{{short description|Global warm period around 9,000–5,000 years ago}} {{Lead too short|date=September 2018}}

The '''Holocene Climate Optimum''' (HCO) was a [[warm period]] in the first half of the [[Holocene]] [[geologic epoch|epoch]], that occurred in the interval roughly 9,500 to 5,500 years [[Before Present|BP]],<ref name="MarcottShakunClarkMix2013">{{cite journal |last1=Marcott |first1=Shaun A. |last2=Shakun |first2=Jeremy D. |last3=Clark |first3=Peter U. |last4=Mix |first4=Alan C. |date=8 March 2013 |title=A Reconstruction of Regional and Global Temperature for the Past 11,300 Years |url=https://www.science.org/doi/10.1126/science.1228026 |journal=[[Science (journal)|Science]] |volume=339 |issue=6124 |pages=1198–1201 |doi=10.1126/science.1228026 |pmid=23471405 |bibcode=2013Sci...339.1198M |s2cid=29665980 |access-date=13 March 2023 |archive-date=3 February 2023 |archive-url=https://web.archive.org/web/20230203102903/https://www.science.org/doi/10.1126/science.1228026 |url-status=live |url-access=subscription }}</ref> with a thermal maximum around 8000 years BP. It has also been known by many other names, such as '''Altithermal''', '''Climatic Optimum''', '''Holocene Megathermal''', '''Holocene Optimum''', '''Holocene Thermal Maximum''', '''Holocene global thermal maximum''', '''Hypsithermal''', and '''Mid-Holocene Warm Period'''.

The warm period was followed by a gradual decline, of about 0.1 to 0.3&nbsp;°C per millennium, until about two centuries ago. However, on a sub-millennial scale, there were regional warm periods superimposed on this decline.<ref>{{cite web|url=https://dotearth.blogs.nytimes.com/2013/04/22/study-charts-2000-years-of-continental-climate-changes/|last=Revkin|first=Andrew|work=New York Times Dot Earth|title=Study Charts 2,000 Years of Continental Climate Change|date=22 April 2013|access-date=26 December 2021|archive-date=26 December 2021|archive-url=https://web.archive.org/web/20211226204705/https://dotearth.blogs.nytimes.com/2013/04/22/study-charts-2000-years-of-continental-climate-changes/|url-status=live}}</ref><ref>{{cite web|url=https://www.newscientist.com/article/dn11647-climate-myths-its-been-far-warmer-in-the-past-whats-the-big-deal/|last=Chandler|first=David|work=[[New Scientist]]|title=Climate myths: It's been far warmer in the past, what's the big deal?|date=16 May 2007|access-date=26 December 2021|archive-date=26 December 2021|archive-url=https://web.archive.org/web/20211226204706/https://www.newscientist.com/article/dn11647-climate-myths-its-been-far-warmer-in-the-past-whats-the-big-deal/|url-status=live}}</ref><ref>{{cite journal|journal=[[Nature (journal)|Nature]]|first1=R|last1=Neukom|last2=Steiger|first2=N|last3=Gómez-Navarro|first3=J.J|title=No evidence for globally coherent warm and cold periods over the preindustrial Common Era|volume=571|pages=550–554|date=24 July 2019|issue=7766|doi=10.1038/s41586-019-1401-2|pmid=31341300|bibcode=2019Natur.571..550N|s2cid=198494930}}</ref> * For other temperature fluctuations, see [[temperature record]]. * For other past climate fluctuation, see [[paleoclimatology]]. * For the [[pollen zone]] and [[Blytt–Sernander period]], associated with the climate optimum, see [[Atlantic (period)]].

== Global effects == [[Image:Holocene Temperature Variations.png|thumb|right|300px|Temperature variations during the Holocene from a collection of different reconstructions and their average. The most recent period is on the right, but the recent warming is seen only in the inset.]] The HCO was approximately 4.9 °C warmer than the [[Last Glacial Maximum]].<ref>{{Cite journal |last1=Shakun |first1=Jeremy D. |last2=Carlson |first2=Anders E. |date=1 July 2010 |title=A global perspective on Last Glacial Maximum to Holocene climate change |url=https://www.sciencedirect.com/science/article/abs/pii/S0277379110000946 |journal=[[Quaternary Science Reviews]] |series=Special Theme: Arctic Palaeoclimate Synthesis (PP. 1674-1790) |volume=29 |issue=15 |pages=1801–1816 |doi=10.1016/j.quascirev.2010.03.016 |bibcode=2010QSRv...29.1801S |issn=0277-3791 |access-date=17 September 2023 |archive-date=3 October 2023 |archive-url=https://web.archive.org/web/20231003171821/https://www.sciencedirect.com/science/article/abs/pii/S0277379110000946 |url-status=live |url-access=subscription }}</ref> A study in 2020 estimated that the average global temperature during the warmest 200 year period of the HCO, around 6,500 years ago, was around 0.7 °C warmer than the mean for nineteenth century AD, immediately before the [[Industrial Revolution]], and 0.3 °C cooler than the average for 2011–2019.<ref>{{cite journal |last1=Kaufman |first1=Darrell |last2=McKay |first2=Nicholas |last3=Routson |first3=Cody |last4=Erb |first4=Michael |last5=Dätwyler |first5=Christoph |last6=Sommer |first6=Philipp S. |last7=Heiri |first7=Oliver |last8=Davis |first8=Basil |date=30 June 2022 |title=Holocene global mean surface temperature, a multi-method reconstruction approach |journal=[[Scientific Data]] |volume=7 |issue=1 |page=201 |doi=10.1038/s41597-020-0530-7 |pmid=32606396 |pmc=7327079 }}</ref> The [[IPCC Sixth Assessment Report|2021 IPCC report]] expressed medium confidence that temperatures in the last decade are higher than they were in the Mid-Holocene Warm Period.<ref>{{Cite book |author=IPCC |url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Full_Report.pdf |title=Climate Change 2021: The Physical Science Basis |publisher=Cambridge University Press (In Press) |year=2021 |isbn= |editor1-last=Masson-Delmotte |editor1-first=V. |series=Contribution of Working Group I to the [[IPCC Sixth Assessment Report|Sixth Assessment Report]] of the Intergovernmental Panel on Climate Change |place= |page=SPM-9 |ref={{harvid|IPCC AR6 WG1|2021}} |author-link=IPCC |editor2-last=Zhai |editor2-first=P. |editor3-last=Pirani |editor3-first=A. |editor4-last=Connors |editor4-first=S. L. |editor5-last=Péan |editor5-first=C. |editor6-last=Berger |editor6-first=S. |editor7-last=Caud |editor7-first=N. |editor8-last=Chen |editor8-first=Y. |editor9-last=Goldfarb |editor9-first=L. |display-editors=4 |editor10-first=M. I. |editor10-last=Gomis |access-date=2021-10-31 |archive-date=2021-08-13 |archive-url=https://web.archive.org/web/20210813201719/https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Full_Report.pdf |url-status=live }}</ref> Temperatures in the [[Northern Hemisphere]] are simulated to be warmer than present average during the summers, but the [[tropics]] and parts of the [[Southern Hemisphere]] were colder than average.<ref>{{cite journal|author1=Kitoh, Akio |author2=Murakami, Shigenori |title=Tropical Pacific climate at the mid-Holocene and the Last Glacial Maximum |journal=[[Paleoceanography and Paleoclimatology]] |volume=17 |issue=3 |page=1047 |year=2002 |doi=10.1029/2001PA000724 |bibcode=2002PalOc..17.1047K |doi-access=free }}</ref> The average temperature change appears to have declined rapidly with latitude and so essentially no change in mean temperature is reported at low and middle latitudes. Tropical reefs tend to show temperature increases of less than 1&nbsp;°C. The tropical ocean surface at the [[Great Barrier Reef]] about 5350 years ago was 1&nbsp;°C warmer and enriched in <sup>18</sup>O by 0.5 per mil relative to modern seawater.<ref name="Gagan1998">{{cite journal |last1=Gagan |first1=Michael K. |last2=Ayliffe |first2=LK |last3=Hopley |first3=D |last4=Cali |first4=JA |last5=Mortimer |first5=GE |last6=Chappell |first6=J |last7=McCulloch |first7=MT |last8=Head |first8=MJ |year=1998 |title=Temperature and Surface-Ocean Water Balance of the Mid-Holocene Tropical Western Pacific |url=https://www.science.org/doi/10.1126/science.279.5353.1014 |journal=[[Science (journal)|Science]] |volume=279 |issue=5353 |pages=1014–8 |bibcode=1998Sci...279.1014G |doi=10.1126/science.279.5353.1014 |pmid=9461430 |access-date=13 March 2023 |archive-date=14 March 2023 |archive-url=https://web.archive.org/web/20230314044448/https://www.science.org/doi/10.1126/science.279.5353.1014 |url-status=live |url-access=subscription }}</ref>

