and heat; greatly reduced air and water pollution; and extensive carbon capture and storage. Alongside the fossil energy system will be a nonfossil energy system approximately as large. Extensive direct and indirect harvesting of renewable energy will have brought about the revital-ization of rural areas and the reclamation of degraded lands. If nuclear power is playing a large role, strong international enforcement mechanisms will have come into being to control the spread of nuclear technology from energy to weapons. Economic growth will have been maintained; the poor and the rich will both be richer. And our descendants will not be forced to exhaust so much treasure, innovation and energy to ward off rising sea level, heat, hurricanes and drought.
Critically, a planetary consciousness will have grown. Humanity will have learned to address its collective desti-ny—and to share the planet. ®
Stabilization Wedges: Solving the Climate Problem for the Next 50 Years with Current Technologies. S. Pacala and R. Socolow in Science, Vol. 305, pages 968-972; August 13, 2004.
The calculations behind the individual wedges are available at www.princeton.edu/~cmi Energy statistics are available at www.eia.doe.gov,www.iea.org and www.bp.com; carbon emissions data can also be found at cdiac.esd.ornl.gov
□ The massive use of petroleum-based fuels for transportation releases immense amounts of carbon dioxide into the atmosphere— 25 percent of the total worldwide.
□ Options for constraining and eventually reducing these emissions include improving vehicle technology, reducing vehicle size, developing different fuels, and changing the way vehicles are used.
□ To succeed, we will most likely have to follow through on all of these choices.
What are the options for decreasing demand for oil and lowering greenhouse gas emissions in cars and light trucks? BY JOHN B. HEYWOOD
If we are honest , most of us in the world's richer countries would concede that we like our transportation systems. They allow us to travel when we want to, usually door-to-door, alone or with family and friends, and with our baggage. The mostly unseen freight distribution network delivers our goods and supports our lifestyle. So why worry about the future and especially about how the energy that drives our transportation might be affecting our environment?
The reason is the size of these systems and their seemingly inexorable growth. They use petroleum-based fuels (gasoline and diesel) on an unimaginable scale. The carbon in these fuels is oxidized to the greenhouse gas carbon dioxide during combustion, and their massive use means that the amount of carbon dioxide entering the atmosphere is likewise immense. Transportation accounts for 25 percent of worldwide greenhouse gas emissions. As the countries in the developing world rapidly motorize, the increasing global demand for fuel will pose one of the biggest challenges to controlling the concentration of greenhouse gases in the atmosphere. The U.S. light-duty vehicle fleet (automobiles, pickup trucks, SUVs, vans and small trucks) currently consumes 150 billion gallons (550 billion liters) of gasoline a year, or 1.3 gallons of gasoline per person a day. If other nations burned gasoline at the same rate, world consumption would rise by a factor of almost 10.
As we look ahead, what possibilities do we have for making transportation much more sustainable, at an acceptable cost?
Our Options several options could make a substantial difference. We could improve or change vehicle technology; we could change how we use our vehicles; we could reduce the size of our vehicles; we could use different fuels. We will most likely have to do all of these to drastically reduce energy consumption and greenhouse gas emissions.
In examining these alternatives, we have to keep in mind several aspects of the existing transportation system. First, it is well suited to its primary context, the developed world. Over decades, it has had time to evolve so that it balances economic costs with users' needs and wants. Second, this vast optimized system relies completely on one convenient source of energy—petroleum. And it has evolved technologies—internal-combustion engines on land and jet engines (gas turbines) for air—that well match vehicle operation with this energy-dense liquid fuel. Finally, these vehicles last a long time. Thus, rapid change is doubly difficult. Constraining and then reducing the local and global impacts of transportation energy will take decades.
We also need to keep in mind that efficiency ratings can be misleading; what counts is the fuel
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consumed in actual driving. Today's gasoline spark-ignition engine is about 20 percent efficient in urban driving and 35 percent efficient at its best operating point. But many short trips with a cold engine and transmission, amplified by cold weather and aggressive driving, significantly worsen fuel consumption, as do substantial time spent with the engine idling and losses in the transmission. These real-world driving phenomena reduce the engine's average efficiency so that only about 10 percent of the chemical energy stored in the fuel tank actually drives the wheels. Amory Lovins, a strong advocate for much lighter, more efficient vehicles, has stated it this way: with a 10 percent efficient vehicle and with the driver, a passenger and luggage—a payload of some 300 pounds, about 10 percent of the vehicle weight—"only 1 percent of the fuel's energy in the vehicle tank actually moves the payload."
We must include in our accounting what it takes to produce and distribute the fuel, to drive the vehicle through its lifetime of 150,000 miles (240,000 kilometers) and to manufacture, maintain and dispose of the vehicle. These three phases of vehicle operation are often called well-to-tank (this phase accounts for about 15 percent of the total lifetime energy use and greenhouse gas emissions), tank-to-wheels (75 percent), and cradle-to-grave (10 percent). Surprisingly, the en-
▲ Concept car from Volkswagen was designed to carry two people around cities and suburbs. Weighing 640 pounds (290 kilograms), the vehicle, which at present exists only as a prototype, gets some 240 miles to the gallon.
ergy required to produce the fuel and the vehicle is not negligible. This total life-cycle accounting becomes especially important as we consider fuels that do not come from petroleum and new types of vehicle technologies. It is what gets used and emitted in this total sense that matters.
Improving existing light-duty vehicle technology can do a lot. By investing more money in increasing the efficiency of the engine and transmission, decreasing weight, improving tires and reducing drag, we can bring down fuel consumption by about one third over the next 20 or so years—an annual 1 to 2 percent improvement, on average. (This reduction would cost between $500 and $1,000 per vehicle; at likely future fuel prices, this amount would not increase the lifetime cost of ownership.) These types of improvements have occurred steadily over the past 25 years, but we have bought larger, heavier, faster cars and light trucks and thus have effectively traded the benefits we could have realized for these other attributes. Though most obvious in the U.S., this shift to larger, more powerful vehicles has occurred elsewhere as well.
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Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.