Interactions of the earth’s systems: environmental degradation

The components of the earth’s systems - the atmosphere, oceans, land and living species - are intricately intertwined. If one part of the earth changes, other parts will be affected - often in ways that are not immediately obvious. For example, removing vegetation from an area of land decreases that land’s absorption of ground water, resulting in possible drinking water shortages for the inhabitants. Or the burning of tropical woodlands can increase the amount of carbon dioxide in the atmosphere. In this section, we illustrate the major concerns of environmental degradation.

Degradation of the atmosphere

Global warming - The concentration of carbon dioxide in the atmosphere has increased nearly 25 percent since the onset of industrialization in the 18th century. To meet the world’s energy needs, the burning of fossil fuels - such as coal, wood and petroleum - frees carbon to join with oxygen in the atmosphere. Deforestation, the destruction of forests by burning or over-logging (see Deforestation below), also contributes to the build-up of carbon dioxide by releasing carbon stored in the plant material.

Atmospheric methane, released from landfills, cattle and fermenting rice paddies, has increased with population growth. The build-up of these greenhouse gases may enhance the natural greenhouse effect and may result in additional warming of the earth’s surface, or global warming. If warming occurs as some scientists predict, the results might include a rise in the sea level, changes in climate, changes in ecosystems, and impacts on public health.

Ozone depletion - Ozone, a rare form of oxygen, is concentrated in the upper atmosphere or ozonosphere, located 11 to 24 km above the earth. This ozone layer, which protects life from the damaging rays of the sun, is being thinned by the release of chlorofluorocarbons (CFCs), chemicals used in refrigeration, foam products and aerosol propellants.

Figure 4 The ozone layer

Many forms of life will be affected as the ozone layer thins and more ultraviolet light reaches the earth. In humans, skin cancer and diseases of the eyes and immune systems are expected to increase. Ultraviolet radiation can penetrate the oceans’ surface, damaging fish and the phytoplankton base of the food chain, possibly impacting significantly on fish-eating populations.

Audubon, May-June 1992

Air pollution - Most of the world’s urban dwellers breathe polluted air at least part of the time. Sulfur dioxide (SO₂), a major pollutant, is a corrosive gas harmful to humans and the environment. The burning of fossil fuels, to generate electricity, is a key source of sulfur dioxide; in developing countries, burning coal and wood also contributes. Other air pollutants include nitrous oxides, carbon monoxide, carbon dioxide and lead from vehicle exhaust. In some countries, particulate matter such as dust, dirt and smoke.

Air pollution inflicts further damage on land and systems: on agricultural crops, forests, rivers and lakes, buildings and human health. Such airborne pollution damages crops and vegetation by injuring the plant tissue, which increases susceptibility to disease and drought. Human health also suffers when pollution damages respiratory tracts.

As primary pollutants react to form secondary pollutants, acidic compounds are sometimes created. When these acidic compounds and other multiple pollutants damage the foliage and the soil, forests decline and die (see Deforestation below). Pollutants in the air are also dissolved in water droplets and held in clouds, sometimes moving long distances before falling back to earth in acid rain, snow, dew or fog.

Degradation of the oceans

Marine pollution - Due to their enormous volume, oceans are frequently used as disposal areas for human societies’ garbage. Raw sewage, consisting of human excreta and domestic wastes, is the major source of ocean pollution. Sewage, livestock waste and fertilizer runoff also make bodies of water over-rich in dissolved nutrients, a process called eutrophication; this phenomenon depletes the water of oxygen, killing fish and other marine life. Other causes of degradation: litter dumped from ships, petroleum spills, and the dumping of radioactive substances.

Local volunteers and professionals clean up debris near Huntington Beach, California, after a 1990 oil spill. Audubon, May-June 1992

Marine pollution can have major consequences:

Human wastes contain disease-causing bacteria and viruses.

Nondegradable materials injure and kill marine mammals.

The spread of hazardous chemicals may damage the marine ecosystem and accumulate in seafood.

Ocean temperature shifts - Current warming trends in the earth’s atmosphere may affect the temperature of the oceans, which may increase the occurrence or severity of the El Nihenomenon, an incursion of warm surface water near the coast of Peru.

Scientific evidence links El Nivents to droughts and heavy rains in a number of countries; these associations are a result of global patterns of atmospheric circulation. For example, the major drought of 1982-83 that affected Africa, India, northeast Brazil, the USA, Australia and Indonesia coincided with the most significant El Nivent ever recorded. A smaller El Nin 1986-87 was associated with the drought in Ethiopia.

Degradation of the water cycles

The various subsystems of the hydrological cycle are so interrelated that interference with one will affect the others. We alter the natural flow of water with dams and reservoirs; we render the ground impermeable to moisture by covering it with concrete and buildings. Removing the soil’s natural vegetation cover reduces the soil’s ability to retain water; this causes rapid runoff of water to drainage areas, leaving less for local use by plants and humans.

When people consume vast amounts of water - for drinking, domestic use, irrigation and industry - the possibility increases that water shortages will occur in the future. Pollution of water by sewage, industrial wastes, pesticides and fertilizers increases the odds that supplies of clean water will not be adequate. Acid precipitation (see above) increases the acidity of the soils, lakes and streams where it falls and is often toxic to plants and animals.