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a)Natural Causes
1. Variations in the Earths Orbital Characteristics
-Changing or earths orbital characteristics within 1000 years from elliptical (aphelion) to nearly circular (perihelion) when the earth is nearest to the sun and receives maximum solar energy and back to elliptical when the earth is farthest from the sun and receives least solar energy.
2. Variation in the Atmospheric Carbon Dioxide
-When natural rise in temperature cause carbon dioxide held up in cold ocean waters to be released to the atmosphere after oceans warmed.
3. Volcanic Eruptions
- When large quantities of volcanic ash and dust thrown out of the ground block some of the solar insolation from reaching the earth’s surface causing temperatures on the earth’s surface to drop for a short period.
- When sulphur dioxide given off during volcanic eruptions reacts with water vapour forming a bright layer within stratosphere reducing the amount of solar radiation reaching the surface by reflecting some of it back which also lowers temperatures on the surface.
4. Variation in Solar Output
-changes in the amount of solar energy given off by the sun whereby at times its less causing drop of temperature on the earth’s surface and at others its gives off more causing rise in temperature on the surface.
b)Human Causes
1. Burning of fossil fuels in industries, transportation, electricity generation etc. which contributes 65% of additional co2 in the atmosphere which is the main green house gas.
2. Burning of vegetation e.g. in shifting cultivation and forest fires which also adds co2 in the atmosphere.
3. Clearing large tracts of forests foe agriculture, settlement etc. which reduces the main disposal system for co2 from the atmosphere by photosynthesis.
4. industrial developments which add gases like methane, nitrous oxide and those containing chlorine and chlorofluorocarbons which damages ozone layer which filters a greater percentage of ultra violet radiation given off by the sun which causes the average temperatures on the earth to rise.
marto answered the question on March 26, 2019 at 05:57
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