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.
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, including hurricanes.
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.
Other sources 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.
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.
Although some scientists disagree about the causes, timing, and consequences of global climate change, an overwhelming majority now agree that there are unmistakable signals of human impacts on the world's climate.
Melting of arctic and alpine glaciers could raise sea levels to disastrous heights, while also drying up water sources on which billions of people depend. Many wild animal and plant species are being driven out of their current ranges as the climate changes. Some, like polar bears and musk oxen, have no place to go, and may become extinct. Some low-lying, small island nations such as Tuvalu are becoming uninhabitable.
In 1997, 160 nations meeting in Kyoto, Japan, signed an agreement to reduce greenhouse gas emissions. Every industrial nation in the world—except the United States—has ratified this agreement, and many are beginning to implement it. Despite evidence from his own scientists about the reality and seriousness of global warming. President Bush continues to call for more study and voluntary efforts to combat this threat.
Many American states, cities, and companies have begun programs to limit greenhouse gas emissions. There are ways that you, too, can lower your impacts on our global climate.
