UNIT 4

THE GREENHOUSE EFFECT

In recent decades, we often hear about the greenhouse effect in somewhat negative terms. The negative concerns are related to the possible impacts of an enhanced greenhouse effect. It is important to remember that without the greenhouse effect, life on earth as we know it would not be possible. While the earth's temperature is dependent upon the greenhouse-like action of the atmosphere, the amount of heating and cooling are strongly influenced by several factors just as greenhouses are affected by various factors.

Lead-in

Discuss the following quotations about ecological problems. Say how they are related to the theme of the unit.

The earth we abuse and the living things we kill will, in the end, take their revenge; for in exploiting their presence we are diminishing our future.

~Marya Mannes, More in Anger, 1958

Economic advance is not the same thing as human progress.

John Clapham, A Concise Economic History of Britain, 1957

For 200 years we've been conquering Nature. Now we're beating it to death. ~Tom McMillan, The Greenhouse Trap, 1990

Our environmental problems originate in the hubris of imagining ourselves as the central nervous system or the brain of nature. We're not the brain, we are a cancer on nature.

~Dave Foreman, Harper's, April 1990

1. Guess the meaning of the words and learn the pronunciation.

2. Read the text, do the exercises.

Life as we know it on the Earth is entirely dependent on the tenuous layer of gas that clings to the surface of the globe, adding about 1 % to its diameter and insignificant amount to its total mass. And yet the atmosphere serves as the Earth’s window and protective shield, as a medium for the transport of heat and water, and as source and sink for exchange of carbon, oxygen, and nitrogen with the biosphere. The atmosphere acts as a compressible fluid tied to the Earth by gravitation; as a receptor of solar energy and a thermal reservoir, it constitutes the working fluid of a heat engine that transports and redistributes matter and energy over the entire globe. The atmosphere is also a major temporary repository of a number of chemical elements that move in a cyclic manner between the hydrosphere, atmosphere, and the upper lithosphere. Finally, the atmosphere is a site for a large variety of complex photochemically initiated reactions involving both natural and anthropogenic substances.

The energy radiated by the earth has a longer wavelength than the incident radiation. Most gases absorb radiation in this range quite efficiently, including those gases such as CO2 and N2O that do not absorb the incident radiation. The energy absorbed by atmospheric gases is re-radiated in all directions; some of it therefore escapes into space, but a portion returns to the Earth and reabsorbed, thus raising its temperature. This is commonly called the greenhouse effect. If the amount of an infrared-absorbing gas such as

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carbon dioxide increases, a larger fraction of the incident solar radiation is trapped, and the mean temperature of the Earth will increase.

Any significant increase in temperature of the oceans would increase the atmospheric concentrations of both water and CO2, producing the possibility of a runaway process that would be catastrophic from a human perspective. Fossil fuel combustion and deforestation during the last two hundred years have increased the atmospheric CO2 concentration by 25 % and this increase is continuing. The same combustion processes responsible for the increasing CO2 concentration also introduce considerable quantities of particulate materials into the upper atmosphere. The effect of these would be to scatter more of the incoming solar radiation, reducing the amount that reaches and heats the earth’s surface. The extent to which this process counteracts the greenhouse effect is still a matter of controversy; all that is known for sure is that the average temperature of the Earth is increasing.

Carbon dioxide is not the only atmospheric gas of anthropogenic origin that can affect the heat balance of the Earth; other examples are SO2 and N2O. Nitrous oxide is of particular interest, since its abundance is fairly high, and is increasing at a rate of about 0.5 % per year.

It is produced mainly by bacteria, and much of the increase is probably connected with introduction of increased nitrate into the environment through agricultural fertilization and sewage disposal. Besides being a strong infrared absorber, N2O is photochemically active, and can react with ozone. Any significant depletion of the ozone content of the upper atmosphere would permit more ultraviolet radiation to reach the Earth. This would have numerous deleterious effects on present life forms, as well as contributing to a temperature increase. The warming effect attributed to anthropogenic additions of greenhouse gases to the atmosphere is estimated to be about 2 watts per m2, or about 1.5 % of the 150 watts per m2 trapped by clouds and atmospheric gases. This is a relatively large perturbation compared to the maximum variation in solar output of 0.5 watts per m2 that has been observed during the past century. Continuation of greenhouse gas emission at present levels for another century could increase the atmospheric warming effect by 6–8 watts per m2.

A less-appreciated side effect of the increase in atmospheric carbon dioxide may be reduction in plant species diversity by selectively encouraging the growth of species which are ordinarily held in check by other species that are able to grow well with fewer nutrients. This effect, for which there is already some evidence, could be especially pronounced when the competing species utilize the C3 and C4 photosynthetic pathways that differ in their sensitivity to CO2.

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(Lower S. K. Survey of Environmental Geobiochemistry. Simon Fraser University, 2004)

1.compared to

2.to hold in check

3.to move in a cyclic manner

4.to be a matter of controversy

5.to be of particular interest

6.to be known for sure

7.to escape into space

Compose your own sentences with two of the expressions.

5. Translate from Russian into English.

Падающая радиация, поглощать, ловить, вышедший из-под контроля процесс, быть ответственным за, рассеивать радиацию, влиять (2 вар.), представлять особый интерес, внесение удобрений в почву, сброс сточных вод, значительное истощение (уменьшение), повышать температуру (2 вар.), сжигание, улетучиваться в космос, вредное воздействие, также как и, оценивать, излучение газов парникового эффекта, антропогенное происхождение, природное топливо, большое возмущение.

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6. Fill in each gap with only one word.

Gases pollute the atmosphere because they are produced 1). …. quickly to be cleared away naturally 2). …. rain, winds or plant life. These poisonous gases 3). … from several sources such as oil producers, industries which burn fuel, and motor vehicle. When the gases are released, they have two deleterious effects. 4). …, some of the gases are caught by rain clouds and fall as acid rain, 5). … damages the environment. Secondly, if the amount of carbon dioxide increases, a larger fraction of the incident solar radiation is trapped, keeping the heat of the sun close 6). … the Earth’s surface just 7). …. a greenhouse keeps heat in. The increase of carbon dioxide is 8).

…worse by the cutting down 9). …. forests. Trees use carbon dioxide, and the fewer trees 10). …, the more of this gas remains 11). … the air. The USA is now leading an international effort to limit deforestation. In 1996, Washington set goals for industry, and several international agreements 12). … already been effective in reducing the production 13).

…harmful gases. Only international cooperation can 14). … this problem which, if 15). … controlled, may threaten all life on earth.

7.Match the definitions.

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8. Look at the chart. Put the sentences below in the correct order.

2b)The heat is partly absorbed by the earth itself

3c) The heat on earth comes from the sun

6f) The heat absorbed is reradiated by the earth as infra-red radiation

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