<P> The greenhouse effect is the process by which radiation from a planet's atmosphere warms the planet's surface to a temperature above what it would be without its atmosphere . </P> <P> If a planet's atmosphere contains radiatively active gases (i.e., greenhouse gases) they will radiate energy in all directions . Part of this radiation is directed towards the surface, warming it . The intensity of the downward radiation--that is, the strength of the greenhouse effect--will depend on the atmosphere's temperature and on the amount of greenhouse gases that the atmosphere contains . </P>

What is the meaning of the greenhouse effect