Ozone in the troposphere, that is, in the lower part of the atmosphere, is another important
greenhouse gas resulting from industrial activities. It is created naturally and also by reactions
in the atmosphere involving gases resulting from human activities, including nitrogen oxides
from motor vehicles and power plants. Based on current data, tropospheric ozone is an
important contributor to the enhanced greenhouse effect. However, in part because ozone is also
produced naturally, and because of its relatively short atmospheric lifetime, the magnitude of
this contribution is uncertain.
Contrary to popular perception, the Antarctic ozone hole does not cause global warming.
Instead, the global depletion of stratospheric ozone caused by CFCs and other gases has
resulted in a small cooling effect as shown in Figure 4.1.
Human activities, such as the burning of fossil fuels and changes in land use, have increased the
abundance of small particles in the atmosphere. These particles can change the amount of
energy that is absorbed and reflected by the atmosphere. They are also believed to modify the
properties of clouds, changing the amount of energy that they absorb and reflect. Intensive
studies of the climatic effects of these particles began only recently and the overall effect is
uncertain. It is likely that the net effect of these small particles is to cool the climate and to
partially offset the warming of increasing concentrations of greenhouse gases.