As Figure 4.5 illustrates, the cause of this environmental pressure has not been distributed equally world-wide. Only in the last 10-20 years have there been signs of a decoupling between economic activity and the use of energy and materials in industrial countries. Concerns about human health and more recently about the natural environment have induced governments of industrial countries to develop and enforce environmental regulations to curb the level of atmospheric emissions. Figure 4.6 shows that as a consequence of these measures, global emissions of sulphur compounds have lately decreased, the emissions of nitrogen oxides have more or less stabilized, but carbon dioxide emissions continue to grow. The growth in the number of motor vehicles world-wide is among the factors responsible for continuing high levels of nitrogen oxides emissions despite technological advances in the design of car engines.
Agricultural activity is another important source of emissions.
Other agricultural sources of greenhouse gases are methane emitted by livestock and released from wet rice fields, and nitrogen oxides from crop fertilizers. As a result of the growth of energy use, deposits of acidifying substances have more than quadrupled compared to pre-industrial levels.