Solar activity and climate#Correlations to solar cycle length

{{See also|Sun#Life phases}}

Earth formed around 4.54 billion years ago{{cite web

| date=1997 | title=Age of the Earth

| url=http://pubs.usgs.gov/gip/geotime/age.html

| publisher=U.S. Geological Survey

| access-date=2006-01-10

| archive-url= https://web.archive.org/web/20051223072700/http://pubs.usgs.gov/gip/geotime/age.html| archive-date= 23 December 2005 | url-status= live}}{{cite journal

| last=Dalrymple | first=G. Brent

| title=The age of the Earth in the twentieth century: a problem (mostly) solved | journal=Special Publications, Geological Society of London

| date=2001 | volume=190

| issue=1 | pages=205–221

| doi=10.1144/GSL.SP.2001.190.01.14 |bibcode = 2001GSLSP.190..205D | s2cid=130092094

}}

{{cite journal

| author= Manhesa, Gérard| author2= Allègre, Claude J.| author3= Dupréa, Bernard| author4= Hamelin, Bruno

| name-list-style= amp | title=Lead isotope study of basic-ultrabasic layered complexes: Speculations about the age of the earth and primitive mantle characteristics

| journal=Earth and Planetary Science Letters

| date=1980 | volume=47

| issue= 3 | pages=370–382

| doi=10.1016/0012-821X(80)90024-2

| bibcode=1980E&PSL..47..370M

}} by accretion from the solar nebula. Volcanic outgassing probably created the primordial atmosphere, which contained almost no oxygen and would have been toxic to humans and most modern life. Much of the Earth was molten because of frequent collisions with other bodies which led to extreme volcanism. Over time, the planet cooled and formed a solid crust, eventually allowing liquid water to exist on the surface.

Three to four billion years ago the Sun emitted only 70% of its current power.{{Cite web|url=http://faculty.wcas.northwestern.edu/~infocom/The%20Website/evolution.html|title=The Sun's Evolution}} Under the present atmospheric composition, this past solar luminosity would have been insufficient to prevent water from uniformly freezing. There is nonetheless evidence that liquid water was already present in the Hadean{{cite journal|doi = 10.2138/rmg.2006.62.18|title = Water in the Early Earth|year = 2006|author = Marty, B.|journal = Reviews in Mineralogy and Geochemistry|volume = 62|issue = 1|pages = 421–450|bibcode = 2006RvMG...62..421M}}{{cite journal |doi = 10.1126/science.1110873|title = Zircon Thermometer Reveals Minimum Melting Conditions on Earliest Earth|year = 2005|last1 = Watson|first1 = E. B.|journal = Science|volume = 308|issue = 5723|pages = 841–844|pmid = 15879213|last2 = Harrison|first2 = TM|bibcode = 2005Sci...308..841W|s2cid = 11114317}} and Archean{{cite journal |doi = 10.1130/0091-7613(1994)022<1067:SWIISL>2.3.CO;2|title = Surface-water influx in shallow-level Archean lode-gold deposits in Western, Australia|year = 1994|last1 = Hagemann|first1 = Steffen G.|last2 = Gebre-Mariam|first2 = Musie|last3 = Groves|first3 = David I.|journal = Geology|volume = 22|issue = 12|pages = 1067|bibcode = 1994Geo....22.1067H}} eons, leading to what is known as the faint young Sun paradox.{{cite journal |last = Sagan|first = C.|author2 = G. Mullen|title = Earth and Mars: Evolution of Atmospheres and Surface Temperatures|journal = Science|volume = 177|issue = 4043|pages = 52–56|year = 1972|doi = 10.1126/science.177.4043.52|pmid = 17756316|bibcode = 1972Sci...177...52S|s2cid = 12566286}} Hypothesized solutions to this paradox include a vastly different atmosphere, with much higher concentrations of greenhouse gases than currently exist.{{cite journal |doi = 10.1126/science.276.5316.1217|title = The Early Faint Sun Paradox: Organic Shielding of Ultraviolet-Labile Greenhouse Gases|year = 1997|last1 = Sagan|first1 = C.|journal = Science|volume = 276|issue = 5316|pages = 1217–1221|pmid = 11536805|last2 = Chyba|first2 = C|bibcode = 1997Sci...276.1217S}}

Over the following approximately 4 billion years, the Sun's energy output increased and the composition of the Earth atmosphere changed. The Great Oxygenation Event around 2.4 billion years ago was the most notable alteration of the atmosphere. Over the next five billion years, the Sun's ultimate death as it becomes a very bright red giant and then a very faint white dwarf will have dramatic effects on climate, with the red giant phase likely already ending any life on Earth.

{{Main|Solar observation}}

Since 1978, solar irradiance has been directly measured by satellites with very good accuracy.{{cite book|year=2008 |title=Understanding and responding to climate change: Highlights of National Academies Reports |edition=2008 |publisher=National Academy of Sciences |location=500 Fifth St. N.W., Washington, D.C. 20001 |author=US National Research Council |url=http://americasclimatechoices.org/climate_change_2008_final.pdf |access-date=2011-05-20 |url-status=dead |archive-url=https://web.archive.org/web/20110717112225/http://americasclimatechoices.org/climate_change_2008_final.pdf |archive-date=July 17, 2011 }}{{Rp|6|date = November 2012}} These measurements indicate that the Sun's total solar irradiance fluctuates by +-0.1% over the ~11 years of the solar cycle, but that its average value has been stable since the measurements started in 1978. Solar irradiance before the 1970s is estimated using proxy variables, such as tree rings, the number of sunspots, and the abundances of cosmogenic isotopes such as ¹⁰Be,{{cite web|url=http://web.sahra.arizona.edu/programs/isotopes/beryllium.html|title=Beryllium: Isotopes and Hydrology|publisher=University of Arizona, Tucson|access-date=10 April 2011|archive-date=5 October 2018|archive-url=https://web.archive.org/web/20181005215904/http://web.sahra.arizona.edu/programs/isotopes/beryllium.html|url-status=dead}} all of which are calibrated to the post-1978 direct measurements.{{cite web

|date = November 2009|author1=Simmon, R. |author2=D. Herring |name-list-style=amp |title = Notes for slide number 5 titled "Over 100 years of total solar irradiance data," in presentation, "Human contributions to global climate change"|url = http://www.climate.gov/#understandingClimate/presentationLibrary|publisher = Presentation library on the U.S. National Oceanic and Atmospheric Administration's Climate Services website|access-date = 2011-06-23|archive-url = https://web.archive.org/web/20110703210729/http://www.climate.gov/|archive-date = 3 July 2011 |url-status = live}}File:Evidence_of_human-induced_global_warming_-_patterns_of_temperature_change_produced_by_various_atmospheric_factors,_1958-1999_(USGCRP).png

Solar activity has been on a declining trend since the 1960s, as indicated by solar cycles 19–24, in which the maximum number of sunspots were 201, 111, 165, 159, 121 and 82, respectively.{{cite web|title = Sunspot numbers|url = http://www.sidc.be/silso/datafiles|website = SILSO Data Files|publisher = Royal Observatory of Belgium, Brussels|access-date = 29 July 2014}} In the three decades following 1978, the combination of solar and volcanic activity is estimated to have had a slight cooling influence.{{sfn|Karl|Melillo|Peterson|2009|page = 15–16}} A 2010 study found that the composition of solar radiation might have changed slightly, with in an increase of ultraviolet radiation and a decrease in other wavelengths."{{cite journal

|issn = 0028-0836|volume = 467|issue = 7316|pages = 696–699|last1 = Haigh|first1 = Joanna D.|first2 = Ann R.|last2 = Winning|first3 = Ralf|last3 = Toumi|first4 = Jerald W.|last4 = Harder|title = An influence of solar spectral variations on radiative forcing of climate|journal = Nature|date = 2010-10-07|doi = 10.1038/nature09426|quote = Currently there is insufficient observational evidence to validate the spectral variations observed by SIM, or to fully characterize other solar cycles, but our findings raise the possibility that the effects of solar variability on temperature throughout the atmosphere may be contrary to current expectations.|pmid = 20930841|bibcode = 2010Natur.467..696H|hdl = 10044/1/18858|s2cid = 4320984|hdl-access = free}}

In the modern era, the Sun has operated within a sufficiently narrow band that climate has been little affected. Models indicate that the combination of solar variations and volcanic activity can explain periods of relative warmth and cold between A.D. 1000 and 1900.

