External forcing - Revision history

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	[[Category:Done ~~2016~~-01~~-15~~]]		[[Category:Done 2026-07-01]]
	[[File:5510488494_03cefcb27a_z.jpg\|360px\|thumb\|right\|Figure 1. Sunspots. Note that in the image~~, these sunspots~~ are actually large enough to ~~engulg~~ the Earth, as sunspots range in diameter from about 1500 km to 50 000 km.<ref>NASA Goddard Space Flight Center. (October 18, 2015). ''Sunspots'' [Online]. Available: https://www.flickr.com/photos/gsfc/5510488494</ref>]]		[[File:5510488494_03cefcb27a_z.jpg\|360px\|thumb\|right\|Figure 1. Sunspots. Note that the sunspots in the image are actually large enough to engulf the Earth, as sunspots range in diameter from about 1500 km to 50 000 km.<ref>NASA Goddard Space Flight Center. (October 18, 2015). ''Sunspots'' [Online]. Available: https://www.flickr.com/photos/gsfc/5510488494</ref>]]
	<onlyinclude>An '''external forcing''' is a type of [[climate forcing]] agent that impacts the [[climate]] system while being outside of the climate system itself.</onlyinclude> External forcings include galactic variations, orbital variations, and solar variations - such as sunspots, shown in Figure 1.<ref name=IPCC_SREX>IPCC, 2012: Glossary of terms. In: Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation [Field, C.B., V. Barros, T.F. Stocker, D. Qin, D.J. Dokken, K.L. Ebi, M.D. Mastrandrea, K.J. Mach, G.-K. Plattner, S.K. Allen, M. Tignor, and P.M. Midgley (eds.)]. A Special Report of Working Groups I and II of the Intergovernmental Panel on Climate Change (IPCC). Cambridge University Press, Cambridge, UK, and New York, NY, USA, pp. 555-564.</ref> These external forcing mechanisms can happen on relatively small time scales - around 10 years - up to extremely large time scales of 10<sup>9</sup> years.<ref name="RE1">Global Climate Change. (November 2, 2015). ''External Forcing Mechanisms" [Online]. Available: http://www.global-climate-change.org.uk/2-5-1.php</ref>		<onlyinclude>An '''external forcing''' is a type of [[climate forcing]] agent that impacts the [[climate]] system while being outside of the climate system itself.</onlyinclude> External forcings include galactic variations, orbital variations, and solar variations - such as sunspots, shown in Figure 1.<ref name=IPCC_SREX>IPCC, 2012: Glossary of terms. In: Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation [Field, C.B., V. Barros, T.F. Stocker, D. Qin, D.J. Dokken, K.L. Ebi, M.D. Mastrandrea, K.J. Mach, G.-K. Plattner, S.K. Allen, M. Tignor, and P.M. Midgley (eds.)]. A Special Report of Working Groups I and II of the Intergovernmental Panel on Climate Change (IPCC). Cambridge University Press, Cambridge, UK, and New York, NY, USA, pp. 555-564.</ref> These external forcing mechanisms can happen on relatively small time scales - around 10 years - up to extremely large time scales of 10<sup>9</sup> years.<ref name="RE1">Global Climate Change. (November 2, 2015). ''External Forcing Mechanisms" [Online]. Available: http://www.global-climate-change.org.uk/2-5-1.php</ref>

	==Types of External Forcings==		==Types of External Forcings==
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	===Galactic Variations===		===Galactic Variations===
	In addition to the planets orbiting the Sun in the Solar System, the Solar System itself orbits the centre of the galaxy, and this rotation has been noted as a possible source of external forcings. Over the course of a galactic year - 303 ''million years'' - there is some level of variation in the composition of the [[matter]] that exists in space between the stars.<ref>Camel Climate Change. (November 7, 2015). ''Galactic Variations'' [Online]. Available: http://www.camelclimatechange.org/topics/view/51cbfc8ef702fc2ba812d48d/</ref> This variation in the makeup of space could influence the amount of [[solar radiation]] that hits the Earth. This change in solar radiation levels makes galactic variations a type of possible [[radiative forcing]]. However, it is difficult to confirm this variation as a type of external forcing because of the extremely long ~~timescale~~.<ref name="RE1"/>		In addition to the planets orbiting the Sun in the Solar System, the Solar System itself orbits the centre of the galaxy, and this rotation has been noted as a possible source of external forcings. Over the course of a galactic year - 303 ''million years'' - there is some level of variation in the composition of the [[matter]] that exists in space between the stars.<ref>Camel Climate Change. (November 7, 2015). ''Galactic Variations'' [Online]. Available: http://www.camelclimatechange.org/topics/view/51cbfc8ef702fc2ba812d48d/</ref> This variation in the makeup of space could influence the amount of [[solar radiation]] that hits the Earth. This change in solar radiation levels makes galactic variations a type of possible [[radiative forcing]]. However, it is difficult to confirm this variation as a type of external forcing because of the extremely long time scale.<ref name="RE1"/>

