(41) Climate Science

Which major cities are leaders in reducing greenhouse gas emissions

How to Reduce Your Greenhouse Gas Emissions

greenhouse gases

Step Two: Transform Energy Technology

Experts suggest that to substantially reduce greenhouse gas emissions, society must make a massive change in the way energy is produced and used. By the middle of the century, humanity must make a transformation to energy sources that produce zero-carbon emissions.

That is, society must move away from an economy based on the use of carbon-based fuels, called the carbon economy, to an economy based on sustainable energy sources, which are those that can be used without compromising the needs of future generations.

Developing Technologies to Reduce Greenhouse Gas Emissions

Zero­carbon and lower carbon energy sources that are already in use-solar, hydro, wind, geothermal, nuclear, and biofuels-could be improved and in some cases expanded. Solar energy taps the Sun directly rather than indirectly, as with fossil fuels. With the proper technology, solar energy can efficiently heat water or a building. Photovoltaic cells, also known as solar cells, convert sunlight directly into electricity. Solar cells arranged in solar panels on rooftops can provide energy to a building. Producing large amounts of electricity requires building huge arrays of solar cells into panels, parabolic troughs, thermal dishes, or power towers. Solar energy is renewable and produces no pollutants or greenhouse gases. The potential for solar power is enormous, particularly in sunny locations such as the southwestern United States.

Hydropower plants harness the energy of water falling over a dam, which spins the blades of a turbine to produce electricity. Hydroelectric energy is renewable and pollutant and greenhouse gas free. While hydropower produces about 24% of the world’s electricity, it cannot be further cultivated in developed countries because their rivers are almost all dammed. In developing nations, there are still free-flowing rivers that can be dammed, although people sometimes object to hydropower development because the water that backs up behind dams may flood regions that are of scenic or social value.

Wind energy is renewable, is nonpolluting, produces no greenhouse gases, and is widely available. To create usable power, wind turns turbine blades that are connected to a generator that transfers the energy into usable electrical current. Small wind turbines can be placed individually in open areas, but the large-scale use of wind energy requires a wind farm. Wind farms can be located anywhere conditions are good.

Offshore wind farms supply about seven times as much energy in the same amount of area as land-based farms, although the machinery is more prone to corrosion.

Wind energy has enormous potential. Estimates are that wind could supply 40 times the current demand for electricity and about 5 times the global consumption of power. Although wind currently only generates about 1,5% of global power usage, that amount represents more than a fourfold increase between 2000 and 2014. Technological improvements have brought down the cost of building wind plants by 80%, making wind arrays less expensive to build than any other type of power plant. Wind energy is still more expensive to generate than fossil fuel or nuclear power, but when the entire cost to health and the environment is factored in, wind is extremely competitive. New wind farms are being planned all over the world and are increasingly popular in the United Kingdom.

Geothermal energy harnesses the power contained in hot rock below Earth’s surface. Hot water may flow directly from hot springs, or water can be pumped into a region of hot rock and heated. The steam created by the contact of water with hot rock is then used to generate electricity. Geothermal energy is renewable, nonpolluting, and does not emit greenhouse gases. At the world’s largest dry steam geothermal field, located at the Geysers in northern California, sewage effluent from nearby cities is injected into the hot rock found there to create steam.

Research is ongoing on a more advanced geothermal technique, Enhanced Geothermal Systems (EGS), in which boreholes are drilled into rock to a depth of about 6 miles (10 km), a depth routinely drilled by the oil industry. The Massachusetts Institute of Technology reported in 2006 that with improved technology, EGS would be able to supply the world’s total energy needs for several thousand years. The steam from the deep holes could be cycled into an existing coal, oil, or nuclear power plant.

Nuclear energy was nearly dead after the 1979 partial core melt-down at the Three Mile Island plant in Pennsylvania and the 1986 explosion and meltdown at Chernobyl, Ukraine. Several European countries abandoned the use of nuclear power entirely, and the United States and countries in other parts of Europe halted the construction of new nuclear power plants. But concerns about global warming have brought about a resurgence of interest in nuclear power, which is clean and produces no greenhouse gases.

