Unit 2: Atmosphere // Section 3: Radiative Balance and the
Natural Greenhouse Effect Earth's surface temperature has been
remarkably constant over geologic time. Even the dramatic
cooling that occurred during the most recent ice age represented
a change of only 3°C in the global average surface temperature,
occurring over thousands of years. Seasonal changes in
temperature, although large in a particular place, correspond to
very tiny changes in global mean temperature. Why have
temperatures held so steady? Earth exchanges energy with its
environment primarily through transfers of electromagnetic
radiation. At any time our planet is simultaneously absorbing
energy from the sun and radiating energy back into space. The
temperature remains stable over long periods of time because the
planet radiates energy back to space at a rate that closely
balances the energy input it receives from the sun (i.e., the
planet is close to being in radiative energy balance). Earth
receives energy from the sun in the form of sola