Editing Climate variability and change (section)

== Impacts ==

=== Life ===
[[File:Aridity ice age vs early holocene vs modern.jpg|thumb|upright=1.35|right|''Top:'' [[Arid]] ice age climate{{Clear}}''Middle:'' [[Atlantic period|Atlantic Period]], warm and wet{{Clear}}''Bottom:'' Potential vegetation in climate now if not for human effects like agriculture.<ref name="OakRidge-1997">{{cite web | editor1-last=Adams | editor1-first=J.M. | editor2-last=Faure | editor2-first=H. | year=1997 | url=http://www.esd.ornl.gov/projects/qen/nerc.html | title=Global land environments since the last interglacial | publisher=Oak Ridge National Laboratory | location=Tennessee | url-status=dead | archive-url=https://web.archive.org/web/20080116122058/http://www.esd.ornl.gov/projects/qen/nerc.html | archive-date=16 January 2008 | df=dmy-all }} QEN members.</ref>]]

==== Vegetation ====
A change in the type, distribution and coverage of vegetation may occur given a change in the climate. Some changes in climate may result in increased precipitation and warmth, resulting in improved plant growth and the subsequent sequestration of airborne CO<sub>2</sub>. Though an increase in CO<sub>2</sub> may benefit plants, some factors can diminish this increase. If there is an environmental change such as drought, increased CO<sub>2</sub>  concentrations will not benefit the plant.<ref>{{Cite journal |last=Swann |first=Abigail L. S. |date=2018-06-01 |title=Plants and Drought in a Changing Climate |url=https://doi.org/10.1007/s40641-018-0097-y |journal=Current Climate Change Reports |language=en |volume=4 |issue=2 |pages=192–201 |doi=10.1007/s40641-018-0097-y |bibcode=2018CCCR....4..192S |issn=2198-6061}}</ref> So even though climate change does increase CO<sub>2</sub>  emissions, plants will often not use this increase as other environmental stresses put pressure on them.<ref>{{Cite journal |last1=Ainsworth |first1=E. A. |last2=Lemonnier |first2=P. |last3=Wedow |first3=J. M. |date=January 2020 |editor-last=Tausz-Posch |editor-first=S. |title=The influence of rising tropospheric carbon dioxide and ozone on plant productivity |journal=Plant Biology |language=en |volume=22 |issue=S1 |pages=5–11 |doi=10.1111/plb.12973 |issn=1435-8603 |pmc=6916594 |pmid=30734441|bibcode=2020PlBio..22S...5A }}</ref> However, sequestration of CO<sub>2</sub> is expected to affect the rate of many natural cycles like [[plant litter]] decomposition rates.<ref>{{cite journal |last1=Ochoa-Hueso |first1=R |last2=Delgado-Baquerizo |first2=N |last3=King |first3=PTA |last4=Benham |first4=M |last5=Arca |first5=V |last6=Power |first6=SA |title=Ecosystem type and resource quality are more important than global change drivers in regulating early stages of litter decomposition |journal=Soil Biology and Biochemistry |date=2019 |volume=129 |pages=144–52 |doi=10.1016/j.soilbio.2018.11.009 |bibcode=2019SBiBi.129..144O |hdl=10261/336676 |s2cid=92606851 |hdl-access=free }}</ref> A gradual increase in warmth in a region will lead to earlier flowering and fruiting times, driving a change in the timing of life cycles of dependent organisms. Conversely, cold will cause plant bio-cycles to lag.<ref>{{cite web |last=Kinver |first=Mark |date=15 November 2011 |title=UK trees' fruit ripening '18 days earlier' |publisher=Bbc.co.uk |url=https://www.bbc.co.uk/news/science-environment-15721263 |access-date=1 November 2012 |archive-date=17 March 2023 |archive-url=https://web.archive.org/web/20230317140816/https://www.bbc.co.uk/news/science-environment-15721263 |url-status=live }}</ref>

