Geoscience Reference
In-Depth Information
accessible to the atmosphere via plants can have a marked influence on the local
energy balance at the land surface. Soil moisture content affects the rate of
evaporation, the reflection by soil of solar radiation, and the thermal conductivity
of the soil. Because soil moisture tends to change fairly slowly it can provide a
land-based 'memory' with an effect on the atmosphere broadly equivalent to that
of slowly changing sea surface temperature.
Biosphere
Terrestrial vegetation, continental fauna, and the flora and fauna of the oceans
make up the biosphere. It is now recognized that the nature of vegetation covering
the ground is not only influenced by the regional hydroclimate, but also itself
influences the hydroclimate of a region. This is because the type of vegetation
present affects the aerodynamic roughness and solar reflectivity of the surface, and
whether water falling as precipitation leaves as evaporation or runoff. The rooting
depth of vegetation matters because it determines the size of the moisture store
available to the atmosphere. Changes in the type of vegetation present may occur
in response to changes in climate, and modern climate prediction models attempt
to represent such evolution. Imposed changes caused by human intervention
through, for example, large-scale deforestation or irrigation also occur and these
can be extensive and alter surface inputs to the atmosphere of continental regions.
The behavior of the biosphere influences the carbon dioxide present in the
atmosphere and oceans through photosynthesis and respiration. It is essential to
include description of these influences when models are used to simulate global
warming. For this reason, advanced sub-models describing the biosphere in mete-
orological models seek to represent the energy, water, and carbon exchanges of the
biosphere simultaneously. Water and carbon exchanges are linked by the fact that
the water transpired and the carbon assimilated by vegetation occurs by molecular
diffusion through the same plant stomata. Models of the biosphere are often
referred to as Land Surface Parameterization Schemes (LSPs) or Soil Vegetation
Atmosphere Transfer Schemes (SVATs); see Chapter 24 for greater detail. Figure 1.4
shows an example of the Simple Biosphere Model (SiB; Sellers
et al.
, 1986), an
example of a SVAT that is currently widely used.
Because the biosphere is sensitive to changes in climate, detailed study of past
changes in its nature and behavior as revealed in fossils and tree rings and in pollen
and coral records is important as a means of documenting the prevailing climate
in previous eras.
Anthroposphere
The word anthroposphere is used to describe the effect of human beings on the
Earth system. For much of our existence human impact on the environment was
small, but as our numbers grew our impact on the atmosphere and landscape
