This article or section should be merged with Solar variation.

Solar variation theory is one attempt to account for global warming. Various hypotheses have been proposed to link terrestrial temperature variations to solar variations. The meteorological community has responded with skepticism, in part because theories of this nature have come and gone over the course of the 20th century [1] (http://www.aip.org/history/climate/solar.htm). The solar variations theory also has counter evidence in the form of measured global dimming which shows that the intensity of sunlight at the Earth's surface actually fell from the 1950s–1990s. To reconcile theories of an increase in solar radiation with the measurements would require other changes either in the spectrum of the sun (which has not been observed) or in the absorption profile of the atmosphere, which would probably imply some kind of climate change. Small icon for merging articles File links The following pages link to this file: Friction Jacobin Private branch exchange Pro-feminist Rotary piston engine Tagalog language Saint Veronica Spoiler effect Parser Password length equation Sudovian language Wikipedia:Why arent these pages copy-edited Static scoping Maximum power theorem General... 20 years of solar irradiance data from satellites Solar variation refers to fluctuation in the amount of energy emitted by the Sun. ... Global mean surface temperatures 1856-2004 Global warming is a term used to describe an increase over time of the average temperature of Earths atmosphere and oceans. ... A hypothesis (= assumption in ancient Greek) is a proposed explanation for a phenomenon. ... 20 years of solar irradiance data from satellites Solar variation refers to fluctuation in the amount of energy emitted by the Sun. ... A NASA photograph showing aircraft contrails and natural clouds. ... Millennia: 1st millennium - 2nd millennium - 3rd millennium Events and trends Technology United States tests the first fusion bomb. ... Events and trends Technology Explosive growth of the Internet; decrease in the cost of computers and other technology Reduction in size and cost of mobile phones leads to a massive surge in their popularity Year 2000 problem (commonly known as Y2K) Microsoft Windows operating system becomes virtually ubiquitous on IBM...

Sami Solanki, the director of the Max Planck Institute for Solar System Research in Göttingen, Germany said: Map of Germany showing Göttingen 1 External links Coat of Arms University of Göttingen Top: The old Auditorium Maximum (1862-65) Bottom: New library building Göttingen is a city in Lower Saxony, Germany. ...

The sun has been at its strongest over the past 60 years and may now be affecting global temperatures... the brighter sun and higher levels of so-called "greenhouse gases" both contributed to the change in the Earth's temperature, but it was impossible to say which had the greater impact. [2] (http://www.washtimes.com/world/20040718-115714-6334r.htm)

Willie Soon and Sallie Baliunas of the Harvard Observatory correlated historical sunspot counts with temperature proxies. They report that when there are fewer sunspots, the earth cooled (see Maunder Minimum, Little Ice Age) — and that when there are more sunspots the earth warmed (see Medieval Warm Period, though since sunspot numbers were only counted from 1700 the link to the MWP warmth is speculative). Willie Soon (Wei-Hock Soon) is an astrophysicist at the Solar and Stellar Physics Division of the Harvard-Smithsonian Center for Astrophysics. ... Sallie Baliunas is at the Harvard-Smithsonian Center for Astrophysics in the Solar, Stellar, and Planetary Sciences Division and formerly Deputy Director of the Mount Wilson Institute. ... The Harvard College Observatory (or HCO) is an institution managing a complex of buildings and multiple instruments used for astronomical research by the Department of Astronomy of Harvard. ... 400 year sunspot history A sunspot is a region on the Suns surface (photosphere) that is marked by a lower temperature than its surroundings, and intense magnetic activity. ... In climate research, a proxy variable is something that is probably not in itself of any great interest, but from which a variable of interest can be obtained. ... The Maunder minimum in a 400 year history of sunspot numbers The Maunder Minimum is the name given to the period roughly from 1645 to 1715 A.D., when sunspots became exceedingly rare, as noted by solar observers of the time. ... The Little Ice Age (LIA) was a period of cooling lasting approximately from the mid-14th to the mid-19th centuries. ... The Medieval Warm Period (MWP) or Medieval Climate Optimum was an unusually warm period in history lasting from about the 10th century to about the 14th century. ...

