Green house gas effect is a phenomenon that takes place in the atmosphere. Have you ever thought why this occur? well the answer is that the greenhouse gases forms a layer in the earths atmosphere. this layer only allows light radiations through it. the suns radiation enters this layer as light radiations.
these light rays are absorbed by the earth on reaching it (remember that earth only absorbs light rays not heat). thus the heat is radiated to the atmosphere.But the greenhouse gas layer forbids this radiation to get out of the earths atmosphere as it is not a light ray anymore. thus the heat is trapped in the earth increasing the earth's temparature. this is greenhouse gas effect. this leads to global warming which further leads to glacier and ice cap depletion.