Solar variation

Solar variation

Overview
Solar variation is the change in the amount of radiation emitted by the Sun and in its spectral distribution over years to millennia. These variations have periodic components, the main one being the approximately 11-year solar cycle
Solar cycle
The solar cycle, or the solar magnetic activity cycle, is a periodic change in the amount of irradiation from the Sun that is experienced on Earth. It has a period of about 11 years, and is one component of solar variation, the other being aperiodic fluctuations. Solar variation causes changes in...

 (or sunspot cycle). The changes also have aperiodic
Periodic function
In mathematics, a periodic function is a function that repeats its values in regular intervals or periods. The most important examples are the trigonometric functions, which repeat over intervals of length 2π radians. Periodic functions are used throughout science to describe oscillations,...

 fluctuations. In recent decades, solar activity has been measured by satellites, while before it was estimated using 'proxy' variables
Proxy (climate)
In the study of past climates is known as paleoclimatology, climate proxies are preserved physical characteristics of the past that stand in for direct measurements , to enable scientists to reconstruct the climatic conditions that prevailed during much of the Earth's history...

.
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Encyclopedia
Solar variation is the change in the amount of radiation emitted by the Sun and in its spectral distribution over years to millennia. These variations have periodic components, the main one being the approximately 11-year solar cycle
Solar cycle
The solar cycle, or the solar magnetic activity cycle, is a periodic change in the amount of irradiation from the Sun that is experienced on Earth. It has a period of about 11 years, and is one component of solar variation, the other being aperiodic fluctuations. Solar variation causes changes in...

 (or sunspot cycle). The changes also have aperiodic
Periodic function
In mathematics, a periodic function is a function that repeats its values in regular intervals or periods. The most important examples are the trigonometric functions, which repeat over intervals of length 2π radians. Periodic functions are used throughout science to describe oscillations,...

 fluctuations. In recent decades, solar activity has been measured by satellites, while before it was estimated using 'proxy' variables
Proxy (climate)
In the study of past climates is known as paleoclimatology, climate proxies are preserved physical characteristics of the past that stand in for direct measurements , to enable scientists to reconstruct the climatic conditions that prevailed during much of the Earth's history...

. Scientists studying climate change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...

 are interested in understanding the effects of variations in the total and spectral solar irradiance on Earth and its climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...

.

Variations in total solar irradiance were too small to detect with technology available before the satellite era, although the small fraction in ultra-violet light has recently been found to vary significantly more than previously thought over the course of a solar cycle. Total solar output is now measured to vary (over the last three 11-year sunspot
Sunspot
Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection by an effect comparable to the eddy current brake, forming areas of reduced surface temperature....

 cycles) by approximately 0.1% or about 1.3 Watt
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...

s per square meter (W/m2) peak-to-trough during the 11-year sunspot cycle. The amount of solar radiation received at the outer surface of Earth's atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...

 averages 1366 W/m2. There are no direct measurements of the longer-term variation, and interpretations of proxy measures of variations differ. The intensity of solar radiation reaching Earth has been relatively constant through the last 2000 years, with variations of around 0.1-0.2%. Solar variation, together with volcanic activity probably contributed to climate change, for example during the Maunder Minimum
Maunder Minimum
The Maunder Minimum is the name used for the period roughly spanning 1645 to 1715 when sunspots became exceedingly rare, as noted by solar observers of the time....

. However, changes in solar brightness are too weak to explain recent climate change.

History of study into solar variations


The longest recorded aspect of solar variations are changes in sunspot
Sunspot
Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection by an effect comparable to the eddy current brake, forming areas of reduced surface temperature....

s. The first record of sunspots dates to around 800 BC in China and the oldest surviving drawing of a sunspot dates to 1128. In 1610, astronomer
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...

s began using the telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...

 to make observations of sunspots and their motions. Initial study was focused on their nature and behavior. Although the physical aspects of sunspots were not identified until the 20th century, observations continued. Study was hampered during the 17th century due to the low number of sunspots during what is now recognized as an extended period of low solar activity, known as the Maunder Minimum
Maunder Minimum
The Maunder Minimum is the name used for the period roughly spanning 1645 to 1715 when sunspots became exceedingly rare, as noted by solar observers of the time....

. By the 19th century, there was a long enough record of sunspot numbers to infer periodic cycles in sunspot activity. In 1845, Princeton University
Princeton University
Princeton University is a private research university located in Princeton, New Jersey, United States. The school is one of the eight universities of the Ivy League, and is one of the nine Colonial Colleges founded before the American Revolution....

 professors Joseph Henry
Joseph Henry
Joseph Henry was an American scientist who served as the first Secretary of the Smithsonian Institution, as well as a founding member of the National Institute for the Promotion of Science, a precursor of the Smithsonian Institution. During his lifetime, he was highly regarded...

 and Stephen Alexander
Stephen Alexander (astronomer)
Stephen Alexander was a noted astronomer and educator. He was born in Schenectady, New York.He graduated from Union College in 1824. He became a tutor in mathematics at Princeton University in 1832, where he would later become professor of astronomy and mathematics...

 observed the Sun with a thermopile
Thermopile
A thermopile is an electronic device that converts thermal energy into electrical energy. It is composed of several thermocouples connected usually in series or, less commonly, in parallel....

 and determined that sunspots emitted less radiation than surrounding areas of the Sun. The emission of higher than average amounts of radiation later were observed from the solar facula
Facula
A facula , Latin for "little torch", is literally a "bright spot." It is used in planetary nomenclature for naming certain surface features of planets and moons, and is also a type of surface phenomenon on the Sun....

e.