Numerous paleoenvironmental reconstructions have looked for relationships between solar variability and climate. Arctic paleoclimate, in particular, has linked total solar irradiance variations and climate variability. A 2001 paper identified a ~1500 year solar cycle that was a significant influence on North Atlantic climate throughout the Holocene.{{cite journal |author=Bond|display-authors=etal|title=Persistent Solar Influence on North Atlantic Climate During the Holocene|journal=Science |volume=294 | issue=5549 |pages=2130–2136|doi=10.1126/science.1065680|pmid=11739949|date=2001-12-07|bibcode=2001Sci...294.2130B|s2cid=38179371|doi-access=free}}

{{Main|Little Ice Age}}

One historical long-term correlation between solar activity and climate change is the 1645–1715 Maunder minimum, a period of little or no sunspot activity which partially overlapped the "Little Ice Age" during which cold weather prevailed in Europe. The Little Ice Age encompassed roughly the 16th to the 19th centuries.H. H. Lamb, "The cold Little Ice Age climate of about 1550 to 1800," in {{cite book|author=H. H. Lamb|title=Fundamentals and Climate Now|url={{google books |plainurl=y |id=-lJ6XesnYYAC|page=107}}|year=1972|publisher=Psychology Press|isbn=978-0-416-11530-7 |page=107}}{{cite book |author=Emmanuel Le Roy Ladurie |title=Times of Feast, Times of Famine: a History of Climate Since the Year 1000 |publisher=Doubleday |location=Garden City, NY |year=1971 |oclc=164590 |others=Barbara Bray |isbn= 978-0-374-52122-6}}{{cite web|url=http://www.solarstorms.org/SClimate.html|title=Environment|work=solarstorms.org|date=2017-04-16}} Whether the low solar activity or other factors caused the cooling is debated.

The Spörer Minimum between 1460 and 1550 was matched to a significant cooling period.{{cite book|title=The general crisis of the seventeenth century|url={{google books |plainurl=y |id=HGLs23umDXAC|page=287}}|first1=Geoffrey |last1=Parker |first2=Lesley M. |last2=Smith|publisher=Routledge|pages=287, 288|isbn=978-0-415-16518-1|year=1997}}

A 2012 paper instead linked the Little Ice Age to volcanism, through an "unusual 50-year-long episode with four large sulfur-rich explosive eruptions," and claimed "large changes in solar irradiance are not required" to explain the phenomenon.{{cite journal |author=Miller |title=Abrupt onset of the Little Ice Age triggered by volcanism and sustained by sea-ice/ocean feedbacks |journal=Geophysical Research Letters |volume=39 |issue=2 |pages=L02708 |date= January 31, 2012 |doi=10.1029/2011GL050168 |display-authors=etal |bibcode=2012GeoRL..39.2708M|s2cid=15313398 |doi-access=free }}

A 2010 paper suggested that a new 90-year period of low solar activity would reduce global average temperatures by about 0.3 °C, which would be far from enough to offset the increased forcing from greenhouse gases.{{cite news|url=https://www.newscientist.com/article/mg20527494.700-a-quiet-sun-wont-save-us-from-global-warming.html|title=A quiet sun won't save us from global warming|date=26 February 2010|work=New Scientist|access-date=7 June 2011}}

{{multiple image|direction=vertical|width=220| footer = Multiple factors have affected terrestrial climate change, including natural climate variability and human influences such as greenhouse gas emissions and land use change on top of any effects of solar variability.|image1=NASAdata1979to2009.jpg|caption1=1979–2009: Over the past 3 decades, terrestrial temperature has not correlated with sunspot trends. The top plot is of sunspots, while below is the global atmospheric temperature trend. El Chichón and Pinatubo were volcanoes, while El Niño is part of ocean variability. The effect of greenhouse gas emissions is on top of those fluctuations.}}

The link between recent solar activity and climate has been quantified and is not a major driver of the warming that has occurred since early in the twentieth century.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 Human-induced forcings are needed to reproduce the late-20th century warming.{{cite book

|year = 2006|chapter = 10. Climate Forcings and Climate Models|title = Surface Temperature Reconstructions for the Last 2,000 Years|publisher = National Academies of Sciences, Engineering, and Medicine|location = Washington, D.C., USA|vauthors = ((Committee on Surface Temperature Reconstructions for the Last 2,000 Years)), ((US National Research Council))|chapter-url = http://books.nap.edu/openbook.php?record_id=11676&page=109|page = 109|isbn = 978-0-309-66144-7|access-date = 2011-06-23|doi = 10.17226/11676}} Some studies associate solar cycle-driven irradiation increases with part of twentieth century warming.{{cite news|title = NASA Study Finds Increasing Solar Trend That Can Change Climate|year = 2003|url = http://www.nasa.gov/centers/goddard/news/topstory/2003/0313irradiance.html|access-date = 2015-08-14|archive-date = 2009-12-29|archive-url = https://web.archive.org/web/20091229205726/http://www.nasa.gov/centers/goddard/news/topstory/2003/0313irradiance.html|url-status = dead}}{{cite journal |doi = 10.1029/2009GL038429|title = Cosmic ray decreases affect atmospheric aerosols and clouds|year = 2009|last1 = Svensmark|first1 = Henrik|last2 = Bondo|first2 = Torsten|last3 = Svensmark|first3 = Jacob|journal = Geophysical Research Letters|volume = 36|issue = 15|pages = n/a|bibcode = 2009GeoRL..3615101S|citeseerx = 10.1.1.394.9780| s2cid=15963013 }}

Three mechanisms are proposed by which solar activity affects climate:

• Solar irradiance changes directly affecting the climate ("radiative forcing"). This is generally considered to be a minor effect, as the measured amplitudes of the variations are too small to have significant effect, absent some amplification process.{{cite press release | title=Changes in Solar Brightness Too Weak To Explain Global Warming | publisher=UCAR | url=http://www.ucar.edu/news/releases/2006/brightness.shtml | date=13 September 2006 | access-date=18 April 2007 | url-status=dead | archive-url=https://web.archive.org/web/20111121174637/http://www.ucar.edu/news/releases/2006/brightness.shtml | archive-date=21 November 2011 }}
• Variations in the ultraviolet component. The UV component varies by more than the total, so if UV were for some (as yet unknown) reason to have a disproportionate effect, this might explain a larger solar signal.
• Effects mediated by changes in galactic cosmic rays (which are affected by the solar wind) such as changes in cloud cover.

Climate models have been unable to reproduce the rapid warming observed in recent decades when they only consider variations in total solar irradiance and volcanic activity. Hegerl et al. (2007) concluded that greenhouse gas forcing had "very likely" caused most of the observed global warming since the mid-20th century. In making this conclusion, they allowed for the possibility that climate models had been underestimating the effect of solar forcing.{{cite book|last1=Hegerl |first1=Gabriele C. |last2=Zwiers |first2=Francis W. |last3=Braconnot |first3=Pascale |last4=Gillett |first4=Nathan P. |last5=Luo |first5=Yong |last6=Marengo Orsini |first6=Jose A. |last7=Nicholls |first7=Neville |last8=Penner |first8=Joyce E. |author-link8=Joyce E. Penner|last9=Stott |first9=Peter A. |chapter=Understanding and Attributing Climate Change |url=https://www.ipcc.ch/site/assets/uploads/2018/02/ar4-wg1-chapter9-1.pdf |title=Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change |editor1-last=Solomon |editor1-first=Susan |editor2-last=Qin |editor2-first=Dahe |editor3-last=Manning |editor3-first=Martin |editor4-last=Marquis |editor4-first=Melinda |editor5-last=Averyt |editor5-first=Kristen |editor-link5=Kristen Averyt|editor6-last=Tignor |editor6-first=Melinda M.B. |editor7-last=Miller Jr. |editor7-first=Henry LeRoy |editor8-last=Chen |editor8-first=Zhenlin |publisher=Cambridge University Press |location=Cambridge, U.K. and New York, N.Y. |date=2007 |access-date=November 10, 2020}}

