The greenhouse gases produced by fossil fuel combustion, agricultural activities, and deforestation are expected by many scientists to cause an unmistakable global warming on earth within the next ten to twenty years. A warming of only a few degrees could endanger a substantial fraction of agricultural production in the Great Plains and Western states. It would also causing melting of polar ice, leading to a rise in sea level that could endanger heavily populated coastal cities. This is only one example of how serious the repercussions can be when mankind is careless of the planet which sustains his life. Environmental problems can cross national boundaries and generations.
Sulfur dioxide emissions in one nation can cause acid rain in another.
Indeed, air pollutants can cause global changes in the atmosphere and climate. The hole in the ozone over the Southern Hemisphere, for example, has been caused by chlorofluorocarbons, used primarily in the Northern Hemisphere to make refrigerants, aerosols, and foams. Even if the emission of these gases stopped today, those already in the atmosphere would linger for over a century, continuing to destroy the ozone that screens out dangerous ultraviolet rays from the sun. The pattern of economic growth that made the industrialized West wealthy cannot be sustained, let alone practiced on a global scale. The traditional understanding of economic growth and industrialization in the West does not take into account the finiteness of the natural environment.