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A planet's climate is decided by its mass, its distance
from the sun and the composition of its atmosphere. Mars
is too small to keep a thick atmosphere. Its atmosphere
consists mainly of carbon dioxide, but the atmosphere
is very thin. The atmosphere of the Earth is a hundred
times thicker.
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Over the last 400,000 years the Earth's climate has been
unstable, with very significant temperature changes, going
from a warm climate to an ice age in as rapidly as a few
decades. These rapid changes suggest that climate may
be quite sensitive to internal or external climate forcings
and feedbacks.
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The Earth has a natural temperature control system. Certain
atmospheric gases are critical to this system and are
known as greenhouse gases.
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Radiative forcing is the change in the balance between
radiation coming into the atmosphere and radiation going
out.
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The table lists some of the main greenhouse gases and
their concentrations in pre-industrial times and in 1994;
atmospheric lifetimes; anthropogenic sources; and Global
Warming Potential.
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CO2 concentrations in the
atmosphere have been measured at an altitude of about
4,000 meters on the peak of Mauna Loa mountain in Hawaii
since 1958.
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Atmospheric CO2 has increased
from a pre-industrial concentration of about 280 ppmv
to about 367 ppmv at present (ppmv= parts per million
by volume).
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This map depicts the unequal distribution of industry
in the world. The significant part of carbon dioxide emissions
comes from energy production, industrial processes and
transport.
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Emissions of carbon dioxide due to changes in land use
mainly come from the cutting down of forests and instead
using the land for agriculture or built-up areas, urbanisation,
roads etc.
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The rich countries of the world historically has emitted
most of the anthropogenic greenhouse gases since the start
of the industrial revolution in the latter half of the
1700s. Per capita, the significant emissions still are
produced by the OECD countries
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The global carbon cycle shows the carbon reservoirs in
GtC (gigatonne= one thousand million tonnes) and fluxes
in GtC/year.
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The amount of aerosols in the air has direct effect on
the amount of solar radiation hitting the Earth's surface.
Aerosols may have significant local or regional impact
on temperature.
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The United Nations Framework Convention on Climate Convention
is the foundation of global efforts to combat global warming.
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In 1988, UNEP and WMO jointly established the Intergovernmental
Panel on Climate Change (IPCC) as concern over climate
change became a political issue. The purpose of the IPCC
was to assess the state of knowledge on the various aspects
of climate change including science, environmental and
socio-economic impacts and response strategies.
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