Environmental Engineering Reference
In-Depth Information
Figure 8.1 The greenhouse effect
The degree of heating produced depends on the concentration and properties of
each gas and on the amount of time during which the gases stay in the atmosphere.
Aerosols (small particles) from volcanoes, from industrial sulfate emission, and
from other sources may absorb and reflect radiation as well. In most cases, aerosols
tend to cool the climate. Aerosols and ozone (both tropospheric and stratospheric)
are also factors that cause an increase in the greenhouse effect; however, the ef-
fect is much smaller and scientific uncertainty is even larger. Moreover, there are
changes in surface “albedo”—a reflectivity measure—altered, for example, by de-
forestation and other changes in land use. Any changes made by human beings in
the radiant balance of the Earth, including those deriving from an increase in the
amount of greenhouse gases or aerosols, will tend to change the atmosphere and
ocean temperature, as well as the associated currents and types of climate. These
changes overlap the natural climate changes.
The most relevant greenhouse gases are carbon dioxide, methane, nitrous oxide,
and halons (chlorofluorocarbons and sulfur hexafluoride). Their concentrations in
the atmosphere vary widely, from 383 parts per million in volume for CO
2
to 770
parts per billion in volume for methane. However, the effectiveness in blocking the
reemission of heat from the Earth into the atmosphere depends on the character-