Temperatures during the HCO were higher than in the present by around 6&nbsp;°C in [[Svalbard]], near the North Pole.<ref>{{Cite journal |last1=Beierlein |first1=Lars |last2=Salvigsen |first2=Otto |last3=Schöne |first3=Bernd R |last4=Mackensen |first4=Andreas |last5=Brey |first5=Thomas |date=16 April 2015 |title=The seasonal water temperature cycle in the Arctic Dicksonfjord (Svalbard) during the Holocene Climate Optimum derived from subfossil Arctica islandica shells |url=http://journals.sagepub.com/doi/10.1177/0959683615580861 |journal=[[The Holocene]] |language=en |volume=25 |issue=8 |pages=1197–1207 |doi=10.1177/0959683615580861 |bibcode=2015Holoc..25.1197B |s2cid=128781737 |issn=0959-6836 |access-date=8 September 2023 |archive-date=18 September 2023 |archive-url=https://web.archive.org/web/20230918023141/https://journals.sagepub.com/doi/10.1177/0959683615580861 |url-status=live |url-access=subscription }}</ref>

Of 140 sites across the western Arctic, there is clear evidence for conditions that were warmer than now at 120 sites. At 16 sites for which quantitative estimates have been obtained, local temperatures were on average 1.6±0.8&nbsp;°C higher during the optimum than now. Northwestern North America reached peak warmth first, from 11,000 to 9,000 years ago, but the [[Laurentide Ice Sheet]] still chilled eastern Canada. Northeastern North America experienced peak warming 4,000 years later. Along the [[Arctic coastal tundra|Arctic Coastal Plain]] in Alaska, there are indications of summer temperatures 2–3&nbsp;°C warmer than now.<ref name="kaufman2004">{{cite journal |author1=D.S. Kaufman |author2=T.A. Ager |author3=N.J. Anderson |author4=P.M. Anderson |author5=J. T. Andrews |author6=P. J. Bartlein |author7=L. B. Brubaker |author8=L.L. Coats |author9=L. C. Cwynar |author10=M. L. Duvall |author11=A. S. Dyke |author12=M.E. Edwards |author13=W.R. Eisner |author14=K. Gajewski |author15=A. Geirsdottir |author16=F.S. Hu |author17=A.E. Jennings |author18=M. R. Kaplan |author19=M. W. Kerwin |author20=A. V. Lozhkin |author21=G.M. MacDonald |author22=G.H. Miller |author23=C.J. Mock |author24=W. W. Oswald |author25=B.L. Otto-Bliesner |author26=D. F. Porinchu |author27=K. Ruhland |author28=J.P. Smol |author29=E.J. Steig |author30=B.B. Wolfe |year=2004 |title=Holocene thermal maximum in the western Arctic (0–180 W) |journal=[[Quaternary Science Reviews]] |volume=23 |pages=529–560 |doi=10.1016/j.quascirev.2003.09.007 |issue=5–6 |bibcode=2004QSRv...23..529K |url=http://oceanrep.geomar.de/27265/1/2004_Kaufman-etal-Holocene_QSR-23.pdf |access-date=2019-12-14 |archive-date=2021-03-02 |archive-url=https://web.archive.org/web/20210302225442/https://oceanrep.geomar.de/27265/1/2004_Kaufman-etal-Holocene_QSR-23.pdf |url-status=live }}</ref> Research indicates that the Arctic had less sea ice than now.<ref name=NSDIC>{{cite web |publisher=[[National Snow and Ice Data Center]] |title=NSIDC Arctic Sea Ice News |url=http://nsidc.org/arcticseaicenews/faq.html#summer_ice |access-date=15 May 2009 |archive-date=28 April 2009 |archive-url=https://web.archive.org/web/20090428173410/http://nsidc.org/arcticseaicenews/faq.html#summer_ice }}</ref> The [[Greenland ice sheet|Greenland Ice Sheet]] thinned, particularly at its margins.<ref>{{Cite journal |last1=Vinther |first1=B. M. |last2=Buchardt |first2=S. L. |last3=Clausen |first3=H. B. |last4=Dahl-Jensen |first4=D. |last5=Johnsen |first5=S. J. |last6=Fisher |first6=D. A. |last7=Koerner |first7=R. M. |last8=Raynaud |first8=D. |last9=Lipenkov |first9=V. |last10=Andersen |first10=K. K. |last11=Blunier |first11=T. |last12=Rasmussen |first12=S. O. |last13=Steffensen |first13=J. P. |last14=Svensson |first14=A. M. |date=17 September 2009 |title=Holocene thinning of the Greenland ice sheet |url=https://www.nature.com/articles/nature08355 |journal=[[Nature (journal)|Nature]] |language=en |volume=461 |issue=7262 |pages=385–388 |doi=10.1038/nature08355 |pmid=19759618 |bibcode=2009Natur.461..385V |s2cid=4426637 |issn=0028-0836 |access-date=11 September 2023 |archive-date=4 February 2024 |archive-url=https://web.archive.org/web/20240204010414/https://www.nature.com/articles/nature08355 |url-status=live |url-access=subscription }}</ref> In addition to being warmer, Arctic Alaska also became wetter.<ref>{{Cite journal |last1=Gaglioti |first1=Benjamin V. |last2=Mann |first2=Daniel H. |last3=Wooller |first3=Matthew J. |last4=Jones |first4=Benjamin M. |last5=Wiles |first5=Gregory C. |last6=Groves |first6=Pamela |last7=Kunz |first7=Michael L. |last8=Baughman |first8=Carson A. |last9=Reanier |first9=Richard E. |date=1 August 2017 |title=Younger-Dryas cooling and sea-ice feedbacks were prominent features of the Pleistocene-Holocene transition in Arctic Alaska |url=https://www.sciencedirect.com/science/article/pii/S0277379117301713 |journal=[[Quaternary Science Reviews]] |language=en |volume=169 |pages=330–343 |doi=10.1016/j.quascirev.2017.05.012 |bibcode=2017QSRv..169..330G |access-date=8 November 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref>