Around 1900, researchers began to explore connections between solar variations and weather on Earth. Of particular note is the work of Charles Greeley Abbot
Charles Greeley Abbot
Charles Greeley Abbot was an American astrophysicist, astronomer and Secretary of the Smithsonian Institution. He was born in Wilton, New Hampshire.-Life:...

. Abbot was assigned by the Smithsonian Astrophysical Observatory
Smithsonian Astrophysical Observatory
The Smithsonian Astrophysical Observatory is a research institute of the Smithsonian Institution headquartered in Cambridge, Massachusetts, where it is joined with the Harvard College Observatory to form the Harvard-Smithsonian Center for Astrophysics .-History:The SAO was founded in 1890 by...

 (SAO) to detect changes in the radiation of the Sun. His team had to begin by inventing instruments to measure solar radiation. Later, when Abbot was head of the SAO, it established a solar station at Calama, Chile
Calama, Chile
Calama is a city and commune in the Atacama Desert in northern Chile. It is the capital of El Loa Province, part of the Antofagasta Region. Calama is one of the driest cities in the world with average annual precipitation of just . The River Loa, Chile's longest, flows through the city...

 to complement its data from Mount Wilson Observatory
Mount Wilson Observatory
The Mount Wilson Observatory is an astronomical observatory in Los Angeles County, California, United States. The MWO is located on Mount Wilson, a 5,715 foot peak in the San Gabriel Mountains near Pasadena, northeast of Los Angeles...

. He detected 27 harmonic periods within the 273-month Hale cycles, including 7, 13, and 39 month patterns. He looked for connections to weather by means such as matching opposing solar trends during a month to opposing temperature and precipitation trends in cities. With the advent of dendrochronology
Dendrochronology
Dendrochronology or tree-ring dating is the scientific method of dating based on the analysis of patterns of tree-rings. Dendrochronology can date the time at which tree rings were formed, in many types of wood, to the exact calendar year...

, scientists such as Waldo S. Glock attempted to connect variation in tree growth to periodic solar variations in the extant record and infer long-term secular variability in the solar constant from similar variations in millennial-scale chronologies.

Statistical studies that correlate weather
Weather
Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate...

 and climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...

 with solar activity have been popular for centuries, dating back at least to 1801, when William Herschel
William Herschel
Sir Frederick William Herschel, KH, FRS, German: Friedrich Wilhelm Herschel was a German-born British astronomer, technical expert, and composer. Born in Hanover, Wilhelm first followed his father into the Military Band of Hanover, but emigrated to Britain at age 19...

 noted an apparent connection between wheat prices and sunspot records. They now often involve high-density global datasets compiled from surface networks and weather satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

 observations and/or the forcing of climate model
Climate model
Climate models use quantitative methods to simulate the interactions of the atmosphere, oceans, land surface, and ice. They are used for a variety of purposes from study of the dynamics of the climate system to projections of future climate...

s with synthetic or observed solar variability to investigate the detailed processes by which the effects of solar variations propagate through the Earth's climate system.

Solar activity and irradiance measurement


Direct irradiance measurements have only been available during the last three cycles and are based on a composite of many different observing satellites. However, the correlation between irradiance measurements and other proxies of solar activity make it reasonable to estimate past solar activity. Most important among these proxies is the record of sunspot observations that has been recorded since ~1610. Since sunspots and associated faculae are directly responsible for small changes in the brightness of the sun, they are closely correlated to changes in solar output. Direct measurements of radio emissions from the Sun at 10.7 cm also provide a proxy of solar activity that can be measured from the ground since the Earth's atmosphere is transparent at this wavelength. Lastly, solar flares are a type of solar activity that can impact human life on Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 by affecting electrical systems, especially satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

s. Flares usually occur in the presence of sunspots, and hence the two are correlated, but flares themselves make only tiny perturbations of the solar luminosity
Luminosity
Luminosity is a measurement of brightness.-In photometry and color imaging:In photometry, luminosity is sometimes incorrectly used to refer to luminance, which is the density of luminous intensity in a given direction. The SI unit for luminance is candela per square metre.The luminosity function...

.

Recently it has been claimed that the total solar irradiance is varying in ways that are not duplicated by changes in sunspot observations or radio emissions, though Willson, DeWitte, and others have pointed out that these shifts in irradiance may be no more than the result of calibration problems in the measuring satellites. These speculations also admit the possibility that a small long-term trend might exist in solar irradiance.

Sunspots


Sunspot
Sunspot
Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection by an effect comparable to the eddy current brake, forming areas of reduced surface temperature....

s are relatively dark areas on the radiating 'surface' (photosphere
Photosphere
The photosphere of an astronomical object is the region from which externally received light originates. The term itself is derived from Ancient Greek roots, φῶς, φωτός/phos, photos meaning "light" and σφαῖρα/sphaira meaning "sphere", in reference to the fact that it is a spheric surface perceived...

