Humans spend, on average, a constant fraction of their time and expenditure on travel. These and a few other constraints allow a new model for projecting regional and world travel, which we use to develop a scenario for carbon emissions from passenger transport. Globally, carbon emissions rise from 0.8 GtC in 1990 to 2.7 GtC in 2050. In every industrialized region aircraft and high-speed trains become the dominant mode; unable to satisfy the rising demand for mobility within a fixed travel time budget, automobile travel declines by 2050. Passenger transport carbon emissions stabilize by 2020 without any further policy intervention. But in developing countries automobile travel is still rising and becomes the dominant source of carbon dioxide from passenger transport. Fear of global warming may require stabilization of these emissions by mid-century. We show that without some action to accelerate an improvement in energy efficiency starting in the next decade, the goal of stabilization is a technically impossible task, unless zero-carbon technologies become available.

© 1999 Elsevier B.V.