[[Northwestern Europe]] experienced warming, but there was cooling in [[Southern Europe]].<ref name="davis2003">{{cite journal |author1=Davis, B.A.S. |author2=Brewer, S. |author3=Stevenson, A.C. |author4=Guiot, J. |year=2003 |title=The temperature of Europe during the Holocene reconstructed from pollen data |journal=[[Quaternary Science Reviews]] |volume=22 |issue=15–17 |pages=1701–16 |bibcode=2003QSRv...22.1701D |citeseerx=10.1.1.112.140 |doi=10.1016/S0277-3791(03)00173-2}}</ref> In the southwestern [[Iberian Peninsula]], forest cover reached its peak between 9,760 and 7,360 years BP as a result of high moisture availability and warm temperatures during the HCO.<ref name="GomesEtAl2020">{{cite journal |last1=Gomes |first1=S. D. |last2=Fletcher |first2=W. J. |last3=Rodrigues |first3=T. |last4=Stone |first4=A. |last5=Abrantes |first5=F. |last6=Naughton |first6=F. |date=15 July 2020 |title=Time-transgressive Holocene maximum of temperate and Mediterranean forest development across the Iberian Peninsula reflects orbital forcing |url=https://www.sciencedirect.com/science/article/abs/pii/S003101822030184X |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=550 |article-number=109739 |doi=10.1016/j.palaeo.2020.109739 |bibcode=2020PPP...55009739G |s2cid=216337848 |access-date=5 November 2022 |archive-date=6 November 2022 |archive-url=https://web.archive.org/web/20221106025509/https://www.sciencedirect.com/science/article/abs/pii/S003101822030184X |url-status=live |url-access=subscription }}</ref> In [[Central Europe]], the HCO was when human impact on the environment first became clearly detectable in sedimentological records,<ref>{{Cite journal |last1=Zolitschka |first1=Bernd |last2=Behre |first2=Karl-Ernst |last3=Schneider |first3=Jürgen |date=1 January 2003 |title=Human and climatic impact on the environment as derived from colluvial, fluvial and lacustrine archives—examples from the Bronze Age to the Migration period, Germany |url=https://www.sciencedirect.com/science/article/pii/S0277379102001828 |journal=[[Quaternary Science Reviews]] |series=Environmental response to climate and human impact in central Eur ope during the last 15000 years - a German contribution to PAGES-PEPIII |volume=22 |issue=1 |pages=81–100 |doi=10.1016/S0277-3791(02)00182-8 |bibcode=2003QSRv...22...81Z |issn=0277-3791 |access-date=11 September 2023 |archive-date=18 March 2012 |archive-url=https://web.archive.org/web/20120318033911/http://www.sciencedirect.com/science/article/pii/S0277379102001828 |url-status=live |url-access=subscription }}</ref> with the portion of the HCO from 9,000 to 7,500 BP being associated with minimal human impact and environmental stability, the portion from 7,500 to 6,300 BP with human impact only observed in pollen records, and the portion after 6,300 BP with substantial human influence on the environment.<ref>{{Cite journal |last1=Kalis |first1=Arie J |last2=Merkt |first2=Josef |last3=Wunderlich |first3=Jürgen |date=1 January 2003 |title=Environmental changes during the Holocene climatic optimum in central Europe - human impact and natural causes |url=https://www.sciencedirect.com/science/article/pii/S0277379102001816 |journal=[[Quaternary Science Reviews]] |series=Environmental response to climate and human impact in central Eur ope during the last 15000 years - a German contribution to PAGES-PEPIII |volume=22 |issue=1 |pages=33–79 |doi=10.1016/S0277-3791(02)00181-6 |bibcode=2003QSRv...22...33K |issn=0277-3791 |access-date=8 September 2023 |archive-date=8 March 2022 |archive-url=https://web.archive.org/web/20220308160950/https://www.sciencedirect.com/science/article/pii/S0277379102001816 |url-status=live |url-access=subscription }}</ref>

In the [[Middle East]], the HCO was associated with frost-free winters and abundant ''[[Pistacia]]'' [[Savanna|savannas]]. It was during this interval that the domestication of [[Cereal|cereals]] and Neolithic population growth occurred in the region.<ref>{{Cite journal |last=Rossignol-Strick |first=Martine |date=1 April 1999 |title=The Holocene climatic optimum and pollen records of sapropel 1 in the eastern Mediterranean, 9000–6000BP |url=https://www.sciencedirect.com/science/article/pii/S0277379198000936 |journal=[[Quaternary Science Reviews]] |volume=18 |issue=4 |pages=515–530 |doi=10.1016/S0277-3791(98)00093-6 |bibcode=1999QSRv...18..515R |issn=0277-3791 |access-date=8 September 2023 |archive-date=19 June 2024 |archive-url=https://web.archive.org/web/20240619094447/https://www.sciencedirect.com/science/article/abs/pii/S0277379198000936 |url-status=live |url-access=subscription }}</ref>

