Air pollution from exhaust emissions and global climate change caused by greenhouse gas emissions present the greatest challenges to achieving green car mobility. Many countries are tackling vehicle air pollution emissions with technical solutions such as low-sulfur fuels, unleaded gasoline and three-way catalytic converters.

In this study, Patrick Moriarty and Damon Honnery (Department of Mechanical Engineering, Monash University, Australia) argue that a technical solution for overcoming transport’s climate change impact is not feasible. The authors emphasize that the world will need to change its surface transport habits, and adopt a system involving less motorized travel.

Worldwide, car ownership is growing and could increase almost three-fold by 2030. With the projected rise in global population, passenger travel by 2030 would increase by a factor of 3.5. In addition to rising travel demand, it is likely that global emissions of greenhouse gases will need to be four times less than their current value to avoid irreversible climate change. When combined, a 14-fold reduction in emissions per p-km may be necessary by 2030.

At best, a 2- to 2.5-fold fuel efficiency gain can be hoped for in the world car fleet by 2030, with most of the gain resulting from a switch to hybrid electric vehicles. Yet these improvements could be offset by continued decline in occupancy rates and increasing energy costs for petroleum-based fuels.

Success therefore depends crucially on electricity derived from renewable energy replacing most petroleum-based fuels. However, most non-carbon energy resources have limited potential, and are not always carbon-neutral.

The authors conclude that without a realistic technical solution, it will be necessary to adopt alternative modes of transport to bring about green car mobility. In countries with high levels of automobile use, it is likely that vehicular travel levels will need to be reduced threefold. Such reductions will require more frequently traveling on foot or bicycle to local destinations, while public transport will need to be made more energy-efficient. Overall, physical travel will need to be curtailed. Similar changes will be necessary in air travel and other sectors of the economy, and may prove nearly as difficult to achieve.

Journal of Cleaner Production, Volume 16, Issue 16, November 2008, Pages 1717-1726

DOI: 10.1016/j.jclepro.2007.10.025