2. •The earth is heated by sunlight and some of the heat
is absorbed by earth is radiated back into space some
of the gases in the lower atmosphere, acting like glass
in a greenhouse, allow the solar radiations (in the
range 300 to 2500 nm, i.e., near UV, visible and near
I.R. region, while filtering the dangerous U.V.
radiation, i.e. <300 nm) but do not allow the earth to
re-radiate the heat into space.
3. • In other words, these gases in the atmosphere are
transparent to the sun-light coming in but they
strongly absorb the intra-red radiation, which the
earth scans back as heat.
• A part of the so trapped in these atmospheric gases is
re-emitted to the earth’s surface. The result is the
heating of the earth’s surface by this phenomenon,
called the “Green have effect”
4. The main green house gases are CO2, water
vapor, CH4, Chlorofluorocarbons (CFC’s).
Radiations Range IR
Radiation in the Range Absorbing Gases
4000 – 8000 nm Water vapor
12000 – 16,300 nm CO2
8000 – 12,000 nm Escape unabsorbed
(region of atmospheric window)
5. CO2 is released by
volcanoes, oceans, decaying plants as well as human
activities like deforestation and combustion of fossil
fuels.
6. CH4 is released by
Coal mines, decomposition of organic matter rice, paddy,
cultivation, guts of termites in forest debris and
stomachs of ruminants are used as coolants in
refrigerator, propellants in sea sprays, plastic, foam
materials like ‘thermocoles’ or foam and in automobile
air conditioners.
7. • Greenhouse gases are responsible for keeping our
planet warm and thus sustaining life on the earth. If
the greenhouse gases are very less or totally absent
in the earth’s atmosphere, then the average
temperature on the earth would have been at sub-
zero levels.
• But if the concentration of green house gases is large,
they may trap too much of heat, which may threat
the existence of life on the earth.
8. • It is estimated that the atmospheric CO2 content has
increased by 25% during the last two centuries and
has been attributed to the industrial revolution over
these two centuries this is one of the reasons for the
light increase in the global temperature (≈ 0.50°C) the
concentration of greenhouse gases have been
continuously increasing, there is an increasing concern
about the possible “global warming”.
9. • It is predicted that the concentration of the
greenhouse gases in the atmosphere my double
within the next 50 – 100 years and if this happen, the
global temperature may increase by 4-5 °C. This will
increase the evaporation of surface water, which may
influence climatic changes depending upon the
pattern of cloud formation.
10. •Low level dew clouds may exert cooling effect
whereas high level thin cloud formation may exert
heating effect due to increase Greenhouse effect.
•Model projection reveal even 1.5°C rise in temperature
can adversely affect the food production in the world.
The biological productivity of the ocean would also
decrease, which in turn may reduce transport of the
nutrients from deeper layer to the surface by biological
circulation.
11. • Global warming result in melting of the polar icecaps, dry
areas becoming drier, humid areas like Amazon, suffering
from more intense Tropical storms, drastic drop in food
production, increased breeding of pets and decrease due to
more humid conditions, and lifting up of the sea level by 20
cm to 1.5 m. Greenhouse effect can be minimized by
reduction in use of fossil fuel, conservation of forests, ban on
CFC, development of environment friendly technologies,
checking of pollution growth and imparting of non-formal
and formal environmental education.