	===Orbital Variations===		===Orbital Variations===
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	The final variation is the variation of precession of the Earth. Two components of the Earth's orbit precess - the first is an axial precession which causes the Earth to "wobble" around its own axis like a spinning top. The second is an elliptical precession where the orbit of the Earth itself shifts slightly with the point at which the Earth passes closest to the Sun changes. These changes occur over a large time scale - around 22 000 years.<ref name="RE1"/> Similar to the Earth's tilt, precession doesn't change how much total energy is received by Earth but changes how it is distributed over time.<ref name="RE2"/>		The final variation is the variation of precession of the Earth. Two components of the Earth's orbit precess - the first is an axial precession which causes the Earth to "wobble" around its own axis like a spinning top. The second is an elliptical precession where the orbit of the Earth itself shifts slightly with the point at which the Earth passes closest to the Sun changes. These changes occur over a large time scale - around 22 000 years.<ref name="RE1"/> Similar to the Earth's tilt, precession doesn't change how much total energy is received by Earth but changes how it is distributed over time.<ref name="RE2"/>

			==For Further Reading==
			*[[Climate forcing]]
			*[[Solar constant]]
			*[[Climate change]]
			*[[Sun]]
			*Or explore a [[Special:Random\|random page]]

	==References==		==References==
	{{reflist}}		{{reflist}}
			[[Category:Uploaded]]

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[[Category:Done 2016-01-15]]
[[File:5510488494_03cefcb27a_z.jpg|360px|thumb|right|Figure 1. Sunspots. Note that in the image, these sunspots are actually large enough to engulg the Earth, as sunspots range in diameter from about 1500 km to 50 000 km.<ref>NASA Goddard Space Flight Center. (October 18, 2015). ''Sunspots'' [Online]. Available: https://www.flickr.com/photos/gsfc/5510488494</ref>]]
<onlyinclude>An '''external forcing''' is a type of [[climate forcing]] agent that impacts the [[climate]] system while being outside of the climate system itself.</onlyinclude> External forcings include galactic variations, orbital variations, and solar variations - such as sunspots, shown in Figure 1.<ref name=IPCC_SREX>IPCC, 2012: Glossary of terms. In: Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation [Field, C.B., V. Barros, T.F. Stocker, D. Qin, D.J. Dokken, K.L. Ebi, M.D. Mastrandrea, K.J. Mach, G.-K. Plattner, S.K. Allen, M. Tignor, and P.M. Midgley (eds.)]. A Special Report of Working Groups I and II of the Intergovernmental Panel on Climate Change (IPCC). Cambridge University Press, Cambridge, UK, and New York, NY, USA, pp. 555-564.</ref> These external forcing mechanisms can happen on relatively small time scales - around 10 years - up to extremely large time scales of 10<sup>9</sup> years.<ref name="RE1">Global Climate Change. (November 2, 2015). ''External Forcing Mechanisms" [Online]. Available: http://www.global-climate-change.org.uk/2-5-1.php</ref>

==Types of External Forcings==
It is important to note that some sources report volcanic activity as being an external forcing instead of an internal forcing. However, here volcanic activity will be classified as a type of internal radiative forcing as a result of their presence within the Earth's physical system. Several sources make the same classification of volcanic activity being internal as a result of their location on the Earth. For information on volcanic activity as an internal forcing see [http://www.global-climate-change.org.uk/2-6-3.php here] and [http://www.eoearth.org/topics/view/54299/ here].
===Solar Variations===
Variations in the amount of solar [[energy]] being released from the [[Sun]] at a given point in time has been considered as an external forcing factor. However, a connection between the cycles of output from the Sun and climate cycles has not been firmly established.