) of the Sun where intense magnetic activity inhibits convection and cools the photosphere
Photosphere
The photosphere of an astronomical object is the region from which externally received light originates. The term itself is derived from Ancient Greek roots, φῶς, φωτός/phos, photos meaning "light" and σφαῖρα/sphaira meaning "sphere", in reference to the fact that it is a spheric surface perceived...

. Faculae are slightly brighter areas that form around sunspot groups as the flow of energy to the photosphere is re-established and both the normal flow and the sunspot-blocked energy elevate the radiating 'surface' temperature. Scientists have speculated on possible relationships between sunspots and solar luminosity since the historical sunspot area record began in the 17th century. Correlations are now known to exist with decreases in luminosity caused by sunspots (generally < - 0.3 %) and increases (generally < + 0.05 %) caused both by faculae that are associated with active regions as well as the magnetically active 'bright network'.

Modulation of the solar luminosity by magnetically active regions was confirmed by satellite measurements of total solar irradiance (TSI) by the ACRIM1 experiment on the Solar Maximum Mission
Solar Maximum Mission
The Solar Maximum Mission satellite was designed to investigate solar phenomenon, particularly solar flares. It was launched on February 14, 1980....

 (launched in 1980). The modulations were later confirmed in the results of the ERB experiment launched on the Nimbus 7 satellite in 1978. Sunspots in magnetically active regions are cooler and 'darker' than the average photosphere
Photosphere
The photosphere of an astronomical object is the region from which externally received light originates. The term itself is derived from Ancient Greek roots, φῶς, φωτός/phos, photos meaning "light" and σφαῖρα/sphaira meaning "sphere", in reference to the fact that it is a spheric surface perceived...

 and cause temporary decreases in TSI of as much as 0.3 %. Faculae in magnetically active regions are hotter and 'brighter' than the average photosphere
Photosphere
The photosphere of an astronomical object is the region from which externally received light originates. The term itself is derived from Ancient Greek roots, φῶς, φωτός/phos, photos meaning "light" and σφαῖρα/sphaira meaning "sphere", in reference to the fact that it is a spheric surface perceived...

 and cause temporary increases in TSI.

The net effect during periods of enhanced solar magnetic activity is increased radiant output of the sun because faculae are larger and persist longer than sunspots. Conversely, periods of lower solar magnetic activity and fewer sunspots (such as the Maunder Minimum
Maunder Minimum
The Maunder Minimum is the name used for the period roughly spanning 1645 to 1715 when sunspots became exceedingly rare, as noted by solar observers of the time....

) may correlate with times of lower terrestrial irradiance from the sun.

There had been some suggestion that variations in the solar diameter might also cause significant variations in output. But recent work, mostly from the Michelson Doppler Imager instrument on SOHO
Solar and Heliospheric Observatory
The Solar and Heliospheric Observatory is a spacecraft built by a European industrial consortium led by Matra Marconi Space that was launched on a Lockheed Martin Atlas IIAS launch vehicle on December 2, 1995 to study the Sun, and has discovered over 2100 comets. It began normal operations in May...

, shows these changes to be small, about 0.001%, much less than the effect of magnetic activity changes (Dziembowski et al., 2001).

Various studies have been made using sunspot number (for which records extend over hundreds of years) as a proxy
Proxy (statistics)
In statistics, 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...

 for solar output (for which good records only extend for a few decades). Also, ground instruments have been calibrated by comparison with high-altitude and orbital instruments. Researchers have combined present readings and factors to adjust historical data. Other proxy data — such as the abundance of cosmogenic isotopes — have been used to infer solar magnetic activity and thus likely brightness. Sunspot activity has been measured using the Wolf number
Wolf number
The Wolf number is a quantity that measures the number of sunspots and groups of sunspots present on the surface of the sun....

for about 300 years. This index (also known as the Zürich number) uses both the number of sunspots and the number of groups of sunspots to compensate for variations in measurement. A 2003 study by Ilya Usoskin of the University of Oulu
University of Oulu
The University of Oulu is one of the largest universities in Finland, located in the city of Oulu. It was founded on July 8, 1958. The university has around 16,000 students and 3,000 staff...

, Finland
Finland
Finland , officially the Republic of Finland, is a Nordic country situated in the Fennoscandian region of Northern Europe. It is bordered by Sweden in the west, Norway in the north and Russia in the east, while Estonia lies to its south across the Gulf of Finland.Around 5.4 million people reside...

 found that sunspots had been more frequent since the 1940s than in the previous 1150 years.

Sunspot numbers over the past 11,400 years have been reconstructed using dendrochronologically
Dendrochronology
Dendrochronology or tree-ring dating is the scientific method of dating based on the analysis of patterns of tree-rings. Dendrochronology can date the time at which tree rings were formed, in many types of wood, to the exact calendar year...

 dated radiocarbon concentrations. The level of solar activity during the past 70 years is exceptional — the last period of similar magnitude occurred around 9,000 years ago (during the warm Boreal period
Boreal (period)
In paleoclimatology of the Holocene, the Boreal was the first of the Blytt-Sernander sequence of north European climatic phases that were originally based on the study of Danish peat bogs, named for Axel Blytt and Rutger Sernander, who first established the sequence. In peat bog sediments, the...

). The Sun was at a similarly high level of magnetic activity for only ~10% of the past 11,400 years, and almost all of the earlier high-activity periods were shorter than the present episode.