The onset of the HCO in the southern [[Ural Mountains]] was simultaneous with that in [[Northern Europe]], while its termination occurred between 6,300 and 5,100 BP.<ref>{{Cite journal |last1=Maslennikova |first1=A. V. |last2=Udachin |first2=V. N. |last3=Aminov |first3=P. G. |date=28 October 2016 |title=Lateglacial and Holocene environmental changes in the Southern Urals reflected in palynological, geochemical and diatom records from the Lake Syrytkul sediments |url=https://www.sciencedirect.com/science/article/pii/S104061821500840X |journal=[[Quaternary International]] |series=The Quaternary of the Urals: Global trends and Pan-European Quaternary records |volume=420 |pages=65–75 |doi=10.1016/j.quaint.2015.08.062 |bibcode=2016QuInt.420...65M |issn=1040-6182 |access-date=8 September 2023 |archive-date=19 June 2024 |archive-url=https://web.archive.org/web/20240619094328/https://www.sciencedirect.com/science/article/abs/pii/S104061821500840X |url-status=live |url-access=subscription }}</ref> Winter warming of 3 to 9&nbsp;°C and summer warming of 2 to 6&nbsp;°C occurred in northern central [[Siberia]].<ref name="koshkarova2004">{{cite journal |author1=Koshkarova, V.L. |author2=Koshkarov, A.D. |year=2004 |title=Regional signatures of changing landscape and climate of northern central Siberia in the Holocene |url=http://www.sibran.ru/psb/show_text.phtml?eng+4213+9+ |journal=Russian Geology and Geophysics |volume=45 |issue=6 |pages=672–685}}{{dead link|date=November 2017|bot=InternetArchiveBot|fix-attempted=yes}}</ref>