Nuclear power still has many opponents who question several aspects of its safety: Nuclear power plants have a history of accidents, transporting nuclear materials exposes many people to potentially harmful radiation, and the waste generated is hard to dispose of because it remains radioactive for more than 10,000 years. Proponents of nuclear power say that the technology is well developed, and plants could come online quickly, allowing the world to lessen its reliance on fossil fuels rapidly. Plus, they say, the problems associated with nuclear power plants are being solved: New designs reduce the possibility of catastrophic accidents, and development is under way for the safe disposal of long-lived radioactive wastes for more than the required 10,000 years at Yucca Mountain, Nevada, in the United States. Still, this debate is likely to continue for a long time. There are two types of nuclear power. Nuclear fission power plants use enriched uranium as their energy source. Nuclear power is clean, but the uranium it needs must be mined and is nonrenewable. Current estimates are that if fossil fuels were replaced by nuclear fission, there would be only enough uranium to last anywhere from 6 to 30 years. Uranium can theoretically be collected from seawater, but that technology is a long way off. In a breeder reactor, the byproducts of nuclear fission are made to breed new fuel. No country yet has a functioning breeder reactor, although this research is ongoing.

Nuclear fusion takes place when the nuclei of light elements combine to form heavier elements, just as the Sun fuses hydrogen into helium. Energy produced from nuclear fusion is enormously desirable: clean and very efficient. Fusion reactions produce far more energy per unit of fuel than nuclear fission or any other energy source. For example, 0.04 ounces (1 gram) of nuclear fuel holds the same amount of energy as 2,483 gallons (9,400 liters) of gasoline. Once started, fusion reactions are self-sustaining.

Some of the qualities that make fusion energy attractive also make it problematic. The fusion of two isotopes of hydrogen, deuterium and tritium, takes place at enormously high temperatures of about 180 million °F (100 million °C). In a hydrogen bomb, fusion is initiated by the detonation of a fission bomb, and the reactions proceed until the material runs out. Because a reactor cannot be the site of a nuclear bomb detonation and cannot contain such enormous temperatures, scientists are researching the possibility of a process called cold fusion, which occurs at normal temperatures and pressures. Although progress is being made, there is no guarantee that fusion will be able to replace carbon-producing energy in any significant way by the middle of this century.

Biofuels harness the Sun’s energy that is stored in plant and animal tissue. Biomass can be used directly, as when wood, charcoal, or manure is burned to cook food or heat homes. Fuel can also be created by changing the form of biomass. Ethanol, for example, is liquid biofuel produced from plant material and can be burned in cars and other vehicles in place of gasoline. Typical ethanol is produced from plant sugar, such as the sugar in corn. Cellulosic ethanol is made from plant fiber, or cellulose, such as corn stalks. Cellulosic ethanol from crop waste could supply about 25% of the energy needed for transportation in the United States while creating about 85% less greenhouse gases than typical gasoline. Biodiesel is another liquid fuel and can be made from fats such as used cooking oil, animal guts, used tires, sewage, and plastic bottles.

Although biofuels burn cleaner than fossil fuels, they are not pollutant free. Ethanol from corn creates about one-third less greenhouse gases than regular gasoline. Because the CO2 was taken from the environment recently, its addition back into the atmosphere has no net effect (unlike fossil fuels, which emit CO2 that was sequestered). Because they burn more cleanly than fossil fuels, biofuels are used as a gasoline additive in the United States. One fuel, called E85, is 85% ethanol and 15% gasoline. Ethanol fuel is as much as 25% less efficient than gasoline per gallon. Biofuels have limits as an alternative fuel source. Cellulosic ethanol is limited by the amount of suitable agricultural waste, which is far less than the amount of fossil fuels used each year. Growing crops to be made into biofuels is extremely inefficient. For example, because fossil fuels are used extensively in pesticides, in fertilizers, and for performing mechanical labor, there is little or no energy gained from biofuels through using crops such as soybeans or rapeseed. Ethanol derived from corn on a large scale is already credited with increasing food prices because corn is a basic crop in much of the food industry, where it is used in a large variety of products, from animal feed to corn syrup. A 2005 paper by David A. Pimentel of Cornell University and Tad W. Patzek of the University of California, Berkeley, stated that the cornto­ethanol process powered by fossil fuels consumes 29% more energy than it produces. The results for switch grass were even worse, the paper said, with a 50% net energy deficit. Dr. Pimentel said in a 2006 interview in The New York Times, “Even if we committed 100% of the corn crop to making ethanol, it would only replace 7% of U.S.

vehicle fossil fuel use.” Other scientists say that biofuels provide a reasonable alternative to fossil fuels if the right crops are used and ethanol plants become more efficient. Algae contain much more usable oil than land-based crops  and could be fed agricultural and other wastes, although at this time research into algae biofuel is in the early stages.

Fuel cells may someday be used in motor vehicles, but will not be ready for mass production for some time. Fuel cells are extremely efficient at harnessing the energy released when hydrogen and oxygen are converted into water. Fuel cells form the basis of what is known as the hydrogen economy.

