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The Greenhouse effect
Understanding Climate Change
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The Earth’s climate is driven by a continuous flow of energy from the sun. Heat from the sun passes through the atmosphere and warms the surface of the Earth. As the temperature increases, the Earth reflects heat (infrared radiation) back into the atmosphere.
Some of this heat is absorbed by greenhouse gases in the atmosphere, such as carbon dioxide (CO2), methane, nitrous oxide, ozone and halocarbons.The greenhouse effect
These gases, which are all naturally occurring, act as a blanket, trapping in the heat and preventing it from being reflected too far from the Earth. They keep the Earth's average temperature at about 15°C: warm enough to sustain life for humans, plants and animals. Without these gases, the average temperature would be about -18°C... too cold for most life forms. This natural warming effect is also sometimes called the greenhouse effect.
Carbon dioxide (CO2)
CO2 is the most significant of the gases in our atmosphere which keep the Earth warm. 4 billion years ago its concentration in the atmosphere was much higher than today - 80% compared to today's 0.03%. But most of it was removed through photosynthesis over time. All this carbon dioxide became locked in organisms and then fossil fuels such as oil, coal and petroleum inside the Earth's crust.
The natural carbon dioxide cycle
A natural carbon dioxide cycle keeps the amount of CO2 in our atmosphere in balance. Decaying plants, volcanic eruptions and the respiration of animals release CO2 into the atmosphere, where it stays for about 100 years. It is removed again from the atmosphere by photosynthesis in plants and by dissolution in water (in the oceans for instance). The amount of CO2 released naturally into the atmosphere is perfectly balanced by the amount naturally removed.
Even small changes caused by human activities can have a significant impact on this balance...