The atmosphere - Global Environmental Issues - page 23

Table 2.2 Estimated impacts of different radiative
forcing agents in watts per square metre (1990-2000)

necessary to allow the various atmospheric and
terrestrial processes to function.
The energy balance of the earth/atmosphere
system is subject to stress from both natural and
anthropogenic sources. Any factor capable of
disturbing that balance is called a radiative
forcing agent (Shine et al. 1990). In the past, the
most common sources of forcing were natural
and involved changes in such elements as solar
radiation, the planetary albedo and atmospheric
aerosol concentrations, which individually and
in combination altered the flow of energy into
and out of the system. These natural forcing
agents, continue to disrupt the balance, but
current concern is with anthropogenic forcing
agents and the climate change that they are likely
to produce.
The depletion of the ozone layer resulting from
human interference disturbs the balance by
allowing additional radiation to reach the
surface, and changes in atmospheric turbidity
disrupt both incoming and outgoing radiation.
In the immediate future, however, the greatest
change in radiative forcing is expected to come
about as a result of the rising levels of greenhouse
gases (see Table 2.2). It is estimated that their
effect on the radiative balance of the earth
radiative forcing agent, natural or anthropogenic
(Shine et al. 1990).
The concept of balance in the earth's heat
budget is a useful one, but it provides only a
global picture, and cannot be applied to specific
areas. There is a definite latitudinal imbalance
in the budget. Annually, the equator receives
about five times the amount of solar radiation
reaching the poles, and those areas equatorwards
of 35 degrees of latitude receive more energy than
is returned to space (Figure 2.6). The excess of
outgoing radiation over incoming, poleward of
35 degrees of latitude, creates a radiation deficit
in higher latitudes (Trewartha and Horn 1980).
In theory, such an imbalance could lead to higher
latitudes becoming infinitely colder and
equatorial latitudes infinitely warmer. In reality,
as soon as the latitudinal differences develop, they
initiate circulation patterns in the atmosphere and
in the oceans, which combine to transfer heat

Source: Based on data in Shine et al. (1990)

Figure 2.6 The latitudinal imbalance in solar and
terrestrial radiation