Solar activity events and approximate dates
Event Start End
Oort minimum (see Medieval Warm Period
Medieval Warm Period
The Medieval Warm Period , Medieval Climate Optimum, or Medieval Climatic Anomaly was a time of warm climate in the North Atlantic region, that may also have been related to other climate events around the world during that time, including in China, New Zealand, and other countries lasting from...

)
1040 1080
Medieval maximum (see Medieval Warm Period
Medieval Warm Period
The Medieval Warm Period , Medieval Climate Optimum, or Medieval Climatic Anomaly was a time of warm climate in the North Atlantic region, that may also have been related to other climate events around the world during that time, including in China, New Zealand, and other countries lasting from...

)
1100 1250
Wolf minimum 1280 1350
Spörer Minimum
Spörer Minimum
The Spörer Minimum was a 90-year span of low solar activity, from about 1460 until 1550, which was identified and named by John A. Eddy in a landmark 1976 paper published in Science titled "The Maunder Minimum"...

 
1450 1550
Maunder Minimum
Maunder Minimum
The Maunder Minimum is the name used for the period roughly spanning 1645 to 1715 when sunspots became exceedingly rare, as noted by solar observers of the time....

 
1645 1715
Dalton Minimum
Dalton Minimum
The Dalton Minimum was a period of low solar activity, named after the English meteorologist John Dalton, lasting from about 1790 to 1830. Like the Maunder Minimum and Spörer Minimum, the Dalton Minimum coincided with a period of lower-than-average global temperatures...

 
1790 1820
Modern Maximum
Modern Maximum
The Modern Maximum refers to the ongoing period of relatively high solar activity that began circa 1900. This period is a natural example of solar variation, and one of many that are known from proxy records of past solar variability. The Modern Maximum reached a double peak once in the 1950s and...

 
1900 present


A list of historical Grand minima of solar activity includes also Grand minima ca. 690 AD, 360 BC, 770 BC, 1390 BC, 2860 BC, 3340 BC, 3500 BC, 3630 BC, 3940 BC, 4230 BC, 4330 BC, 5260 BC, 5460 BC, 5620 BC, 5710 BC, 5990 BC, 6220 BC, 6400 BC, 7040 BC, 7310 BC, 7520 BC, 8220 BC, 9170 BC.

Solar cycles


The sun undergoes various quasi-periodic changes, the principal one referred to as the solar cycle
Solar cycle
The solar cycle, or the solar magnetic activity cycle, is a periodic change in the amount of irradiation from the Sun that is experienced on Earth. It has a period of about 11 years, and is one component of solar variation, the other being aperiodic fluctuations. Solar variation causes changes in...

 has an 11-year quasi-period. Only the 11 and closely related 22 year cycles are clear in the observations.

  • 11 years: Most obvious is a gradual increase and more rapid decrease of the number of sunspots over a period ranging from 9 to 12 years, called the Schwabe cycle, named after Heinrich Schwabe
    Heinrich Schwabe
    Samuel Heinrich Schwabe a German astronomer remembered for his work on sunspots.Schwabe was born at Dessau. At first an apothecary, he turned his attention to astronomy, and in 1826 commenced his observations on sunspots. Schwabe was trying to discover a new planet inside the orbit of Mercury...

    . Differential rotation of the sun's convection zone (as a function of latitude) consolidates magnetic flux tubes, increases their magnetic field
    Magnetic field
    A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

     strength and makes them buoyant (see Babcock Model
    Babcock Model
    The Babcock Model describes a mechanism which can explain magnetic and sunspot patterns observed on the Sun.A modern understanding of sunspots starts with George Ellery Hale, in which magnetic fields and sunspots are linked. Hale suggested that the sunspot cycle period is 22 years, covering two...

    ). As they rise through the solar atmosphere they partially block the convective flow of energy, cooling their region of the photosphere
    Photosphere
    The photosphere of an astronomical object is the region from which externally received light originates. The term itself is derived from Ancient Greek roots, φῶς, φωτός/phos, photos meaning "light" and σφαῖρα/sphaira meaning "sphere", in reference to the fact that it is a spheric surface perceived...

    , causing 'sunspots'. The Sun's apparent surface, the photosphere, radiates more actively when there are more sunspots. Satellite monitoring of solar luminosity since 1980 has shown there is a direct relationship between the solar activity (sunspot) cycle and luminosity with a solar cycle peak-to-peak amplitude of about 0.1 %. Luminosity has also been found to decrease by as much as 0.3 % on a 10 day timescale when large groups of sunspots rotate across the Earth's view and increase by as much as 0.05 % for up to 6 months due to faculae associated with the large sunspot groups.

  • 22 years: Hale cycle, named after George Ellery Hale
    George Ellery Hale
    George Ellery Hale was an American solar astronomer.-Biography:Hale was born in Chicago, Illinois. He was educated at MIT, at the Observatory of Harvard College, , and at Berlin . As an undergraduate at MIT, he is known for inventing the spectroheliograph, with which he made his discovery of...

    . The magnetic field of the Sun reverses during each Schwabe cycle, so the magnetic poles return to the same state after two reversals.
  • 87 years (70–100 years): Gleissberg cycle, named after Wolfgang Gleißberg, is thought to be an amplitude modulation of the 11-year Schwabe Cycle (Sonnett and Finney, 1990), Braun, et al., (2005).
  • 210 years: Suess cycle (a.k.a. de Vries cycle). Braun, et al., (2005).
  • 2,300 years: Hallstatt cycle
  • 6000 years (Xapsos and Burke, 2009).

