• Global warming is an average increase in the
temperature of the atmosphere near the Earth's
surface and in the troposphere, which can contribute
to changes in global climate patterns.
• The Intergovernmental Panel on Climate Change
(IPCC) reported that the 20th century saw an increase
in global average surface temperature of
approximately 0.6 °C (1.1 °F).
• Rising average temperatures are affecting the
environment. Some observed changes include
shrinking of glaciers, thawing of permafrost, later
freezing and earlier break-up of ice on rivers and lakes,
lengthening of growing seasons, shifts in plant and
animal ranges and earlier flowering of trees
CAUSES OF GLOBAL WARMING:
THE GREEN HOUSE EFFECT
The greenhouse effect is the natural process by which the
atmosphere traps some of the Sun's energy, warming the Earth
enough to support life.
It is the warming that results when solar radiation is trapped by
the atmosphere; caused by atmospheric gases that allow sunshine
to pass through but absorb heat that is radiated back from the
warmed surface of the earth
Without greenhouse warming the Earth’s average surface
temperature would be around –18°C (0°F) and unable to support
Scientists believe a human-driven increase in "greenhouse gases" is
increasing the effect artificially.
Modern global warming is the result of an increase in magnitude
of the called greenhouse effect, a warming of Earth’s surface and
lower atmosphere caused by the presence of water vapour, carbon
dioxide, methane, and other greenhouse gases
Greenhouse gases include water vapour, Carbon dioxide,
Methane, Nitrous oxide, Halogenated Fluorocarbons,
Ozone, Perfluorinated carbons, and Hydrofluorocarbons.
Greenhouse gases warm Earth’s surface by increasing the
net downward longwave radiation reaching the surface
Global warming is also caused by an increase in the levels
of these gases brought about by human activity. The
greatest impact on the greenhouse effect has come from
industrialization and increases in the amounts of carbon
dioxide, methane, and nitrous oxide.
SOME GREEN HOUSE GASES
Water vapour is the most important
greenhouse gas, but human activity doesn’t
have much direct impact on its amount in
The primary role of water vapour is not as a
direct agent of radiative forcing but rather as
a climate feedback
Increased evaporation leads to a greater
concentration of water vapour in the lower
atmosphere capable of absorbing longwave
radiation and emitting it downward
Carbon dioxide (CO2) is is a colourless, odorless non-
flammable gas and is the most prominent Greenhouse gas
in Earth's atmosphere
Carbon dioxide is used by plants during photosynthesis to
It is produced during respiration by plants, and by all
animals, fungi and microorganisms that depend either
directly or indirectly on plants for food
Carbon Dioxide is also produced by burning of fossil fuels
Methane (CH ) is the second most
important greenhouse gas.
Methane is a colourless, odorless,
Natural sources of methane include
tropical and northern wetlands, methaneoxidizing bacteria that feed on organic
material consumed by termites, volcanoes,
seepage vents of the seafloor in regions
rich with organic sediment
Methane is also released from rice
paddies, livestock farms and landfill sites
Nitrous Oxide (N2O) is a colourless non-flammable
gas, with a pleasant, slightly sweet odor.
It is a significant Greenhouse gas
Nitrous oxide is emitted during agricultural and
industrial activities, as well as during combustion of
fossil fuels and solid waste.
Hydrofluorocarbons, Perfluorocarbons, and Sulfur
Hexafluoride are synthetic, powerful greenhouse gases
that are emitted from a variety of industrial processes.
Fluorinated gases are sometimes used as substitutes for
ozone-depleting substances (that is, CFCs, HCFCs, and
These gases are typically emitted in smaller quantities, but
they are potent greenhouse gases