Technologies and Strategies
No silver bullet
The task of reducing emissions by the required amount is daunting but not impossible. This final section will summarize the more promising technologies and strategies necessary to solve the problem.
The bottomless oil well
The cheapest and fastest way to reduce emissions is through energy efficiency. After the energy crisis of the early ‘70s, the US saw more than a decade of flat emissions due to increased conservation and a faltering economy.
By the late ‘80s, emissions began increasing again, but there was a lasting effect:
Until 1973, energy intensity was dropping at a very small 0.4% per year. This is the amount of energy consumed in relation to the size of the economy. After the first oil shock, efforts to improve energy efficiency resulted in an annual drop of 2.1% per year. If the country stayed on the path it was on, energy production would currently consume about 12% of gross domestic product instead of 7%. This is a difference of about $700 billion annually. Roughly two-thirds is due to improvements in energy efficiency, while one third is due to the transition from manufacturing to a more service-oriented economy.
California is the sixth largest economy in the world and a leader in energy efficiency, both in building codes and in appliance and automotive standards. The result is California’s per-capita electricity use has stayed flat for over 30 years, while the rest of the country has increased 50%. 
Of course, California’s total electricity use has increased during this time because its population has increased, so achieving efficiencies such as these is just a start.
Utility divorce court
California’s efficiency gains are due in large part to decoupling utilities. That is, the revenue of utility companies is not tied directly to the amount of energy that they produce. This allows the emphasis to shift from selling energy to conserving it. Companies estimate their sales and fixed costs. Regulators set the rate based on these estimates. If the estimates are too high and customers overpay, the difference is credited back to them. If estimates are too low, the shortfall is made up the next time rates are adjusted. Other states have followed California’s lead.
Greenlighting green buildings
Buildings account for more than 40% of US greenhouse gas emissions and three quarters of electricity. Every year, a certain amount of buildings are built, renovated, and demolished. Three quarters of all buildings 30 years from now have not yet been built or will be renovated before then. That is a huge opportunity for savings, but the full benefit will not be possible unless increasingly tough standards are in place beginning today . A $22 billion investment in energy efficient buildings using only existing technologies would recover over $8 billion per year for consumers and allow twenty-two aging 500 megawatt coal fired power plants to be retired without replacement.
A combination of tax incentives for builders and consumers, rebates from the utility companies, special low interest loans for energy efficiency upgrades, and an education program to explain the cost savings to consumers are all strategies that spur efficiency.
Is your refrigerator running?
Appliance standards are another opportunity for energy and cost savings. The classic example is refrigerators.
Despite increasing in size 20%, refrigerators use one quarter of the energy they did 30 years ago and cost less than half as much. Improvements in just furnaces, air conditioners, refrigerators, and lighting saves almost $100 billion annually.
A smart electrical grid allows utilities and consumers to make better use of available electricity by adding an element of communication. Combined with smart appliances, a smart grid can record not just total energy use, but the energy use of individual appliances. Consumers can then identify which appliances are the largest energy hogs.
Another important consideration is energy demand. Generally speaking, demand is high during the day and low at night. Prices should reflect this reality. Appliances that are aware of the demand can be programmed to operate differently depending on the load. For example, if the owner chooses to save a little money, air conditioning systems might automatically adjust temperatures higher when the load on the grid is sufficiently high.
Path of least resistance
Another upgrade to the electrical grid is the incorporation of High Voltage Direct Current (HVDC) transmission lines, which are more efficient than standard alternating current (AC) lines over long distances. Actual gains depend on the specific circumstances, but an example of the cost effectiveness of HVDC over AC is shown below.
The heat is on
Generating electricity often creates a large amount of waste heat which accounts for 68% of the original energy.
One way to reduce this loss is by capturing the waste heat and then piping it to buildings. This is called combined heat and power (CHP) or “co-generation.” Modern CHP plants can recover up to 90% of the original energy content. This idea is not limited to large centralized power plants. Individual buildings or small communities can generate their own electricity and capture the resulting heat for their own use.
The potential for CHP varies by region, but significant growth is possible. Below shows the current portion of electricity production with CHP (dark blue), versus its potential in 2015 (red) and 2030 (light blue).
Because it eliminates the need to build so many power plants and transmission lines, fully realizing CHP’s potential by 2030 would result in a savings of about $800 billion worldwide.
Say no to filth
As discussed in the previous section, certain aerosols cause localized warming — in particular, emissions from diesel engines and the burning of wood and animal dung. Cleaner engines are now possible with ultra-low sulfur diesel. The new fuel allows for advanced emissions controls which would otherwise become clogged due to the sulfur. New diesel engines are built to much higher emissions standards.
Emissions from stoves, especially in the third world, are reduced with inexpensive yet highly efficient alternatives. The stove below was designed specifically to meet the cooking needs of the Darfur region, and can be assembled on site for between $20 and $30.
It is 72% more efficient than traditional wood burning cook stoves, and saves each household an average of 18 hours per week foraging for firewood.
