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There are various solar/celestial effects that exist which have an effect on Earth's climate. These effects usually occur in cycles, and primarily include how Earth's obliquity, the eccentricity of Earth's orbit, and the precession of the equinoxes and solstices affect Earth's climate. In addition to these effects, there are also other factors that have an effect on Earth's climate. These other factors include how sun activity affects climate and how celestial phenomena, such as meteors, affect Earth's climate. Some of these factors aren't yet well understood, for instance the ice ages occur on 100,000 year cycles, and it's not completely understood why the various effects with this periodicity have such a strong effect on glaciation (see the 100,000-year problem).
Contents
Overview
Climate in general is an extremely complex system, dealing with temperature and weather conditions over an extended period of time. There are many things which influence Earth's climate. Among these many things, are various solar effects. Earth’s climate is affected by a number of factors dealing with the Earth as a whole, in relation to its position in the space relative to the sun. These factors include the angle of Earth’s axial tilt (also known as Earth’s obliquity), the eccentricity of Earth’s orbit (how circular/elliptical Earth’s orbit is), and Earth’s position in time in the precession of the solstices and equinoxes (with different Earth-Sun distances during any given season).
Although these are the primary three factors in shaping Earths climate, there are other, external, factors that can help shape Earth’s climate. These external factors usually affect Earth climate on a very different time scale than the other three, and include factors such as meteors striking Earth and geomagnetic storms. These external forces usually contribute to climate change on a time scale, as meteorites strike the earth, on average, every 50 to 100 million years, where as geomagnetic storms occur periodically through the sun’s eleven-year activity cycle. With all of these factors affecting climate in their own way, it becomes easy to see that Earth’s climate is in fact, largely dependent on various solar effects/circumstances.
Earth's axial tilt
Perhaps one of the most apparent factors contributing to Earth climate change is the angle at which the earth is tilted. This is the angle at which Earth’s axis of rotation is from the vertical, also known as Earth’s obliquity. Earth’s current tilt angle is approximately 23.5 degrees. The axial tilt angle affects climate largely by determining which parts of the earth get more sunlight during different stages of the year. This is the primary cause for the different seasons Earth experiences throughout the year, as well as the intensity of the seasons for higher latitudes. For example, in the Northern Hemisphere, if there were no axial tilt, i.e. Earth’s obliquity would be zero degrees, then there would be no change in the seasons from year to year. This would be because there would be no difference in the amount of solar irradiation received, year-round, anywhere on Earth. On the other hand, if Earth’s axial tilt angle was great (45+ degrees), the seasonality of each hemisphere, individually, would be highly exaggerated. Summers would be extremely hot, with substantially more hours of daylight than night each day. Winters would be extremely cold, with substantially more hours of night than daylight each day. This is because, during summer for the northern hemisphere, if the earth is tilted more (pointed towards the sun more), there would be more available hours in which the suns rays can strike any certain place, thereby increasing the number of daylight hours at any given place, with more and more daylight hours at higher latitudes. Also, because the northern hemisphere would be tilted much more towards the sun, it would be physically closer to the sun, thereby increasing the intensity of the sun’s rays hitting the northern hemisphere, thereby causing the northern hemisphere to become hotter. Likewise, during winter for the northern hemisphere, there would be fewer hours of daylight because the northern hemisphere would essentially be pointed away from the sun. Fewer daylight hours means less solar radiation hitting the northern hemisphere, especially at higher latitudes, and therefore causing the northern hemisphere to become colder. The same things can also be said about the southern hemisphere, particularly at high latitudes. In either case, the climate around the equator is not affected nearly as much as the higher latitudes, thereby creating a sizable difference in how obliquity affects different latitudes. This is all, of course, dependent on what the actual tilt angle is at any given point in time. The thing is, though, that Earth does in fact change obliquity over time in a cyclic pattern. Earth’s obliquity does not change much, though, as obliquity has been determined to cycle between the small range of 22.2 degrees to 24.5 degrees, in a cycle that lasts approximately 41,000 years. Therefore with the small tilt variation over time, the Earth has always been thought to have had a seasonal climate, at least in the high latitudes due to the solar affect of changing Earth obliquity.
