greenhouse effect is the heating of the surface of a planet
or moon due to the presence of an atmosphere containing
gases that absorb and emit infrared radiation. Thus, greenhouse
gases trap heat within the surface-troposphere system. This
mechanism is fundamentally different from that of an actual
greenhouse, which works by isolating warm air inside the
structure so that heat is not lost by convection.
is the movement of molecules within fluids (i.e. liquids,
gases and rheids). It cannot take place in solids, since
neither bulk current flows or significant diffusion can
take place in solids.
greenhouse effect was discovered by Joseph
Fourier in 1824, first reliably experimented on by
John Tyndall in 1858, and first
reported quantitatively by Svante
Arrhenius in 1896.
black body temperature of the Earth is 5.5 °C. Since
the Earth's surface reflects about 28% of incoming sunlight,
the planet's mean temperature would be far lower - about
-18 or -19 °C - in the absence of the effect. Because
of the effect, it is instead much higher at about 14 °C.
Global warming, a recent warming of the Earth's surface
and lower atmosphere, is believed to be the result of an
"enhanced greenhouse effect" mostly due to human-produced
increases in atmospheric greenhouse gases. This human induced
part is referred to as anthropogenic global warming (AGW).
The Earth receives energy from the Sun mostly in the form
of visible light and nearby wavelengths. About 50% of the
sun's energy is absorbed at the Earth's surface. Like all
bodies with a temperature above absolute zero the Earth's
surface radiates energy in the infrared range. Greenhouse
gases in the atmosphere absorb most of the infrared radiation
emitted by the surface and pass the absorbed heat to other
atmospheric gases through molecular collisions. The greenhouse
gases also radiate in the infrared range. Radiation is emitted
both upward, with part escaping to space, and downward toward
Earth's surface. The surface and lower atmosphere are warmed
by the part of the energy that is radiated downward, making
our life on earth possible.