web|url=http://www.cpc.noaa.gov/products/analysis_monitoring/ensostuff/ensofaq.shtml#HOWOFTEN|title=ENSO FAQ: How often do El Niño and La Niña typically occur?|author=Climate Prediction Center|date=19 December 2005|publisher=[[National Centers for Environmental Prediction]]|url-status=dead|archive-url=https://web.archive.org/web/20090827143632/http://www.cpc.noaa.gov/products/analysis_monitoring/ensostuff/ensofaq.shtml#HOWOFTEN|archive-date=27 August 2009|access-date=26 July 2009|author-link=Climate Prediction Center}}</ref> The cold tongue of the equatorial Pacific Ocean is not warming as fast as the rest of the ocean, due to increased [[upwelling]] of cold waters off the west coast of South America.<ref>{{cite web|url=https://lamont.columbia.edu/news/part-pacific-ocean-not-warming-expected-why|title=Part of the Pacific Ocean Is Not Warming as Expected. Why|author=Kevin Krajick|publisher=Columbia University Lamont-Doherty Earth Observatory|access-date=2 November 2022|archive-date=5 March 2023|archive-url=https://web.archive.org/web/20230305101155/https://lamont.columbia.edu/news/part-pacific-ocean-not-warming-expected-why|url-status=live}}</ref><ref>{{cite web|url=https://www.newsweek.com/mystery-stretch-pacific-ocean-warming-world-1445990?amp=1|title=Mystery Stretch of the Pacific Ocean Is Not Warming Like the Rest of the World's Waters|author=Aristos Georgiou|date=26 June 2019 |publisher=Newsweek|access-date=2 November 2022|archive-date=25 February 2023|archive-url=https://web.archive.org/web/20230225140142/https://www.newsweek.com/mystery-stretch-pacific-ocean-warming-world-1445990?amp=1|url-status=live}}</ref>
* the [[Madden–Julian oscillation]] (MJO) – An eastward moving pattern of increased rainfall over the tropics with a period of 30 to 60 days, observed mainly over the Indian and Pacific Oceans.<ref>{{Cite web|url=https://www.climate.gov/news-features/blogs/enso/what-mjo-and-why-do-we-care|title=What is the MJO, and why do we care?|website=NOAA Climate.gov|language=en|access-date=6 April 2019|archive-date=15 March 2023|archive-url=https://web.archive.org/web/20230315025156/https://www.climate.gov/news-features/blogs/enso/what-mjo-and-why-do-we-care|url-status=live}}</ref>
* the [[North Atlantic oscillation]] (NAO) – Indices of the [[North Atlantic oscillation|NAO]] are based on the difference of normalized [[sea-level pressure]] (SLP) between [[Ponta Delgada|Ponta Delgada, Azores]] and [[Stykkishólmur]]/[[Reykjavík]], Iceland. Positive values of the index indicate stronger-than-average westerlies over the middle latitudes.<ref name="NCAR">National Center for Atmospheric Research. [http://www.cgd.ucar.edu/cas/jhurrell/indices.info.html Climate Analysis Section.] {{webarchive|url=https://web.archive.org/web/20060622232926/http://www.cgd.ucar.edu/cas/jhurrell/indices.info.html|date=22 June 2006}} Retrieved on 7 June 2007.</ref>
* the [[Quasi-biennial oscillation]] – a well-understood oscillation in wind patterns in the [[stratosphere]] around the equator. Over a period of 28 months the dominant wind changes from easterly to westerly and back.<ref>{{Cite journal|last1=Baldwin|first1=M. P.|last2=Gray|first2=L. J.|last3=Dunkerton|first3=T. J.|last4=Hamilton|first4=K.|last5=Haynes|first5=P. H.|last6=Randel|first6=W. J.|last7=Holton|first7=J. R.|last8=Alexander|first8=M. J.|last9=Hirota|first9=I.|s2cid=16727059|date=2001|title=The quasi-biennial oscillation|journal=Reviews of Geophysics|language=en|volume=39|issue=2|pages=179–229|doi=10.1029/1999RG000073|bibcode=2001RvGeo..39..179B|doi-access=free}}</ref>
* [[Pacific Centennial Oscillation]] - a [[climate oscillation]] predicted by some [[climate model]]s
