Air Pollution and Global Change 177
five revisions of it) prescribed the imposition of limitations and gradual
abolition of the production and use of the most dangerous CFCs by 1996,
with a provision for a total abolition of the less active ones until 2030.
Some developing countries delayed signing the Montreal Protocol and continued using CFCs for the production of refrigerators and air conditioners
for some years. Nevertheless, the international cooperation that led to the
rapid confrontation of the problem is considered to be a model one. Some
scientific research has already shown an improvement of the ozone condition, although a complete recovery should not be expected before the end
of the 21st century.
9.4 thE grEEnhouSE EFFEct
9.4.1 composition and thermal Equilibrium
of the atmosphere
Although it ranges among the extremely low temperatures of space, Earth’s
surface maintains a temperature that is mild and favourable to life, with a
mean value of about 15°C. Its direct warming by the sun, along with a small
contribution of heat from the planet’s interior, justify an average temperature not higher than –18°C. The observed positive difference of 33°C is due
to the natural process called the greenhouse effect which warms the lower
atmosphere (troposphere) and conduces to the creation of an environment
that is friendlier to life. Contributors to the phenomenon are some trace
gases of the Earth’s atmosphere that are usually referred to as greenhouse
gases. They are relatively transparent for the incident visible and ultraviolet
solar radiation but they absorb infrared radiation; as a result, they trap,
like a greenhouse, the infrared radiation emitted from the surface of the
Earth. The Earth is warmed by the whole spectrum of the incident solar
radiation and it emits infrared radiation (according to the Stefan-Boltzman
law, Chapter 2, Section 2.7); consequently it achieves a state of thermal
equilibrium. The presence of the greenhouse effect results in the increase of
the average temperature of the planet’s thermal equilibrium by 33°C.
An increase of the concentrations of greenhouse gases in the atmosphere
causes a change in the radiation equilibrium and a concomitant disturbance
of the existing thermal equilibrium due to an increase of the energy quantity
that is trapped in the troposphere. That entails more violent atmospheric
phenomena (storms, typhoons etc.), an increase of the average temperature
of the atmosphere and the oceans and generally changes to the planet’s
climate. There are strong indications that air pollution caused by human
activities amplifies the concentrations of greenhouse gases and therefore
the intensity of the greenhouse effect which, whereas in the past was a
five revisions of it) prescribed the imposition of limitations and gradual
abolition of the production and use of the most dangerous CFCs by 1996,
with a provision for a total abolition of the less active ones until 2030.
Some developing countries delayed signing the Montreal Protocol and continued using CFCs for the production of refrigerators and air conditioners
for some years. Nevertheless, the international cooperation that led to the
rapid confrontation of the problem is considered to be a model one. Some
scientific research has already shown an improvement of the ozone condition, although a complete recovery should not be expected before the end
of the 21st century.
9.4 thE grEEnhouSE EFFEct
9.4.1 composition and thermal Equilibrium
of the atmosphere
Although it ranges among the extremely low temperatures of space, Earth’s
surface maintains a temperature that is mild and favourable to life, with a
mean value of about 15°C. Its direct warming by the sun, along with a small
contribution of heat from the planet’s interior, justify an average temperature not higher than –18°C. The observed positive difference of 33°C is due
to the natural process called the greenhouse effect which warms the lower
atmosphere (troposphere) and conduces to the creation of an environment
that is friendlier to life. Contributors to the phenomenon are some trace
gases of the Earth’s atmosphere that are usually referred to as greenhouse
gases. They are relatively transparent for the incident visible and ultraviolet
solar radiation but they absorb infrared radiation; as a result, they trap,
like a greenhouse, the infrared radiation emitted from the surface of the
Earth. The Earth is warmed by the whole spectrum of the incident solar
radiation and it emits infrared radiation (according to the Stefan-Boltzman
law, Chapter 2, Section 2.7); consequently it achieves a state of thermal
equilibrium. The presence of the greenhouse effect results in the increase of
the average temperature of the planet’s thermal equilibrium by 33°C.
An increase of the concentrations of greenhouse gases in the atmosphere
causes a change in the radiation equilibrium and a concomitant disturbance
of the existing thermal equilibrium due to an increase of the energy quantity
that is trapped in the troposphere. That entails more violent atmospheric
phenomena (storms, typhoons etc.), an increase of the average temperature
of the atmosphere and the oceans and generally changes to the planet’s
climate. There are strong indications that air pollution caused by human
activities amplifies the concentrations of greenhouse gases and therefore
the intensity of the greenhouse effect which, whereas in the past was a