Another line of evidence comes from looking at how temperatures at different levels in the Earth's atmosphere have changed.{{cite web

|date = November 2009|author1=Simmon, R. |author2=D. Herring |name-list-style=amp |title = Notes for slide number 7, titled "Satellite evidence also suggests greenhouse gas warming," in presentation, "Human contributions to global climate change"|url = http://www.climate.gov/#understandingClimate/presentationLibrary|publisher = Presentation library on the U.S. National Oceanic and Atmospheric Administration's Climate Services website|access-date = 2011-06-23|archive-url = https://web.archive.org/web/20110703210729/http://www.climate.gov/|archive-date = 3 July 2011 |url-status = live}} Models and observations show that greenhouse gas results in warming of the troposphere, but cooling of the stratosphere.Hegerl et al., [http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch9.html Chapter 9: Understanding and Attributing Climate Change] {{Webarchive|url=https://web.archive.org/web/20111128182203/http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch9.html |date=2011-11-28 }}, [http://www.ipcc.ch/publications_and_data/ar4/wg1/en/faq-9-2.html Frequently Asked Question 9.2: Can the Warming of the 20th century be Explained by Natural Variability?] {{Webarchive|url=https://web.archive.org/web/20181120014906/http://www.ipcc.ch/publications_and_data/ar4/wg1/en/faq-9-2.html |date=2018-11-20 }} Depletion of the ozone layer by chemical refrigerants stimulated a stratospheric cooling effect. If the Sun was responsible for observed warming, warming of the troposphere at the surface and warming at the top of the stratosphere would be expected as the increased solar activity would replenish ozone and oxides of nitrogen.{{sfn|Karl|Melillo|Peterson|2009|page = 20}}

The assessment of the solar activity/climate relationship involves multiple, independent lines of evidence.

File:Temp-sunspot-co2.svg

Early research attempted to find a correlation between weather and sunspot activity, mostly without notable success.{{Cite book | first=Spencer | last=Weart | author-link=Spencer R. Weart | title=The Discovery of Global Warming | chapter=Changing Sun, Changing Climate? | publisher=Harvard University Press | year=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/ | url-status=dead }}{{cite book |author=Fritts, Harold C. |title=Tree rings and climate |publisher=Academic Press |location=Boston |year=1976 |isbn=978-0-12-268450-0 }} Later research has concentrated more on correlating solar activity with global temperature.

File:Solar Forcing GISS model.gif

Accurate measurement of solar forcing is crucial to understanding possible solar impact on terrestrial climate. Accurate measurements only became available during the satellite era, starting in the late 1970s, and even that is open to some residual disputes: different teams find different values, due to different methods of cross-calibrating measurements taken by instruments with different spectral sensitivity.{{Cite web |url=http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-7-1-1.html |title=Archived copy |access-date=2015-08-11 |archive-date=2015-09-24 |archive-url=https://web.archive.org/web/20150924123506/http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-7-1-1.html |url-status=dead }} Scafetta and Willson argue for significant variations of solar luminosity between 1980 and 2000,{{cite journal |first1=Nicola |last1=Scafetta |first2=Richard |last2=Willson |title=ACRIM-gap and Total Solar Irradiance (TSI) trend issue resolved using a surface magnetic flux TSI proxy model |journal=Geophysical Research Letters |volume=36 |pages=L05701 |year=2009 |doi=10.1029/2008GL036307 |bibcode=2009GeoRL..36.5701S |issue=5|s2cid=7160875 |doi-access=free }} but Lockwood and Frohlich{{cite journal |first1=Mike |last1=Lockwood |first2=Claus |last2=Fröhlich |title=Recent oppositely directed trends in solar climate forcings and the global mean surface air temperature. II. Different reconstructions of the total solar irradiance variation and dependence on response time scale |journal=Proceedings of the Royal Society A |volume=464 |issue=2094 |pages=1367–1385 |date=8 June 2008 |doi=10.1098/rspa.2007.0347 |bibcode=2008RSPSA.464.1367L|s2cid=131159896 }} find that solar forcing declined after 1987.

The 2001 Intergovernmental Panel on Climate Change (IPCC) Third Assessment Report (TAR) concluded that the measured impact of recent solar variation is much smaller than the amplification effect due to greenhouse gases, but acknowledged that scientific understanding is poor with respect to solar variation.{{Cite book|name-list-style=amp |last1=Forster |first1=Piers |last2=Ramaswamy |first2=Venkatachalam |last3=Artaxo |first3=Paulo |last4=Berntsen |first4=Terje |last5=Betts |first5=Richard |last6=Fahey |first6=David W. |last7=Haywood |first7=James |last8=Lean |first8=Judith |author8-link=Judith Lean |last9=Lowe |first9=David C. |last10=Myhre |first10=Gunnar |last11=Nganga |first11=John |last12=Prinn |first12=Ronald |last13=Raga |first13=Graciela |last14=Schulz |first14=Michael |last15=Van Dorland |first15=Robert|chapter=2.9.1 Uncertainties in Radiative Forcing|chapter-url=http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-9-1.html#table-2-11 |title=Chapter 2: Changes in Atmospheric Constituents and Radiative Forcing, in Climate Change 2007 – The Physical Science Basis |url=http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2.html |editor1-last=Solomon |editor1-first=Susan |editor2-last=Qin |editor2-first=Dahe |editor3-last=Manning |editor3-first=Martin |editor4-last=Marquis |editor4-first=Melinda |editor5-last=Averyt |editor5-first=Kristen |editor6-last=Tignor |editor6-first=Melinda M.B. |editor7-last=Miller Jr. |editor7-first=Henry LeRoy |editor8-last=Chen |editor8-first=Zhenlin |publisher=Cambridge University Press |location=Cambridge, U.K. and New York, N.Y. |date=2007 |isbn=978-0-521-88009-1 | page=199 |access-date=November 10, 2020}}{{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 | display-editors=3 | title=Climate Change 2001: Working Group I: The Scientific Basis | year=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 | url-status=dead | archive-url=https://web.archive.org/web/20060614020652/http://www.grida.no/climate/ipcc_tar/wg1/fig6-6.htm | archive-date=14 June 2006 }}

Estimates of long-term solar irradiance changes have decreased since the TAR. However, empirical results of detectable tropospheric changes have strengthened the evidence for solar forcing of climate change. The most likely mechanism is considered to be some combination of direct forcing by TSI changes and indirect effects of ultraviolet (UV) radiation on the stratosphere. Least certain are indirect effects induced by galactic cosmic rays.{{cite web|url=http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-7.html#2-7-1|title=2.7 Natural Forcings|work=ipcc.ch|access-date=2015-08-11|archive-date=2013-12-07|archive-url=https://web.archive.org/web/20131207151831/http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-7.html#2-7-1|url-status=dead}}

In 2002, Lean et al.{{Cite journal | first1=J.L. | last1=Lean | first2=Y.-M. | last2=Wang | first3=N.R. | last3=Sheeley Jr. | title=The effect of increasing solar activity on the Sun's total and open magnetic flux during multiple cycles: Implications for solar forcing of climate | year=2002 | pages=77–1 to 77–4 | volume=29 | issue=24 | journal=Geophysical Research Letters | doi=10.1029/2002GL015880 | bibcode=2002GeoRL..29.2224L | s2cid=31369370 | doi-access=free }} stated that while "There is ... growing empirical evidence for the Sun's role in climate change on multiple time scales including the 11-year cycle", "changes in terrestrial proxies of solar activity (such as the 14C and 10Be cosmogenic isotopes and the aa geomagnetic index) can occur in the absence of long-term (i.e., secular) solar irradiance changes ... because the stochastic response increases with the cycle amplitude, not because there is an actual secular irradiance change." They conclude that because of this, "long-term climate change may appear to track the amplitude of the solar activity cycles," but that "Solar radiative forcing of climate is reduced by a factor of 5 when the background component is omitted from historical reconstructions of total solar irradiance ...This suggests that general circulation model (GCM) simulations of twentieth century warming may overestimate the role of solar irradiance variability." A 2006 review suggested that solar brightness had relatively little effect on global climate, with little likelihood of significant shifts in solar output over long periods of time.{{Cite journal | first1=P. | last1=Foukal | first2=C. | last2=Fröhlich | first3=H. | last3=Spruit | first4=T. M. L. | last4=Wigley | title=Variations in solar luminosity and their effect on the Earth's climate | url=http://www.mpa-garching.mpg.de/mpa/publications/preprints/pp2006/MPA2001.pdf | doi=10.1038/nature05072 | journal=Nature | pmid=16971941 | volume=443 | issue=7108 | year=2006 | pages=161–166 | bibcode=2006Natur.443..161F | s2cid=205211006 | url-status=dead | archive-url=https://web.archive.org/web/20070623023541/http://www.mpa-garching.mpg.de/mpa/publications/preprints/pp2006/MPA2001.pdf | archive-date=2007-06-23 }} Lockwood and Fröhlich, 2007, found "considerable evidence for solar influence on the Earth's pre-industrial climate and the Sun may well have been a factor in post-industrial climate change in the first half of the last century", but that "over the past 20 years, all the trends in the Sun that could have had an influence on the Earth's climate have been in the opposite direction to that required to explain the observed rise in global mean temperatures."{{cite journal

