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Natural processes
There are many naturally occurring processes that cause the climate to either warm or cool. These natural cycles have, in the past, resulted in regional and global climates that are very different than our climate today.
Milankovitch Cycles
The Milankovitch cycles relate the Earth’s movement to the effect that this movement has on the Earth’s climate. (1)
There are three Milankovitch cycles:
The Earth’s patterns of movement are always changing. This variation follows cyclical patterns that take thousands of years to repeat. The point the Earth is at in the cycle changes the distribution of solar radiation, and therefore, cooling or warming, in different parts of the world.
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Eccentricity (orbit)
The eccentricity is the change in the Earth’s orbit around the Sun. The path that the Earth takes around the Sun varies in its “roundness”: the Earth’s path around the Sun is at times almost circular, and at others more elliptical. The eccentricity is the ratio between the Earth’s greatest distance from the Sun and the Earth’s shortest distance from the Sun. A greater eccentricity is indicative of a more elliptical path around the Sun.
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Obliquity (tilt)
The obliquity is the shift in the tilt of the Earth’s axis. The tilt varies by just over 2°, with values ranging between approximately 22° and 24°. This change affects the amount of solar radiation received by the higher latitudes. More tilt results in more solar radiation being received at higher latitudes during the summer, while less tilt results in less solar radiation being received at higher latitudes during the summer.
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Precession (wobble)
Precession refers to changes in the position of the earth in its orbit around the sun at the moment of the equinoxes and solstices. This changes the part of the planet tipped towards the Sun at different points of the earth's eccentric orbit. This effects the amount of solar radiation received at that part of the planet. This in turn affects the climate in the region.
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The Sun
Solar radiation powers our planet by providing the energy necessary to support life. Without the Sun, Earth would be a lifeless planet.
The Sun also plays in important role in the Earth’s climate. The amount and distribution of solar energy that Earth has received (due the Earth’s natural orbital variations) is thought to be responsible for triggering major climate events in the past, such as ice ages.
Although there are records of sunspot observations dating back hundreds of years, it has only been possible to instrumentally record changes in solar output since the late 1970s. This does not provide a long enough record to be able to identify any sort of trend. (2) Based on the data that has been obtained thus far, we have observed that there is a cycle of increases and decreases in solar output that occurs, but its effect on warming is much less than the effect that can be attributed to greenhouse gases.
For more see The Sun in the more Frequently Asked Questions (FAQ) area of this website.
