The Greenhouse Effect is a natural phenomenon caused by the presence of certain molecules in the Earth's atmosphere (water vapor, Carbon Dioxide, Ozone, Methane...)
The Earth's surface is heated solely by solar energy (geothermal sources are 10,000 times less important). Half of this solar energy is captured by the Earth, while the rest is absorbed by the atmosphere and, to a small extent, reflected back into space. The Earth, thus heated, itself emits radiation, but in the infrarouge. The greenhouse gases in the atmosphere absorb primarily these infrared wavelengths, and re-emit 80% of this energy back toward the Earth. It is this energy trap that we call the Greenhouse Effect. It is responsible for permitting water in the liquid state to exist on our planet, and so it favored the development of Life on Earth: without the Greenhouse Effect, ground temperature would be around -18°C.
But human activities are beginning to disturb this equilibrium by increasing the atmospheric concentrations of several greenhouse gases, most notably Carbon Dioxide (CO2 ) and Methane (CH4).
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