| last = Lockwood

| first = Mike

|author2=Claus Fröhlich

| title = Recent oppositely directed trends in solar climate forcings and the global mean surface air temperature

| journal = Proceedings of the Royal Society A

| volume =463

| pages = 2447–2460

| quote = Our results show that the observed rapid rise in global mean temperatures seen after 1985 cannot be ascribed to solar variability, whichever of the mechanisms is invoked and no matter how much the solar variation is amplified.

| url = http://www.atmos.washington.edu/2009Q1/111/Readings/Lockwood2007_Recent_oppositely_directed_trends.pdf

| doi = 10.1098/rspa.2007.1880

| year = 2007

| bibcode=2007RSPSA.463.2447L

| issue = 2086| s2cid = 14580351

}} In a study that considered geomagnetic activity as a measure of known solar-terrestrial interaction, Love et al. found a statistically significant correlation between sunspots and geomagnetic activity, but not between global surface temperature and either sunspot number or geomagnetic activity.{{cite journal|author=Love, J. J.|author2=Mursula, K. |author3=Tsai, V. C. |author4=Perkins, D. M. |title= Are secular correlations between sunspots, geomagnetic activity, and global temperature significant?|journal= Geophysical Research Letters|year=2011 |volume=38|issue=21 |pages=n/a |doi=10.1029/2011GL049380 |bibcode=2011GeoRL..3821703L|s2cid=11218724 |doi-access=free}}

Benestad and Schmidt{{cite journal

| last = Benestad

| first = R. E.

|author2=G. A. Schmidt

| title = Solar trends and global warming

| journal = Journal of Geophysical Research: Atmospheres

| volume = 114

| issue = D14

| pages = D14101

| date = 21 July 2009

| quote = the most likely contribution from solar forcing a global warming is 7 ± 1% for the 20th century and is negligible for warming since 1980.

| url = http://pubs.giss.nasa.gov/docs/2009/2009_Benestad_Schmidt.pdf

| archive-url = https://web.archive.org/web/20111021024622/http://pubs.giss.nasa.gov/docs/2009/2009_Benestad_Schmidt.pdf

| url-status = dead

| archive-date = 21 October 2011

| doi = 10.1029/2008JD011639

| bibcode=2009JGRD..11414101B

}} concluded that "the most likely contribution from solar forcing a global warming is 7 ± 1% for the 20th century and is negligible for warming since 1980." This paper disagreed with Scafetta and West, who claimed that solar variability has a significant effect on climate forcing. Based on correlations between specific climate and solar forcing reconstructions, they argued that a "realistic climate scenario is the one described by a large preindustrial secular variability (e.g., the paleoclimate temperature reconstruction by Moberg et al.){{cite journal |last1=Moberg |title=Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data |journal=Nature |volume=433 |pages=613–617 |url=http://www.ncdc.noaa.gov/paleo/pubs/moberg2005/moberg2005.html |doi=10.1038/nature03265 |pmid=15703742 |year=2005 |first1=A |last2=Sonechkin |first2=DM |last3=Holmgren |first3=K |last4=Datsenko |first4=NM |last5=Karlén |first5=W |last6=Lauritzen |first6=SE |issue=7026 |bibcode=2005Natur.433..613M|s2cid=4359264 }} with TSI experiencing low secular variability (as the one shown by Wang et al.).{{Cite journal |title=Modeling the Sun's Magnetic Field and Irradiance since 1713 |journal=The Astrophysical Journal |volume=625 |issue=1 |pages=522–538 |date= May 2005|doi=10.1086/429689 |last1=Wang |first1=Y.-M. |last2=Lean |first2=J. L. |last3=Sheeley |first3=N. R. |bibcode=2005ApJ...625..522W|s2cid=20573668 |doi-access= }}) Under this scenario, they claimed the Sun might have contributed 50% of the observed global warming since 1900.{{cite journal |last1=Scafetta |first1=N. |first2=B. J. |last2=West |title=Phenomenological solar signature in 400 years of reconstructed Northern Hemisphere temperature record |journal=Geophys. Res. Lett. |volume=33 |pages=L17718 |year=2006 |doi=10.1029/2006GL027142 |url=http://www.agu.org/journals/gl/gl0617/2006GL027142/ |bibcode=2006GeoRL..3317718S |issue=17|doi-access=free }} Stott et al. estimated that the residual effects of the prolonged high solar activity during the last 30 years account for between 16% and 36% of warming from 1950 to 1999.{{Cite journal| title=Do Models Underestimate the Solar Contribution to Recent Climate Change| first=Peter A.| last=Stott| author2= Gareth S. Jones | author3= John F. B. Mitchell| journal= Journal of Climate|year=2003| volume=16| pages=4079–4093 | url=http://climate.envsci.rutgers.edu/pdf/StottEtAl.pdf | access-date=5 October 2005 | doi = 10.1175/1520-0442(2003)016<4079:DMUTSC>2.0.CO;2 |bibcode = 2003JCli...16.4079S| issue=24 | citeseerx=10.1.1.177.6737| issn=1520-0442}}

File:Update of solar change and climate.png4 dataset; the mixing ratio of Carbon dioxide in Earth's atmosphere from observations (blue dots) and ice cores (mauve line); the international sunspot number $R\_\{ISN\}$, smoothed using averaging intervals $\backslash tau$ between 8 years and 14 years (the black line connects the yellow points where the mean is independent of $\backslash tau$ and so shows the solar activity trend without making an assumption about the solar cycle length); the total solar irradiance ($TSI$) the blue dots are the PMOD composite of observations {{Cite web|url=https://www.pmodwrc.ch/en/research-development/solar-physics/tsi-composite/ |title=TSIcomposite |website=Observatorium Davos PMOD and World Radiation Center WRC}} and the black and mauve lines are annual and 11-year means of the SATIRE-T2 model of the effect of sunspots and faculae {{Cite journal |last1=Dasi-Espuig |first1= M. |last2=Jiang |first2= J. |last3=Krivova |first3= N.A. |last4=Solanki |first4= S.K. |year=2014 |title=Modelling total solar irradiance since 1878 from simulated magnetograms |url=https://www.aanda.org/articles/aa/pdf/2014/10/aa24290-14.pdfn |journal=Astron. Astrophys. |volume=570 |pages= A23 |doi=10.1051/0004-6361/201424290|arxiv= 1409.1941 |bibcode= 2014A&A...570A..23D |s2cid= 119288896 }} with the addition of a quiet-Sun variation derived from cosmic ray fluxes and cosmogenic isotopes;{{Cite journal |last1=Lockwood |first1=M. |last2= Ball |first2=W. |date=May 2020 |title=Placing limits on long-term variations in quiet-Sun irradiance and their contribution to total solar irradiance and solar radiative forcing of climate |url=https://centaur.reading.ac.uk/90804/ |journal=Proceedings of the Royal Society A |language=en |volume=476 |issue=2238 |pages=20200077 |issn=1364-5021 |doi=10.1098/rspa.2020.0077|pmid=32831591 |pmc=7428030 |bibcode=2020RSPSA.47600077L }} the open solar flux $F\_S$ from (mauve line) geomagnetic observations and (blue dots) spacecraft data;{{cite journal |first1=Mike|last1=Lockwood |first2=Heikki|last2= Nevanlinna |first3=Luke|last3=Barnard |first4=Mat|last4=Owens |first5=R. Giles|last5=Harrison |first6=Alexis |last6=Rouillard |first7=Chris S.|last7=Scott |year=2014 |title= Reconstruction of Geomagnetic Activity and Near-Earth Interplanetary Conditions over the Past 167 Years: 4. Near-Earth Solar Wind Speed, IMF, and Open Solar Flux |journal= Annales Geophysicae |volume=32 |issue=4 |pages=383–399 |doi=10.5194/angeo-32-383-2014|bibcode=2014AnGeo..32..383L |doi-access=free }} Oulu neutron monitor cosmic ray counts, $O$, (blue dots) observed and (mauve line) extrapolated using cosmogenic isotope data;{{Cite journal|last1=Usoskin |first1=I.G. |date=March 2017 |title=A history of solar activity over millennia |journal=Living Reviews in Solar Physics |language=en |volume=15 |issue=3 |page=3 |doi=10.1007/s41116-017-0006-9|bibcode=2017LRSP...14....3U |s2cid=195340740 |doi-access=free }} and (grey) monthly and (mauve) annual international sunspot numbers, $R\_\{ISN\}$. The green and yellow shaded bands show sunspot cycles 14 and 24]]