* the [[Pacific decadal oscillation]] – The dominant pattern of sea surface variability in the North Pacific on a decadal scale. During a "warm", or "positive", phase, the west Pacific becomes cool and part of the eastern ocean warms; during a "cool" or "negative" phase, the opposite pattern occurs. It is thought not as a single phenomenon, but instead a combination of different physical processes.<ref>{{Cite journal|last1=Newman|first1=Matthew|last2=Alexander|first2=Michael A.|last3=Ault|first3=Toby R.|last4=Cobb|first4=Kim M.|last5=Deser|first5=Clara|last6=Di Lorenzo|first6=Emanuele|last7=Mantua|first7=Nathan J.|last8=Miller|first8=Arthur J.|last9=Minobe|first9=Shoshiro|s2cid=4824093|date=2016|title=The Pacific Decadal Oscillation, Revisited|journal=Journal of Climate|volume=29|issue=12|pages=4399–4427|doi=10.1175/JCLI-D-15-0508.1|issn=0894-8755|bibcode=2016JCli...29.4399N}}</ref>
* the [[Interdecadal Pacific oscillation]] (IPO) – Basin wide variability in the Pacific Ocean with a period between 20 and 30 years.<ref>{{Cite web|url=https://www.niwa.co.nz/node/111124|title=Interdecadal Pacific Oscillation|date=19 January 2016|website=NIWA|language=en|access-date=6 April 2019|archive-date=17 March 2023|archive-url=https://web.archive.org/web/20230317140832/https://niwa.co.nz/node/111124|url-status=live}}</ref>
* the [[Atlantic multidecadal oscillation]] – A pattern of variability in the North Atlantic of about 55 to 70 years, with effects on rainfall, droughts and hurricane frequency and intensity.<ref>{{Cite journal|last1=Kuijpers|first1=Antoon|last2=Bo Holm Jacobsen|last3=Seidenkrantz|first3=Marit-Solveig|last4=Knudsen|first4=Mads Faurschou|date=2011|title=Tracking the Atlantic Multidecadal Oscillation through the last 8,000 years|journal=Nature Communications|language=en|volume=2|issue=1 |pages=178–|doi=10.1038/ncomms1186|pmid=21285956|issn=2041-1723|pmc=3105344|bibcode=2011NatCo...2..178K}}</ref>
* [[North African climate cycles]] – climate variation driven by the [[North African Monsoon]], with a period of tens of thousands of years.<ref>{{cite journal|last1=Skonieczny|first1=C.|date=2 January 2019|title=Monsoon-driven Saharan dust variability over the past 240,000 years|journal=Science Advances|volume=5|issue=1|pages=eaav1887|doi=10.1126/sciadv.aav1887|pmc=6314818|pmid=30613782|bibcode=2019SciA....5.1887S}}</ref>
* the [[Arctic oscillation]] (AO) and [[Antarctic oscillation]] (AAO) – The annular modes are naturally occurring, hemispheric-wide patterns of climate variability. On timescales of weeks to months they explain 20–30% of the variability in their respective hemispheres. The Northern Annular Mode or [[Arctic oscillation]] (AO) in the Northern Hemisphere, and the Southern Annular Mode or [[Antarctic oscillation]] (AAO) in the southern hemisphere. The annular modes have a strong influence on the temperature and precipitation of mid-to-high latitude land masses, such as Europe and Australia, by altering the average paths of storms. The NAO can be considered a regional index of the AO/NAM.<ref>{{cite web |last1=Thompson |first1=David |title=Annular Modes – Introduction |url=http://www.atmos.colostate.edu/~davet/ao/introduction.html |access-date=11 February 2020 |archive-date=18 March 2023 |archive-url=https://web.archive.org/web/20230318094533/https://www.atmos.colostate.edu/~davet/ao/introduction.html |url-status=live }}</ref> They are defined as the first [[Empirical orthogonal functions|EOF]] of sea level pressure or geopotential height from 20°N to 90°N (NAM) or 20°S to 90°S (SAM).
* [[Dansgaard–Oeschger cycles]] – occurring on roughly 1,500-year cycles during the [[Last Glacial Maximum]]