水土保持专业英语_水土保持与荒漠化
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W2 Greenhouse gases and global warming
Key note
Carbon dioxide concentration in the atmosphere
Carbon dioxide(CO2)is the main vehicle of carbon flux between atmosphere, oceans and biota.Foil fuels(coal,oil and natural gas)present in the atmosphere lay dormant until recent centuries.The concentration of CO2 in the atmosphere has increased from about 280 parts per million(ppm)in 1750 to about 350 ppm in 1990 and is still rising , with the main reason for the increase being the combustion of foil fuels.Estimates of future CO2 emiions, and the combustion to be expected in the atmosphere vary, but it appears likely that the concentration will rise to a mean about 500 ppm by the year 2050.The greenhouse effect
The greenhouse effect is a theory which proposes that pollution by common anthropogenic(i.e.created by humans)pollutants such as CO2 and methane may lead to an increased global temperature.Over the last century , CO2 concentrations have risen and global air temperatures have increased by 0.4-0.7℃,which supports this theory.The atmosphere formed around the earth insulates the planet from full effects of heats lo by trapping heat in the atmosphere using greenhouse gases ,which include water vapor as well as CO2 and other anthropogenic pollutants.Doubling of the atmospheric CO2 concentration from its present level is predicted to lead to a further warming of around 3.5℃.Related topics
Solar radiation and climate(C1)
Ozone depletion(W3)
Air, water and soil pollutants(W1)Carbon dioxide concentrations in the atmosphere
Photosynthesis and respiration are the two opposing procees driving the global carbon cycle.It is predominantly a gaseous cycle, with CO2 as the main vehicle of flux between atmosphere , oceans and biota.Historically, the lithosphere played only a minor role;foil fuels(coal,oil and natural gas)lay dormant until recent centuries.The concentration of CO2 in the atmosphere has increased from about 280(ppm)in 1750 to about 350 ppm in 1990 and is still rising.Since 1958 the atmosphere CO2 concentration has risen from 315 ppm to 350 ppm in 1990(Fig.1).The principal cause of the increase in atmospheric CO2 in recent years has been the combustion of foil fuels, which in 1990 released about 5.5×109 tons of carbon into the atmosphere.The exploitation of rain forest has also caused a significant release of CO2.The burning that follows most forest clearance quickly converts some of the vegetation to CO2, while decomposition of the remaining vegetation releases CO2 over a longer period.If forests have been cleared to provide for permanent agriculture, the carbon content of the soil is reduced through decomposition of soil organic matter and/or by erosion.In total it is estimated that about 1.0×109 tons year-1 of carbon released through changes in tropic land use.The total amount of carbon released each year to the atmosphere as a result of man's activities around 6.5×109 tons compared with 100×109 tons released into the atmosphere naturally by respiration of the world's biota.The observed increase in atmospheric CO2 is 2.9×109 tons year-1.Much of the remainder of the additional CO2 is removed by diolution in the oceans.It is poible that terrestrial communities act as a net sink for atmosphere CO2 , and terrestrial ecosystem may be able to aimilate the extra carbon as bioma;It is already known that increasing the atmospheric concentration of in controlled environments increase the rate photosynthesis and growth of many plants species.Estimates of future CO2 emiions and the concentration to be expected in the atmosphere vary, but it appears likely that the concentration will rise to a mean of about 550 ppm by the year 2050.The greenhouse effect Ten out of the 16 years between 1980 and 1995 were among the hottest on record;Accurate records have been kept since 1881.Global climate change resulting from human activity is one of the most contentious topics in ecology.The major source of generated power comes from the burning of foil fuels.Foil fuels are organic in nature and when they are burned, CO2 is released into the atmosphere.The fear is that pollution by common anthropogenic(created by humans)pollutants, such as CO2 and methane, may lead to increased global temperature.Accurate measurements of CO2 concentrations in air have been recorded for the last 116 years, and during this time period increases in CO2 levels have been recorded along with an 0.4-0.7℃ rise in global temperature.This close correlation supports the argument that industrial emiions,in particular gases released by the burning of foil fuels,will lead to further climate change over the next century.On the basis of the distance of the earth from the sun, global temperatures should be 33℃ lower than they are, with an average temperature of-18℃.However, from the time of planetary fusion, the earth has been radiating heat.Atmosphere formed around the earth insulates the planet from the full effects of heat lo.This atmosphere allows much of the incoming radiation to strike the earth.A large proportion of this light energy is transferred into heat energy, and the heat energy held by the earth during the day is irradiated back at night.Much of the energy transformed to heat is trapped by atmospheric gases, particularly water vapor, CO2 methane and nitrous oxides.The warming of the earth attributable to atmospheric gases is termed the greenhouse effect.The natural thermal insulation of the greenhouse gases raises the average global temperature from-18 ℃ to 15℃.The greenhouse effect is thought to be increased as concentrations of carbon dioxide increase.Doubling of the atmosphere CO2 concentration from its present level is predicted to lead to a further warming of around 3.5℃.The effects of this would be profound, as polar ice would melt and the oceans would expand with heat, raising sea levels and resulting in large-scale changes to the global climate.In addition, global may cause organism to migrate in order to seek optimal temperatures(organism tracking), or to adapt to the changed conditions or face extinction.This movement of organism may include tropical diseases, which may as a result of the climate change move from tropical to temperate climates(e.g.Malaria).
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