Download GREEN HOUSE EFFECT A glass house used for raising delicate

GREEN HOUSE EFFECT
A glass house used for raising delicate plants is called green house. A green
house has higher temperature inside than outside though the interior receives less radiations, it is
called green house effect.
The temperature of the earth’s surface is determined by the energy balance
between the heat energy reaching the earth’s surface and the heat energy that is radiated back
into space.
Much of the short wavelength visible light from the sun that reaches the earth is
reradiated as a long wavelength infra red radiation. Some atmospheric gases, like carbon dioxide,
chlorofluoro carbons, methane, nitrous oxide etc., which are IR active selectively absorb longer
wavelengths (infra red) and reflect heat back to earth. Since this effect is similar to the one under
the glass house is known as green house effect. The green house gases act as a thermal blanket
around the globe, raising the earth’s surface temperature beyond the equivalent temperature
calculated from the models. If the earth did not already have a green house effect its temperature
would have been -18o C. Since actual average temperature of the earth is15o C, it seems that the
green house effect adds 33o C of warming to the surface of the earth.
Gases
Atm. Conc
(ppm)
Annual conc.
Increase (%)
Relative
green house
efficiency
Current
green house
contribution
Table 4.1 The following table summarises some of the characteristics of these green
house gases.
CO2
CFCs
CH4
N2O
351
0.00225
1.675
0.31
0.4
5
1
0.2
1
15000
25
230
57 %
25%
12%
6%
Sources
CO2 : Burning of fossil fuels, automobile
exhaust,
CFCs: Air conditioners, fire extinguishers
refrigerators, propellants in aerosol spray cans.
CH4: Garbage dumps, paddy fields, natural gas,
petroleum refineries.
N2O: Lightening, nylon production, break down
of nitrogen fertilizers, respiration of anaerobic
fungi
.
As is now well known, anthropogenic sources of a number of gases are enhancing the
green house effect, leading us into a further uncertain global climate. By1990 the concentration
of CO2 had reached 355ppm and was climbing at about 1.5ppm per year
4.7.1 Effects of Global Warming:
(i) Effects on weather and Climate: In 20th century, the global mean temperature has increased
by about 0.6C. The average temperature of the earth may increase by 1.4 to 5.8C by the year
2100 from the year 1990. It is expected that the rise in temperature will be more marked in the
regions of middle and higher altitudes. The moisture carrying capacity of the atmosphere is also
expected to increase due to warming of the atmosphere. The troposphere will warm up and the
stratosphere will cool down. This would cause wide-spread change in the precipitation pattern
due to changed pattern of air mass movement. The precipitation will increase at higher altitudes
and but will decrease at lower altitudes. The frequency of extreme drought and floods will
increase.
(ii) Rise in Sea Level: The global warming also contributes to rise in sea level due to thermal
expansion of ocean and melting of glaciers and Green land ice sheets. The level of sea has been
rising by 1 to 2 mm per year during the 20th century. If the rise in sea level goes on increasing
with the present rate, the global mean sea level will increase upto 0.88 mm from the 1990 level.
A rise of even half a meter in the sea level would affect human population, one-third of which
lives within 60 km of a coast line. Many of the world’s important cities and coastal areas are
likely to be hit by storms and floods. Several low lying islands may be submerged. Many
important birds and fishes inhabiting in coastal salt marshes and estuaries, will become extinct
due to destruction of their breeding grounds. Thus, rise in sea level will have a negative impact
on human settlements, tourism, fisheries, agriculture, water supply and coastal ecosystems.
(iii) Effect on Range of Species Distribution: Each plant and animal species occurs within a
specific range of temperature. The global warming will shift the temperature ranges, which
would affect altitudinal and latitudinal distribution pattern of organisms. Many species may shift
slowly pole ward or towards high elevation of mountain areas. Rapid rise in temperature may
cause large scale death of many trees, as they are sensitive to temperature stress, and the area
may be occupied by scrub vegetation. Many species may disappear, as they are unable to migrate
fast enough to track temperature change.
(iv) Food Production: Global warming will reduce crop yield due to increase in incidence of
plant diseases and pests, explosive growth of weeds and enhanced basal rate of respiration of
plants. In tropical and subtropical regions even a small rise in temperature will have detrimental
effect on crop productivity. It is estimated that the yield of rice along in South East Asia will
decrease by 5% for each 1C rise in temperature.
Control Measures:
1. The dependence on fossil fuel should be reduced and use of non-conventional energy should
be encouraged.
2. Afforestation and reforestation should be encouraged.
3. Reduction of N2O emission by minimizing the use of nitrogen fertilizers.
4. Development of substitutes for chlorofluorocarbons.