FIGURE 3.1 The chain of factors that determine how much CO₂ accumulates in the atmosphere. Each of the boxes represents a potential intervention point. The blue boxes represent factors that can potentially be influenced to affect the outcomes in the purple circles.

tion, atmospheric CO₂ concentrations can be altered by managing carbon sinks and sources in the biosphere and by chemical means that withdraw CO₂ from the atmosphere (post-emission carbon management). Figure 3.1 summarizes these major areas of opportunity, or potential points of intervention, in the effort to reduce atmospheric GHG concentrations. Each of these intervention points is discussed individually in the following sections, but it should be acknowledged that, in some instances (for example, in shaping future urban development patterns), major advances will require systems-level solutions, involving intervention at several of these points simultaneously.

The first box in Figure 3.1 identifies various factors that have been shown to influence the overall level of demand for goods and services in an economy. Curbing U.S. population growth (either through policies to influence reproductive choices or immigration), or deliberately curbing U.S. economic growth, almost certainly would reduce energy demand and GHG emissions. Because of considerations of practical acceptability, however, this report does not attempt to examine strategies for manipulating either of these factors expressly for the purpose of influencing GHG emissions.

An issue of key relevance is the practicality and acceptability of intervening to alter consumer behavior and preferences in ways that would reduce the demand for goods and services that result in energy consumption and GHG emissions. (We note this is different from the question explored in the following section: how to meet demand