8.6.1+Models+of+Warming

=Models of Global warming=

8.6.1 Describe some possible models of global warming.
About 30% of the visible light from the Sun is reflected back into space, while the other 70% is absorbed by the ground and oceans, resulting in heating the Earth.

There are several models in order to explain global warming. All those models have strengths in explaining it, but there is most probably more than one explanation for why the Earth's temperature is warming up. Some of those models include changes in the composition of greenhouse gases in the atmosphere, increased solar flare activity, cyclical changes in the Earth's orbit and volcanic activity.

"Carbon dioxide (**CO2**) absorbs infrared radiation and accounts for about 18%, methane (**CH4**) accounts for about 6% and ozone (**O3**) accounts for about 5% of heating the atmosphere..
 * ====Greenhouse Gases====
 * CO2** has stayed at the proper percentage in the atmosphere until recently, when an increasing amount of the gas has been emitted due to the burning of fossil fuels. Automobile exhaust and industrial smoke contribute the most **CO2**."

Because of changes in the concentration of greenhouse gases, there is less light that reaches the ground, which causes global dimming. "The amount of sunlight reaching the ground dropped 4% from 1960 to 1990, primarily due to air pollution."

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 * ====Increased Solar Flare Activity====

The level of sun radiations going to the Earth is not constant, as the sun goes through "regular cycles of activity on timescales of 10 – 10,000 years and that its heat output and activity are related." Nevertheless, "the solar contribution to the increase [in temperature] is variously estimated to be around 4-20% leaving greenhouse gases to make up the remaining 80%."

The solar flare activity is not the main cause of global warming, but " factors such as solar variability could amplify or subdue the effect" of temperature change.

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 * ====Cyclical Changes in the Earth's Orbit====

"The first cyclical variation, known as eccentricity, controls the shape of the Earth's orbit around the sun. The orbit gradually changes from being elliptical to being nearly circular and then back to elliptical in a period of about 100,000 years. The difference in the Earth's distance from the sun [...] is responsible for approximately a 7% variation in the amount of solar energy received at the top of the atmosphere. When the difference in this distance is at its maximum (9%), the difference in solar energy received is about 20%."

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Since the amount of sunlight received on Earth changes, the temperature also changes.


 * ====Volcanic Activity====

The impact of volcanic activity on the planet is quite uncertain. "Volcanic eruptions can enhance global warming by adding CO2 to the atmosphere," which is global warming, but not as much as humans. However, volcanoes produce dust and ash, and those "suspended particles can block out the earth's sunlight, thus reducing solar radiation and lowering mean global temperatures," which is the haze effect. Volcanoes can therefore both lower or higher the earth's temperature.

"The haze effect often generates exceptionally red sunsets due to the scattering of red wavelengths."

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