高級英語教程(2)（簡體書）

Carbodioxide （C02） iS the most abundant of the greenhouse gases. It occurs as a natural consequence of respiration. However， much larger quantities are put into the atmosphere as a waste product of energy production. Coal， oil， natural gas， and biomass are all burned to provide heat and electricity for industrial processes， home heating， and cooking. These sources are increasing the amount of carbodioxide ithe atmosphere. Measurement of carbodioxide levels at the Mauna Loa Observatory iHawaii show that the carbodioxide Ievel has increased from about 315 ppm （ parts per miliion） i1958 to about 360 ppm i1995. A major step toward slowing giobal warrrung would be to increase the efficiency of energy utilization. This would also be of value iconserving the shrinking supplies of energy resources. It makes sense to increase energy efficiency， thus reduang carbodioxide production， eveif global warming is not a concern. One way to stimulate a move toward greater efficiency would be the imposihoof a carbotax. A carbotax would increase the cost of fuels by taxing the amount of carboput into the atmosphere by their use. This would increase the demand for fuel effiaency because the cost of fuel would rise. It would also stimulate the development of alternative fuels with a lower carbocontent and generate funds for research imany aspects of fuel efficiency and altemative fuel technologies. Another approach to the problem is to increase the amount of carbodioxide removed from the atmosphere. If enough biomass is present， the excess carbodioxide cabe utilized by vegetatioduring photosynthesis， thereby reducing the impact of carbodioxide released by fossil-fuel burning. Australia， the United States， and several other countries have announced plans to plant billions of trees to help remove carbodioxide from the atmosphere. Many critics argue that this approach will only provide a short-term benefit since， eventually， the trees will mature and die， and their decay will release carbodioxide into the atmosphere at some later time. Aassociated conceris the destructioof vast areas of rainforest itropical regions of the world. These ecosystems are extremely efficient at removing carbodioxide and storing the carboatoms ithe structure of the plant. The burning of tropical rainforests to provide farm or grazing land not only adds carbodioxide to the atmosphere but also reduces the ability to remove carbodioxide from the atmosphere， since the grasslands or farms created do not remove carbodioxide as efficiently as do the original rainforests. Furthermore， the grazing lands and farms isuch regions of the world are ofteabandoned after a few years and do not returto their original forest condjtion. Chlorofluorocarbons are entirely the result of humaactivity. They were widely used as refrigerant gases irefrigerators and air conditioners， as cleaning solvents， as propellants iaerosol containers， and as expanders ifoam products. Although they are present ithe atmosphere iminute quantities， they are extremely efficient as greenhouse gases （ about 15，000 times more efficient at retarding heat loss thais carbodioxide）. Since all chlorofluorocarbons are made by people for specific purposes， their levels cabe easily controlled. The use of chlorofluorocarbons as propellants iaerosol spray cans or as expanders ifoam products is not necessary. Other more benigmaterials， such as hydrocarbons， could be used. Since the 1970s， whechlorofluorocarbons were linked to the depletioof the ozone layer ithe upper atmosphere， their use iaerosol cans has beebanned ithe United States， Canada， Norway， and Sweden， and the EuropeaEconomic Community agreed to reduce use of chlorofluorocarbons iaerosol cans. However， worldwide， chlorofluorocarbons are still widely used as aerosol propellants. Ifoam and solvents， care cabe taketo recover the chlorofluorocarbons for reuse rather thaallow them to escape into the atmosphere. Alternative refrigerants are available， and care could be taketo recycle refrigerant gases rather thajust venting them into the air. IJanuary 1991 ， DuPont announced the development of new refrigerants that would not harm the ozone layer. These will be installed irefrigerators and air conditioners ithe future. We will need to exploit all these options if we want to reduce chlorofluorocarboproduction. Until substitutes bee available， the mandatory recycling of chlorofluorocarbons will reduce the rate at which new gases are added to the atmosphere. ……