(39) Global Warming

UNEP - Promoting Cleaner Fuels and Vehicles for Better Air Quality (Video)

European Environment Agency - Use of cleaner and alternative fuels

Promoting Cleaner Fuels and Vehicles Worldwide



Ethanol-Corn, Sugar, Cellulose

Ethanol, or grain alcohol, can be produced from corn, sugar beets, sugar cane, or other crops primarily by fermentation. Ethanol came onto the scene largely as a means of moving toward energy independence. Brazil currently uses ethanol to meet an estimated 40 percent of its transportation requirements. Presently, roughly 20 percent of the corn grown in the United States is converted to ethanol. Current farming methods use a high percentage of petrochemicals, which to some extent defeats the intent of displacing oil.

Mixtures of ethanol and gasoline (such as 15 percent ethanol and 85 percent gasoline, or E85) are becoming common as an alternative fuel in certain areas of the United States. The energy payback from corn-grown ethanol, however, is marginal. Depending on agricultural conditions, ethanol produces on average only 25-30 percent more energy than the energy it took to produce it. These results in a net energy benefit, with the actual numbers depending on the specific production conditions, including how much carbon dioxide emissions are needed grow, harvest, process, and distribute the ethanol. A higher percentage of ethanol in the fuel blend may require engine modifications. Some automobile manufacturers are now offering flexible fuel vehicles (FFVs) to accommodate either gasoline or higher-percentage ethanol mixes. Because of its chemical structure (carbon–oxygen bonds rather than  the more energetic carbon–hydrogen bonds found in petroleum-based fuels), ethanol delivers about 30 percent less energy per gallon than gasoline. This may not be as noticeable with low-ethanol blends but may become more of an issue when there is more ethanol in the mix.

Since ethanol contains carbon in its chemical structure, it, like any other carbon containing fuel, produces carbon dioxide when burned. For a given amount of energy produced from the same size fuel tank, both ethanol and gasoline produce comparable amounts of carbon dioxide. One difference is that the carbon dioxide that gets released to the atmosphere when ethanol is burned came from the atmosphere through the process of photosynthesis that produced the corn. Ethanol can be thought of as just returning the carbon it removed from the atmosphere. This does not give ethanol a real advantage over gasoline, however, because if the corn wasn’t removing carbon dioxide, presumably some other crop would be there in its place. Growing corn to produce fuel requires farmland that otherwise could grow food crops. This could introduce price pressure on food at a time when increasing flood and drought conditions might diminish the usefulness of some agricultural areas around the world.

The process of producing ethanol involves a fermentation step that produces carbon dioxide. For every 0.51 kg of ethanol produced, 1 kg of carbon dioxide is produced. Capturing this carbon dioxide would improve ethanol’s effectiveness in terms of greenhouse gas reduction. Additional carbon dioxide is released when ethanol is burned, but it is made up of the same carbon atoms that were removed from the atmosphere to grow the feedstock to produce the ethanol.

Brazil has pioneered the use of ethanol. The government mandated 25 percent use of ethanol as a means toward energy independence. Government support, available agricultural acreage, and a climate conducive to growing sugar beets helped to promote this effort. Whether or not other countries can replicate Brazil’s experience with ethanol, the experience today does serve as a success story in implementing a change in a country’s approach to energy production and use. While achieving the twin goals of energy independence and pollution reduction, it is questionable whether ethanol can make much of a dent in the level of carbon dioxide emissions in the short term. Potential efficiency improvements in the ethanol growth and production cycle may improve this situation, this especially if organic farm wastes such as corn stalks, grasses, wheat and rice straw, leaves, and other agricultural leftovers (called lignocellulosic materials) are used as a starting material.

Cellulosic crops are attractive because they have higher yields than high carbohydrate crops such as corn and sugar beets. They grow more easily in areas that are not suitable for grains or other food crops without the need for extensive fertilization. They do not necessarily compete with crops grown for human or animal consumption. The cellulosic materials can provide some of the process heat needed to separate the ethanol after the fermentation process, avoiding the need for consuming additional fossil fuels in the process. At this point, substantial more research is needed to make this a commercial option.


