As world population rises (2.5, 4.1, and 6.5 billion individuals in 1950,1975, and 2005, respectively; United Nations 2005), human-induced environmental pressures mount. By some measures, one of the most pressing environmental issues is global climate change related to rising atmospheric concentrations of greenhouse gases (GHGs). The link between observed rising atmospheric concentrations of CO2 and other GHGs, and observed rising global mean temperature and other climatic changes, is not unequivocally established. Nevertheless, the accumulating evidence makes the putative link harder to dismiss.

As early as 2000, the United Nations–sponsored Intergovernmental Panel on Climate Change (Houghton et al.2001) found the evidence sufficiently strong to state that “there is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities” and that “[t]he balance of evidence suggests a discernible human influence on global climate.” If one views anthropogenic climate change as an undesirable eventuality, it follows that modifying the ways we conduct various aspects of our lives is required in order to reduce GHG emissions. Many changes can realistically only occur following policy changes (e.g.,switching some transportation volume to less CO2-intensive modes). However, in addition to policy-level issues, energy consumption is strongly affected by individual personal, daily-life choices.