The HCO was highly asynchronous in Central and East Asia,<ref>{{Cite journal |last1=Gao |first1=Fuyuan |last2=Jia |first2=Jia |last3=Xia |first3=Dunsheng |last4=Lu |first4=Caichen |last5=Lu |first5=Hao |last6=Wang |first6=Youjun |last7=Liu |first7=Hao |last8=Ma |first8=Yapeng |last9=Li |first9=Kaiming |date=15 March 2019 |title=Asynchronous Holocene Climate Optimum across mid-latitude Asia |url=https://linkinghub.elsevier.com/retrieve/pii/S0031018218301688 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |language=en |volume=518 |pages=206–214 |doi=10.1016/j.palaeo.2019.01.012 |bibcode=2019PPP...518..206G |s2cid=135199089 |access-date=5 September 2023 |archive-date=23 July 2023 |archive-url=https://web.archive.org/web/20230723090158/https://linkinghub.elsevier.com/retrieve/pii/S0031018218301688 |url-status=live |url-access=subscription }}</ref> though it at least occurred contemporaneously in the Loess Plateau, the Inner Mongolian Plateau, and Xinjiang.<ref>{{Cite journal |last1=Feng |first1=Z.-D. |last2=An |first2=C. B. |last3=Wang |first3=H. B. |date=January 2006 |title=Holocene climatic and environmental changes in the arid and semi-arid areas of China: a review |url=http://journals.sagepub.com/doi/10.1191/0959683606hl912xx |journal=[[The Holocene]] |language=en |volume=16 |issue=1 |pages=119–130 |doi=10.1191/0959683606hl912xx |bibcode=2006Holoc..16..119F |issn=0959-6836 |access-date=21 July 2024 |via=Sage Journals}}</ref> As a result of rising sea levels and decay of [[ice sheets]] in the Northern Hemisphere, the East Asian Summer Monsoon (EASM) rain belt expanded to the northwest, penetrating deep into the Asian interior.<ref>{{cite journal |last1=Yang |first1=Shiling |last2=Ding |first2=Zhongli |last3=Li |first3=Yangyang |last4=Wang |first4=Xu |last5=Jiang |first5=Wengying |last6=Huang |first6=Xiaofang |date=12 October 2015 |title=Warming-induced northwestward migration of the East Asian monsoon rain belt from the Last Glacial Maximum to the mid-Holocene |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=112 |issue=43 |pages=13178–13183 |doi=10.1073/pnas.1504688112 |pmid=26460029 |pmc=4629344 |bibcode=2015PNAS..11213178Y |doi-access=free }}</ref> The EASM, being significantly weaker before and after the HCO, peaked in strength during this interval,<ref name="WangEtAl2019PPP">{{cite journal |last1=Wang |first1=Wei |last2=Liu |first2=Lina |last3=Li |first3=Yanyan |last4=Niu |first4=Zhimei |last5=He |first5=Jiang |last6=Ma |first6=Yuzhen |last7=Mensing |first7=Scott A. |date=15 August 2019 |title=Pollen reconstruction and vegetation dynamics of the middle Holocene maximum summer monsoon in northern China |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018218309180 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=528 |pages=204–217 |doi=10.1016/j.palaeo.2019.05.023 |bibcode=2019PPP...528..204W |s2cid=182641708 |access-date=6 December 2022 |archive-date=6 December 2022 |archive-url=https://web.archive.org/web/20221206001858/https://www.sciencedirect.com/science/article/abs/pii/S0031018218309180 |url-status=live |url-access=subscription }}</ref> though the exact timing of its maximum intensity varied by region;<ref>{{cite journal |last1=An |first1=Zhisheng |last2=Porter |first2=Stephen C. |last3=Kutzbach |first3=John E. |last4=Xihao |first4=Wu |last5=Suming |first5=Wang |last6=Xiaodong |first6=Liu |last7=Xiaoqiang |first7=Li |last8=Weijian |first8=Zhou |date=April 2000 |title=Asynchronous Holocene optimum of the East Asian monsoon |url=https://www.sciencedirect.com/science/article/abs/pii/S0277379199000311 |journal=[[Quaternary Science Reviews]] |volume=19 |issue=8 |pages=743–762 |doi=10.1016/S0277-3791(99)00031-1 |bibcode=2000QSRv...19..743A |access-date=9 July 2023 |archive-date=10 July 2023 |archive-url=https://web.archive.org/web/20230710033732/https://www.sciencedirect.com/science/article/abs/pii/S0277379199000311 |url-status=live |url-access=subscription }}</ref> intensified westerlies occasionally caused dry spells in China during the HCO.<ref>{{Cite journal |last1=Zhang |first1=Jingwei |last2=Kong |first2=Xinggong |last3=Zhao |first3=Kan |last4=Wang |first4=Yongjin |last5=Liu |first5=Shushuang |last6=Wang |first6=Zhenjun |last7=Liu |first7=Jianwei |last8=Cheng |first8=Hai |last9=Edwards |first9=R. Lawrence |date=15 November 2020 |title=Centennial-scale climatic changes in Central China during the Holocene climatic optimum |url=https://linkinghub.elsevier.com/retrieve/pii/S0031018220303953 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |language=en |volume=558 |article-number=109950 |doi=10.1016/j.palaeo.2020.109950 |bibcode=2020PPP...55809950Z |access-date=21 July 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref> Current desert regions of [[Central Asia]] were extensively forested because of higher rainfall, and the warm temperate forest belts in China and Japan were extended northwards.<ref>{{cite web |url=http://www.esd.ornl.gov/projects/qen/nercEURASIA.html |title=Eurasia During the Last 150,000 Years |access-date=7 June 2012 |archive-url=https://web.archive.org/web/20120608032955/http://www.esd.ornl.gov/projects/qen/nercEURASIA.html|archive-date=8 June 2012}}</ref> In the [[Yarlung Tsangpo]] valley of southern Tibet, precipitation was up to twice as high as it is today during the middle Holocene.<ref>{{cite journal |last1=Hudson |first1=Adam M. |last2=Olsen |first2=John W. |last3=Quade |first3=Jay |last4=Lei |first4=Guoliang |last5=Huth |first5=Tyler |last6=Zhang |first6=Hucai |date=May 2016 |title=A regional record of expanded Holocene wetlands and prehistoric human occupation from paleowetland deposits of the western Yarlung Tsangpo valley, southern Tibetan Plateau |url=https://www.researchgate.net/publication/303438450 |journal=[[Quaternary Research]] |volume=86 |issue=1 |pages=13–33 |doi=10.1016/j.yqres.2016.04.001 |bibcode=2016QuRes..86...13H |access-date=22 April 2023 |archive-date=19 June 2024 |archive-url=https://web.archive.org/web/20240619094513/https://www.researchgate.net/publication/303438450_A_regional_record_of_expanded_Holocene_wetlands_and_prehistoric_human_occupation_from_paleowetland_deposits_of_the_western_Yarlung_Tsangpo_valley_southern_Tibetan_Plateau |url-status=live }}</ref> In the Huai River basin, the HCO began 9,100 to 8,000 BP.<ref>{{Cite journal |last1=Jiang |first1=Shiwei |last2=Luo |first2=Wuhong |last3=Tu |first3=Luyao |last4=Yu |first4=Yanyan |last5=Fang |first5=Fang |last6=Liu |first6=Xiaoyan |last7=Zhan |first7=Tao |last8=Fang |first8=Lidong |last9=Zhang |first9=Xiaolin |last10=Zhou |first10=Xin |date=14 August 2018 |title=The Holocene optimum (HO) and the response of human activity: A case study of the Huai River Basin in eastern China |url=https://linkinghub.elsevier.com/retrieve/pii/S1040618218307997 |journal=[[Quaternary International]] |language=en |volume=493 |pages=31–38 |doi=10.1016/j.quaint.2018.08.011 |bibcode=2018QuInt.493...31J |access-date=21 July 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref> Pollen records from [[Lake Tai]] in [[Jiangsu]], [[China]] shed light on increased summer precipitation and a warmer and wetter overall climate in the region.<ref>{{cite journal |last1=Qiu |first1=Zhenwei |last2=Jiang |first2=Hongen |last3=Ding |first3=Lanlan |last4=Shang |first4=Xue |date=9 June 2020 |title=Late Pleistocene-Holocene vegetation history and anthropogenic activities deduced from pollen spectra and archaeological data at Guxu Lake, eastern China |journal=[[Scientific Reports]] |volume=10 |issue=1 |page=9306 |doi=10.1038/s41598-020-65834-z |pmid=32518244 |pmc=7283361 |bibcode=2020NatSR..10.9306Q }}</ref> The stability of the Middle Holocene climate in China fostered the development of agriculture and animal husbandry in the region.<ref>{{Cite journal |last1=Zhang |first1=Zhiping |last2=Liu |first2=Jianbao |last3=Chen |first3=Jie |last4=Chen |first4=Shengqian |last5=Shen |first5=Zhongwei |last6=Chen |first6=Jie |last7=Liu |first7=Xiaokang |last8=Wu |first8=Duo |last9=Sheng |first9=Yongwei |last10=Chen |first10=Fahu |date=January 2021 |title=Holocene climatic optimum in the East Asian monsoon region of China defined by climatic stability |url=https://linkinghub.elsevier.com/retrieve/pii/S0012825220304967 |journal=[[Earth-Science Reviews]] |language=en |volume=212 |article-number=103450 |doi=10.1016/j.earscirev.2020.103450 |bibcode=2021ESRv..21203450Z |s2cid=229436491 |access-date=5 September 2023 |archive-date=27 October 2022 |archive-url=https://web.archive.org/web/20221027074703/https://linkinghub.elsevier.com/retrieve/pii/S0012825220304967 |url-status=live |url-access=subscription }}</ref> In the Korean Peninsula, arboreal pollen records the HCO as occurring from 8,900 to 4,400 BP, with its core period being 7,600 to 4,800 BP.<ref>{{cite journal |last1=Park |first1=Jungjae |last2=Park |first2=Jinheum |last3=Yi |first3=Sangheon |last4=Kim |first4=Jin Cheul |last5=Lee |first5=Eunmi |last6=Choi |first6=Jieun |date=25 July 2019 |title=Abrupt Holocene climate shifts in coastal East Asia, including the 8.2 ka, 4.2 ka, and 2.8 ka BP events, and societal responses on the Korean peninsula |journal=[[Scientific Reports]] |volume=9 |issue=1 |page=10806 |doi=10.1038/s41598-019-47264-8 |pmid=31346228 |pmc=6658530 |bibcode=2019NatSR...910806P }}</ref> Sea levels in the [[Sea of Japan]] were 2–6 metres higher than in the present, with [[sea surface temperature]]s being 1–2 °C higher. The [[East Korea Warm Current]] reached as far as [[Primorye]] and pushed cold water off of the cooler Primorsky Current to the northeast. The [[Tsushima Current]] warmed the northern shores of [[Hokkaido]] penetrated into the [[Sea of Okhotsk]].<ref>{{cite journal |last1=Evstigneeva |first1=T. A. |last2=Naryshkina |first2=N. N. |date=8 January 2011 |title=The Holocene climatic optimum at the southern coast of the Sea of Japan |url=https://link.springer.com/article/10.1134/S0031030110100047 |journal=[[Paleontological Journal]] |volume=44 |issue=10 |pages=1262–1269 |doi=10.1134/S0031030110100047 |s2cid=59574305 |access-date=28 January 2023 |archive-date=29 January 2023 |archive-url=https://web.archive.org/web/20230129002737/https://link.springer.com/article/10.1134/S0031030110100047 |url-status=live |url-access=subscription }}</ref> In the northern [[South China Sea]], the HCO was associated with colder winters due to a stronger East Asian Winter Monsoon (EAWM), causing frequent coral die-offs.<ref>{{Cite journal |last1=Yu |first1=Ke-Fu |last2=Zhao |first2=Jian-Xin |last3=Liu |first3=Tung-Sheng |last4=Wei |first4=Gang-Jian |last5=Wang |first5=Pin-Xian |last6=Collerson |first6=Kenneth D |date=30 July 2004 |title=High-frequency winter cooling and reef coral mortality during the Holocene climatic optimum |url=https://linkinghub.elsevier.com/retrieve/pii/S0012821X04002870 |journal=[[Earth and Planetary Science Letters]] |language=en |volume=224 |issue=1–2 |pages=143–155 |doi=10.1016/j.epsl.2004.04.036 |bibcode=2004E&PSL.224..143Y |access-date=8 September 2023 |archive-date=18 May 2023 |archive-url=https://web.archive.org/web/20230518230418/https://linkinghub.elsevier.com/retrieve/pii/S0012821X04002870 |url-status=live |url-access=subscription }}</ref>

