Environmental Engineering Reference
In-Depth Information
Figure 1.6
Origin of the Anthropogenic (Human-induced) Greenhouse Effect
The existing
natural greenhouse effect
makes life on Earth possible.
Without the natural greenhouse effect, Earth would emit most of its heat
radiation into space. Incident sunlight heats the Earth's surface, and the mean
global ambient temperature is roughly +15°C due to the retention of this
heating energy.
Over millions of years, nature has created a balance in the concentration
of atmospheric gases. This has made life as we know it today possible. Several
natural temperature variations have occurred over the preceding millennia, as
evidenced by different ice ages.
Additional greenhouse gases are emitted to the atmosphere as a result of
energy consumption and other human-induced influences. These gases cause
the anthropogenic greenhouse effect. Table 1.7 summarizes the characteristics
of the most important greenhouse gases.
Anthropogenic
carbon dioxide
(CO
2
) results from burning fossil fuels and
biomass. It contributes 61 per cent to the greenhouse effect and is the most
relevant greenhouse gas. Biomass is carbon dioxide neutral if it is used at the
same rate as it is grown again. On the other hand, fire clearing in the rain
forest produces vast amounts of CO
2
that has been bound by these plants over
decades or centuries and thus can be considered a contributor to the
greenhouse effect. However, the burning of fossil fuels emits the largest amount
of anthropogenic carbon dioxide. The share of fossil fuel-related carbon
dioxide emissions is currently 75 per cent, and is increasing. The carbon
dioxide concentration in the outer atmosphere has already risen from 280