When Rudolph Diesel introduced the engine that now bears his name at the 1900 World’s Fair in Paris, he used peanut oil as its fuel, which by today’s standards could be considered biodiesel rather than petrodiesel. Thus the current resurgence of interest in the use of organic sources of fuel for diesel engines brings us full circle. Diesel engines are 30-40 percent more efficient than the more common internal combustion engines that use a spark plug to ignite a gasoline-air mixture. A diesel engine uses the heat generated by compression of the fuel mixture to produce the combustion that drives the engine. Diesel engines are far more popular in Europe today than in the United States, where they are used commonly in buses and trucks. Throughout their life cycle, biodiesel fuels produce 60-75 percent less carbon dioxide than an equivalent amount of gasoline.

One of the things that makes biodiesel attractive in a way that does not apply to ethanol is that biodiesel can be made from recycled oil that has been used for cooking. The amount of waste oil available for this purpose, however, would be insignificant compared with the amount needed. Biodiesel appears less promising, however, than cellulosic ethanol in terms of cost and potential for commercialization. In general, biofuels are limited by the amount of farmland around the world that can be dedicated to energy crop growth and by the availability of agricultural waste streams that can be converted to biofuels.


From the point of view of global warming, hydrogen is perfect as a fuel. Hydrogen fuel produces no carbon dioxide and releases only water to the environment. Whether the hydrogen is burned in an internal combustion engine or reacts chemically in a fuel cell to produce electricity, it is by far the cleanest fuel imaginable.

Three things need to happen to make hydrogen fuel a reality:

1. An efficient and cost-effective method to generate hydrogen must be developed. The source is no problem. Hydrogen can be produced by passing an electric current through water. However, if the energy used to separate the hydrogen comes from a coal-fired electrical power plant, it defeats the purpose of using hydrogen in the first place. Use of a renewable form of energy such as wind or solar electricity would result in a net reduction of carbon dioxide emission. (Another way to produce hydrogen is to separate the hydrogen atoms in methane.)

2. Hydrogen would need to be transported to where it is to be used. If, for instance, gasoline trucks are used to bring the hydrogen from a separation plant to a “hydrogen fi lling station,” as much carbon dioxide might be to the atmosphere as might have been saved by using hydrogen in the first place. Local generation of hydrogen close to its point of use is a better option but one that would requiring modifying the way gas stations work today.

3. Finally, an infrastructure of filling stations would need to be established throughout the transportation system. Technical problems would need to be addressed, such as the fact that hydrogen leaks much more easily than other gases such as natural gas and would need more robust containment and distribution systems.

Hydrogen-powered vehicles, including cars and buses, have been developed and have been proven to be technically feasible. They are ideal for the environment. However, the best estimates for the infrastructure to support a hydrogen economy are decades away. A lot of carbon dioxide will be generated in the next several decades in the meantime.

Land Use

IPCC estimates put carbon dioxide emissions from deforestation, including decomposition following logging operations, to be between 7 and 16 percent of the world’s contribution in 2004. Natural contributors to greenhouse gas production and sinking are larger than the added contributions from fossil fuel combustion and other human activities. Every year, a large amount of carbon dioxide (roughly 100 billion metric tons) is removed from the atmosphere and stored in plants and soil. Removal and release of carbon dioxide are roughly in balance worldwide. The U.S. Department of Energy estimates that plants absorbed 17 percent of the carbon dioxide produced by burning fossil fuels in 1992.

Forests hold an enormous reservoir of carbon. The U.S. Forest Service estimates that forests in the United States hold 56 billion metric tons of carbon, equivalent to nearly 40 years of emissions from fossil fuel combustion. Overall, U.S. forests, just as those in other countries, have been a net carbon sink in recent years.


Natural gas. Methane emissions come from several natural and human contributed sources. Reducing the human component centers on several industries. Since methane is the main constituent of natural gas, greater care during the production, processing, transmission, and distribution of natural gas will result in a lower level of emissions.