Neither direct measurements nor proxies of solar variation correlate well with Earth global temperature,{{ cite journal | first=A. | last=Schurer | display-authors=etal | title=Small influence of solar variability on climate over the past millennium |date=December 2013 | pages=104–108 | volume=7 | issue=2 | journal=Nature Geoscience | doi=10.1038/ngeo2040| url=https://www.pure.ed.ac.uk/ws/files/14512097/PDF_Schurer.et.al.2014_POSTPRINT.pdf | bibcode=2014NatGe...7..104S | hdl=20.500.11820/6f8f8e9d-28d2-40bb-9176-ffc10b07a365 }} particularly in recent decades when both quantities are best known.{{cite journal | first1=L. | last1=Lockwood | first2=C. | last2=Fröhlich | title=Recent oppositely directed trends in solar climate forcings and the global mean surface air temperature |date=October 2007 | pages=2447–2460 | volume=463 | issue=2086 | journal=Proceedings of the Royal Society A | doi=10.1098/rspa.2007.1880 | bibcode=2007RSPSA.463.2447L| s2cid=14580351 }}{{cite journal | first=P. | last=Foukal | display-authors=etal | title=Variations in solar luminosity and their effect on the Earth's climate |date=September 2006 | pages=161–166 | volume=443 | journal=Nature | doi=10.1038/nature05072 | pmid=16971941 | issue=7108| bibcode=2006Natur.443..161F | s2cid=205211006 }}

The oppositely-directed trends highlighted by Lockwood and Fröhlich in 2007, with global mean temperatures continuing to rise while solar activity fell, have continued and become even more pronounced since then. In 2007 the difference in the trends was apparent after about 1987 and that difference has grown and accelerated in subsequent years. The updated figure (right) shows the variations and contrasts solar cycles 14 and 24, a century apart, that are quite similar in all solar activity measures (in fact cycle 24 is slightly less active than cycle 14 on average), yet the global mean air surface temperature is more than 1 degree Celsius higher for cycle 24 than cycle 14, showing the rise is not associated with solar activity. The total solar irradiance (TSI) panel shows the PMOD composite of observations {{Cite web|url=https://www.pmodwrc.ch/en/research-development/solar-physics/tsi-composite/ |title=TSIcomposite |website=Observatorium Davos, PMOD and World Radiation Center WRC}} with a modelled variation from the SATIRE-T2 model of the effect of sunspots and faculae with the addition of a quiet -Sun variation (due to sub-resolution photospheric features and any solar radius changes) derived from correlations with comic ray fluxes and cosmogenic isotopes. The finding that solar activity was approximately the same in cycles 14 and 24 applies to all solar outputs that have, in the past, been proposed as a potential cause of terrestrial climate change and includes total solar irradiance, cosmic ray fluxes, spectral UV irradiance, solar wind speed and/or density, heliospheric magnetic field and its distribution of orientations and the consequent level of geomagnetic activity.

Global average diurnal temperature range has decreased.{{cite journal | first=Thomas | last=Karl | display-authors=etal | title=A New Perspective on Recent Global Warming: Asymmetric Trends of Daily Maximum and Minimum Temperature | year=1993 | pages=1007–1023 | volume=74 | issue=6 | journal=Bulletin of the American Meteorological Society | doi=10.1175/1520-0477(1993)074<1007:anporg>2.0.co;2| bibcode=1993BAMS...74.1007K | s2cid=67795894 | doi-access=free }}{{cite journal | first=K | last=Braganza | display-authors=etal | title=Diurnal temperature range as an index of global climate change during the twentieth century |date=July 2004 | volume=31 | issue=13 | pages=L13217 | journal=Geophysical Research Letters | doi = 10.1029/2004gl019998 | bibcode=2004GeoRL..3113217B| hdl=11343/32780 | s2cid=55358506 | hdl-access=free }}{{cite journal | first=L. | last=Zhou | display-authors=etal | title=Detection and attribution of anthropogenic forcing to diurnal temperature range changes from 1950 to 1999: comparing multi-model simulations with observations |date=August 2009 | pages=1289–1307 | volume=35 | issue=7–8 | journal=Climate Dynamics | doi=10.1007/s00382-009-0644-2| doi-access=free }} Daytime temperatures have not risen as fast as nighttime temperatures. This is the opposite of the expected warming if solar energy (falling primarily or wholly during daylight, depending on energy regime) were the principal means of forcing. It is, however, the expected pattern if greenhouse gases were preventing radiative escape, which is more prevalent at night.{{cite journal | first=S. | last=Peng | display-authors=etal | title=Rice yields decline with higher night temperature from global warming |date=June 2004 | pages=9971–9975 |doi=10.1073/pnas.0403720101 | pmid=15226500 | issue=27 | journal=Proceedings of the National Academy of Sciences | volume=101 | pmc=454199 | bibcode=2004PNAS..101.9971P | doi-access=free }}

The Northern Hemisphere is warming faster than the Southern Hemisphere.{{ cite journal | first=A. | last=Armstrong | title=Northern warming | volume=6 | issue=3 |date=February 2013 | journal=Nature Geoscience | doi=10.1038/ngeo1763 | pages=158| doi-access=free }}{{cite journal |title=Global and Hemispheric Temperature Anomalies - Land and Marine Instrumental Records |first1=P. D. |last1=Jones |first2=D. E. |last2=Parker |first3=T. J. |last3=Osborn |first4=K. R. |last4=Briffa |doi=10.3334/CDIAC/cli.002 |url=http://cdiac.ornl.gov/trends/temp/jonescru/jones.html |access-date=17 Oct 2014|year=2009 |osti=1389299 }} This is the opposite of the expected pattern if the Sun, currently closer to the Earth during austral summer, were the principal climate forcing. In particular, the Southern Hemisphere, with more ocean area and less land area, has a lower albedo ("whiteness") and absorbs more light. The Northern Hemisphere, however, has higher population, industry and emissions.{{Citation needed|date = July 2015}}

Furthermore, the Arctic region is warming faster than the Antarctic and faster than northern mid-latitudes and subtropics, despite polar regions receiving less sun than lower latitudes.{{Cite journal |last1=Post |first1=Eric |last2=Alley |first2=Richard B. |last3=Christensen |first3=Torben R. |last4=Macias-Fauria |first4=Marc |last5=Forbes |first5=Bruce C. |last6=Gooseff |first6=Michael N. |last7=Iler |first7=Amy |last8=Kerby |first8=Jeffrey T. |last9=Laidre |first9=Kristin L. |last10=Mann |first10=Michael E. |last11=Olofsson |first11=Johan |last12=Stroeve |first12=Julienne C. |last13=Ulmer |first13=Fran |last14=Virginia |first14=Ross A. |last15=Wang |first15=Muyin |date=2019-12-06 |title=The polar regions in a 2°C warmer world |journal=Science Advances |language=en |volume=5 |issue=12 |pages=eaaw9883 |doi=10.1126/sciadv.aaw9883 |issn=2375-2548 |pmc=6892626 |pmid=31840060|bibcode=2019SciA....5.9883P }}

