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Their low reactivity (inertness) and long lifetimes of 100s to 1000s of years have made
them attractive chemicals for use as foam blowing agents, coolants, propellants, fire
retardants and other industrial applications. The links between human production of
these compounds, the build-up in their stratospheric concentrations, and the recent
decrease in stratospheric O3 have been firmly established by numerous observational and
modeling studies, as summarized in WMO (1999).
Greenhouse warming is a natural phenomenon that occurs due to naturally occurring
greenhouse gases (GHGs) in the Earth’s atmosphere. These GHGs absorb much of the
Earth’s infrared radiation that would otherwise escape to space. The trapped radiation
warms the lower atmosphere and the Earth, keeping the Earth’s surface over 30oC
warmer than it would be otherwise. This phenomenon, known as the ‘greenhouse effect’,
enables life to survive on this planet. The major greenhouse gases contributing to this
natural effect are those with significant natural sources: water vapour (H2O), carbon
dioxide (CO2), methane (CH4), nitrous oxide (N2O) and tropospheric ozone (O3).
The problem of global warming is what is known as the enhanced greenhouse effect.
Since the beginning of industrial times, the greenhouse effect has been enhanced by
steadily increasing GHG concentrations in the atmosphere. These concentrations have
been increasing due to emissions from human-related activities. Increasing concentrations
alter the radiative balance of the Earth and result in a warming of the Earth's surface. The
main GHGs affected by human activities are CO2, CH4, N2O, tropospheric O3 and CFCs
(mainly CFC-11 and CFC-12), which are also responsible for stratospheric O3 loss.
Aerosols resulting from human activities, particularly from fossil fuel combustion, can
scatter or absorb solar and infrared radiation, both cooling and/or heating the Earth’s
surface. Emissions, concentrations and radiative effects of these gases and aerosols are
the topics to be addressed in this chapter.
Human-induced changes in climate and in the stratospheric ozone layer impact the entire
Earth system, from terrestrial and marine ecosystems to the health and welfare of man.
International agreements have already begun to control the use of halocarbons, paving the
way for the recovery of stratospheric ozone. However, reducing emissions of the other
GHGs that contribute to the enhanced greenhouse effect is a far more complex problem
than that of reducing halocarbons alone. Measures imposing substantial reductions in
CO2 and other GHG emissions would severely limit global energy use. If GHG emissions
are not limited, there are strong scientific grounds to believe they will cause significant
global warming in the next few decades. Such a warming would be global, but with
regional impacts of varying severity. Concomitant changes are expected to occur in
regional patterns of temperature, precipitation, and sea level, with resultant impacts on
most societal, economic, and environmental aspects of existence on this planet. With
increasing world population, impacts can be expected not only in the areas of agriculture
and water resources, affecting food security, but also via the sea level rise affecting
coastal settlements including a number of the world’s major cities. These impacts are
expected to impinge on the economy and the welfare of every nation.