Key Terms Defined

Cap-and-trade system (carbon allowances)
This program would set a mandatory nationwide limit, or cap, on carbon dioxide emissions and create a market in which allowances to emit the gas could be traded. To reduce CO₂, the cap would be set lower than historical emissions and would be reduced over time. Under this system, suppliers or users of fossil fuels (which are the main source of carbon dioxide) would hold the rights, or allowances, for each ton of CO₂ emissions they produce. How well this system would work depends partly on whether the allowances would be bought or distributed free of charge. If they were free, those who have polluted the most could unduly benefit by being given allowances of considerable value--possibly totaling tens of billions to hundreds of billions of dollars (see "grandfather"). Once the allowances were distributed, they could be bought and sold, or traded. Cap-and-trade programs are already being used in the United States to reduce emissions of sulfur dioxide and nitrogen oxides, with varying degrees of success.

Carbon tax, carbon fee, carbon cost
A carbon tax is one way to pay for environmental and health costs that aren't yet factored into the cost of power generation while also making cleaner energy more financially competitive.

Kyoto Protocol
The Kyoto Protocol is an amendment to the United Nations Framework Convention on Climate Change, an international treaty that addresses what can be done to reduce global warming. The protocol adds more-powerful and legally binding measures, assigning mandatory targets for the reduction of greenhouse gases.

CalPERS, CalSTRS
The California Public Employees' Retirement System (CalPERS) and the California State Teachers' Retirement System (CalSTRS) are the nation's largest and third-largest pension funds, respectively. Together they have targeted investments of more than $1 billion for environmentally friendly endeavors.

Biomass, biofuel
Biomass is the dry weight of plant or animal-waste matter. Biomass burned to generate electricity includes fast-growing trees such as willow and eucalyptus, waste from pulp mills, and even garden landscaping waste. Biofuel is the shorthand term for the kinds of biomass that are used for liquid transportation fuel--like ethanol.

Carbon capture and sequestration
Scientists are working on ways to safely corral the carbon dioxide now spouting from coal plants and other CO₂-emitting industries to keep it from contributing to global warming. They plan to trap the CO₂ and "sequester" it by pumping the gas into the earth, deep into the ocean, or into saline reservoirs.

Fixing carbon, carbon sink
Another form of carbon sequestration is both natural and free. Earth has long stored, or "fixed," carbon dioxide in its fields, forests, and seas, all examples of carbon sinks. In plants, photosynthesis removes CO₂ from the atmosphere, converts it to biomass, and releases oxygen. In oceans, not only do marine plants serve this function, but also the seas themselves act as a kind of pump that transports atmospheric CO₂ from the ocean's surface to deep underwater. In soil, carbon is fixed when chemical reactions convert CO₂ into inorganic carbon compounds like calcium carbonate and magnesium carbonate. When plant matter decomposes, some of the CO₂ released by the process is sequestered as soil organic carbon.

Corn ethanol
To make ethanol, corn is ground up and combined with enzymes; the resulting cornstarch is then broken down into sugar. After it's been fermented with yeast, the sugary mash is distilled and converted into ethanol. Though corn ethanol burns cleaner than gasoline, corn cultivation relies heavily on petroleum-derived fertilizers and diesel-fueled tractors, and its refining process currently requires large quantities of fossil fuels. In the United States, corn ethanol is commonly combined with 15 percent gasoline to produce the E85 mixture sold at some gas stations.

Brazilian ethanol
Brazil has achieved near energy independence by using sugarcane to produce ethanol. Cane is cheaper than corn to process because it's already sugar and doesn't need converting before distillation. Brazil's farm policies also make its ethanol cheaper: Brazil ended most of its subsidies for the sugar industry in the 1990s, which forced producers to become more efficient.

Cellulosic ethanol
Cellulose, or plant fiber, can be converted into ethanol. Switchgrass, a prairie grass native to the Midwest, is one source of cellulosic ethanol currently under development. It requires far fewer pesticides than corn and soy. But, according to Massachusetts Institute of Technology publication Technology Review, cellulosic ethanol is expensive, requiring more-costly equipment and additional processing steps because the conversion of cellulose into sugar is more complicated than for corn. However, reports the magazine, "Research is already improving parts of the process, [and] researchers have created a cocktail of enzymes for converting cellulose into sugar that is a hundred times cheaper than previous methods."

Grandfather
This form of regulatory nepotism grants an exemption to an existing operation when new rules come into force. Right now there are hundreds of coal plants operating in the United States and 150 more in various stages of permitting and construction. Industry wants these new plants to be grandfathered in, i.e., exempted from any laws that restrict carbon dioxide emissions in the future. If the United States moves to a cap-and-trade system, CO₂ from these plants could become an asset, or allowance, that companies could sell on the open market. Senators Barbara Boxer (D-Calif.) and Jeff Bingaman (D-N.Mex.) have warned utilities not to expect new plants to be grandfathered.

Time-of-use meters
These electricity meters show customers how much energy they are using at any given time in their home. By charging customers more during peak demand periods, utilities hope to reduce electricity consumption between noon and 6 P.M. weekdays. If they succeed, it's a win-win proposition: Customers use off-peak electricity at a lower price, while power companies avoid having to build new plants to meet peak load demands.