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THE CHANGING ATMOSPHERE-CHALLENGES AND OPPORTUNITIES


• Our national security is directly affected by the weather, both in the daily operations of our land, air, and naval forces and in the development of defense systems used by these forces. Aerial operations and targeting are affected by cloud cover and winds, and command and control systems on land and at sea are impacted by weather conditions such as heavy rains, snow, or dust storms. The more complex a defense system is, the more complicated are the weather and environmental issues that must be treated in the design, development, and operation of the system.


1.2 Human Causes of Climate Change

Increasing population, technological advances, and economic demands for greater use of energy resources have not only made societies more vulnerable than ever to weather and climate, but have created for the first time a situation where humans have actually begun to cause important changes in weather and climate. Degradation of local environments through air pollution and of regional environments through acid rain are well-known consequences of this growth. It is becoming obvious now that environmental changes caused by human activity are not restricted to local and regional environments but also affect the weather and climate worldwide.

Because of the enormous effect they have on the earth's radiation budget, changes in the atmospheric chemical composition are a major factor in climate change. The atmosphere's composition has changed over the earth's history through natural causes. For example, biological processes over 400 million years slowly removed carbon dioxide from the atmosphere and stored it in vast reservoirs of fossil fuel. Human activity is reversing the process and changing the atmospheric composition. Not only are we burning the fossil fuel, thus returning to the atmosphere the carbon stored over millions of years, but we are also increasing atmospheric carbon dioxide by destroying millions of acres of forests, particularly those in the tropics. The result is a change in atmospheric composition that is very rapid compared to changes that have occurred naturally in the past. 

Evidence of human-caused climate and sea level change is already with us. The increase in atmospheric carbon dioxide since the beginning of the industrial revolution is perhaps the best-known global consequence of human activities; but other trace gases, such as methane, have also increased. Higher concentrations of these gases have affected the atmospheric radiation budget (the "greenhouse effect"), likely contributing to a global mean surface temperature rise of about 1° Fahrenheit during the past 100 years. This warming, in turn, is probably responsible for the four-inch rise in global sea level from the melting of ice and the

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