Editing Solar cycle (section)

==== Climate ====
Both long-term and short-term variations in solar activity are proposed to potentially affect global climate, but it has proven challenging to show any link between solar variation and climate.<ref name="haigh">Joanna D. Haigh "[http://solarphysics.livingreviews.org/Articles/lrsp-2007-2/ The Sun and the Earth's Climate]", ''Living Reviews in Solar Physics'' (access date 31 January 2012)</ref>

Early research attempted to correlate weather with limited success,<ref name="spencer">{{Cite book | first=Spencer | last=Weart | author-link=Spencer Weart | title=The Discovery of Global Warming | chapter=Changing Sun, Changing Climate? | publisher=Harvard University Press | date=2003 | isbn=978-0-674-01157-1 | url=http://www.aip.org/history/climate/ | chapter-url=http://www.aip.org/history/climate/solar.htm | access-date=17 April 2008 | archive-date=4 August 2011 | archive-url=https://web.archive.org/web/20110804232058/http://www.aip.org/history/climate/ }}</ref> followed by attempts to correlate solar activity with global temperature. The cycle also impacts regional climate. Measurements from the SORCE's Spectral Irradiance Monitor show that solar UV variability produces, for example, colder winters in the U.S. and northern Europe and warmer winters in Canada and southern Europe during solar minima.<ref name="SolarForcing">{{cite journal | title=Solar forcing of winter climate variability in the Northern Hemisphere | journal=[[Nature Geoscience]] |date=October 9, 2011 |author=Ineson S. |author2=Scaife A.A. |author3=Knight J.R.|author4=Manners J.C. |author5=Dunstone N.J.|author6=Gray L.J. |author7=Haigh J.D. |volume=4 |pages=753–7 |doi=10.1038/ngeo1282 | issue=11|bibcode = 2011NatGe...4..753I | hdl=10044/1/18859 |url=http://spiral.imperial.ac.uk/bitstream/10044/1/18859/2/Nature%20Geoscience_4_11_2011.pdf |hdl-access=free }}</ref>

Three proposed mechanisms mediate solar variations' climate impacts:
* Total solar irradiance ("[[Radiative forcing]]").
* Ultraviolet irradiance. The UV component varies by more than the total, so if UV were for some (as yet unknown) reason having a disproportionate effect, this might affect climate.
* Solar wind-mediated galactic [[cosmic ray]] changes, which may affect cloud cover.

The solar cycle variation of 0.1% has small but detectable effects on the Earth's climate.<ref>{{cite journal |author=Labitzke K.|author2=Matthes K. |title=Eleven-year solar cycle variations in the atmosphere: observations, mechanisms and models |journal=The Holocene |volume=13 |issue=3 |pages=311–7 |date=2003 |doi=10.1191/0959683603hl623rp  |bibcode=2003Holoc..13..311L|s2cid=129100529 }}</ref><ref>Pablo J.D. Mauas & Andrea P. Buccino. "[https://arxiv.org/abs/1003.0414 Long-term solar activity influences on South American rivers]" page 5. Journal of Atmospheric and Solar-Ter
restrial Physics on Space Climate, March 2010. Accessed: 20 September 2014.</ref><ref>{{cite journal | last1 = Zanchettin | first1 = D. | last2 = Rubino | first2 = A. | last3 = Traverso | first3 = P. | last4 = Tomasino | first4 = M. | date = 2008 | title = [Impact of variations in solar activity on hydrological decadal patterns in northern Italy] | journal = Journal of Geophysical Research | volume = 113 | issue = D12 | page = D12102 | doi = 10.1029/2007JD009157 | bibcode=2008JGRD..11312102Z| s2cid = 54975234 | doi-access = free }}</ref> Camp and Tung suggest that solar irradiance correlates with a variation of 0.18&nbsp;K ±0.08&nbsp;K (0.32&nbsp;°F ±0.14&nbsp;°F) in measured average global temperature between solar maximum and minimum.<ref name="solar-climate">{{cite journal |author=C. D. Camp|author2=K. K. Tung|name-list-style=amp |journal=Geophysical Research Letters |volume=34 |issue= 14|pages= L14703 | title=Surface warming by the solar cycle as revealed by the composite mean difference projection |date=2007 |doi= 10.1029/2007GL030207  |bibcode=2007GeoRL..3414703C|s2cid=16596423|doi-access=free}}</ref>

