Chapter 14. The role of air pollution in the global climate change

Table of Contents

14.1. Effects of atmospheric composition on the radiation budget
14.2. Anthropogenic perturbation of the greenhouse gases
14.3. Radiative forcing of atmospheric components
14.4. Future scenarios
14.4.1. SRES scenarios
14.4.2. Representative Concentration Pathways (RCPs)

Since the beginning of the Industrial Revolution in the mid-18th century, growing anthropogenic emission of air pollutants cause increasing trends in their atmospheric concentration levels. During combustion of fossil fuels for industrial and domestic usage and biomass burning, large amount of greenhouse gases and aerosol particles are produced which affect the atmospheric composition. Air pollution has become an increasingly serious problem causing several harmful effects on the environment (see Chapter 13). At the end of the 19th century, Swedish chemist, Svante Arrhenius first quantified the contribution of carbon dioxide to the greenhouse effect and assumed that the variation of atmospheric concentration of carbon dioxide can contribute to the variation of Earth’s climate (Arrhenius, 1896). Since then it has become clear that anthropogenic perturbation of the atmospheric composition and enhanced greenhouse effect change the the radiative forcing and have a potential impact on regional and global climate (see e.g. IPCC, 2007).

14.1. Effects of atmospheric composition on the radiation budget

Atmospheric contaminants play important role in the radiation budget of the Earth-atmosphere system through the modification of the intensity of both incoming solar radiation and outgoing terrestrial radiation. One of the main results of these processes is the greenhouse effect (Figure 14.1).

The greenhouse effect

Figure 14.1: The greenhouse effect: the absorption and re-emission of a part of long wave radiation from the Earth by greenhouse gases heating the atmosphere.

The greenhouse effect is a natural process in the atmosphere, by which a part of long wave radiation from Earth’s surface is absorbed by atmospheric greenhouse gases (GHGs), and is re-emitted in all directions, thereby heating the atmosphere. Due to this process, the Earth’s atmosphere is more than 33 °C warmer that it would be without it (see table 14.1). However, human activities can modify this greenhouse effect by the increased emission of greenhouse gases, which is the most important factor in recent climate change. Most abundant greenhouse gases are water vapour (H2O), carbon-dioxide (CO2), methane (NH3), nitrous-oxide (N2O), tropospheric ozone (O3) and chlorofluorocarbons (CFCs).

Table 14.1: The most important greenhouse gases and their contribution to the atmospheric greenhouse effect

Name

Formula

Effect

Water vapour

H2O

+ 20.6 °C

Carbon-dioxide

CO2

+ 7.2 °C

Tropospheric ozone

O3

+ 2.4 °C

Nitrous oxide

N2O

+ 1.4 °C

Methane

CH4

+ 0.8 °C

Others

 

+ 0.6 °C

 

Sum:

+ 33 °C

Aerosol particles have also significant effects on the radiation budget. These effects can be direct radiative forcing due the scattering absorption radiation or indirect radiative forcing through cloud formation effects (see details in Chapter 7).