The combination of low vehicle ownership and robust economies has led to very rapid growth in the vehicle fleets in China and India in recent years. The number of vehicles in China has been growing at an annual rate of almost 13 percent for 30 years, nearly doubling every 5 years. India's fleet has been expanding at more than 7 percent per year [6]. While together these two countries now account for only a small percentage of the vehicles on the road, that percentage can be expected to grow as these countries continue to industrialize in the years to come.

The growing use of internal combustion vehicles, especially in urban areas, will increase congestion, raise the demand for oil, worsen air pollution, and increase emissions of a variety of greenhouse gases, including methane, ozone, carbon monoxide, nitrous oxide, and, most important, CO2.

Worldwide, motor vehicles currently emit well over 900 million metric tons of CO2 each year. These emissions account for more than 15 percent of global fossil fuel CO2 releases [7]. Because of their large vehicle fleets, developed countries are responsible for a commensurately large share of emissions. In 1993, the countries of the Organisation for Economic Co-Operation and Development (OECD) accounted for about two thirds of total world CO2 emissions from motor vehicles, although these countries represented only 16 percent of the world's population. If the linear growth in emissions characterizing the past 20 years were to continue into the next century, OECD countries would still account for fully 60 percent of global motor vehicle emissions by the year 2050 [8].

Given the likely growth of the world vehicle fleet, the problems of global warming and urban air pollution will almost certainly need to be addressed by making a long-term shift away from oil as the universal energy source for transportation. But designing a new generation of resource-efficient, environmentally friendly vehicles is one of the most challenging technological problems facing the industrialized world. Most of the major automakers around the world are responding to this challenge and are actively developing more efficient conventionally fueled vehicles as well as so-called alternatively fueled vehicles. The latter are variously powered by fossil fuels (called hybrid vehicles), electric batteries, or hydrogen. In all cases, the vehicles have electric drives, meaning they are ultimately driven by electric motors.

In a typical hybrid configuration, a small, clean, internal combustion engine or gas turbine generates electricity that can power the car directly through its motors or charge on-board batteries. In some designs, the gasoline (or other liquid hydrocarbon, such as methanol) is broken down into hydrogen and CO2 and the hydrogen is then used to power a fuel cell that produces electricity, which in turn powers the vehicle. Hybrid vehicles powered by fossil fuels are much more efficient than today's standard vehicle designs but still emit CO2. In this sense, they are not a long-term solution.

Battery-powered vehicles are actively being developed by several automakers, and a small number are currently in use. The driving range of battery-powered vehicles using two of the most promising long-range batteries -- nickel-metal hydrid and lithium batteries -- is well over 62 kilometers, but battery costs are still very high. In one promising battery system, developed by Electric Fuel, Ltd., of Israel, long-range zinc-air batteries are removed entirely from the vehicles after they run down and replaced by fresh ones, shortening the refueling time. The run-down batteries are then recharged and used again. Large-scale tests of this system in Germany have yielded positive results so far. Fuel-cell vehicles with the hydrogen stored in high pressure tanks have also been tested; the biggest remaining problem is developing a less bulky, low-cost storage system for the hydrogen.

Because developments in car design and propulsion are progressing rapidly, there is no indication yet which combination of hydrogen fuel cells, batteries, or other technologies will power the vehicles of the 21st Century.

References and notes

1. United Nations (U.N.) Population Division, World Population Prospects 1950-2050 (The 1996 Revision), on diskette (U.N., New York, 1996).

2. Ibid.

3. Op. cit. 1.

4. United Nations (U.N.) Population Division, World Population Prospects 1950-2050: The 1996 Revision, Annex 1: Demographic Indicators (U.N., New York, 1997), pp. 11-45.

5. Ibid., p. 121.

6. Op. cit. 4, pp. 124-125.

7. Op. cit. 1.

8. Op. cit. 4, Table A.18, pp. 120-122.