One of the best known solar cycles is the sunspot cycle, which takes place over a period of 11 years.<ref>Nasa Solar Science. (November 7, 2015). ''Sunspot Cycle'' [Online]. Available: http://solarscience.msfc.nasa.gov/SunspotCycle.shtml</ref> From observations it has been found that at times of numerous sunspots, the value of the [[solar constant]] increases and thus [[solar irradiance]] increases with it. Changes of the solar irradiance like the ones that occur during sunspot cycles could force [[climate change]]s. Although there are measurable changes during this cycle, it is difficult to associate any observed climate change to these variations as the variations themselves are so small.<ref name="RE1"/> Additionally, in times where sunspot cycles are less intense it appears there is an associated decrease in the Earth's temperature - however this connection is still not proven. Other solar cycles include the change in solar diameter.<ref name="RE1"/>

===Galactic Variations===
In addition to the planets orbiting the Sun in the Solar System, the Solar System itself orbits the centre of the galaxy, and this rotation has been noted as a possible source of external forcings. Over the course of a galactic year - 303 ''million years'' - there is some level of variation in the composition of the [[matter]] that exists in space between the stars.<ref>Camel Climate Change. (November 7, 2015). ''Galactic Variations'' [Online]. Available: http://www.camelclimatechange.org/topics/view/51cbfc8ef702fc2ba812d48d/</ref> This variation in the makeup of space could influence the amount of [[solar radiation]] that hits the Earth. This change in solar radiation levels makes galactic variations a type of possible [[radiative forcing]]. However, it is difficult to confirm this variation as a type of external forcing because of the extremely long timescale.<ref name="RE1"/>

===Orbital Variations===
There are a number of different changes in the Earth's orbit around the Sun that have been investigated as possible external forcings. The overall theory of astronomical causes of climate variations is known as the '''Milankovitch theory''', and evidence has been found to support the ideas in the theory. There are three major variations - the tilt of the Earth's axis, it's precession, and eccentricity of the Earth's orbit around the Sun.

[[File:2000px-Earth_obliquity_range.svg.png|360px|thumb|right|Figure 2. A diagram showing how the tilt of the Earth can change.<ref>Wikimedia Commons. (November 7, 2015). ''Earth Obliquity Range'' [Online]. Available: https://upload.wikimedia.org/wikipedia/commons/thumb/a/ae/Earth_obliquity_range.svg/2000px-Earth_obliquity_range.svg.png</ref>]]

The tilt of the Earth on its axis of rotation can change between 22° and 24.5° over the course of 41 000 years (with the angle currently at 23.4°).<ref name="RE1"/> The tilt of the Earth changes how solar radiation is distributed over the Earth's surface. Although the tilt doesn't change how much solar radiation hits the Earth, the amount of solar radiation hitting a certain area differs. A change in tilt has a minimal effect around the equator, but near the poles as the tilt increases so too does the amount of [[sunlight]] that hits this area. This increase in temperature at higher latitudes can cause certain climate effects.<ref name="RE2">NOAA Paleoclimatology. (November 7, 2015). ''Solar Variations'' [Online]. Available: http://www.ncdc.noaa.gov/paleo/milankovitch.html</ref>

Also, the Earth's orbit around the Sun follows an elliptical, not circular path. The strength of the ellipse or the '''eccentricity''' of it is another orbital variation.<ref name="RE2"/> The orbit of the Earth has been found to vary between almost nearly circular (with an eccentricity of 0.005, the closer the value is to 1 the more elliptical the orbit is) to fairly elliptical (with an eccentricity of 0.06).<ref name="RE1"/> The changes in eccentricity change how much solar [[radiation]] hits the top of the [[atmosphere]], with maximum eccentricity solar radiation hitting the Earth can very 30% over the course of the Earth's orbit.

The final variation is the variation of precession of the Earth. Two components of the Earth's orbit precess - the first is an axial precession which causes the Earth to "wobble" around its own axis like a spinning top. The second is an elliptical precession where the orbit of the Earth itself shifts slightly with the point at which the Earth passes closest to the Sun changes. These changes occur over a large time scale - around 22 000 years.<ref name="RE1"/> Similar to the Earth's tilt, precession doesn't change how much total energy is received by Earth but changes how it is distributed over time.<ref name="RE2"/>

==References==
{{reflist}}