Greenhouse Effect

Essay by Rod JohnsonHigh School, 10th gradeA-, November 1996

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The greenhouse effect, in environmental science, is a popular term for the

effect that certain variable constituents of the Earth's lower atmosphere have on

surface temperatures. These gases--water vapor (H2O), carbon dioxide (CO2), and

methane (CH4)--keep ground temperatures at a global average of about 15 degrees

C (60 degrees F). Without them the average would be below the freezing point of

H20. The gases have this effect because as incoming solar radiation strikes the

surface, the surface gives off infrared radiation, or heat, that the gases trap and

keep near ground level. The effect is comparable to the way in which a greenhouse

traps heat, hence the term.

Environmental scientists are concerned that changes in the variable contents

of the atmosphere (particularly changes caused by human activities) could cause the

Earth's surface to warm up to a dangerous degree. Even a limited rise in average

surface temperature might lead to at least partial melting of the polar ice caps and

hence a major rise in sea level, along with other severe environmental agitation.


example of a runaway greenhouse effect is Earth's near-twin planetary neighbor

Venus. Because of Venus's thick CO2 atmosphere, the planet's cloud-covered

surface is hot enough to melt lead.

Water vapor is an important 'greenhouse' gas. It is a major reason why

humid regions experience less cooling at night than do dry regions. However,

variations in the atmosphere's CO2 content are what have played a major role

in past climatic changes. In recent decades there has been a global increase in

atmospheric CO2, largely as a result of the burning of fossil fuels. If the many

other determinants of the Earth's present global climate remain more or less

constant, the CO2 increase should raise the average temperature at the Earth's

surface. As the atmosphere warmed, the amount...