Greenhouse effect
The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this reradiation is back towards the surface and the lower atmosphere, it results in an elevation of the average surface temperature above what it would be in the absence of the gases. Solar radiation at the frequencies of visible light largely passes through the atmosphere to warm the planetary surface, which then emits this energy at the lower frequencies of infrared thermal radiation. Infrared radiation is absorbed by greenhouse gases, which in turn reradiate much of the energy to the surface and lower atmosphere. The mechanism is named after the effect of solar radiation passing through glass and warming a greenhouse, but the way it retains heat is fundamentally different as a greenhouse works by reducing airflow, isolating the warm air inside the structure so that heat is not lost by convection.
Greenhouse gas
A greenhouse gas (sometimes abbreviated GHG) is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone. In the Solar System, the atmospheres of Venus, Mars, and Titan also contain gases that cause greenhouse effects. Greenhouse Mars, and Titan also contain gases that cause greenhouse effects. Greenhouse earth without them, Earth's surface would average about 33 °C (59 °F) colder than the present average of 14 °C (57°F).
Greenhouse gases are those that can absorb and emit infrared radiation, but not radiation in or near the visible spectrum. In order, the most abundant greenhouse gases in Earth's atmosphere are:
- Water vapor (H2O)
- Carbon dioxide (CO2)
- Methane (CH4)
- Nitrous oxide (N2O)
- Ozone (O3)
- CFCs
By their percentage contribution to the greenhouse effect on Earth the four major gases are:
- Water vapor, 36–70%
- Carbon dioxide, 9–26%
- Methane, 4–9%
- Ozone, 3–7%
The Greenhouse Effect and Greenhouse Gasses
Have you ever been inside a greenhouse on a cold winter day? It might be cold outside, but inside the greenhouse lush green plants flourish in the warmth and sunshine. Greenhouses are made of glass and are designed to hold heat inside. Our planet's atmosphere traps energy just like a greenhouse.
Energy from the Sun can enter the Earth’s atmosphere, but not all of it can easily find its way out again. What blocks the Sun’s energy from escaping from the Earth? Unlike a greenhouse, the Earth does not have a layer of glass over it! Instead, molecules in our atmosphere called greenhouse gasses absorb the heat.
Greenhouse gasses include water vapor, methane, ozone, nitrous oxide, and carbon dioxide. There may not be much of some of these gasses in our atmosphere, but they can have a big impact. Each greenhouse gas molecule is made of three or more atoms that are bonded loosely together. These molecules are able to absorb heat, which makes them vibrate. They eventually release the heat energy and it is often absorbed by another greenhouse gas molecule.
The greenhouse effect is useful because trapping some energy keeps the temperatures on our planet mild and suitable for living things. Without its atmosphere and the greenhouse effect, the average temperature at the surface of the Earth would be zero degrees Fahrenheit. However, too many greenhouse gases can cause the temperature to increase out of control. Such is the case on Venus where greenhouse gases are abundant and the average temperature at the surface is more than 855 degrees Fahrenheit (457 degrees Celsius).
You might hear people talking about the greenhouse effect as if it is a bad thing. It is not a bad thing, but people are concerned because Earth’s greenhouse is warming up very rapidly. This is happening because we are currently adding more greenhouse gases to our atmosphere, causing an increased greenhouse effect. The increased Greenhouse Effect is causing changes in our planet that can affect our lives.
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