The Earth is the only planet in our solar system that supports life. The complex process of evolution occurred on Earth only because
of some unique environmental conditions that were present:
water, an oxygen-rich atmosphere, and a suitable surface temperature.
About 30% of incoming energy from the sun is reflected back
to space while the rest reaches the earth, warming the air,
oceans, and land, and maintaining an average surface temperature
of about 15 oC.
The atmostphere carries out
the critical function of maintaining life-sustaining conditions
on Earth, in the following way: each day, energy from the
sun is assorbed by the land, seas, mountains,etc. If all this
enerygy were to be assorbed completely, the earth would gradually
become hotter and hotter. But actually, the earth both absorbs
and, simutanously releases it in the form of infra red waves.
All this rising heat is not lost to space, but is partly absorbed
by some gases present in very small (or trace) quantities
in the atmosphere, called GHGs (greenhouse gases).
Greenhouse gases(for example,
carbon dioxide, methane, nitrous oxide, water vapour, ozone),
reemit some of this heat to the earth's surface. It they did
not perform this useful function, most of the heat energy
would escape, leaving the earth cold (about -18oC) and until
to support life.
However, ever since the Industrial
Revolution began about 150 years ago, man-made activities
have added significant quantities of GHGs to the atmosphere.
The atmospheric concentrations of carbon dioxide, methane,
and nitrous oxide have grown by about 31%, 151% and 17% ,
respectively, between 1750 and 2000.
An increase in the levels
of GHGs could lead to greater warming, which in turn could
have an impact on the world's Climate, leading to the phenomenon
known as climate change. Climate change refers to a statistically
significant variation in either the mean state of the climate
or in its variability, persisting for an extended period (typically
decades or longer). Indeed, scientists have observed that
over the 20th century, the mean global surface temperature
increased by 0.6 C. They also observed that since 1860 ( the
year temperature began to be recorded systematically using
a thermometer), the 1990's have been the warmest decade. Basic
information about the climate change are given below.
activities are releasing greenhouse gases into the atmosphere.
Carbon dioxide is producted when fossil fuels are used
to generate energy and when forests are cut down and burned.
Methane and nitrous oxide ar emitted from agricultural activities,
changes in land use, and other sources. Artificial chemicals
called halocarbons (CFCs, HFC, PFCs) and other long-lived
gases such as suphur hexafluoride (SF) are released by industrial
levels of greenhouse gases are already changing the climate.
In response to humanity's emissions, the climate has
started to adjust to a "thicker blanket" of greenhouse
gases in order to maintain the balance between energy arriving
from the sun and energy escaping back into space. Observations
show that global temperatures have risen by about 0.6 C over
the 20th century. There is new and stronger evidence that
most of the observed warming over the last 50 years is attributable
to human activities.
models predict that the global temperature will rise by about
1.4 - 5.8 C by the year 2100. This change would
be much larger than any climate change experienced over at
least the last 10,000 years. The projection is based on a
wide range of assumptions about the main forces driving future
emissions (such as population growth and technological change)
but does not reflect any efforts to control emissions due
to concerns about climate change.
change is likely to have a significant impact on the global
environment. In general, the faster the climate
changes, the greater will be the risk of damage. The mean
sea level is expected to rise 9-88 cm by the year 2100, causing
flooding of low-lying areas and other damage. Other effects
could include an increase in global precipitation and changes
in the serverity or frequency of extreme events.
society will face new risks and pressures. Food
security is unlikely to be threatened at the global level,
but some regions are likely to experience food shortages and
hunger. Water resources will be affected as precipitation
and evaporation patterns change around the world. Physical
infrasture will be damaged, particularly by sea-level rise
and by extreme weather events.
and ecosystems will need to adapt to future climatic regimes.
Past and current emissions have aleady committed the earth
to some degree of climate change in the 21st century. Adapting
to these effects will require a good understanding of socio-economic
and natural systems, their sensitivity to climate change,
and their inherent ability to adapt. Fortunately, many strategies
are available for adapting to the expected effect of climate
atmospheric concentrations of greenhouse gases will demand
a major effort. Without emissions-control policies
motivated by concerns about climate change, atmospheric concentrations
of carbon dioxide are expected to rise from today's 367 parts
per million to 490 -1,260 ppm by the year 2100. This would
representa 75 -350% increase since the year 1750. Stabilizing
concerntrations at, for example, 450 ppm would require worldwide
emissions to fall below 1990 levels within the next few decades.
Kyoto Protocol would require government to take even stronger
action. In 1997, the Parties to the Convention
agreed by consensus that developed countries should accept
a legally binding commitment to reduce their collective emissions
of six greenhouse gases by at least 5% compared to 1990 levels
by the period 2008-2012. The Protocol also establishes an
emission trading regime and a "Clean development mechanism".
Howeever, the Protocol has not yet received enough ratifications
to enter into force.