react under UV radiations and generate chlorine radicals, ClÁ, that may affect and
destroy the ozone layer: one chlorine radical can destroy up to 100 000 molecules
of ozone. When their effect was recognized in 1974 at the University of California
by Prof. F. Sherwood Rowland and Dr. Mario Molina, serious measures toward the
limitation of their use were taken in 1987 with the Montreal Protocol and, finally,
most of them were banned on January 1, 1996 and progressively substituted with
less stable molecules that are more easily destroyed and do not reach the stratosphere. As an effect of such policy, the “ozone hole” strongly decreased over the
last 20 years. CFCs also behave as greenhouse gases.
3.4 Greenhouse Gases, Their Atmospheric Level,
and Effect on Climate Change
The natural atmospheric concentration of greenhouse gases (GHGs: water vapor—
the most abundant, carbon dioxide, methane, nitrous oxide, ozone, and some
synthetic chemicals such as CFCs) has been kept under control by the respective
natural cycles developed in million years. In Fig. 2.1, the carbon cycle is shown.
The continuous increase of the atmospheric level of GHGs and CO 2 , in particular,
due to anthropogenic activities and the fact that the excess amount cannot be
buffered by the natural cycle is rising serious worries about the impact on the
environment. Even, such increase is correlated to the climate change on our planet.
As mentioned above, the production of energy from fossil-C is performed with low
efficiency that averages 32%. This is true for the production of electric energy from
coal, oil, and methane, for the production of heat, and for the use of gasoline and
diesel in the transport sector. Noteworthy, the remaining 68% thermal energy is
released to the atmosphere in the form of high-temperature heat that causes a direct
heating of the atmosphere. More fossil-C we burn, more heat we transfer to the
atmosphere.
3.5 The Greenhouse Effect
But what is the greenhouse effect? Is it natural? How anthropic activities can
influence the natural effect?
Solar radiations (constituted mainly of visible light, with ca. 8% UV component)
during daytime reach the Earth’s atmosphere: part is reflected back into the space,
part is absorbed by land and oceans, heating the Earth (Fig. 3.6). During night, heat
radiates from Earth toward the space in the form of infrared radiations: some of this
heat is trapped by greenhouse gases present in the atmosphere, keeping the Earth
warm enough (average temperature 13–14 °C) to sustain life. Without the
“greenhouse effect (GHE)” the Earth average temperature would be some 33 °C
lower making impossible life to exist. However, the greenhouse effect is natural and
38
3 The Atmosphere, the Natural Cycles and the “Greenhouse Effect”
destroy the ozone layer: one chlorine radical can destroy up to 100 000 molecules
of ozone. When their effect was recognized in 1974 at the University of California
by Prof. F. Sherwood Rowland and Dr. Mario Molina, serious measures toward the
limitation of their use were taken in 1987 with the Montreal Protocol and, finally,
most of them were banned on January 1, 1996 and progressively substituted with
less stable molecules that are more easily destroyed and do not reach the stratosphere. As an effect of such policy, the “ozone hole” strongly decreased over the
last 20 years. CFCs also behave as greenhouse gases.
3.4 Greenhouse Gases, Their Atmospheric Level,
and Effect on Climate Change
The natural atmospheric concentration of greenhouse gases (GHGs: water vapor—
the most abundant, carbon dioxide, methane, nitrous oxide, ozone, and some
synthetic chemicals such as CFCs) has been kept under control by the respective
natural cycles developed in million years. In Fig. 2.1, the carbon cycle is shown.
The continuous increase of the atmospheric level of GHGs and CO 2 , in particular,
due to anthropogenic activities and the fact that the excess amount cannot be
buffered by the natural cycle is rising serious worries about the impact on the
environment. Even, such increase is correlated to the climate change on our planet.
As mentioned above, the production of energy from fossil-C is performed with low
efficiency that averages 32%. This is true for the production of electric energy from
coal, oil, and methane, for the production of heat, and for the use of gasoline and
diesel in the transport sector. Noteworthy, the remaining 68% thermal energy is
released to the atmosphere in the form of high-temperature heat that causes a direct
heating of the atmosphere. More fossil-C we burn, more heat we transfer to the
atmosphere.
3.5 The Greenhouse Effect
But what is the greenhouse effect? Is it natural? How anthropic activities can
influence the natural effect?
Solar radiations (constituted mainly of visible light, with ca. 8% UV component)
during daytime reach the Earth’s atmosphere: part is reflected back into the space,
part is absorbed by land and oceans, heating the Earth (Fig. 3.6). During night, heat
radiates from Earth toward the space in the form of infrared radiations: some of this
heat is trapped by greenhouse gases present in the atmosphere, keeping the Earth
warm enough (average temperature 13–14 °C) to sustain life. Without the
“greenhouse effect (GHE)” the Earth average temperature would be some 33 °C
lower making impossible life to exist. However, the greenhouse effect is natural and
38
3 The Atmosphere, the Natural Cycles and the “Greenhouse Effect”