Radiant energy from the sun warms the surface of the Earth, both sea and land. This incoming radiation is mostly in the visible part of the spectrum and passes through the atmosphere without being absorbed. As the Earth warms up, it radiates heat back out towards space (infra-red radiation). Unfortunately most of this heat is trapped by certain gases in the atmosphere e.g. water vapour and carbon dioxide. The gases of the lower atmosphere warm up and although some of this heat energy escapes into space much is radiated back and this warms the Earth up even more.
Carbon dioxide is one of the products of burning fossil fuels such as coal
and oil. It is an important natural part of air and it helps to control the
Earth's temperature and, unlike many pollutants does not actively damage living
things. Why is it called a greenhouse gas? Well, just like the glass
in a
greenhouse, it absorbs the radiation of longer wavelengths radiated back from
the Earth.