In the [[Indian subcontinent|Indian Subcontinent]], the Indian Summer Monsoon (ISM) heavily intensified, creating a hot and wet climate in India along with high sea levels.<ref>{{Cite journal |last1=Shaji |first1=Jithu |last2=Banerji |first2=Upasana S. |last3=Maya |first3=K. |last4=Joshi |first4=Kumar Batuk |last5=Dabhi |first5=Ankur J. |last6=Bharti |first6=Nisha |last7=Bhushan |first7=Ravi |last8=Padmalal |first8=D. |date=30 December 2022 |title=Holocene monsoon and sea-level variability from coastal lowlands of Kerala, SW India |url=https://www.sciencedirect.com/science/article/pii/S104061822200074X |journal=[[Quaternary International]] |series=Shifting Quaternary Climate over Indian sub-Continent |volume=642 |pages=48–62 |doi=10.1016/j.quaint.2022.03.005 |bibcode=2022QuInt.642...48S |s2cid=247553867 |issn=1040-6182 |access-date=11 September 2023 |archive-date=19 June 2024 |archive-url=https://web.archive.org/web/20240619094443/https://www.sciencedirect.com/science/article/abs/pii/S104061822200074X |url-status=live |url-access=subscription }}</ref>

Relative sea level in the [[Spermonde Archipelago]] was approximately 0.5 metres higher than it is today.<ref>{{cite journal |last1=Mann |first1=Thomas |last2=Rovere |first2=Alessio |last3=Schöne |first3=Tilo |last4=Klicpera |first4=André |last5=Stocchi |first5=Paolo |last6=Lukman |first6=Muhammad |last7=Westphal |first7=Hildegard |date=15 March 2016 |title=The magnitude of a mid-Holocene sea-level highstand in the Strait of Makassar |url=https://www.sciencedirect.com/science/article/abs/pii/S0169555X15302427 |journal=[[Geomorphology (journal)|Geomorphology]] |volume=257 |pages=155–163 |doi=10.1016/j.geomorph.2015.12.023 |bibcode=2016Geomo.257..155M |access-date=21 April 2023 |archive-date=22 April 2023 |archive-url=https://web.archive.org/web/20230422070955/https://www.sciencedirect.com/science/article/abs/pii/S0169555X15302427 |url-status=live |url-access=subscription }}</ref><ref>{{cite journal |last1=Bender |first1=Maren |last2=Mann |first2=Thomas |last3=Stocchi |first3=Paolo |last4=Kneer |first4=Dominik |last5=Schöne |first5=Tilo |last6=Illigner |first6=Julia |last7=Jompa |first7=Jamaluddin |last8=Rovere |first8=Alessio |title=Late Holocene (0–6 ka) sea-level changes in the Makassar Strait, Indonesia |url=https://cp.copernicus.org/articles/16/1187/2020/ |journal=[[Climate of the Past]] |year=2020 |volume=16 |issue=4 |pages=1187–1205 |doi=10.5194/cp-16-1187-2020 |bibcode=2020CliPa..16.1187B |s2cid=221681240 |access-date=21 April 2023 |doi-access=free |archive-date=27 April 2023 |archive-url=https://web.archive.org/web/20230427044427/https://cp.copernicus.org/articles/16/1187/2020/ |url-status=live |hdl=10278/3747458 |hdl-access=free }}</ref> Sedimentary infill of lagoons was retarded by the sea level highstand and accelerated after the HCO, when sea levels dropped.<ref>{{cite journal |last1=Kappelmann |first1=Yannis |last2=Westphal |first2=Hildegard |last3=Kneer |first3=Dominik |last4=Wu |first4=Henry C. |last5=Wizemann |first5=André |last6=Jompa |first6=Jamaluddin |last7=Mann |first7=Thomas |date=28 March 2023 |title=Fluctuating sea-level and reversing Monsoon winds drive Holocene lagoon infill in Southeast Asia |journal=[[Scientific Reports]] |volume=13 |issue=1 |page=5042 |doi=10.1038/s41598-023-31976-z |pmid=36977704 |pmc=10050433 |bibcode=2023NatSR..13.5042K |url=https://www.researchgate.net/publication/369592049 |access-date=12 July 2023 |archive-date=19 June 2024 |archive-url=https://web.archive.org/web/20240619094330/https://www.researchgate.net/publication/369592049_Fluctuating_sea-level_and_reversing_Monsoon_winds_drive_Holocene_lagoon_infill_in_Southeast_Asia |url-status=live }}</ref>

[[File:Journal.pone.0076514.g004.png|thumb|270px|Vegetation and water bodies in northern and central Africa in the [[Eemian]] (bottom) and [[Holocene]] (top)]] West African sediments additionally record the [[African humid period]], an interval between 16,000 and 6,000 years ago during which [[Africa]] was much wetter than now. That was caused by a strengthening of the [[African monsoon]] by changes in summer radiation, which resulted from long-term variations in the [[Earth's orbit]] around the [[Sun]]. The "[[Green Sahara]]" was dotted with numerous [[Lake|lakes]], containing typical African lake [[crocodile]] and [[hippopotamus]] fauna. A curious discovery from the marine sediments is that the transitions into and out of the wet period occurred within decades, not the previously-thought extended periods.<ref name="usgcrp980217dd">{{cite web | title=Abrupt Climate Changes Revisited: How Serious and How Likely? | work=USGCRP Seminar, 23 February 1998 | url=http://www.usgcrp.gov/usgcrp/seminars/980217DD.html | access-date=May 18, 2005 | archive-date=11 June 2007 | archive-url=https://web.archive.org/web/20070611060531/http://www.usgcrp.gov/usgcrp/seminars/980217DD.html }}</ref> It is hypothesized that humans played a role in altering the vegetation structure of North Africa at some point after 8,000 years ago by introducing domesticated animals, which contributed to the rapid transition to the arid conditions that are now found in many locations in the [[Sahara]].<ref>{{Cite journal |last=Wright |first=David K. |date=26 January 2017 |title=Humans as Agents in the Termination of the African Humid Period |journal=[[Frontiers in Earth Science]] |volume=5 |page=4 |doi=10.3389/feart.2017.00004 |bibcode=2017FrEaS...5....4W |doi-access=free }}</ref> Further south, in [[Central Africa]], the [[Savanna|savannas]] that make up the coastal lowlands of the [[Congo River]] drainage basin in the present were entirely absent.<ref>{{Cite journal |last1=Jansen |first1=J. H. F. |last2=Van Weering |first2=T. C. E. |last3=Gieles |first3=R. |last4=Van Iperen |first4=J. |date=1 October 1984 |title=Middle and late quaternary oceanography and climatology of the Zaire-Congo fan and the adjacent Eastern Angola basin |journal=Netherlands Journal of Sea Research |volume=17 |issue=2 |pages=201–249 |doi=10.1016/0077-7579(84)90048-6 |bibcode=1984NJSR...17..201J |issn=0077-7579 }}</ref> Southwestern Africa experienced increased humidity during the HCO.<ref>{{Cite journal |last=Gingele |first=Franz X. |date=June 1996 |title=Holocene climatic optimum in Southwest Africa—evidence from the marine clay mineral record |url=https://linkinghub.elsevier.com/retrieve/pii/0031018296000764 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |language=en |volume=122 |issue=1–4 |pages=77–87 |doi=10.1016/0031-0182(96)00076-4 |bibcode=1996PPP...122...77G |access-date=8 September 2023 |archive-date=14 April 2024 |archive-url=https://web.archive.org/web/20240414094504/https://linkinghub.elsevier.com/retrieve/pii/0031018296000764 |url-status=live |url-access=subscription }}</ref>