Larger, faster or more radical changes, however, may result in vegetation stress, rapid plant loss and [[desertification]] in certain circumstances.<ref name="Sahney-2010">{{cite journal |last1=Sahney |first1=S. |last2=Benton |first2=M.J. |last3=Falcon-Lang |first3=H.J. |year=2010 |title=Rainforest collapse triggered Pennsylvanian tetrapod diversification in Euramerica |journal=Geology |doi=10.1130/G31182.1 |bibcode=2010Geo....38.1079S |volume=38 |issue=12 |pages=1079–82 |url=https://www.academia.edu/368820 |format=PDF |access-date=27 November 2013 |archive-date=17 March 2023 |archive-url=https://web.archive.org/web/20230317140814/https://www.academia.edu/368820 |url-status=live }}</ref><ref>{{cite journal |last1=Bachelet |first1=D. |author-link1=Dominique Bachelet|last2=Neilson |first2=R. |last3=Lenihan |first3=J. M. |last4=Drapek |first4=R.J. |year=2001 |title=Climate Change Effects on Vegetation Distribution and Carbon Budget in the United States |journal=[[Ecosystems]] |doi=10.1007/s10021-001-0002-7 |volume=4 |issue=3 |pages=164–85 |bibcode=2001Ecosy...4..164B |s2cid=15526358 }}</ref><ref>{{Cite journal |last1=Ridolfi |first1=Luca |last2=D'Odorico |first2=P. |last3=Porporato |first3=A. |last4=Rodriguez-Iturbe |first4=I. |date=2000-07-27 |title=Impact of climate variability on the vegetation water stress |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2000JD900206 |journal=Journal of Geophysical Research: Atmospheres |language=en |volume=105 |issue=D14 |pages=18013–18025 |doi=10.1029/2000JD900206 |bibcode=2000JGR...10518013R |issn=0148-0227}}</ref> An example of this occurred during the [[Carboniferous Rainforest Collapse]] (CRC), an extinction event 300 million years ago. At this time vast rainforests covered the equatorial region of Europe and America. Climate change devastated these tropical rainforests, abruptly fragmenting the habitat into isolated 'islands' and causing the extinction of many plant and animal species.<ref name="Sahney-2010" />

==== Wildlife ====
One of the most important ways animals can deal with climatic change is migration to warmer or colder regions.{{Sfn|Burroughs|2007|p=273}} On a longer timescale, evolution makes ecosystems including animals better adapted to a new climate.<ref>{{Cite journal|last1=Millington|first1=Rebecca|last2=Cox|first2=Peter M.|last3=Moore|first3=Jonathan R.|last4=Yvon-Durocher|first4=Gabriel|date=10 May 2019|title=Modelling ecosystem adaptation and dangerous rates of global warming|journal=Emerging Topics in Life Sciences|language=en|volume=3|issue=2|pages=221–31|doi=10.1042/ETLS20180113|pmid=33523155|issn=2397-8554|hdl=10871/36988|s2cid=150221323|hdl-access=free}}</ref> Rapid or large climate change can cause [[mass extinctions]] when creatures are stretched too far to be able to adapt.{{Sfn|Burroughs|2007|p=267}}

==== Humanity ====
Collapses of past civilizations such as the [[Maya civilization|Maya]] may be related to cycles of precipitation, especially drought, that in this example also correlates to the [[Western Hemisphere Warm Pool]]. Around 70 000 years ago the [[Toba Volcano|Toba supervolcano]] eruption created an especially cold period during the ice age, leading to a possible [[Toba bottleneck|genetic bottleneck]] in human populations.

=== Changes in the cryosphere ===

==== Glaciers and ice sheets ====
[[Glacier]]s are considered among the most sensitive indicators of a changing climate.<ref name="Seiz-2007">{{cite report|last=Seiz |first=G. |author2=N. Foppa |title=The activities of the World Glacier Monitoring Service (WGMS) |year=2007 |url=http://www.meteoswiss.admin.ch/web/en/climate/climate_international/gcos/inventory/wgms.Par.0008.DownloadFile.tmp/gcosreportwgmse.pdf |access-date=21 June 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090325100331/http://www.meteoswiss.admin.ch/web/en/climate/climate_international/gcos/inventory/wgms.Par.0008.DownloadFile.tmp/gcosreportwgmse.pdf |archive-date=25 March 2009 }}</ref> Their size is determined by a [[mass balance]] between snow input and melt output. As temperatures increase, glaciers retreat unless snow precipitation increases to make up for the additional melt. Glaciers grow and shrink due both to natural variability and external forcings. Variability in temperature, precipitation and hydrology can strongly determine the evolution of a glacier in a particular season.