Other effects include one study which found a relationship with wheat prices,<ref>[https://www.newscientist.com/article.ns?id=dn6680 Sunspot activity impacts on crop success] [[New Scientist]], 18 November 2004</ref> and another one that found a weak correlation with the flow of water in the [[Paraná River]].<ref>[https://www.newscientist.com/channel/earth/mg20026814.100-sunspot-activity-may-be-linked-to-rainfall.html "Sunspot activity may be linked to rainfall"], [[New Scientist]], 8 Nov., 2008, p. 10.</ref> Eleven-year cycles have been found in tree-ring thicknesses<ref name=Luthardt2017 /> and layers at the bottom of a lake<ref name=NeoP /> hundreds of millions of years ago.

The current [[scientific consensus on climate change]] is that solar variations only play a marginal role in driving [[global climate change]],<ref name="haigh" /> since the measured magnitude of recent solar variation is much smaller than the forcing due to greenhouse gases.<ref name="grida fig6-6">{{Cite book | editor1-first=J.T. | editor1-last=Houghton | editor1-link=John T. Houghton | editor2-first=Y. | editor2-last=Ding | editor3-first=D.J. | editor3-last=Griggs | editor4-first=M. | editor4-last=Noguer | title=Climate Change 2001: Working Group I: The Scientific Basis | url=http://www.grida.no/climate/ipcc_tar/wg1/index.htm | date=2001 | publisher=[[Intergovernmental Panel on Climate Change]] | chapter=6.11 Total Solar Irradiance—Figure 6.6: Global, annual mean radiative forcings (1750 to present) | chapter-url=http://www.grida.no/climate/ipcc_tar/wg1/fig6-6.htm | access-date=15 April 2007}}; see also the IPCC Fourth Assessment Report, in which the magnitude of variation in solar irradiance was revised downward, although the evidence of connections between solar variation and certain aspects of climate increased over the same time period: [http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-7.html#2-7-1 Assessment Report-4, Working group 1, chapter 2] {{Webarchive|url=https://web.archive.org/web/20131207151831/http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-7.html#2-7-1 |date=2013-12-07 }}</ref> Also, average solar activity in the 2010s was no higher than in the 1950s (see above), whereas average global temperatures had risen markedly over that period. Otherwise, the level of understanding of solar impacts on weather is low.<ref>{{Citation
 | year=2007
 | isbn=978-0-521-88009-1
 | chapter=Changes in Atmospheric Constituents and Radiative Forcing: §&nbsp;2.9.1 Uncertainties in Radiative Forcing
 | chapter-url=https://archive.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-9-1.html#table-2-11
  | title=Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007
  | url=https://archive.ipcc.ch/publications_and_data/ar4/wg1/en/ch2.html
  | author1=Forster, P. |author2=V. Ramaswamy |author3=P. Artaxo |author4=T. Berntsen |author5=R. Betts |author6=D.W. Fahey |author7=J. Haywood |author8=J. Lean |author9=D.C. Lowe |author10=G. Myhre |author11=J. Nganga |author12=R. Prinn |author13=G. Raga |author14=M. Schulz |author15=R. Van Dorland
| publisher=Cambridge University Press
 |editor=Solomon, S. |editor2=D. Qin |editor3=M. Manning |editor4=Z. Chen |editor5=M. Marquis |editor6=K.B. Averyt |editor7=M. Tignor |editor8=H.L. Miller
  }}</ref>

Solar variations also affect the [[orbital decay]] of objects in [[low Earth orbit]] (LEO) by altering the density of the upper [[thermosphere]].<ref name=sair>{{cite journal |last=Molaverdikhani|first=Karan|author2=Ajabshirizadeh, A.|title=Complexity of the Earth's space–atmosphere interaction region (SAIR) response to the solar flux at 10.7 cm as seen through the evaluation of five solar cycle two-line element (TLE) records|journal=Advances in Space Research|date=2016|volume=58|issue=6|pages=924–937
|doi=10.1016/j.asr.2016.05.035 |bibcode= 2016AdSpR..58..924M|doi-access=free}}</ref>