Chapter Summary

The nature of atmospheric gases make our air relatively transparent to visible light that warms the earth’s surface and supports photosynthesis. The same gases trap outgoing energy, keeping the earth warm enough for life as we know it. Excessive “greenhouse gases,” though, appear to be causing global warming, which will have complex effects.

When air is warmed by the earth’s surface, it expands and rises, creating convection currents. These vertical updrafts carry water vapor aloft and initiate circulation patterns that redistribute energy and water from areas of surplus to areas of deficit. Pressure gradients created by this circulation drive great air masses around the globe and generate winds that determine both immediate weather and long-term climate.

The earth’s climate changes over time. The El Niño/Southern Oscillation (ENSO) is an important example. ENSO cycles involve a complex interaction between oceans and atmosphere that has far-reaching climatic, ecological, and social effects. Anthropogenic global warming is another important climate change. International agreements, including the Kyoto Protocol, have sought to limit CO₂ production, but so far, economic concerns have prevented adoption in America, the world’s largest CO₂ producer. Numerous changes, especially at high latitudes, suggest that global warming already has begun, but doubters claim these may all be merely natural climate anomalies.

Air pollution interacts with climate in important ways: climate patterns concentrate or distribute pollution around the globe, and air pollution can alter climate conditions. Among the most important of these processes are long-range transport of pollutants and photochemical reactions in trapped inversion layers over urban areas. The Clean Air Act regulates major types and sources of air pollution in the United States, and this law has dramatically improved ambient air quality in the past 30 years.

Encouraging improvements have been made in ambient outdoor air quality over most of the United States in the last few decades. We have made considerable progress in designing and installing pollution-control equipment to reduce the major conventional pollutants. Much remains to be done, especially in developing countries and in Eastern Europe, but air pollution control is, perhaps, our greatest success in environmental protection and an encouraging example of what can be accomplished in this field.