Northwestern [[Patagonia]], in a region known as the [[Arid Diagonal]], was significantly drier during the [[Early Holocene|Early]] and [[Middle Holocene]], with the region becoming more humid during the Late Holocene following the end of the HCO.<ref name="LlanoEtAl2020">{{cite journal |last1=Llano |first1=Carina |last2=De Porras |first2=María Eugenia |last3=Barberena |first3=Ramiro |last4=Timpson |first4=Adrian |last5=Beltrame |first5=M. Ornela |last6=Marsh |first6=Erik J. |date=1 November 2020 |title=Human resilience to Holocene climate changes inferred from rodent middens in drylands of northwestern Patagonia (Argentina) |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018220303394 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=557 |article-number=109894 |doi=10.1016/j.palaeo.2020.109894 |bibcode=2020PPP...55709894L |s2cid=221881153 |access-date=6 December 2022 |archive-date=6 December 2022 |archive-url=https://web.archive.org/web/20221206092956/https://www.sciencedirect.com/science/article/abs/pii/S0031018220303394 |url-status=live |url-access=subscription }}</ref>

In the far Southern Hemisphere (New Zealand and Antarctica), the warmest period during the [[Holocene]] appears to have been roughly 10,500 to 8,000 years ago, immediately after the end of the [[Last Glacial Period|last ice age]].<ref name="masson2001">{{cite journal |author1=Masson, V. |author2=Vimeux, F. |author3=Jouzel, J. |author4=Morgan, V. |author5=Delmotte, M. |author6=Ciais,P. |author7=Hammer, C. |author8=Johnsen, S. |author9=Lipenkov, V.Y. |author10=Mosley-Thompson, E. |author11=Petit, J.-R. |author12=Steig, E.J. |author13=Stievenard, M. |author14=Vaikmae, R. |date=November 2000 |title=Holocene climate variability in Antarctica based on 11 ice-core isotopic records |journal=[[Quaternary Research]] |volume=54 |pages=348–358 |doi=10.1006/qres.2000.2172 |issue=3 |bibcode=2000QuRes..54..348M |s2cid=129887335 |url=https://www.sciencedirect.com/science/article/abs/pii/S0033589400921720 |access-date=21 June 2023 |archive-date=22 June 2023 |archive-url=https://web.archive.org/web/20230622041715/https://www.sciencedirect.com/science/article/abs/pii/S0033589400921720 |url-status=live |url-access=subscription }}</ref><ref name="williams2004">{{cite journal | journal=[[The Holocene]] | volume=14 |issue=2 |year=2004 | pages=194–208 |author1=P.W. Williams |author2=D.N.T. King |author3=J.-X. Zhao K.D. Collerson | title=Speleothem master chronologies: combined Holocene <sup>18</sup>O and <sup>13</sup>C records from the North Island of New Zealand and their paleoenvironmental interpretation | doi=10.1191/0959683604hl676rp| bibcode=2004Holoc..14..194W | s2cid=131290609}}</ref> The [[Amery Ice Shelf]] retreated approximately 80 kilometres landward during this warm interval.<ref>{{cite journal |last1=Hemer |first1=Mark A. |last2=Harris |first2=Peter T. |date=1 February 2003 |title=Sediment core from beneath the Amery Ice Shelf, East Antarctica, suggests mid-Holocene ice-shelf retreat |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/31/2/127/192545/Sediment-core-from-beneath-the-Amery-Ice-Shelf?redirectedFrom=fulltext |journal=[[Geology (journal)|Geology]] |volume=31 |issue=2 |pages=127–130 |doi=10.1130/0091-7613(2003)031<0127:SCFBTA>2.0.CO;2 |bibcode=2003Geo....31..127H |access-date=26 January 2023 |archive-date=27 January 2023 |archive-url=https://web.archive.org/web/20230127083851/https://pubs.geoscienceworld.org/gsa/geology/article-abstract/31/2/127/192545/Sediment-core-from-beneath-the-Amery-Ice-Shelf?redirectedFrom=fulltext |url-status=live |url-access=subscription }}</ref> By 6,000 years ago, which is normally associated with the Holocene Climatic Optimum in the Northern Hemisphere, those regions had reached temperatures similar to today, and they did not participate in the temperature changes of the north. However, some authors have used the term "Holocene Climatic Optimum" to describe the earlier southern warm period as well; typically, the term "Early Holocene Climatic Optimum" is used for the Southern Hemisphere warm interval.<ref>{{Cite journal |last1=Ciais |first1=P |last2=Petit |first2=J R |last3=Jouzel |first3=J |last4=Lorius |first4=C |last5=Barkov |first5=N I |last6=Lipenkov |first6=V |last7=Nicolaïev |first7=V |date=January 1992 |title=Evidence for an early Holocene climatic optimum in the Antarctic deep ice-core record |url=http://link.springer.com/10.1007/BF00193529 |journal=[[Climate Dynamics]] |language=en |volume=6 |issue=3–4 |pages=169–177 |doi=10.1007/BF00193529 |bibcode=1992ClDy....6..169C |s2cid=128416497 |issn=0930-7575 |access-date=5 September 2023|url-access=subscription }}</ref><ref>{{Cite journal |last1=Bostock |first1=H. C. |last2=Prebble |first2=J. G. |last3=Cortese |first3=G. |last4=Hayward |first4=B. |last5=Calvo |first5=E. |last6=Quirós-Collazos |first6=L. |last7=Kienast |first7=M. |last8=Kim |first8=K. |date=31 March 2019 |title=Paleoproductivity in the SW Pacific Ocean During the Early Holocene Climatic Optimum |url=https://onlinelibrary.wiley.com/doi/abs/10.1029/2019PA003574 |journal=[[Paleoceanography and Paleoclimatology]] |language=en |volume=34 |issue=4 |pages=580–599 |doi=10.1029/2019PA003574 |bibcode=2019PaPa...34..580B |issn=2572-4517 |access-date=5 September 2023 |hdl=10261/181776 |s2cid=135452816 |hdl-access=free |archive-date=19 June 2024 |archive-url=https://web.archive.org/web/20240619094915/https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019PA003574 |url-status=live |url-access=subscription }}</ref>

