Environmental Engineering Reference
In-Depth Information
expect an increase in the proportion of the gas to trap more long-wave radiation emission
from the surface and increase the mean temperature of the globe. Investigations have
shown a close relationship on a long-term basis between global temperatures and CO
2
levels, though it is not clear which increases first or whether the changes are
synchronous. Since 1958 precise measurements of CO
2
levels have been taken at the
Mauna Loa observatory on Hawaii. They show an increase from 315 ppm by volume to
about 370 ppm today, an increase of about 15 per cent in only forty-two years. The
increase is largely the effect of fossil fuel burning, though deforestation and other landuse
changes have an impact. Other gases such as methane, nitrogen oxides and
chlorofluorocarbons (CFCs) are even more effective at absorbing long-wave radiation. At
present their concentrations in the atmosphere are low, though they are all increasing as a
result of human activities (Figure 9.14). Theory and climate models predict that their
increasing concentrations will have an impact on global temperatures.
Although less publicized, the increase in methane (CH
4
) is causing concern, as it is a
by-product of both energy consumption and agricultural activity. It is believed that a
large portion of the methane increase may be the
Figure 9.14
Main anthropogenic sources of greenhouse
gases. Sizes of the boxes are proportional to the contribution
to radiative warming. For each gas, the size of the arrows
indicates the relative importance of each source to the total
concentration change.
Source: Warrick et al. (1990).
