296
tional systems in recent years there are still substantial inaccuracies in our
knowledge of the 3-dimensional radiational forcing and the hydrological
cycle. The global average incoming radiation from the sun is 341 W/m 2
(1/4 of the solar constant), of which about 30% is reflected back to space
due to reflections from clouds, from the surface of the earth and from backscattering by the air and dust particles in the air (planetary albedo). Of
the remaining 240 W/m 2 some 146 W/m 2 reach the surface while the remaining part is absorbed in the atmosphere. The same amount of heat, 240
W/m2, leaves the planet through terrestrial radiation. However, that takes
place in a complex way, since the surface is cooled (and the atmosphere
correspondingly heated) by both surface radiative emission and fluxes of
sensible and latent heat. The atmosphere in return radiates back to the
surface (due to water vapour and greenhouse gases) and the outgoing net
surface long wave radiation amounts only to some 45 W/m2. The sensible heat flux from the surface is 14-20 W/m 2 and the latent heat flux is
estimated to be as high as 80-88 W/m2. It is important to note that the
moisture flux (evaporation) is cooling the surface of the earth some 80%
more than the net radiative cooling. Data for absorption of short wave
radiation in the atmosphere have recently been found to be higher than
previously estimated. The same is true for the long wave radiation. The
figures here are based on recent estimates, e. g. from Hartmann (1993),
Ohmura and Gilgen (1993), Hahn et al.(1994), Giorgetta and Wild (1995).
In general the accuracies of most energy fluxes are of the order of some 5
W/m2. The ERBE data for example has a residual error of 6 W/m 2 in the
globally averaged energy balance. The different heating between pole and
equator generates kinetic energy through the work of the pressure and the
Coriolis force. However, only some 3 W/m 2 is being converted into kinetic
energy, so the earth is a very inefficient engine having an efficiency factor
of less than 1 %! The overall direct effect of the greenhouse gases can be
calculated under simplified although not particularly realistic conditions.
Assuming radiation balance under clear sky it is found that the average
temperature of the earth's surface now at +15°C would fall to -18°C.
The relative contributions from the optically active gaseous components
are: water vapour (H20) -21 K, carbon dioxide (C02) -7 K and the remaining part from the other greenhouse gases including methane (CH4 ) ,
nitrous oxide (N20) and ozone (03), (Kondratyev and Moskalenko, 1984).
Our closest planets in the solar system are also very much influenced
by the greenhouse gases, particularly Venus (Fig. 2). However, it is not
tional systems in recent years there are still substantial inaccuracies in our
knowledge of the 3-dimensional radiational forcing and the hydrological
cycle. The global average incoming radiation from the sun is 341 W/m 2
(1/4 of the solar constant), of which about 30% is reflected back to space
due to reflections from clouds, from the surface of the earth and from backscattering by the air and dust particles in the air (planetary albedo). Of
the remaining 240 W/m 2 some 146 W/m 2 reach the surface while the remaining part is absorbed in the atmosphere. The same amount of heat, 240
W/m2, leaves the planet through terrestrial radiation. However, that takes
place in a complex way, since the surface is cooled (and the atmosphere
correspondingly heated) by both surface radiative emission and fluxes of
sensible and latent heat. The atmosphere in return radiates back to the
surface (due to water vapour and greenhouse gases) and the outgoing net
surface long wave radiation amounts only to some 45 W/m2. The sensible heat flux from the surface is 14-20 W/m 2 and the latent heat flux is
estimated to be as high as 80-88 W/m2. It is important to note that the
moisture flux (evaporation) is cooling the surface of the earth some 80%
more than the net radiative cooling. Data for absorption of short wave
radiation in the atmosphere have recently been found to be higher than
previously estimated. The same is true for the long wave radiation. The
figures here are based on recent estimates, e. g. from Hartmann (1993),
Ohmura and Gilgen (1993), Hahn et al.(1994), Giorgetta and Wild (1995).
In general the accuracies of most energy fluxes are of the order of some 5
W/m2. The ERBE data for example has a residual error of 6 W/m 2 in the
globally averaged energy balance. The different heating between pole and
equator generates kinetic energy through the work of the pressure and the
Coriolis force. However, only some 3 W/m 2 is being converted into kinetic
energy, so the earth is a very inefficient engine having an efficiency factor
of less than 1 %! The overall direct effect of the greenhouse gases can be
calculated under simplified although not particularly realistic conditions.
Assuming radiation balance under clear sky it is found that the average
temperature of the earth's surface now at +15°C would fall to -18°C.
The relative contributions from the optically active gaseous components
are: water vapour (H20) -21 K, carbon dioxide (C02) -7 K and the remaining part from the other greenhouse gases including methane (CH4 ) ,
nitrous oxide (N20) and ozone (03), (Kondratyev and Moskalenko, 1984).
Our closest planets in the solar system are also very much influenced
by the greenhouse gases, particularly Venus (Fig. 2). However, it is not