A fuel cell is made of an anode compartment (negative cell) and a cathode compartment (positive cell), which are separated by a porous disc known as the proton exchange membrane. A catalyst, which aids in chemical reactions, is located on the membrane. The membrane conducts positively charged ions and blocks electrons. In a hydrogen and oxygen fuel cell, pressurized hydrogen gas is sent into the anode compartment, and oxygen gas is sent into the cathode compartment. At the anode, hydrogen gas is forced through the catalyst and is split into electrons and protons. The protons move to the cathode side, and the electrons are conducted through the external circuit to produce electricity. At the cathode, the oxygen gas is sent through the catalyst and splits into two oxygen atoms. These ions have a strong negative charge and attract the two positively charged hydrogen ions and two of the electrons from the external circuit. The catalyst is dipped into each compartment, which assists in the reaction of oxygen and hydrogen.

The products of this reaction are water vapor and heat. To convert a significant amount of energy, fuel cells must be stacked together. Unfortunately, there are many problems with fuel cell technology. Hydrogen does not exist in vast reservoirs, but must be created. It is also difficult to store and use. One solution is to use a reformer, which turns hydrocarbon or alcohol fuels, such as natural gas, propane, or methanol, into hydrogen. Most of the  current generation of fuel cells runs on the hydrogen in natural gas. But collecting the compound uses up a great deal of energy and, at this time, produces more CO2 than burning the fossil fuel directly. Obtaining hydrogen from natural gas decreases fuel cell efficiency and increases the production of waste heat and gases.

Fuel cell technology is promising in other ways. Besides the incredible efficiency when pure hydrogen is used, the oxygen needed for hydrogen-oxygen fuel cells is widely available in the air. However, while vehicles that run with hydrogen fuel cells create no emissions, they do produce CO2. Unless this gas is sequestered, using hydrogen fuel cells to run vehicles will not solve the global warming problem. Fuel cells that use compounds other than hydrogen are now in development. While the use of fuel cells is still in its infancy, it is now entering a rapid growth phase, with revenue projected to grow to $15.1 billion in 2014. According to the Society of Automotive Engineers in 2007, “Fuel cell energy is now expected to replace traditional power sources in coming years-from micro fuel cells to be used in cell phones to high-powered fuel cells for stock car racing.” Fuel cells are already replacing batteries in portable electronic devices because they last longer and are rechargeable. Even so, many drawbacks remain in developing fuel cells as energy sources, as discussed above. Converting hydrogen to another form of energy requires electricity, which must be generated from conventional energy sources with their typical costs. In a 2005 Science article, a team of Stanford researchers suggests that these costs would be minimized, and pollutants would be negligible, if the hydrogen was pumped into the fuel cells using wind power. The authors state, “Switching from a fossil-fuel economy to a hydrogen economy would be subject to technological hurdles, the difficulty of creating a new energy infrastructure, and considerable conversion costs but could provide health, environmental, climate, and economic benefits and reduce the reliance on diminishing oil supplies.”

Power from coal is so integral to modern society that many energy experts believe that technologies must be developed to make coal burning more environmentally sound. As a result, clean coal, which is more efficient and produces far fewer emissions than normal coal, is becoming an important, but controversial, topic. To produce clean coal, emissions from coal-fired power plants are reduced by gasification. In gasification, the coal is heated to about 2,500°F (1400°C) under pressure to produce syngas, an energy-rich flammable gas. After cleansing, syngas is combusted in a turbine that drives a generator, and then the waste heat powers a second, steam-powered generator.

Syngas burns cleanly and is easily filtered for pollutants. Overall emissions of most air pollutants from syngas are about 80% less than emissions from traditional coal plants. Greenhouse gas emissions, particularly CO2, are also lower. Gasification has other positive features: It makes dirty coal usable, which benefits regions where only dirty coal is available. Also, because the gas is cleansed before it is burned, gasification plants don’t need expensive scrubbers-the devices that eliminate particulates, SO2, hydrogen sulfide, and other pollutants from the waste gases. Clean coal can also be liquefied and burned like gasoline.

Gasification has many downsides. A gasification plant costs 15% to 50% more to build and 20% to 30% more to run than a normal coal-fired plant. Due to these additional costs, conversions to clean coal plants will probably not become widespread until industry is given financial incentives or emissions caps. To produce syngas, gasification uses a great deal of energy, about 10% to 40% more than a standard coal-fired power plant. Also, coal mining is very often environmentally damaging. As yet, although gasification has been tested, it has not been used in a full-scale power plant.