The most promising source of renewable energy is clearly the Sun. Even in Seattle, the amount of solar energy delivered to the roofs or south facades of buildings far exceeds the energy needs of typical homes and businesses. 
Photovoltaic panels have traditionally been very expensive and are difficult to mass produce. Newer technologies, such as thin film solar cells, are much cheaper but not as efficient. Even with relatively low efficiencies, a large portion of needed electricity can be generated on site.
Storing solar energy remains an issue, but it is not a major problem because the highest energy demand is in the day. Any excess electricity can be sold back to the grid so it does not go to waste.
Solar energy does not have to be so high tech, however. Solar hot water heaters and building designs that make use of natural lighting are also major energy savers.
Low tech solar on a grand scale.
Some areas obviously have more potential than others. The southwest US is particularly suited for generating electricity from solar.
Africa receives more solar radiation than any continent. The development of cost effective solar technology guarantees unlimited clean energy to the world’s poorest people.
For such large scale deployment, concentrated solar power makes the most sense. This is relatively simple technology that uses mirrors to focus sunlight and generate steam. The steam turns traditional turbines. Much of this energy can be stored for later use by piping the heated water or oil through molten salt. The salt retains the heat through the night.
It’s blowing in the wind
Wind is another practical source of renewable electricity which is already competitive with more traditional forms of energy. The US has significant wind resources as shown below, with purples and reds showing the greatest potential.
Wind is similar to solar in that it is intermittent. However, wind tends to blow at night when the Sun isn’t shining and it tends to blow the most in areas that don’t have strong solar potential. Solar and wind complement each other.
The energy storage problem can be addressed in a few ways. One is to use a portion of the electricity to compress air within spent natural gas fields or similar underground chambers. When the wind isn’t blowing, the air is released, turning a turbine.
Another method is “pumped storage.” Part of the electricity is used to pump water to a reservoir at higher elevations. When the wind isn’t blowing, the water is allowed to flow down to a second reservoir, turning a turbine and recovering a portion of the energy.
These methods of storing energy aren’t specific to wind. They can be used for any intermittent source of power, including solar.
Geothermal uses the heat of the Earth’s core to boil water and generate electricity.
Using one method, water is pumped down a well to depths where temperatures are high. The steam is forced to the surface where it turns a turbine. The water is then pumped back into the ground in a closed loop.  Below shows the geothermal potential at depths of 10 km, which is within the capabilities of modern drilling equipment.
Geothermal is particularly attractive because it can provide constant, “base load” electricity.
To distribute solar, wind, and geothermal generated electricity to the rest of the country, a new HVDC backbone would be created to tie them to the major population centers.
Transportation represents another huge opportunity to reduce emissions. One method is to increase availability of mass transit. However, even with such improvements, the US will remain relatively dependent on personal transportation due to low population density. The US is about one quarter the population density of the European Union and one eleventh the density of Japan, so mass transit would not see the same practical benefits as it currently does in other developed regions. Increasing fuel economy of cars and light trucks must be a major focus for the US.
Between 1975 and 1987, the average fuel economy of new passenger cars and light trucks cars (”light duty vehicles”) increased from 13.1 to 22 mpg, an increase of 68% in just 12 years. 
Unfortunately, by 2007 the combined fuel economy of new light duty vehicles was 8% worse than it was 20 years before. Standards remained stagnant and any advances in efficiency were more than offset by an increase in power and weight.
Legislation passed in 2007 requires that the combined fuel economy of light duty vehicles increase from the laboratory rating of 25 mpg in 2007 to 35 mpg by 2020. This is technically difficult, but can be achieved through a combination of increased engine and drivetrain efficiency, aerodynamics, lightweight materials, de-emphasis of large vehicles, and conversion of some vehicles to alternative fuels such as compressed natural gas.
Plug-in and drop out
Perhaps the most significant development in personal transportation is the imminent debut of plug-in hybrid electric vehicles (PHEVs). These have a high capacity battery pack that is charged from the electrical grid. A vehicle with an electric range of just 40 miles is more than sufficient to cover the daily commute of most drivers. As a result, filling up the tank would be a rare occurrence, and mostly limited to long trips.
This energy is not free of course, but it is a fraction of the cost of oil. With a national average of 8.5 cents per kilowatt-hour, a PHEV would cost the equivalent of about 75 cents per gallon of gasoline to operate. 
Any PHEV dramatically reduces oil usage, but from a global warming standpoint, the goal is to reduce emissions below a standard hybrid vehicle. Below shows the CO2 emissions of a PHEV with a 20 mile all-electric range, charged with a variety of energy sources.
A conventional vehicle is on the left, and a standard hybrid is second to the left. In terms of emissions, only a PHEV charged with 100% coal generated electricity has worse emissions than a standard hybrid, and as the electrical grid becomes cleaner, cars automatically become cleaner as well. A shift to sustainable biofuels (see below) will dramatically reduce remaining emissions.