Solar forcing should warm Earth's atmosphere roughly evenly by altitude, with some variation by wavelength/energy regime. However, the atmosphere is warming at lower altitudes while cooling higher up. This is the expected pattern if greenhouse gases drive temperature,{{ cite journal | first= H. | last=Lewis | display-authors=etal | title=Response of the Space Debris Environment to Greenhouse Cooling |date=April 2005 | page=243 | journal=Proceedings of the 4th European Conference on Space Debris | volume=587 | bibcode=2005ESASP.587..243L }}{{cite web |title=Unpacking interplay of solar variability and climate change: A trio of researchers discuss the current understanding of the effect solar |first=Matt |last=Ford |date=Feb 20, 2008 | url=https://arstechnica.com/science/2008/02/unpacking-interplay-of-solar-variability-and-climate-change/ | access-date=17 Oct 2014}} as on Venus.{{cite journal | first1=J. | last1=Picone | first2=J. | last2=Lean | display-authors=etal | title=Global Change in the Thermosphere: Compelling Evidence of a Secular Decrease in Density | year=2005 | pages=225–227 | journal=2005 NRL Review}}

A 1994 study of the US National Research Council concluded that TSI variations were the most likely cause of significant climate change in the pre-industrial era, before significant human-generated carbon dioxide entered the atmosphere.{{cite book |title = Solar Influences on Global Change|publisher = National Academy Press|location = Washington, D.C|year = 1994|page = 36|isbn = 978-0-309-05148-4|url = http://books.nap.edu/openbook.php?record_id=4778&page=R1|vauthors = ((Board on Global Change)), ((Commission on Geosciences, Environment, and Resources)), ((National Research Council))|doi = 10.17226/4778|hdl = 2060/19950005971}}

Scafetta and West correlated solar proxy data and lower tropospheric temperature for the preindustrial era, before significant anthropogenic greenhouse forcing, suggesting that TSI variations may have contributed 50% of the warming observed between 1900 and 2000 (although they conclude "our estimates about the solar effect on climate might be overestimated and should be considered as an upper limit."){{cite journal |last1=Scafetta |first1=N. |first2=B. J. |last2=West |title=Phenomenological reconstructions of the solar signature in the Northern Hemisphere, surface temperature records since 1600 |journal=J. Geophys. Res. |volume=112 |issue=D24 |pages=D24S03 |year=2007 |doi=10.1029/2007JD008437 |url=http://www.fel.duke.edu/~scafetta/pdf/2007JD008437.pdf |bibcode=2007JGRD..11224S03S |url-status=dead |archive-url=https://web.archive.org/web/20080308021713/http://www.fel.duke.edu/~scafetta/pdf/2007JD008437.pdf |archive-date=2008-03-08 }} (access date 2012-1-31) If interpreted as a detection rather than an upper limit, this would contrast with global climate models predicting that solar forcing of climate through direct radiative forcing makes an insignificant contribution.{{cite journal |last1=Hansen |first1=J |title=Efficacy of climate forcings |journal=J. Geophys. Res. |volume=110 |issue=D18 |pages=D18104 |year=2005 |doi=10.1029/2005JD005776 |bibcode=2005JGRD..11018104H|s2cid=53957314 |doi-access=free }}

File:Sunspot-temperature-10000yr.svg

In 2000, Stott and others{{cite journal | author=Stott, Peter A. | display-authors=etal | title=External Control of 20th Century Temperature by Natural and Anthropogenic Forcings | journal=Science | year=2000 | volume=290 |pages=2133–2137 | doi=10.1126/science.290.5499.2133 | pmid=11118145 | issue=5499 |bibcode = 2000Sci...290.2133S | s2cid=9771224 }} reported on the most comprehensive model simulations of 20th century climate to that date. Their study looked at both "natural forcing agents" (solar variations and volcanic emissions) as well as "anthropogenic forcing" (greenhouse gases and sulphate aerosols). They found that "solar effects may have contributed significantly to the warming in the first half of the century although this result is dependent on the reconstruction of total solar irradiance that is used. In the latter half of the century, we find that anthropogenic increases in greenhouses gases are largely responsible for the observed warming, balanced by some cooling due to anthropogenic sulphate aerosols, with no evidence for significant solar effects." Stott's group found that combining these factors enabled them to closely simulate global temperature changes throughout the 20th century. They predicted that continued greenhouse gas emissions would cause additional future temperature increases "at a rate similar to that observed in recent decades".{{Cite journal | first1=K.S. | last1=Carslaw | first2=R. G. | last2=Harrison | first3=J. | last3=Kirkby | title=Cosmic Rays, Clouds, and Climate | journal=Science | volume=298 | pages=1732–1737 | year=2002 | doi=10.1126/science.1076964 | pmid=12459578 | issue=5599 |bibcode = 2002Sci...298.1732C | s2cid=12917901 }}

In addition, the study notes "uncertainties in historical forcing" — in other words, past natural forcing may still be having a delayed warming effect, most likely due to the oceans.

Stott's 2003 work largely revised his assessment, and found a significant solar contribution to recent warming, although still smaller (between 16 and 36%) than that of greenhouse gases.

A study in 2004 concluded that solar activity affects the climate - based on sunspot activity, yet plays only a small role in the current global warming.{{cite press release | title=How Strongly Does the Sun Influence the Global Climate? — Studies at the Max Planck Institute for Solar System Research reveal: solar activity affects the climate but plays only a minor role in the current global warming | publisher=Max Planck Society | date=2 August 2004 | access-date= 16 August 2015| url=http://www.mpg.de/research/sun-influence-global-climate }}

In 1991, Friis-Christensen and Lassen claimed a strong correlation of the length of the solar cycle with northern hemispheric temperature changes.{{cite journal |last1=Friis-Christensen |first1=E. |last2=Lassen |first2=K. |date=1 November 1991 |title=Length of the Solar Cycle: An Indicator of Solar Activity Closely Associated with Climate |journal=Science |volume=254 |issue=5032 |pages=698–700 |bibcode=1991Sci...254..698F |doi=10.1126/science.254.5032.698 |pmid=17774798 |s2cid=31048860}} [http://www.friendsofscience.org/assets/files/documents/Solar%20Cycle%20-%20Friis-Chr_Lassen-.pdf] They initially used sunspot and temperature measurements from 1861 to 1989 and later extended the period using four centuries of climate records. Their reported relationship appeared to account for nearly 80 per cent of measured temperature changes over this period. The mechanism behind these claimed correlations was a matter of speculation.

In a 2003 paper{{Cite journal |last=Laut |first=Peter |title=Solar activity and terrestrial climate: an analysis of some purported correlations |journal=J Atmos Sol-Terr Phys |volume=65 |issue=7 |pages=801–812 |date= May 2003|doi=10.1016/S1364-6826(03)00041-5 |bibcode = 2003JASTP..65..801L |citeseerx=10.1.1.539.8293 }} Laut identified problems with some of these correlation analyses. Damon and Laut claimed:{{Cite journal | title=Pattern of Strange Errors Plagues Solar Activity and Terrestrial Climate Data | url=http://stephenschneider.stanford.edu/Publications/PDF_Papers/DamonLaut2004.pdf | access-date=5 October 2005| journal=Eos, Transactions, American Geophysical Union| volume=85| issue=39|date=September 28, 2004| pages=370–374| first=Paul E.| last=Damon|author2=Paul Laut | doi=10.1029/2004EO390005| bibcode=2004EOSTr..85..370D}}; see also discussion and references at [http://www.skepticalscience.com/solar-cycle-length.htm skeptical science]

the apparent strong correlations displayed on these graphs have been obtained by incorrect handling of the physical data. The graphs are still widely referred to in the literature, and their misleading character has not yet been generally recognized.

Damon and Laut stated that when the graphs are corrected for filtering errors, the sensational agreement with the recent global warming, which drew worldwide attention, totally disappeared.

In 2000, Lassen and Thejll updated their 1991 research and concluded that while the solar cycle accounted for about half the temperature rise since 1900, it failed to explain a rise of 0.4 °C since 1980.{{cite magazine | first=Robert | last=Adler | title=Don't blame the Sun | magazine=New Scientist | issue=2237 | url=https://www.newscientist.com/article/mg16622370.800-dont-blame-the-sun/ | date=6 May 2000 | access-date=2007-04-19}} Benestad's 2005 review{{cite journal |first=R.E. |last=Benestad |title=A review of the solar cycle length estimates |journal=Geophys. Res. Lett. |volume=32 |issue= 15|pages=L15714 |date=13 August 2005 |doi=10.1029/2005GL023621 |bibcode = 2005GeoRL..3215714B |s2cid=129300529 |doi-access= }} found that the solar cycle did not follow Earth's global mean surface temperature.

