DEEPENING: Climate Change
Is it important ?
We can estimate that without greenhouse gases the earth would have
an average temperature over 30°C lower than now, and would be
uninhabitable.
During the ice ages there was less CO2 in the atmosphere, which
helped to strengthen the cooling due to changes in radiation received
from the sun.
It is therefore expected that any increase in the concentrations
of greenhouse gases will intensify the greenhouse effect and will
lead to higher temperatures on the earth.
What are the main greenhouse gases?
Water vapuor is by far the most important natural greenhouse gas
in our atmosphere.
Of man-made greenhouse gases, the most important are acrbon dioxide
(CO2), methane (CH4), nitrous oxide (N2O), and the halocarbons,
of which the chlorofluorocarbons (CFCS) are the most significant.
Ozone (O3) in the lower atmosphere, whose concentration is affected
by man's activities, is also an important greenhouse gas.
Apart from the CFCS these gases also occur naturally.
Water vapour is intimately involved in the greenhouse question because
its concentration is linked with those of other gases through a
"feedback mechanism".
Warming, brought about by other greenhouse gases, increase evaporation
and allow the atmosphere to hold more water vapour, thus in turn
enhancing the warming.
Different gases absorb and trap infra-red radiation from the earth
at different levels of efficiency.
In the table are shown the relative efficiency of greenhouse gases
and hence their relative climatic effect.
All the "new" greenhouse gases are more effective per
molecule than CO2; one molecule of CFC 12, for example, has the
same effect as about 25,000 CO2 molecules.
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