Removing Carbon After It Is Emitted

An alternative to reducing greenhouse gas emissions is sequestering the emissions after they have been created. Carbon can be sequestered in natural systems, or technologies can be developed for carbon sequestration.

Natural carbon sequestration can be enhanced, for example, by reforesting on a large scale. Unfortunately, the opposite is happening as enormous expanses of forest are being cleared for slash-and-­burn agriculture. Forest preservation and reforestation are economically and politically complex issues.

Another approach to sequestration that has been researched is iron fertilization. In those parts of the ocean where the presence of nutrient iron is limited, scientists have discovered that adding iron dust to the ocean stimulates a plankton bloom. The plankton remove CO2 from the atmosphere, although for this to work as a means of sequestering carbon, the plankton must then sink out of the system into the deep sea or into seafloor sediments. While small-scale experiments have confirmed that iron fertilization stimulates plankton growth, no one is certain how large-scale fertilization would affect plankton, or how large-scale blooms would affect the oceans. Recent work has shown that there are few locations in the oceans where the plankton would be removed from the system, and climate scientists currently think that iron fertilization will not make much difference to global warming. Finally, another way to sequester carbon is by increasing the content of organic matter in soils in order to increase the amount of carbon in that soil. Farming techniques that protect soil, such as no till farming and crop rotation, can help sequester carbon.

Artificial carbon sequestration is another possible approach. CO2 from power plants and other large sources can be captured and stored. Carbon is easily captured in gasification plants, where CO2 emissions can be reduced by 80% to 90%, and from natural gas and biofuel plants. Once the CO2 is captured, it is transported by pipelines or by ship to a storage site. CO2 can be stored in rock formations, the oceans, or carbonate minerals. The most promising idea is to inject CO2 into salt layers or coal seams where the gas cannot escape to the surface. (When CO2 is added to nearly spent oil and gas fields, it actually flushes out some of the uncollected oil.) Reports by the Intergovernmental Panel on Climate Change (IPCC) suggest that sites could be developed that would trap CO2 for millions of years, with less than a 1% leakage rate for every 1,000 years.

Several sequestration projects are currently under way. Norway is injecting CO2 from natural gas into a salt formation in the North Sea. CO2 from a coal gasification plant in North Dakota is being used to enhance oil recovery in a reservoir in Canada. British Petroleum is involved in a project in Algeria that will store 17 million tons of CO2.

The Wrong Direction

Besides concerns about greenhouse gas emissions, fossil fuel supplies are dwindling.

Sometime before 2010, society will pass peak oil. Peak oil occurs when half of the oil that was ever available for extraction has already been pumped. Although it might seem that a lot of oil would still be left, what remains is generally lower grade, located in remote locations, and harder to extract. Besides that, if the carbon economy continues unaltered, by 2030 the demand for fossil fuels could be nearly 50% higher than it is today,

largely due to increased use by developing countries: China’s demand is expected to double over 15 years, and India’s may double in 30 years. For all of these reasons, the energy industry is looking for other sources of energy, particularly fossil fuels. Two of these possible sources are oil shale and tar sands.

A rock that contains oil that has not migrated into a reservoir is called an oil shale. Oil shale is mined in open pits. After mining, the rock is crushed, heated to between 840°F and 930°F (450°C and 500°C), and then washed with enormous amounts of water. This entire process creates petroleum, which can then be extracted from the rock. The amount of fuel available as oil shale is comparable to the amount remaining in conventional oil reserves. The United States holds 60% to 70% of the world’s oil shale, mostly in the arid

regions of Wyoming, Utah, and Colorado. These oil shale resources underlie a total area of 16,000 square miles (40,000 km), a little less than the combined area of Massachusetts and New Hampshire. Tar sands are rocky materials mixed with oil that is too thick to pump. Tar sands are strip mined, so many tons of overlying rocks are dumped as waste. Separating the oil from the rocky material requires processing with hot water and caustic soda. Tar sands represent as much as 66% of the world’s total reserves of oil; about 75% of this reserve is in the Canadian province of Alberta and in Venezuela. Extraction of both these sources of oil comes with environmental costs. Both require large amounts of water for processing- by chance, many of these deposits are found in arid areas. Plus, since the oil and tar are spread out, the rock must be mined over a large area. Not only does this degrade the landscape and create a large amount of waste rock, environmental restoration after mining is difficult. As for climate change, extracting usable energy from tar sands produces four times as much greenhouse gas as processing the same amount of conventional oil. This is true to a lesser extent of oil shale as well.

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