Because most charging will be done at night, very little additional capacity would need to be built. If plug-in hybrids displace 50% of all passenger vehicles by 2050, they would require only a 4% increase in electrical capacity.
By charging at night, PHEVs allow their owners to sell electricity back to the grid when demand is high. This is called “vehicle to grid” (V2G) and is another possibility with a smart electrical grid.
Fuel, food or forests?
There are many potential biofuel feedstocks, but most tie up land that is otherwise used for agriculture. As world population goes to 9 billion people, there will be much pressure to convert as much land as possible for food and fuel. This at a time when we should be restoring carbon sinks to some semblance of their natural state — rainforests, in particular.
Biofuels make sense only if they meet a variety of criteria.
They should not compete with food crops.
They should not use large amounts of fresh water.
They should not require large energy and fertilizer inputs.
They should not displace large natural carbon sinks.
Finally, and not surprisingly, they must be economically viable.
Perennial grasses show great promise. The energy crop miscanthus, a giant perennial grass, when grown on marginal land with little or no inputs yields two and a half times that of corn grown on fertile land. A simple mix of ordinary but diverse perennial grasses achieves an energy balance many times that of corn ethanol. Perennial grasses are also a carbon negative - pulling more CO2 out of the air than they emit when burned. The root systems accumulate year to year which not only rebuilds the topsoil but sequesters a large amount of carbon in the process.
Perhaps the most promising biofuel feedstock is algae.  Due to its high oil content and fast growth, it is at least theoretically possible for algae to displace all petroleum using a fraction of the world’s desert land. Algae can be grown in salt water or in nutrient rich agricultural or municipal waste streams. Unfortunately, regulating the growth of algae is not easy, and dewatering it without using a lot of energy is also difficult.
There are a few other feedstocks worth mentioning. Waste from forestry and agriculture, both plant and animal, can be used for biofuel production. In tropical and subtropical areas, the oil-rich jatropha tree can be grown on marginal land with little or no inputs.
Grass is not gas
Much hope rests on cellulosic technologies that break down hard cell walls so that biomass can be fermented into alcohols such as ethanol, or preferably butanol. This is no easy matter, and much work is being done to solve that problem. Not all biofuels are alcohol based, however. Some feedstocks create vegetable oil for biodiesel. Furthermore, many feedstocks can be gasified and then converted to a variety of synthetic fuels using a process called Fischer-Tropsch.
A very promising carbon negative solution involves “pyrolysis.” Biomass is heated in the absence of oxygen so no CO2 is formed. The process can be adjusted to create varying combinations of charcoal and bio-oil . Charcoal, or “bio-char,” locks up a large portion of the carbon and greatly enhances the productivity of soil. Bio-oil can be burned as an energy source, or refined to produce more complex fuels.
Don’t treat soil like dirt
Reduction of greenhouse gas emissions from agriculture involves many uncertainties, but there are a few strategies that stand out.
The most promising strategies, from left to right:
Improved management of cropland offers the largest potential improvement. This includes such practices as better crop rotation and optimized use of fertilizers.
Grazing land management also offers large improvements. For example, properly timing when and how long an area is grazed improves the health of the soil and the plantlife.
Draining peatland causes large emissions of nitrous oxide and CO2 as the organic soils decay. This should be avoided if possible and there are ways to mitigate emissions if not.
Restoration of degraded lands is possible when replanted with grasses (such as for biofuel production as described above) and through proper land management that reintroduces nutrients and retains water.
What about ______ ?
Any discussion of the future of energy invariably includes three technologies that are generally considered to be oversold.
The first is nuclear. Nuclear remains extremely expensive, with modern plants costing over $7 billion plus substantial ongoing costs. If the goal is to reduce emissions as painlessly as possible, there are far better ways to spend money. This is shown below in terms of kilograms of CO2 avoided per dollar spent. Nuclear is on the left (higher is better). 
In addition, the waste problem has yet to be addressed. A single “wedge” (see last section) of new nuclear energy on top of existing capacity would require ten Yucca mountains to store the waste. Proliferation of weapons grade material further limits the scope of this solution.
Another technology is carbon capture and sequestration (CCS). This involves capturing the CO2 from coal or natural gas, and then piping it to an underground formation that is suitable for storing the CO2 forever. The US government and coal industry have attempted to create a pilot plant ("FutureGen"), but after years of false starts this has gone nowhere. One wedge of coal with carbon capture and sequestration would require an infrastructure for storing CO2 equal to the entire system of pumping oil out of the ground, so this is no trivial undertaking.
Finally is hydrogen. Hydrogen is most often touted as a replacement for oil since it is portable and its only emission is water. However, hydrogen is only a way of storing energy. It is not an energy source. Battery technology is already more efficient and we already have an electrical grid to build upon. Building a hydrogen infrastructure is quite difficult by comparison.
All of these technologies have some potential, and may see limited deployment in specific regions and for specific applications. Breakthroughs are always possible, however. They should continue to be developed to keep all options open. We may need all of them.
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