Chapter Summary

Global climate change may well be the most momentous issue in environmental science today. To understand why this is happening and what we can do about it, we need to know something about atmospheric processes. Weather is a description of local conditions; climate describes long-term weather patterns.

The atmosphere and living organisms have evolved together so that the present chemical composition of the air is both suitable for, and largely the result of, biological processes. Upper layers of the atmosphere play an important role in protecting the earth’s surface by intercepting dangerous ultraviolet radiation from the sun. The atmosphere is relatively transparent to visible light that warms the earth’s surface and is captured by photosynthetic organisms and stored as potential energy in organic chemicals.

Heat is lost from the earth’s surface as infrared radiation, but fortunately for us, carbon dioxide and water vapor naturally present in the air capture the radiation and keep the atmosphere warmer than it would otherwise be. When air is warmed by conduction or radiation of heat from 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 rotation causes wind deflection called the Coriolis effect, which makes air masses circulate in spiraling patterns. Strong cyclonic convection currents fueled by temperature and pressure gradients and latent energy in water vapor can create devastating storms. Tornadoes, while classified as cyclonic storms, are not set spinning by Coriolis forces. Instead, shear forces caused by differential wind speeds, together with rapidly rising warm convection currents and cold downdrafts are thought to create intensely focused spinning vortices. Although top wind speeds in tornadoes can be higher than those in hurricanes, total damage in the former is usually smaller because the area covered is smaller.

Another source of storms are the seasonal winds, or monsoons, generated by temperature differences between the ocean and a landmass. Monsoons often bring torrential rains and disastrous floods, but they also bring needed moisture to farmlands that feed a majority of the world’s population. When the rains fail, as they do in drought cycles, ecosystem disruption and human suffering can be severe.

The El Niño/Southern Oscillation is a complex interaction between oceans and atmosphere that has far-reaching climatic, ecological, and social effects. ENSO cycles can affect things as widely different as forest fires in Indonesia, anchovy fishing in Peru, rainfall in the Sahara Desert, and how the corn grows in Iowa. Knowing something about how weather works can be helpful in our everyday life.

Many procedures claiming to control the weather are ineffectual, but some human actions—both deliberate and inadvertent—appear to be changing local weather and long-term climate. Many scientists warn that the gaseous pollutants we release into the atmosphere trap radiant energy and could cause a global warming trend that would drastically disrupt human activities and natural ecosystems. Understanding and protecting this complex, vital aspect of our world is clearly essential.