Is global warming different to the greenhouse effect?

Answer 1

Yes, they are different. If the greenhouse effect increases globally then it basically causes global warming.

Global warming is the phenomena of average global temperatures increasing for any reason - including the greenhouse effect. Other phenomena unrelated to the greenhouse effect that can result in net global warming include increased solar activity, decreased cloud cover due to decreasing particulates in the atmosphere, or the earth wobbling on its axis (As the Earth spins, it does not achieve perfect rotation. It actually wobbles slightly, thus alternately exposing the northern and southern latitudes to more and less solar radiation. This wobble in the Earth's rotation has been causing changes in the temperature of the atmosphere for many millions of years.)

The greenhouse effect is a very specific source of global warming. Certain gases such as water vapor are much more transparent to energy in the wavelengths radiated by the sun than they are to energy re-radiating from the earth or reflecting from the ground. (Water vapor accounts for the majority of the greenhouse effect of the atmosphere - greater in humid areas, less in very arid ones - which is why some deserts get so hot during the day and get so cold at night.) Other gasses that can have a significant greenhouse effect are Carbon Dioxide and Methane. The air is fairly transparent to light in the wavelengths emitted by the sun. Some harmful wavelengths - especially in the UV range - are fortunately soaked up by the upper atmosphere and never reach the surface. The light that does reach the surface is either reflected or absorbed. The reflected light is somewhat selective in the wavelengths that reflect - thus we see colors in the things around us outside. The wavelengths of the reflected light tend to be absorbed by the greenhouse gases because they are just right to coincide with the natural vibrational frequencies of the molecules of those gases so instead of passing through, they get absorbed and amplify the vibrations making the molecules more energetic - which corresponds to what we experience as heat. Likewise, the energy absorbed by the surface of the earth eventually tries to re-radiate back out, but now at very low frequencies which are readily absorbed by the greenhouse gas molecules. The overall effect is to retain heat.

The same effect is observed when sunlight passes through glass and is trapped inside a car - the glass is transparent to sunlight but blocks the energy trying to radiate back out from the interior of the car - making the car much hotter inside than the outside air. This is used to advantage in commercial greenhouses which enclose an area with glass panels so that the energy of the sun can be trapped inside to provide an environment that is much warmer than the surroundings. Even at night when there is no sunlight, greenhouses hold in much of the energy that entered during the day since the glass is comparatively opaque at the wavelengths of the energy trying to leave the greenhouse. This is the origin of the term "greenhouse effect" which was first proposed by Svante Arrhenius and was the source of a protracted argument that he had with Knut Ångström.