The most significant climate processes since the middle to late [[Pliocene]] (approximately 3 million years ago) are the glacial and [[interglacial]] cycles. The present interglacial period (the [[Holocene]]) has lasted about 11,700 years.<ref name="ICS-2008">{{cite web|url=http://www.stratigraphy.org/column.php?id=Chart/Time%20Scale|title=International Stratigraphic Chart|year=2008|publisher=International Commission on Stratigraphy|access-date=3 October 2011|url-status=dead|archive-url=https://web.archive.org/web/20111015042711/http://www.stratigraphy.org/column.php?id=Chart%2FTime%20Scale|archive-date=15 October 2011}}</ref> Shaped by [[Milankovitch cycles|orbital variations]], responses such as the rise and fall of [[Continental climate|continental]] ice sheets and significant sea-level changes helped create the climate. Other changes, including [[Heinrich event]]s, [[Dansgaard–Oeschger event]]s and the [[Younger Dryas]], however, illustrate how glacial variations may also influence climate without the [[orbital forcing]].

==== Sea level change ====
During the [[Last Glacial Maximum]], some 25,000 years ago, sea levels were roughly 130 m lower than today. The deglaciation afterwards was characterized by rapid sea level change.{{Sfn|Burroughs|2007|p=279}} In the early [[Pliocene]], global temperatures were 1–2˚C warmer than the present temperature, yet sea level was 15–25 meters higher than today.<ref>{{cite web|url=http://www.giss.nasa.gov/research/briefs/hansen_15/|archive-url=https://web.archive.org/web/20110724050602/http://www.giss.nasa.gov/research/briefs/hansen_15/|url-status=dead|archive-date=24 July 2011|title=Science Briefs: Earth's Climate History|last=Hansen|first=James|publisher=NASA GISS|access-date=25 April 2013}}</ref>

==== Sea ice ====
[[Sea ice]] plays an important role in Earth's climate as it affects the total amount of sunlight that is reflected away from the Earth.<ref>{{Cite journal|last1=Belt|first1=Simon T.|last2=Cabedo-Sanz|first2=Patricia|last3=Smik|first3=Lukas|last4=Navarro-Rodriguez|first4=Alba|last5=Berben|first5=Sarah M. P.|last6=Knies|first6=Jochen|last7=Husum|first7=Katrine|display-authors=3|date=2015|title=Identification of paleo Arctic winter sea ice limits and the marginal ice zone: Optimised biomarker-based reconstructions of late Quaternary Arctic sea ice|journal=Earth and Planetary Science Letters|volume=431|pages=127–39|doi=10.1016/j.epsl.2015.09.020|bibcode=2015E&PSL.431..127B|issn=0012-821X|hdl=10026.1/4335|hdl-access=free}}</ref> In the past, the Earth's oceans have been almost entirely covered by sea ice on a number of occasions, when the Earth was in a so-called [[Snowball Earth]] state,<ref>{{Cite journal|last1=Warren|first1=Stephen G.|last2=Voigt|first2=Aiko|last3=Tziperman|first3=Eli|last4=Sadler|first4=Peter M.|last5=Rose|first5=Catherine V.|last6=Rose|first6=Brian E. J.|last7=Ramstein|first7=Gilles|last8=Partin|first8=Camille A.|last9=Maloof|first9=Adam C.|display-authors=3|date=1 November 2017|title=Snowball Earth climate dynamics and Cryogenian geology-geobiology|journal=Science Advances|volume=3|issue=11|pages=e1600983|doi=10.1126/sciadv.1600983|pmid=29134193|issn=2375-2548|pmc=5677351|bibcode=2017SciA....3E0983H}}</ref> and completely ice-free in periods of warm climate.<ref>{{Cite journal|last1=Caballero|first1=R.|last2=Huber|first2=M.|date=2013|title=State-dependent climate sensitivity in past warm climates and its implications for future climate projections|journal=Proceedings of the National Academy of Sciences|volume=110|issue=35|pages=14162–67|doi=10.1073/pnas.1303365110|pmid=23918397|pmc=3761583|bibcode=2013PNAS..11014162C|issn=0027-8424|doi-access=free}}</ref> When there is a lot of sea ice present globally, especially in the tropics and subtropics, the climate is [[Climate sensitivity|more sensitive to forcings]] as the [[ice–albedo feedback]] is very strong.<ref>{{Cite journal|last1=Hansen James|last2=Sato Makiko|last3=Russell Gary|last4=Kharecha Pushker|date=2013|title=Climate sensitivity, sea level and atmospheric carbon dioxide|journal=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences|volume=371|issue=2001|pages=20120294|doi=10.1098/rsta.2012.0294|pmc=3785813|pmid=24043864|arxiv=1211.4846|bibcode=2013RSPTA.37120294H}}</ref>