Earth's eccentricity
Earth’s eccentricity can also play a large role in Earth climate change. The role is perhaps not as large of an impact as Earth’s Obliquity, but still large nonetheless. Eccentricity is defined as the difference in shape between an ellipse and a perfect circle. It is also known by a simpler definition as simply being a measurement of how elliptical something is. In the case of climate, eccentricity is applied to the shape of Earth’s orbit. In a similar fashion to Earth’s obliquity, the more uniform Earth’s orbit is (more like a perfect circle), the less difference there is in climate change throughout the year. Unlike obliquity, eccentricity affects the entire planet approximately the same, instead of primarily changing polar climate. The base idea with eccentricity is this: “How far away is the earth as a whole from the sun?” If there is no eccentricity to Earth’s orbit, then Earth will remain at the same distance from the sun throughout the year, therefore producing no climate change, seeing as how the Earth’s orbit would be perfectly circular around the sun. On the other hand, if Earth’s orbit has a very high eccentricity, Earth would be very close to the sun (compared to a perfectly circular orbit) during two opposite seasons, and very far away from the sun during the other two opposite seasons. This effect can be seen by analyzing any ellipse, and observing how flat or how skinny the ellipse becomes as its eccentricity increases.
Mathematically, the eccentricity of an ellipse is given by the following equation:
∈=√(a2-b2 )/a.
where “a” is the ellipse’s semi-major axis (half of the longest diameter of the ellipse) and “b” is the ellipse’s semi-minor axis (half of the shortest diameter of the ellipse). Thus, for example, if summer and winter are on the part of the orbital ellipse that is furthest away from the sun, then Earth will have the least yearly solar radiation received during those two seasons, and the most yearly solar irradiation received during spring and autumn. With this difference in solar irradiation received, climate should noticeably change throughout the year, each year. Currently, Earth’s eccentricity is approximately 0.0167, which is closer to the circular side of the eccentricity range Earth cycles through. Earth’s eccentricity has always varied over time, and varies within the range of 0.005 to 0.0607 in one eccentricity cycle with a time period of about 100,000 years. There is another eccentricity cycle with a period of approximately 413,000 years, however, it’s primarily only noticed as small variations within the 100,000 year eccentricity cycle. When this climate effect is considered with Earth’s obliquity, they merge to offset the magnitude fraction of solar irradiation received in a given hemisphere, thus wonderfully adding to the complexity of the Earth climate system.
Precession of solstices and equinoxes
The precession of solstices and equinoxes is the third factor that plays a role in Earth climate change that deals directly with the earth itself. The basis of the precession of solstices and equinoxes is that it causes the seasons to occur at different times in Earth’s revolution around the sun throughout a cycle recurring about every 23,000 years.
In the Northern Hemisphere, when the Earth is at its furthest point from the sun (aphelion) the variation in temperature between winter and summer are less extreme. When the earth is closest to the sun (perihelion), about 5,750 years later, then the variations are at their most extreme. At present the Earth is at its furthest, so the northern hemisphere summers and winters are less extreme and the southern hemisphere climate is more extreme.
This precession movement is the result of two other processes. The first is Earth’s slow Axial precession (also known as Earth’s wobbling motion), Ruddiman likens it to a top, how the top spins rapidly, revolves around a point on the surface it’s spinning on, and also ‘wobbles’ at the top of the top. The second process is referred to as apsidal precession - or the precession of the ellipse. In this second process, the entire ellipse of Earth’s orbital path rotates around the sun.
When these two processes are put together, they cause the solstices and equinoxes to effectively move around the earth’s orbital path to change how much solar irradiation the hemispheres get during any given season. For details and other subtle effects on the motion, see Precession of the equinoxes#Cause
Synopsis
In summary, Earth’s climate is determined by a compilation of many things and factors. It can be somewhat easy to overlook the solar effects on Earth’s climate, however to overlook these would be a tragedy, seeing as how solar factors actually can have a huge impact and influence over Earth’s climate. These effects include effects from the primary factors of Earth’s axial tilt angle, Earth’s orbital eccentricity, and the precession of solstices and equinoxes, as well as some secondary, external effects, such as meteorite/asteroid impacts on the earth’s surface and solar activity from the sun, including sunspots, solar flares, and solar winds/geomagnetic storms. Overall, the Earth climate system is an amazingly, wonderfully complex design with many factors and components. Including things such as the ever so important solar effects on Earth’s climate, how those solar effects can affect mankind in everyday life, as well as how those effects can stretch their influence throughout the ages, even until the end of time.