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Greenhouse means a building made of
glass with heat and humidity regulated
for growing plants. In it visible light
passes through the glass and heats up
the soil warming the plants. The warm
soil emits radiation in longer wave
lengths, i.e. infrared. As the glass is
opaque to longer wavelength of infrared
radiation it partly reflects and partly
absorbs these radiations. Due to this
mechanism the greenhouse is warmer than
the outer atmosphere.
The earth’s atmosphere acts like a
greenhouse where CO2 acts
like a greenhouse gas which transmits
shorter wavelength solar radiation but
reflect the longer wavelength heat
radiation coming from warmed surface of
the earth. CO2 molecules are
transparent to sunlight but not to heat
radiation. So they trap and reinforce
the solar heat stimulating an effect
popularly referred to as greenhouse
effect.
The 4 major greenhouse gases are carbon
dioxide (CO2), methane (CH4),
nitrous oxide (N2O) and
chlorofluorocarbons (CFC)
The contribution of greenhouse gases is
as under
·
CO2 = 55%.
A CO2 molecule remains in the atmosphere for about
50-250 years which is the maximum span
of any greenhouse gas.
·
CH4 =20%
CH4 traps about 25 times more heat in the
atmosphere than a CO2
molecule over a period of 100 years.
·
CFC = 14%
Each CFC molecule can trap heat equivalent to 10,000
molecules of CO2.The life
span of CFC’s is 120 years.
·
N2O = 10-11%
The heat absorption capacity of N2O is 250-290
times that of CO2 and it
remains in the atmosphere for about 160
years.
Sources of Greenhouse Gases:
CARBON DIOXIDE (CO2)
·
Power stations based on fossil fuels are the major source of CO2
·
Automobiles, railways and aircraft use large quantity of diesel and
petrol releasing huge amount of CO2
·
Deforestation adds to amount of co2 in
the atmosphere.
·
A large number of factories burn immense
quantity of coal, oil and thus produce
carbon dioxide.
METHANE (CH4)
It is mainly released from garbage dumps
and paddy fields.
·
The rice crop releases through its roots
glucose which when acted upon by a group
of anaerobic bacteria called
methanogenes produces methane.
·
CH4 is also produced from
biomass i.e. residue of tress, plants
and rice crop
CHLOROFLUROCARBONS
Chlorofluorocarbons are the compounds of
chlorine and fluorine eg Freon and
Halons
·
Air conditioners, refrigerators. aerosol
propellants, fire extinguishers
NITROGEN OXIDES
·
Lightning is a major source of nitrogen
oxides. The high temperature and
pressure in the air along the path of
lightning flash causes the breakup of
nitrogen and oxygen molecules into
fragments that recombine to form
nitrogen oxides.
·
Burning of fossil fuels releases
nitrogen oxides
·
Agricultural activity using chemical
fertilizers contributes about 15-28% of
the nitrogen oxides produced.
·
Some anaerobic fungi also release
nitrogen oxide as a by –product during
respiration.
·
Nitrogen oxides are also formed during
the process of nitrification and
denitrification
CLIMATE CHANGE
·
The glaciers are melting and the melted
ice raises the sea level thus flooding
the low lying regions.
·
There are incidents of occurrence of
natural fires due to global warming
·
Global warming also effects the nesting
cycle of the birds, altering the
habitats, breeding and migration of
animals.
·
It affects the agriculture as CO2
is a natural fertilizer and the plants
grow larger and faster with increasing
CO2 in the atmosphere. This
abnormal fast growth of plants might be
beneficial as the yield of major crops
increases but the soils may become
impoverished more rapidly.
·
In temperate regions, the winters are
becoming shorter and warmer and the
summers will be longer and hotter.
·
There is enormous increase in rainfall
but the problems of desertification,
drought and soil erosion will further
worsen.
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