HKDSE Geography/M7/Natural Factors in Global Warming
A change in the earth's orbit is said to be a cause. The earth's orbit shifts between elliptical and circular. When it is elliptical, it will be closer to the sun during winter months and farther away in summer, and thus the Northern hemisphere has warmer winters, causing snowmelt while the Southern Hemispher has hotter winters, causing glaciation
The earth's axis is tilted. At the moment, it is 23.5 degrees to the vertical, but it shifts between 22.2 to 24.5 over thousands of years, and is becoming more tilted at the moment. When the earth is more tilted, there will be a larger annual range of temperature and thus glaciation is discouraged by hot summers.
Volcanic eruptions are a natural source of aerosols, including volcanic ash and dust, which induce temporary cooling. However, they also release methane and carbon dioxide into the atmosphere, intensifying the greenhouse effect.
Natural Sources of Greenhouse Gases
-Water vapour (1-4%) :Evaporation from the Earth's surface
-Carbon dioxide (0.036%) :Respiration of organisms, decomposition of dead plants and animals, release from warm seas and oceans
-Methane (0.00017%) :Breakdown of organic matter by bacteria in an anaerobic environment, such as in swampy areas and rice paddies
-Nitrous oxide (0.00003%) :Release from oceans and bacteria in soils