Other patterns have been detected:
  • In carbon-14
    Carbon-14
    Carbon-14, 14C, or radiocarbon, is a radioactive isotope of carbon with a nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues , to date archaeological, geological, and hydrogeological...

    : 105, 131, 232, 385, 504, 805, 2,241 years (Damon and Sonnett, 1991).
  • During the Upper Permian
    Permian
    The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

     240 million years ago, mineral layers created in the Castile Formation show cycles of 2,500 years.


The sensitivity of climate to cyclical variations in solar forcing will be higher for longer cycles due to the thermal inertia of the ocean, which acts to damp high frequencies. Using a phenomenological approach, Scafetta
Nicola Scafetta
Nicola Scafetta is a research scientist at Duke University Physics Department. His research interests are in theoretical and applied statistics and nonlinear models of complex processes...

 and West (2005) found that the climate was 1.5 times as sensitive to 22 year cyclical forcing relative to 11 year cyclical forcing, and that the thermal inertial induced a lag of approximately 2.2 years in cyclic climate response in the temperature data.

Predictions based on patterns

  • A simple model based on emulating harmonics by multiplying the basic 11-year cycle by powers of 2 produced results similar to Holocene
    Holocene
    The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...

     behavior. Extrapolation suggests a gradual cooling during the next few centuries with intermittent minor warmups and a return to near Little Ice Age
    Little Ice Age
    The Little Ice Age was a period of cooling that occurred after the Medieval Warm Period . While not a true ice age, the term was introduced into the scientific literature by François E. Matthes in 1939...

     conditions within the next 500 years. This cool period then may be followed approximately 1,500 years from now by a return to altithermal conditions similar to the previous Holocene Maximum.
  • There is weak evidence for a quasi-periodic variation in the sunspot cycle amplitudes with a period of about 90 years (Gleisberg cycle). These characteristics indicate that the next solar cycle should have a maximum smoothed sunspot number of about 145±30 in 2010 while the following cycle should have a maximum of about 70±30 in 2023.
  • Because carbon-14 cycles are quasi periodic, Damon and Sonett (1989) predict future climate:



Solar irradiance, or insolation
Insolation
Insolation is a measure of solar radiation energy received on a given surface area in a given time. It is commonly expressed as average irradiance in watts per square meter or kilowatt-hours per square meter per day...

, is the amount of sunlight which reaches the Earth. The equipment used might measure optical brightness, total radiation, or radiation in various frequencies. Historical estimates use various measurements and proxies.
Cycle length Cycle name Last positive
carbon-14 anomaly
Next "warming"
232 --?-- AD 1922 (cool) AD 2038
208 Suess AD 1898 (cool) AD 2210
88 Gleisberg AD 1986 (cool) AD 2030

Solar irradiance of Earth and its surface


There are two common meanings:


  • the radiation reaching the upper atmosphere
  • the radiation reaching some point within the atmosphere, including the surface.


Various gases within the atmosphere absorb some solar radiation at different wavelengths, and clouds and dust also affect it. Measurements above the atmosphere are needed to determine variations in solar output, to avoid the confounding effects of changes within the atmosphere. There is some evidence that sunshine at the Earth's surface has been decreasing in the last 50 years (see global dimming
Global dimming
Global dimming is the gradual reduction in the amount of global direct irradiance at the Earth's surface that was observed for several decades after the start of systematic measurements in the 1950s. The effect varies by location, but worldwide it has been estimated to be of the order of a 4%...

) possibly caused by increased atmospheric pollution, whilst over roughly the same timespan solar output has been nearly constant.

Milankovitch cycle variations


Some variations in insolation are not due to solar changes but rather due to the Earth moving closer or further from the Sun, or changes in the latitudinal distribution of radiation. These have caused variations of as much as 25% (locally; global average changes are much smaller) in solar insolation over long periods. The most recent significant event was an axial tilt of 24° during boreal summer at near the time of the Holocene climatic optimum
Holocene climatic optimum
The Holocene Climate Optimum was a warm period during roughly the interval 9,000 to 5,000 years B.P.. This event has also been known by many other names, including: Hypsithermal, Altithermal, Climatic Optimum, Holocene Optimum, Holocene Thermal Maximum, and Holocene Megathermal.This warm period...

.

Solar interactions with Earth


There are several hypotheses for how solar variations may affect Earth. Some variations, such as changes in the size of the Sun, are presently only of interest in the field of astronomy
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...

.

Changes in total irradiance

  • Total solar irradiance changes slowly on decadal and longer timescales.
  • The variation during recent solar magnetic activity cycles has been about 0.1% (peak-to-peak).
  • Variations corresponding to solar changes with periods of 9–13, 18–25, and >100 years have been detected in sea-surface temperatures.
  • In contrast to older reconstructions, most recent reconstructions of total solar irradiance point to an only small increase of only about 0.05 % to 0.1 % between Maunder Minimum and the present.
  • Different composite reconstructions of total solar irradiance observations by satellites show different trends since 1980; see the global warming section below.

