The greenhouse effect

What is it?
When speaking about the occurrence of life, temperature is a factor of immense importance; and temperature is closely linked to the greenhouse effect. As it happens, this process heats up the surface of the Earth, thus making it warm enough to be inhabited by humans. If it were not for the greenhouse effect, the average temperature on Earth would have been 33 degrees celsius colder, making it -18 degrees celsius; and it would have been completely different from the flourishing, luxuriant planet we know it as.

In essence, the greenhouse effect is the process in which gasses in the atmosphere absorb and reflect heat radiation. This is a natural process, but human activity has lately led to an increased greenhouse effect (see Causes of Increased Greenhouse Effect and Measures to prevent increased greenhouse effect), which has very adverse consequences for the environment.

The process in itself, however, is both natural and important. While the shortwave heat radiation from the sun gets past the greenhouse gasses, the longwave radiation from the Earth stays in the atmosphere. Only a minor part (approximately 30%) of the radiation from the sun is reflected back into space, while the rest is absorbed by the atmosphere and the surface of the earth. The energy absorbed by the ground is transformed into heat and released as longwave radiation*, before being absorbed by the greenhouse gasses, half of it being reflected back to the Earth. Thus, the planet is heated up, and made habitable for humans, plants and animals.

* Not all the energy is released as radiation; some of it instead leads to evaporation of water and convection.

Consequences of increased greenhouse effect
(Emma, Thomas)

Measures to prevent increased greenhouse effect
(Georg, Pål)

Energy balance in the atmosphere
(Martin, Emilia)