Лекция: Deforestation

Deforestation affects world climate in two main ways – first, by altering the atmospheric composi­tion and, second, by affecting the hydrological cycle and local soil conditions:

1 Forests store great amounts of carbon dioxide, so buffering the carbon dioxide cycle in the atmosphere. The carbon retained in the vegeta­tion of the Amazon basin is equivalent to at least 20 per cent of the entire atmospheric CO2. Des­truction of the vegetation would release about four-fifths of this to the atmosphere, about one-half of which would dissolve in the oceans, but the other half would be added to the 16 per cent increase of atmospheric CO2 already observed this century. The effect of this would be to accel­erate the increase of world temperatures. A further effect of tropical forest destruction would be to reduce the natural production of nitrous oxide. Tropical forests and their soils produce up to one-half of the world's nitrous oxide, which helps to destroy stratospheric ozone. Any increase in ozone would warm the stratosphere, but lower global surface temperatures.

2 Dense tropical forests have a great effect on the hydrological cycle through their high evapotranspiration and their reduction of surface runoff (about one-third of the rain never reaches the ground, being intercepted and evaporating off the leaves). Forest destruction decreases evapotranspiration, atmospheric humidity, local rain­fall amounts, interception, effective soil depth, the height of the water table and surface rough­ness (and thereby atmospheric turbulence and heat transfer). Conversely, deforestation increases the seasonality of rainfall, surface runoff, soil erosion, soil temperatures and surface albedo (and therefore near-surface air temperatures). All these tendencies operate to degrade existing pri­mary and secondary tropical forests into savanna. Models designed to simulate the operation of Amazonian forests having a 27°C air tempera­ture and a mean monthly rainfall of 220 mm (falling in four showers every third day, each last­ing 30 minutes at an intensity of 0.003 mm s-1) predict that their degradation to savanna condi­tions would lead to a decrease of evapotranspiration by up to 40 per cent, an increase of runoff from 14 per cent of rainfall to 43 per cent, and an average increase of soil temperature from 27 to 32°C.


Упражнение 10.

В правой колонке найдите русские эквиваленты следующих английских словосочетаний из текста Deforestation:

1. soil conditions 2. tropical forests 3. evapotranspiration 4. at least 5. surface ranoff 6. water table 7. surface roughness 8. heat transfer 9. nitrous oxide 10. atmospheric composition a. по крайней мере b. окись азота c. водное зеркало d. перенос тепла e. шероховатость поверхности f. совокупное испарение g. структура почвы h. тропические леса i. состав атмосферы j. поверхностный сток


Упражнение 11.

Найдите в каждом предложении текста Deforestation подлежащее и сказуемое. Определите время и залог сказуемого.


Упражнение 12.

Письменно переведите текст. (Контрольное время – 15 минут)


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