Changes in ultraviolet irradiance

  • Ultraviolet irradiance (EUV) varies by approximately 1.5 percent from solar maxima to minima, for 200 to 300 nm UV.
  • Energy changes in the UV wavelengths involved in production and loss of ozone
    Ozone
    Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...

     have atmospheric effects.
    • The 30 hPa
      HPA
      -Organizations:*Halifax Port Authority, a port authority in Canada*Hamburg Port Authority, the port authority for the Port of Hamburg, Germany*Health Protection Agency, a health organization in the United Kingdom...

       atmospheric pressure level has changed height in phase with solar activity during the last 4 solar cycles.
    • UV irradiance increase causes higher ozone production, leading to stratospheric heating and to poleward displacements in the stratospheric and tropospheric wind systems.
  • A proxy study estimates that UV has increased by 4.3% since the Maunder Minimum.

Changes in the solar wind and the Sun's magnetic flux

  • A more active solar wind and stronger magnetic field reduces the cosmic rays striking the Earth's atmosphere.
  • Variations in the solar wind affect the size and intensity of the heliosphere
    Heliosphere
    The heliosphere is a bubble in space "blown" into the interstellar medium by the solar wind. Although electrically neutral atoms from interstellar volume can penetrate this bubble, virtually all of the material in the heliosphere emanates from the Sun itself...

    , the volume larger than the Solar System filled with solar wind particles.
  • Cosmogenic production of 14C, 10Be and 36Cl show changes tied to solar activity.
  • Cosmic ray ionization in the upper atmosphere does change, but significant effects are not obvious.
  • As the solar coronal-source magnetic flux doubled during the past century, the cosmic-ray flux has decreased by about 15%.
  • The Sun's total magnetic flux rose by a factor of 1.41 from 1964–1996 and by a factor of 2.3 since 1901.

Effects on clouds


Changes in ionization affect the abundance of aerosols that serve as the nuclei of condensation for cloud formation. As a result, ionization levels potentially affect levels of condensation, low clouds, relative humidity, and albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

 due to clouds. Clouds formed from greater amounts of condensation nuclei are brighter, longer lived, and likely to produce less precipitation. Changes of 3–4% in cloudiness and concurrent changes in cloud top temperatures have been correlated to the 11 and 22 year solar (sunspot) cycles
Solar cycle
The solar cycle, or the solar magnetic activity cycle, is a periodic change in the amount of irradiation from the Sun that is experienced on Earth. It has a period of about 11 years, and is one component of solar variation, the other being aperiodic fluctuations. Solar variation causes changes in...

, with increased GCR levels during "antiparallel" cycles.
Global average cloud cover change has been found to be 1.5–2%. Several studies of GCR and cloud cover variations have found positive correlation at latitudes greater than 50° and negative correlation at lower latitudes. However, not all scientists accept this correlation as statistically significant, and some that do attribute it to other solar variability (e.g. UV or total irradiance variations) rather than directly to GCR changes. 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.
  • Cosmic rays have been hypothesized to affect formation of clouds through possible effects on production of cloud condensation nuclei.
  • 1983–1994 data from the International Satellite Cloud Climatology Project
    International Satellite Cloud Climatology Project
    The International Satellite Cloud Climatology Project was established as the first project of the World Climate Research Program . Since its inception in 1982, there have been two phases, 1983–1995 and 1995–present. The project is responsible for collection and analysis of weather satellite...

     (ISCCP) showed that global low cloud formation was highly correlated with cosmic ray flux; subsequent to this the correlation breaks down.
  • Several percent variation in cosmic rays and in tropospheric ionization occurs when the interplanetary magnetic field changes over the solar cycle, greater than the typically 0.1% variation in total solar irradiance meanwhile.
  • Particularly at high latitude
    Latitude
    In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

    s where the shielding effect of Earth's magnetic field is less, some studies suggest cosmic ray variation may impact terrestrial low altitude cloud cover (unlike a lack of correlation with high altitude clouds), making such partially influenced by the solar-driven interplanetary magnetic field (as well as passage through the galactic arms over longer timeframes).

Other effects due to solar variation


Interaction of solar particles, the solar magnetic field, and the Earth's magnetic field, cause variations in the particle and electromagnetic fields at the surface of the planet. Extreme solar events can affect electrical devices. Weakening of the Sun's magnetic field is believed to increase the number of interstellar cosmic rays which reach Earth's atmosphere, altering the types of particles reaching the surface. It has been speculated that a change in cosmic rays could cause an increase in certain types of clouds, affecting Earth's albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

.

Geomagnetic effects


The Earth's polar aurorae are visual displays created by interactions between the solar wind, the solar magnetosphere, the Earth's magnetic field, and the Earth's atmosphere. Variations in any of these affect aurora displays.

Sudden changes can cause the intense disturbances in the Earth's magnetic fields which are called geomagnetic storm
Geomagnetic storm
A geomagnetic storm is a temporary disturbance of the Earth's magnetosphere caused by a disturbance in the interplanetary medium. A geomagnetic storm is a major component of space weather and provides the input for many other components of space weather...

s.

Solar proton events


Energetic proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....

s can reach Earth within 30 minutes of a major flare's peak. During such a solar proton event
Solar proton event
A Solar proton event occurs when protons emitted by the Sun become accelerated to very high energies either close to the Sun during a solar flare or in interplanetary space by the shocks associated with coronal mass ejections. These high energy protons cause several effects. They can penetrate the...