Petroleum. Crude oil production releases methane through venting from storage tanks and other equipment. This presents an opportunity to reduce emissions. Since methane is a fuel, if it can be captured in useful quantities, it could offset in part the cost of collecting it. Each molecule of methane that burns (completely) releases one molecule of carbon dioxide, which, as we know, is also a greenhouse gas. However, the ability of the carbon dioxide molecule to absorb energy is far less than the methane molecule. For this reason, given the choice of burning methane or releasing it, it is preferable to burn it.

Coal. Venting and possible reuse of methane captured from underground or surface coal mines is a way to reduce methane emission.

Agriculture. Improved feeding practices, such as using concentrates to replace foraged food and adding oils to the diet of livestock, can cut down on the methane produced on farms.

Landfills. Reducing the amount of waste that is brought to landfills is a good step toward reducing the release of methane. Collecting the methane generated and using it as a fuel, if possible, or burning it, if necessary, would cut down on methane release from landfills.

Steps Toward a Solution

It is inevitable that greenhouse gas emissions will continue to rise over the next several decades as the world grapples with an appropriate response. The question is the point at which the emissions are stabilized. Robert H. Socolow and Stephen W. Pacala suggested that doubling of the carbon dioxide above preindustrial levels would be a reasonable “boundary separating the truly dangerous consequences from the merely unwise.”

They define two scenarios:

1. Emission levels continue to grow at current rates for the next 50 years, reaching 14 billion tons of carbon by the year 2056.

2. Emission levels are frozen at 7 billion tons a year for the next 50 years (and then reduced by half over the next 50 years).

One way to define an effective solution is to identify actions that will bring the world from the first scenario above to the much more benign condition represented in the second scenario. This gives us a better idea of what it will actually take to have a meaningful impact on the problem of global warming. To stabilize carbon dioxide emissions at current levels, it would be necessary to emit 7 billion tons a year less than current levels for the next 50 years. Such an action likely would stabilize greenhouse gas concentrations well below 560 ppm (anticipating substantial absorption of the increased emissions by the oceans). Each of the following actions independently would prevent the release of 25 million tons of carbon if phased in over the next 50 years. One or two of them alone is not enough; it will take seven of these steps (or their equivalent) worldwide to stabilize greenhouse gas levels. Any seven of the actions (or combination) from the following list would result in that stabilization.

1. Increase average automobile mileage from 30–60 mpg-for 2 billion drivers.

2. Reduce average automobile driving distance from 10,000–5000 miles per year-for 2 billion cars.

3. Reduce worldwide electricity use by 25 percent.

4. Improve the efficiency of at least 1600 large coal-fired electricity generating plants by from 40-60 percent.

5. Replace 1400 large coal-fi red plants with natural gas-fired plants.

6. Install carbon capture and storage systems at 800 large coal-fired electricity-generating plants.

7. Install carbon capture and storage systems at coal plants that produce hydrogen for 1.5 billion vehicles.

8. Install carbon capture and storage systems at coal-to-syngas plants producing 30 million barrels of syngas daily.

9. Double the amount of nuclear-generated electricity to replace coal.

10. Increase the use of wind-generated electricity by a factor of 40 to replace coal.

11. Increase photovoltaic power generation by a factor of 700 to replace coal.

12. Generate enough hydrogen by increasing wind-generated electricity by a factor of 80 to produce hydrogen for cars.

13. Drive 2 billion cars on ethanol (Note: using one-sixth of the world’s farmland and assuming substantial reductions in the carbon footprint of producing and transporting ethanol compared with ethanol produced today from corn).

14. Stop all deforestation.

15. Expand conservation tillage to 100 percent of cropland (growing crops without first tilling the soil).

These steps include a broad range of options that will stabilize and potentially reverse the climate changes that have been set in motion. To stabilize greenhouse gas concentrations below 500–600 ppm, substantial reductions in carbon dioxide emissions from coal generated electricity generation and internal combustion engines will be needed. This will not be achieved by a series of well intended gestures on the part of individuals. Instead, the world must fundamentally rethink how it produces and uses energy.

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