In 2022, Chatzistergos updated the cycle length series with recent sunspot and solar plages data, extending them to more recent periods than previous studies, and also considering the various available time series.{{Cite journal |last=Chatzistergos |first=Theodosios |date=2022-12-27 |title=Is there a link between the length of the solar cycle and Earth's temperature? |journal=Rendiconti Lincei. Scienze Fisiche e Naturali |volume=34 |pages=11–21 |language=en |doi=10.1007/s12210-022-01127-z |issn=2037-4631|doi-access=free }}{{Cite journal |last1=Clette |first1=Frédéric |last2=Lefèvre |first2=Laure |date=November 2016 |title=The New Sunspot Number: Assembling All Corrections |url=http://link.springer.com/10.1007/s11207-016-1014-y |journal=Solar Physics |language=en |volume=291 |issue=9–10 |pages=2629–2651 |doi=10.1007/s11207-016-1014-y |issn=0038-0938|arxiv=1510.06928 |bibcode=2016SoPh..291.2629C |s2cid=255070723 }}{{Cite journal |last1=Usoskin |first1=Ilya |last2=Kovaltsov |first2=Gennady |last3=Kiviaho |first3=Wilma |date=January 2021 |title=Robustness of Solar-Cycle Empirical Rules Across Different Series Including an Updated Active-Day Fraction (ADF) Sunspot Group Series |url=http://link.springer.com/10.1007/s11207-020-01750-9 |journal=Solar Physics |language=en |volume=296 |issue=1 |pages=13 |doi=10.1007/s11207-020-01750-9 |arxiv=2012.08415 |bibcode=2021SoPh..296...13U |s2cid=255071885 |issn=0038-0938}}{{Cite journal |last1=Chatzistergos |first1=Theodosios |last2=Usoskin |first2=Ilya G. |last3=Kovaltsov |first3=Gennady A. |last4=Krivova |first4=Natalie A. |last5=Solanki |first5=Sami K. |date=June 2017 |title=New reconstruction of the sunspot group numbers since 1739 using direct calibration and "backbone" methods |journal=Astronomy & Astrophysics |volume=602 |pages=A69 |doi=10.1051/0004-6361/201630045 |arxiv=1702.06183 |bibcode=2017A&A...602A..69C |issn=0004-6361|doi-access=free }}{{Cite journal |last1=Chatzistergos |first1=Theodosios |last2=Ermolli |first2=Ilaria |last3=Krivova |first3=Natalie A. |last4=Solanki |first4=Sami K. |last5=Banerjee |first5=Dipankar |last6=Barata |first6=Teresa |last7=Belik |first7=Marcel |last8=Gafeira |first8=Ricardo |last9=Garcia |first9=Adriana |last10=Hanaoka |first10=Yoichiro |last11=Hegde |first11=Manjunath |last12=Klimeš |first12=Jan |last13=Korokhin |first13=Viktor V. |last14=Lourenço |first14=Ana |last15=Malherbe |first15=Jean-Marie |date=July 2020 |title=Analysis of full-disc Ca II K spectroheliograms: III. Plage area composite series covering 1892–2019 |journal=Astronomy & Astrophysics |volume=639 |pages=A88 |doi=10.1051/0004-6361/202037746 |arxiv=2005.01435 |bibcode=2020A&A...639A..88C |issn=0004-6361|doi-access=free }} This is important because of the plentiful updates and corrections that have been applied to the sunspot data over the last decade. He showed that cycle lengths significantly diverge from Earth's temperatures and concluded that the strong correlation reported by Friis-Christensen and Lassen was an artefact of their analysis. Owing largely to their guess of next extrema times, arbitrarily restricting the analysis over a specific time period, along with other arbitrarities in their methodology.{{Cite journal |last1=Usoskin |first1=I. G. |last2=Kovaltsov |first2=G. A. |last3=Chatzistergos |first3=T. |date=December 2016 |title=Dependence of the Sunspot-Group Size on the Level of Solar Activity and its Influence on the Calibration of Solar Observers |url=http://link.springer.com/10.1007/s11207-016-0993-z |journal=Solar Physics |language=en |volume=291 |issue=12 |pages=3793–3805 |doi=10.1007/s11207-016-0993-z |issn=0038-0938|arxiv=1609.00569 |bibcode=2016SoPh..291.3793U |s2cid=255065956 }}{{Cite journal |last1=Vaquero |first1=J. M. |last2=Svalgaard |first2=L. |last3=Carrasco |first3=V. M. S. |last4=Clette |first4=F. |last5=Lefèvre |first5=L. |last6=Gallego |first6=M. C. |last7=Arlt |first7=R. |last8=Aparicio |first8=A. J. P. |last9=Richard |first9=J.-G. |last10=Howe |first10=R. |date=November 2016 |title=A Revised Collection of Sunspot Group Numbers |url=http://link.springer.com/10.1007/s11207-016-0982-2 |journal=Solar Physics |language=en |volume=291 |issue=9–10 |pages=3061–3074 |doi=10.1007/s11207-016-0982-2 |issn=0038-0938|arxiv=1609.04882 |bibcode=2016SoPh..291.3061V |s2cid=255073423 }}

Solar activity may also impact regional climates, such as for the rivers ParanáPablo 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-Terrestrial Physics on Space Climate, March 2010. Accessed: 20 September 2014. and Po.{{cite journal | last1 = Zanchettin | first1 = D. | last2 = Rubino | first2 = A. | last3 = Traverso | first3 = P. | last4 = Tomasino | first4 = M. | year = 2008| title = [Impact of variations in solar activity on hydrological decadal patterns in northern Italy] | journal = Journal of Geophysical Research | volume = 113| issue = D12 | doi = 10.1029/2007JD009157 | bibcode = 2008JGRD..11312102Z | doi-access = free }} Measurements from NASA's Solar Radiation and Climate Experiment show that solar UV output is more variable than total solar irradiance. Climate modelling suggests that low solar activity may result in, for example, colder winters in the US and northern Europe and milder winters in Canada and southern Europe, with little change in global averages.{{cite journal | title=Solar forcing of winter climate variability in the Northern Hemisphere | journal=Nature Geoscience |date=9 October 2011 |author1=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=753–757 |doi=10.1038/ngeo1282 | issue=11 | bibcode=2011NatGe...4..753I| hdl=10044/1/18859 |hdl-access=free }} More broadly, links have been suggested between solar cycles, global climate and regional events such as El Niño.{{cite web|url=https://www.nsf.gov/news/news_summ.jsp?cntn_id=115207|title=National Science Foundation (NSF) News - Solar Cycle Linked to Global Climate - NSF - National Science Foundation|work=nsf.gov}} Hancock and Yarger found "statistically significant relationships between the double [~21-year] sunspot cycle and the 'January thaw' phenomenon along the East Coast and between the double sunspot cycle and 'drought' (June temperature and precipitation) in the Midwest."{{cite journal |vauthors=Hancock DJ, Yarger DN |title=Cross-Spectral Analysis of Sunspots and Monthly Mean Temperature and Precipitation for the Contiguous United States |journal=Journal of the Atmospheric Sciences |volume=36 |issue=4 |pages=746–753 |year=1979 |doi=10.1175/1520-0469(1979)036<0746:CSAOSA>2.0.CO;2 |url=http://www.solarstorms.org/USPrecip.html |issn=1520-0469|bibcode = 1979JAtS...36..746H |doi-access=free }}

Recent research at CERN's CLOUD facility examined links between cosmic rays and cloud condensation nuclei, demonstrating the effect of high-energy particulate radiation in nucleating aerosol particles that are precursors to cloud condensation nuclei.{{cite press release|title=CERN's CLOUD experiment provides unprecedented insight into cloud formation |publisher=CERN |url=http://press.cern/press-releases/2011/08/cerns-cloud-experiment-provides-unprecedented-insight-cloud-formation |date=25 August 2011 |access-date=20 November 2016}}