, Earth is showered in energetic solar particles (primarily protons) released from the flare site. Some of these particles spiral down Earth's magnetic field lines, penetrating the upper layers of our atmosphere where they produce additional ionization and may produce a significant increase in the radiation environment.

Galactic cosmic rays



An increase in solar activity (more sunspots) is accompanied by an increase in the "solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...

," which is an outflow of ionized particles, mostly protons and electrons, from the sun. The Earth's geomagnetic field, the solar wind, and the solar magnetic field deflect galactic cosmic ray
Galactic cosmic ray
Galactic cosmic rays are cosmic rays that have their origin inside our Galaxy. GCRs are high-energy charged particles, and are usually protons, electrons, and fully ionized nuclei of light elements...

s (GCR). A decrease in solar activity increases the GCR penetration of the troposphere and stratosphere. GCR particles are the primary source of ionization in the troposphere above 1 km (below 1 km, radon
Radon
Radon is a chemical element with symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as the decay product of uranium or thorium. Its most stable isotope, 222Rn, has a half-life of 3.8 days...

 is a dominant source of ionization in many areas).

Levels of GCRs have been indirectly recorded by their influence on the production of carbon-14 and beryllium-10. The Hallstatt solar cycle length of approximately 2300 years is reflected by climatic Dansgaard-Oeschger events. The 80–90 year solar Gleissberg cycles appear to vary in length depending upon the lengths of the concurrent 11 year solar cycles, and there also appear to be similar climate patterns occurring on this time scale.

Carbon-14 production


The production of carbon-14
Carbon-14
Carbon-14, 14C, or radiocarbon, is a radioactive isotope of carbon with a nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues , to date archaeological, geological, and hydrogeological...

 (radiocarbon: 14C) also is related to solar activity. Carbon-14 is produced in the upper atmosphere when cosmic ray bombardment of atmospheric nitrogen (14N) induces the Nitrogen to undergo β+ decay, thus transforming into an unusual isotope of Carbon with an atomic weight of 14 rather than the more common 12. Because cosmic rays are partially excluded from the Solar System by the outward sweep of magnetic fields in the solar wind, increased solar activity results in a reduction of cosmic rays reaching the Earth's atmosphere and thus reduces 14C production. Thus the cosmic ray intensity and carbon-14 production vary inversely to the general level of solar activity.

Therefore, the atmospheric 14C concentration is lower during sunspot maxima and higher during sunspot minima. By measuring the captured 14C in wood and counting tree rings, production of radiocarbon relative to recent wood can be measured and dated. A reconstruction of the past 10,000 years shows that the 14C production was much higher during the mid-Holocene
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...

 7,000 years ago and decreased until 1,000 years ago. In addition to variations in solar activity, the long term trends in carbon-14 production are influenced by changes in the Earth's geomagnetic field and by changes in carbon cycling within the biosphere
Biosphere
The biosphere is the global sum of all ecosystems. It can also be called the zone of life on Earth, a closed and self-regulating system...

 (particularly those associated with changes in the extent of vegetation since the last ice age
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...

).

Variation, and connection to global warming


Solar variations are of interest outside their own field primarily because of their potential impact on climate, although the scientific consensus is that solar variations do not play a major role in determining present-day global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...

. The Intergovernmental Panel on Climate Change
Intergovernmental Panel on Climate Change
The Intergovernmental Panel on Climate Change is a scientific intergovernmental body which provides comprehensive assessments of current scientific, technical and socio-economic information worldwide about the risk of climate change caused by human activity, its potential environmental and...

 Third Assessment Report
IPCC Third Assessment Report
The IPCC Third Assessment Report, Climate Change 2001, is an assessment of available scientific and socio-economic information on climate change by the IPCC. The IPCC was established in 1988 by the United Nations Environment Programme and the UN's World Meteorological Organization ".....

 states that the measured magnitude of recent solar variation is much smaller than the amplification effect due to greenhouse gases.

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.http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-7.html#2-7-1

In 2002, Lean et al. 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. 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."

A paper by Benestad and Schmidt 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, 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.) with the total solar irradiance experiencing low secular variability (as the one shown by Wang et al.). Under this scenario, according to Scafetta and West, the Sun might have contributed 50% of the observed global warming since 1900. 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.

Crucial to the understanding of possible solar impact on terrestrial climate is accurate measurement of solar forcing. Unfortunately accurate measurement of incident solar radiation is only available since the satellite era, and even that is open to dispute: different groups find different values, due to different methods of cross-calibrating essentially the same datasets.http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-7-1-1.html Scafetta and Willson found significant variations of solar luminosity between 1980 and 2000. But Lockwood and Frohlich find that solar forcing has declined since 1987.


Solar variation theory


Variations in total solar irradiance (TSI) were found to be the most likely cause of significant climate change prior to the industrial era by a U.S. National Academy of Sciences study. A 2007 paper by Scafetta and West linked solar proxy data and lower tropospheric temperature suggesting that TSI variations during the industrial era may have contributed to global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...

. This contrasts with the results from global circulation models that predict solar forcing of climate through direct radiative forcing
Radiative forcing
In climate science, radiative forcing is generally defined as the change in net irradiance between different layers of the atmosphere. Typically, radiative forcing is quantified at the tropopause in units of watts per square meter. A positive forcing tends to warm the system, while a negative...

 is too small to explain a significant contribution. The relative significance of solar variability and other forcings of climate change during the industrial era is an area of ongoing research.

