The molecules of carbon dioxide in the Earth's
atmosphere affect the heat balance of the Earth by
acting as a one-way screen. Although these molecules
allow radiation at visible wavelengths, where most of
the energy of sunlight is concentrated, to pass
through, they absorb some of the longer-wavelength,
infrared emissions radiated from the Earth's surface,
radiation that would otherwise be transmitted back
into space. For the Earth to maintain a constant aver age
temperature, such emissions from the planet must
balance incoming solar radiation. If there were no carbon
dioxide in the atmosphere, heat would escape from the
Earth much more easily. The surface temperature would
be so much lower that the oceans might be a solid mass
of ice.