Looking Ahead
This chapter sets the stage for a comprehensive survey of the earth system. We'll begin with the atmosphere, the subject of chapter 3. The structure and composition of our present day atmosphere has been relatively stable for millions of years. During the depths of the ice ages, the carbon dioxide content of the atmosphere especially decreased which helped keep air temperatures cool. But levels of oxygen have remained fairly constant, even through the ice ages for the last 50 million years or so. But, the composition of the atmosphere especially greenhouse gases like carbon dioxide and methane are changing at rates much greater than they did in the past. These changes are in part due to natural forces, but increasingly are due to the activities of humans.
Figure 2.33 Concentrations of Greenhouse Gases from 0 to 2005
(Courtesy IPCC)
In Chapter 3 "The Atmosphere" we'll examine the composition of the atmosphere and the importance of particular gases to the functioning of the earth system. We'll look out the structure of the atmosphere and how scientists have subdivided it based on vertical temperature patterns and the function of the different atmospheric layers. We'll also peek into the future to see what changes we can expect in our atmosphere as it changes in reponse to the activities of an ever-increasing population and an evolving world economy.