Sami Solanki
Sami Solanki
Sami Khan Solanki is the former Managing Director of the Max Planck Institute for Solar System Research , Director of the Sun-Heliosphere Department of MPS, a scientific member of the Max Planck Society, and a Chair of the International Max Planck Research School on Physical Processes in the...

, the director of the Max Planck Institute for Solar System Research
Max Planck Institute for Solar System Research
The Max Planck Institute for Solar System Research is a research institute in Astronomy/Astrophysics, located in Lindau , Germany; 20 km north east of Göttingen. The exploration of our solar system is the central theme for the scientific research done at this Institute...

 in Katlenburg-Lindau
Katlenburg-Lindau
Katlenburg-Lindau is a municipality in the Landkreis of Northeim, in Lower Saxony, Germany. It is situated approx. 10 km southeast of Northeim, and 20 km northeast of Göttingen...

, Germany said:
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.


Nevertheless, Solanki agrees with the scientific consensus
Scientific opinion on climate change
The predominant scientific opinion on climate change is that the Earth is in an ongoing phase of global warming primarily caused by an enhanced greenhouse effect due to the anthropogenic release of carbon dioxide and other greenhouse gases...

 that the marked upswing in temperatures since about 1980 is attributable to human activity.
"Just how large this role [of solar variation] is, must still be investigated, since, according to our latest knowledge on the variations of the solar magnetic field, the significant increase in the Earth’s temperature since 1980 is indeed to be ascribed to the greenhouse effect caused by carbon dioxide."


The theories have usually represented one of three types:
  • Solar irradiance changes directly affecting the climate. This is generally considered unlikely, as the amplitudes of the variations in solar irradiance are much too small to have the observed relation absent some amplification process.
  • Variations in the ultraviolet component having an effect. 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 explain a larger solar signal in climate.
  • 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 the 2003 paper "Solar activity and terrestrial climate: an analysis of some purported correlations" Peter Laut demonstrates problems with some of the most popular, notably those by Svensmark and by Lassen (below). Damon and Laut report in Eos 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). Damon and Laut, however, argue 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. Note that the prior link to "graph" is one such example of this.

Sallie Baliunas
Sallie Baliunas
Sallie Baliunas is an astrophysicist at the Harvard-Smithsonian Center for Astrophysics in the Solar, Stellar, and Planetary Sciences Division and formerly Deputy Director of the Mount Wilson Observatory. She serves as Senior Scientist at the George C. Marshall Institute in Washington, DC, and...

, 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."

On May 6, 2000, however, New Scientist magazine reported that Lassen and astrophysicist Peter Thejll
Peter Thejll
Peter Andreas Thejll is a noted Danish astrophysicist and climate researcher. His research in solar variation helped provide conclusive evidence of the greenhouse effect on the Earth's climate in the late 20th century...

 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."

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. 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. A graphical representation 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
Intergovernmental Panel on Climate Change
The Intergovernmental Panel on Climate Change is a scientific intergovernmental body which provides comprehensive assessments of current scientific, technical and socio-economic information worldwide about the risk of climate change caused by human activity, its potential environmental and...

 (IPCC).

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

Historical perspective


Physicist and historian Spencer R. Weart
Spencer R. Weart
Spencer R. Weart was the director of the Center for History of Physics of the American Institute of Physics from 1971 until his retirement in 2009. Originally trained as a physicist, he is now a historian....

 in The Discovery of Global Warming (2003) writes:

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."

See also



  • Solar cycle
    Solar cycle
    The solar cycle, or the solar magnetic activity cycle, is a periodic change in the amount of irradiation from the Sun that is experienced on Earth. It has a period of about 11 years, and is one component of solar variation, the other being aperiodic fluctuations. Solar variation causes changes in...

  • Sunlight
    Sunlight
    Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...

  • Sunspot
    Sunspot
    Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection by an effect comparable to the eddy current brake, forming areas of reduced surface temperature....

  • Sunspot cycle

  • List of solar cycles
  • Formation and evolution of the Solar System
    Formation and evolution of the Solar System
    The formation and evolution of the Solar System is estimated to have begun 4.568 billion years ago with the gravitational collapse of a small part of a giant molecular cloud...

  • Sun Life cycle
  • Stellar evolution
    Stellar evolution
    Stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from only a few million years to trillions of years .Stellar evolution is not studied by observing the life of a single...



Footnotes




External links

  • Solar Climatic Effects (Recent Influence) — Summary. Center for the Study of Carbon Dioxide and Global Change
    Center for the Study of Carbon Dioxide and Global Change
    The Center for the Study of Carbon Dioxide and Global Change is a 501 non-profit organization based in Arizona in the United States...

    . 19 March 2003. http://www.co2science.org/subject/s/summaries/solarrecin.htm
  • NOAA / NESDIS / NGDC (2002) Solar Variability Affecting Earth NOAA CD-ROM NGDC-05/01. This CD-ROM contains over 100 solar-terrestrial and related global data bases covering the period through April 1990. http://www.ngdc.noaa.gov/stp/CDROM/solar_variability.html Aeronomy Laboratory, NOAA/ERL, Boulder, Colorado. U.S. National Report to IUGG, 1991–1994
  • Recent Total Solar Irradiance data updated every Monday