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CAUSES OF CLIMATE CHANGE
- The atmospheric greenhouse gases function as the glass of a greenhouse,
allowing solar energy to reach the Earth's surface
but trapping the heat energy emitted by the Earth.
Thus, these gases have a direct relation to the global mean surface air temperature.
In the past two centuries, measured increases in the concentration
of greenhouse gases have been accompanied
by increases in global mean surface air temperature.
The latter affects the volume of the polar icecaps,
the density of oceanic water and, consequently, the global
mean sea level (IPCC, 1996a).
- Recent data shows that the 1995 global mean surface air temperature
was 0.4{\hspace{0.01in}$^{\circ}$}C above the 1961-90 average,
and 0.04{\hspace{0.01in}$^{\circ}$}C above 1990,
which was the previous warmest year in the record
(Halpert et al., 1996).
- At the current concentration of 363 parts per million by volume (ppmv) (1998),
carbon dioxide is the most significant greenhouse gas.
Other greenhouse gases such as methane, nitrous oxide,
and chlorofluorocarbons (CFC's) are present in smaller quantities.
Whereas methane and nitrous oxide are produced
by both natural and artificial processes, CFC's are entirely anthropogenic.
As a greenhouse gas, methane is 20.6 times more effective
than carbon dioxide; however, its concentration is only 1.72 ppmv,
equivalent to 9.8 percent of the carbon dioxide.
Nitrous oxide is 206 times more effective than carbon dioxide,
but its concentration is 0.312 ppmv, equivalent to 17.7 percent of the carbon dioxide.
CFC's are 12200 to 15600 more effective than carbon dioxide,
but their concentration is only about 0.001 ppmv, equivalent to
3.83 percent of the carbon dioxide (IPCC, 1996a).
- The global phaseout of CFC's is well underway (IPCC, 1996a),
However, research to establish the sources and sinks of methane
and nitrous oxide continues. In this paper we consider only carbon dioxide,
by far the most important greenhouse gas.
- We first examine inputs and outputs, and then,
the historical concentration levels in the atmosphere.
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