The theories have usually represented one of three types:

• Solar irradiance changes directly affecting the climate. This is generally considered unlikely, as the variations seem to be too small.
• Variations in the ultraviolet component having an effect. The UV component varies by more than the total.
• Effects mediated by changes in cosmic rays (which are affected by the solar wind, which is affected by the solar output) such as changes in cloud cover.

Although correlations often can be found, the mechanism behind these correlations is a matter of speculation. Many of these speculative accounts have fared badly over time, and in a paper "Solar activity and terrestrial climate: an analysis of some purported correlations" (J. Atmos. and Solar-Terr. Phy., 2003 p801–812) Peter Laut demonstrates problems with some of the most popular, notably those by Svensmark and by Lassen (below). Damon and Laut report in Eos [3] (http://stephenschneider.stanford.edu/Publications/PDF_Papers/DamonLaut2004.pdf) that 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.

In 1991, Knud Lassen of the Danish Meteorological Institute in Copenhagen and his colleague Eigil Friis-Christensen found a strong correlation between the length of the solar cycle and temperature changes throughout the northern hemisphere. Initially, they used sunspot and temperature measurements from 1861 to 1989, but later found that climate records dating back four centuries supported their findings. This relationship appeared to account for nearly 80 per cent of the measured temperature changes over this period (see graph (http://solar-center.stanford.edu/images/solactivity.jpg)). Damon and Laut, however, show that when the graphs are corrected for filtering errors, the sensational agreement with the recent global warming, which drew worldwide attention, has totally disappeared. Nevertheless,the authors and other researchers keep presenting the old misleading graph [4] (http://stephenschneider.stanford.edu/Publications/PDF_Papers/DamonLaut2004.pdf). Note that the prior link to "graph" is one such example of this.

Sallie Baliunas, an astronomer at the Harvard-Smithsonian Center for Astrophysics, has been among the supporters of the theory that changes in the sun "can account for major climate changes on Earth for the past 300 years, including part of the recent surge of global warming." [5] (http://www.news.harvard.edu/gazette/1997/11.06/BrighteningSuni.html) Sallie Baliunas is at the Harvard-Smithsonian Center for Astrophysics in the Solar, Stellar, and Planetary Sciences Division and formerly Deputy Director of the Mount Wilson Institute. ...

On May 6, 2000, however, New Scientist magazine reported that Lassen and astrophysicist Peter Thejll had updated Lassen's 1991 research and found that while the solar cycle still accounts for about half the temperature rise since 1900, it fails to explain a rise of 0.4 °C since 1980. "The curves diverge after 1980," Thejll said, "and it's a startlingly large deviation. Something else is acting on the climate.... It has the fingerprints of the greenhouse effect."[6] (http://archive.newscientist.com/secure/article/article.jsp?rp=1&id=mg16622370.800)

Later that same year, Peter Stott and other researchers at the Hadley Centre in the United Kingdom published a paper in which they reported on the most comprehensive model simulations to date of the climate of the 20th century. 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 team found that combining all of 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". It should be noted that their solar forcing included "spectrally-resolved changes in solar irradiance" and not the indirect effects mediated through cosmic rays for which there is still no accepted mechanism — these ideas are still being fleshed out.Cosmic Rays, Clouds, and Climate, K. S. Carslaw, R. G. Harrison, and J. Kirkby Science Nov 29 2002: 1732-1737 and those articles citing it (http://www.sciencemag.org/cgi/content/abstract/298/5599/1732) 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.[7] (http://www.sciencemag.org:80/cgi/content/full/290/5499/2133) A graphical representation (http://www.grida.no/climate/ipcc_tar/wg1/fig12-7.htm) 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). [8] (http://www.grida.no/climate/ipcc_tar/wg1/index.htm) The Intergovernmental Panel on Climate Change (IPCC) was established in 1988 by two United Nations organizations, the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) to assess the risk of human-induced climate change. The Panel is open to all members of the WMO and UNEP. Its...