"The scientific consensus is that solar variations do not play a major role in determining present-day observed climate change.[50] The Intergovernmental Panel on Climate Change Third Assessment Report states that the measured magnitude of recent solar variation is much smaller than the amplification effect due to greenhouse gases.[51]

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 changes in total solar irradiance, and indirect effects of ultraviolet (UV) radiation on the stratosphere. Least certain are indirect effects induced by galactic cosmic rays [1].

In 2002, Lean et al.[52] 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." More recently, a study and review of existing literature published in Nature in September 2006 suggests that the evidence is solidly on the side of solar brightness having relatively little effect on global climate, with little likelihood of significant shifts in solar output over long periods of time.[11][53] Lockwood and Fröhlich, 2007, find that there "is 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."[54]

A paper by Benestad and Schmidt [55] concludes 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 disagrees with the conclusions of a Scafetta and West study,[56] who claim that solar variability is a major if not dominant climate forcing. Based on correlations between specific climate and solar forcing reconstructions, they argue 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.)[57] with the total solar irradiance experiencing low secular variability (as the one shown by Wang et al.)[58]. Under this scenario, according to Scafetta and West, the Sun might have contributed 50% of the observed global warming since 1900.[10] Stott et al. estimate 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.[59]"

References footnoted in the WIkipedia article on Solar Variation::

1. Satellite observations of total solar irradiance

10. 10.^ a b Scafetta, N.; West, B. J. (2006). "Phenomenological solar signature in 400 years of reconstructed Northern Hemisphere temperature record". Geophys. Res. Lett. 33: L17718. doi:10.1029/2006GL027142. http://www.agu.org/journals/gl/gl0617/2006GL027142/.

50.^ Joanna Haigh

51.^ Houghton, J.T.; Ding, Y.; Griggs, D.J. et al., eds (2001). "6.11 Total Solar Irradiance—Figure 6.6: Global, annual mean radiative forcings (1750 to present)". Climate Change 2001: Working Group I: The Scientific Basis. Intergovernmental Panel on Climate Change. http://www.grida.no/climate/ipcc_tar/wg1/fig6-6.htm. Retrieved 15 April 2007.

52.^ Lean, J.L.; Wang, Y.-M; Sheeley Jr., N.R (2002). ""The effect of increasing solar activity on the Sun's total and open magnetic flux during multiple cycles: Implications for solar forcing of climate"". Geophysical Research Letters 29 (24): 77–1~77–4. doi:10.1029/2002GL015880. http://www.agu.org/pubs/crossref/2002.../2002GL015880.shtml.

53.^ Foukal, P.; Fröhlich, C.; Spruit, H.; Wigley, T. M. L. (2006). "Variations in solar luminosity and their effect on the Earth's climate" (PDF). Nature 443 (7108): 161. doi:10.1038/nature05072. http://www.mpa-garching.mpg.de/mpa/publications/preprints/pp2006/MPA2001.pdf.

54.^ Lockwood, Mike; Claus Fröhlich (2007). "Recent oppositely directed trends in solar climate forcings and the global mean surface air temperature" (PDF). Proceedings of the Royal Society A 463: 2447. doi:10.1098/rspa.2007.1880. http://www.atmos.washington.edu/2009Q1/111/Readings/Lockwood2007_Recent_oppositely_directed_trends.pdf. "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.".

55.^ Benestad,, R. E.; G. A. Schmidt (21 July 2009). "Solar trends and global warming". Journal of Geophysical Research - Atmospheres. doi:10.1029/2008JD011639. http://pubs.giss.nasa.gov/docs/2009/2009_Benestad_Schmidt.pdf. "the most likely contribution from solar forcing a global warming is 7 ± 1% for the 20th century and is negligible for warming since 1980.".

56.^ a b Scafetta, N.; West, B. J. (2007). "Phenomenological reconstructions of the solar signature in the Northern Hemisphere, surface temperature records since 1600". J. Geophys. Res. 112: D24S03. doi:10.1029/2007JD008437. http://www.agu.org/pubs/crossref/2007/2007JD008437.shtml. as PDF

57.^ Moberg, A; Sonechkin, DM; Holmgren, K; Datsenko, NM; Karlén, W; Lauritzen, SE (2005). "Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data". Nature 433 (7026): 613–7. doi:10.1038/nature03265. PMID 15703742. http://www.ncdc.noaa.gov/paleo/pubs/moberg2005/moberg2005.html.

58.^ Wang, Y.‐M.; Lean, J. L.; Sheeley, Jr., N. R. (May 2005). "Modeling the Sun's Magnetic Field and Irradiance since 1713". The Astrophysical Journal 625: 522–38. doi:10.1086/429689. http://www.journals.uchicago.edu/doi/full/10.1086/429689. )

59.^ a b Stott, Peter A.; Gareth S. Jones and John F. B. Mitchell (15 2003). "Do Models Underestimate the Solar Contribution to Recent Climate Change". Journal of ClimateDecember 16: 4079–4093. http://climate.envsci.rutgers.edu/pdf/StottEtAl.pdf. Retrieved 2005.