In New Zealand, the HCO was associated with a 2&nbsp;°C temperature gradient across the subtropical front (STF), a sharp contrast with the 6 °C observed today. Westerly winds in New Zealand were reduced.<ref>{{Cite journal |last1=Prebble |first1=J. G. |last2=Bostock |first2=H. C. |last3=Cortese |first3=G. |last4=Lorrey |first4=A. M. |last5=Hayward |first5=B. W. |last6=Calvo |first6=E. |last7=Northcote |first7=L. C. |last8=Scott |first8=G. H. |last9=Neil |first9=H. L. |date=August 2017 |title=Evidence for a Holocene Climatic Optimum in the southwest Pacific: A multiproxy study: Holocene Optimum in SW Pacific |url=http://doi.wiley.com/10.1002/2016PA003065 |journal=[[Paleoceanography and Paleoclimatology]] |language=en |volume=32 |issue=8 |pages=763–779 |doi=10.1002/2016PA003065 |access-date=8 September 2023 |hdl=10261/155815 |hdl-access=free |archive-date=19 June 2024 |archive-url=https://web.archive.org/web/20240619094849/https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016PA003065 |url-status=live }}</ref>

==Comparison of ice cores== A comparison of the delta profiles at [[Byrd Station]], West Antarctica (2164 m ice core recovered, 1968), and [[Camp Century]], Northwest Greenland, shows the post-glacial climatic optimum.<ref name="Dansgaard">{{cite book |author=Dansgaard W |title=Frozen Annals Greenland Ice Sheet Research |publisher=Narayana Press |year=2004 |isbn=978-87-990078-0-6 |location=[[Odder]], Denmark |page=124}}</ref> Points of correlation indicate that in both locations, the HCO (post-glacial climatic optimum) probably occurred at the same time. A similar comparison is evident between the Dye 3 1979 and the Camp Century 1963 cores regarding this period.<ref name=Dansgaard/>

The [[Hans Tausen Ice Cap]], in [[Peary Land]] (northern [[Greenland]]), was drilled in 1977, with a new deep drill to 325 m. The ice core contained distinct melt layers all the way to the bedrock. That indicates that Hans Tausen Iskappe contains no ice from the last glaciation and so the world's northernmost ice cap melted away during the post-glacial climatic optimum and was rebuilt when the climate cooled some 4000 years ago.<ref name=Dansgaard/>

From the delta-profile, the [[Renland]] ice cap in the [[Scoresby Sound]] has always been separated from the inland ice, but all of the delta-leaps revealed in the Camp Century 1963 core recurred in the Renland 1985 ice core.<ref name=Dansgaard/> The Renland ice core from East Greenland apparently covers a full glacial cycle from the Holocene into the previous [[Eemian]] interglacial. The Renland ice core is 325 m long.<ref name=Hansson1>{{ cite journal |vauthors=Hansson M, Holmén K |title= High latitude biospheric activity during the Last Glacial Cycle revealed by ammonium variations in Greenland Ice Cores |journal=[[Geophysical Research Letters]] |date=15 November 2001 |volume=28 |issue=22 |pages=4239–42 |doi=10.1029/2000GL012317 |bibcode=2001GeoRL..28.4239H |doi-access= |s2cid= 140677584 }}</ref>

Although the depths are different, the GRIP and NGRIP cores also contain the climatic optimum at very similar times.<ref name=Dansgaard/>

== Milankovitch cycles == [[Image:Orbital variation.svg|thumb|right|Milankovitch cycles.]] The climatic event was probably a result of predictable changes in the Earth's orbit ([[Milankovitch cycles]]) and a continuation of changes that caused the end of the last [[ice age|glacial period]].{{Citation needed|date=October 2007}}

The effect would have had the maximum heating of the Northern Hemisphere 9,000 years ago, when the axial tilt was 24° and the nearest approach to the Sun ([[perihelion]]) was during the Northern Hemisphere's summer. The calculated [[Milankovitch Forcing]] would have provided 0.2% more [[solar radiation]] (+40&nbsp;W/m<sup>2</sup>) to the Northern Hemisphere in summer, which tended to cause more heating. There seems to have been the predicted southward shift in the global band of thunderstorms, the [[Intertropical Convergence Zone]].{{Citation needed|date=November 2022}}

However, [[orbital forcing]] would predict maximum climate response several thousand years earlier than those observed in the Northern Hemisphere. The delay may be a result of the continuing changes in climate, as the Earth emerged from the last glacial period and related to [[ice–albedo feedback]]. Different sites often show climate changes at somewhat different times and lasting for different durations. At some locations, climate changes may have begun as early as 11,000 years ago or have persisted until 4,000 years ago. As noted above, the warmest interval in the far south significantly preceded warming in the north.{{Citation needed|date=November 2022}}

== Other changes == Significant temperature changes do not appear to have occurred at most low-latitude sites, but other climate changes have been reported, such as significantly wetter conditions in Africa, Australia and Japan and desert-like conditions in the [[Midwestern United States]]. Areas around the [[Amazon basin|Amazon]] show temperature increases and drier conditions.<ref name="mayle2004">{{cite journal | author=Francis E. Mayle, [[David J. Beerling]], William D. Gosling, Mark B. Bush | title=Responses of Amazonian ecosystems to climatic and atmospheric carbon dioxide changes since the Last Glacial Maximum | journal=Philosophical Transactions: Biological Sciences | year=2004 | volume=359 | issue=1443| pages=499–514 | doi=10.1098/rstb.2003.1434 | pmid=15212099 | pmc=1693334}}</ref>

==See also== * {{annotated link|8.2-kiloyear event}} * {{annotated link|Hockey stick graph (global temperature)}} * {{annotated link|Little Ice Age}} * {{annotated link|Medieval Warm Period}} * {{annotated link|Next glacial maximum}} * {{annotated link|Timeline of environmental history}} * {{annotated link|Younger Dryas}}

== References == {{reflist|2}}

{{DEFAULTSORT:Holocene Climatic Optimum}} [[Category:History of climate variability and change]] [[Category:Holocene]]

[[de:Atlantikum]]