Kirkby (CLOUD team leader) said, "At the moment, it [the experiment] actually says nothing about a possible cosmic-ray effect on clouds and climate."{{cite press release | title=Cloud formation may be linked to cosmic rays | publisher=Nature News | url=http://www.nature.com/news/2011/110824/full/news.2011.504.html |date=24 August 2011| access-date=19 October 2011 }}{{cite journal| title=Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation |journal=Nature |date=25 August 2011 |author=Kirkby J |volume=476 |issue=7361 |pages=429–433 |doi=10.1038/nature10343| author2=Curtius J| author3=Almeida J| author4=Dunne E| author5=Duplissy J| display-authors=5| last6=Ehrhart| first6=Sebastian| last7=Franchin| first7=Alessandro| last8=Gagné| first8=Stéphanie| last9=Ickes| first9=Luisa| pmid=21866156 |bibcode = 2011Natur.476..429K |s2cid=4326159 |url=https://authors.library.caltech.edu/25275/2/nature10343-s1.pdf }} After further investigation, the team concluded that "variations in cosmic ray intensity do not appreciably affect climate through nucleation."{{cite journal|last1=Dunne|first1=E. M.|display-authors=etal|title=Global atmospheric particle formation from CERN CLOUD measurements|journal=Science|date=2016|volume=354|issue=6316|pages=1119–1124|doi=10.1126/science.aaf2649|pmid=27789796|bibcode=2016Sci...354.1119D|doi-access=free}}

1983–1994 global low cloud formation data from the International Satellite Cloud Climatology Project (ISCCP) was highly correlated with galactic cosmic ray (GCR) flux; subsequent to this period, the correlation broke down. Changes of 3–4% in cloudiness and concurrent changes in cloud top temperatures correlated to the 11 and 22-year solar (sunspot) cycles, with increased GCR levels during "antiparallel" cycles.{{Cite journal | first=Henrik | last=Svensmark | author-link=Henrik Svensmark | title=Influence of Cosmic Rays on Earth's Climate | journal=Physical Review Letters | year=1998 | volume=81 | issue=22 | pages=5027–5030 | url=http://www.cosis.net/abstracts/COSPAR02/00975/COSPAR02-A-00975.pdf | doi=10.1103/PhysRevLett.81.5027 | access-date=17 June 2011 | bibcode=1998PhRvL..81.5027S| citeseerx=10.1.1.522.585 }} Global average cloud cover change was measured at 1.5–2%. Several GCR and cloud cover studies found positive correlation at latitudes greater than 50° and negative correlation at lower latitudes.{{Cite book|contribution = Atmospheric Ionization and Clouds as Links Between Solar Activity and Climate|first1 = Brian A.|last1 = Tinsley|first2 = Fangqun|last2 = Yu|year = 2004|volume = 141|pages = 321–339|editor1-first = Judit M.|editor1-last = Pap|editor2-first = Peter|editor2-last = Fox|title = Solar Variability and its Effects on Climate|isbn = 978-0-87590-406-1|contribution-url = http://www.utdallas.edu/physics/pdf/Atmos_060302.pdf|access-date = 19 April 2007|publisher = American Geophysical Union|work = Geophysical monograph series|archive-date = 4 June 2007|archive-url = https://web.archive.org/web/20070604183050/http://www.utdallas.edu/physics/pdf/Atmos_060302.pdf|url-status = dead}} However, not all scientists accept this correlation as statistically significant, and some who do attribute it to other solar variability (e.g. UV or total irradiance variations) rather than directly to GCR changes.{{cite journal | author1=E. Pallé | author2=C.J. Butler | author3=K. O'Brien | title=The possible connection between ionization in the atmosphere by cosmic rays and low level clouds | journal=Journal of Atmospheric and Solar-Terrestrial Physics | volume=66 | issue=18 | year=2004 | doi=10.1016/j.jastp.2004.07.041 | url=http://www.arm.ac.uk/preprints/433.pdf | pages=1779–1790 | bibcode=2004JASTP..66.1779P | access-date=2015-08-11 | archive-url=https://web.archive.org/web/20070927223917/http://www.arm.ac.uk/preprints/433.pdf | archive-date=2007-09-27 | url-status=dead }}{{Cite journal | first1=E. | last1=Pallé | title=Possible satellite perspective effects on the reported correlations between solar activity and clouds | journal=Geophysical Research Letters | volume=32 | issue=3| year=2005 | pages=L03802.1–4| doi=10.1029/2004GL021167 | url=http://bbso.njit.edu/Research/EarthShine/literature/Palle_2005_GRL.pdf | bibcode=2005GeoRL..32.3802P| s2cid=10052196 }} Difficulties in interpreting such correlations include the fact that many aspects of solar variability change at similar times, and some climate systems have delayed responses.

Physicist and historian Spencer R. Weart in The Discovery of Global Warming (2003) wrote:

{{blockquote|The study of [sun spot] cycles was generally popular through the first half of the century. Governments had collected a lot of weather data to play with and inevitably people found correlations between sun spot cycles and select weather patterns. If rainfall in England didn't fit the cycle, maybe storminess in New England would. Respected scientists and enthusiastic amateurs insisted they had found patterns reliable enough to make predictions. Sooner or later though every prediction failed. An example was a highly credible forecast of a dry spell in Africa during the sunspot minimum of the early 1930s. When the period turned out to be wet, a meteorologist later recalled "the subject of sunspots and weather relationships fell into dispute, especially among British meteorologists who witnessed the discomfiture of some of their most respected superiors." Even in the 1960s he said, "For a young [climate] researcher to entertain any statement of sun-weather relationships was to brand oneself a crank."}}

• Radiative forcing
• Solar phenomena
• Solar cycle
• Solar observation
• Space climate
• Space weather

{{Reflist|30em}}

• {{cite web |title=Global Climate Change Impacts in the United States |url=https://www.nrc.gov/docs/ML1006/ML100601201.pdf |first1=Thomas R. |last1=Karl |first2=Jerry M. |last2=Melillo |first3=Thomas C. |last3=Peterson |access-date=30 January 2024 |website= |publisher=Cambridge University Press |year=2009}}
• {{Cite web | title=The Sun's role in Climate Changes | work=Proc. of The International Conference on Global Warming and The Next Ice Age, 19–24 August 2001, Halifax, Nova Scotia. | url=http://zeus.nascom.nasa.gov/~pbrekke/articles/halifax_brekke.pdf | access-date = 2005-02-21| url-status=dead |archive-url = https://web.archive.org/web/20041022012450/http://zeus.nascom.nasa.gov/~pbrekke/articles/halifax_brekke.pdf |archive-date = 22 October 2004}}
• {{Cite journal |last=White |first=Warren B. |author2=Lean, Judith |author3=Cayan, Daniel R. |author4= Dettinger, Michael D. |year=1997 |title=Response of global upper ocean temperature to changing solar irradiance |journal=Journal of Geophysical Research |volume=102 |issue=C2 |pages=3255–3266 |doi=10.1029/96JC03549 |bibcode=1997JGR...102.3255W|doi-access=free }}
• A graphical representation{{cite web | title=graphical representation | url=http://www.grida.no/climate/ipcc_tar/wg1/fig12-7.htm | access-date=2005-10-05 | url-status=dead | archive-url=https://web.archive.org/web/20120204034715/http://www.grida.no/climate/ipcc_tar/wg1/fig12-7.htm | archive-date=2012-02-04 }} of the relationship between natural and anthropogenic factors contributing to climate change appears in "Climate Change 2001: The Scientific Basis", a report by the Intergovernmental Panel on Climate Change (IPCC).{{cite web | title=Climate Change 2001: The Scientific Basis | 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 | display-editors = 3 | url=http://www.grida.no/climate/ipcc_tar/wg1/index.htm | access-date = 2005-10-05}}

• {{Cite journal |author1=Gerrit Lohmann |author2=Norel Rimbu |author3=Mihai Dima |title=Climate signature of solar irradiance variations: analysis of long-term instrumental, historical, and proxy data |journal=International Journal of Climatology |volume=24 |issue=8 |pages=1045–1056 |year=2004 |doi=10.1002/joc.1054|bibcode = 2004IJCli..24.1045L |s2cid=53698312 |url=https://epic.awi.de/id/eprint/11077/1/Loh2004a.pdf }}

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Category:Climate forcing