Environmental Engineering Reference
In-Depth Information
The gas concentration and average atmospheric lifetime must also
be taken into account. The effect of methane, with a lifetime of about
12 years, is therefore less damaging than one might expect in view of its
GWP.Wemust nevertheless bear inmind that themechanisms involved in
atmospheric circulation of these gases and their exchanges with the soil
and the oceans are complex. This leads to uncertainties regarding the long-
term behaviour of CO 2 in the atmosphere and on the time required to
return to equilibrium, in case of disturbance. The return to equilibrium
occurs initially through absorption over several centuries of most of the
CO 2 in the atmosphere by the oceans and the biosphere, followedby a very
slow mineralisation reaction during which CO 2 is incorporated into
carbonated rock, over a timescale of up to 100 000 years. This timescale
extends well beyond our current forecast capabilities, especially since a
new ice age is predicted to occur in 10 000 years. Whatever the case,
spontaneous return to equilibrium can only be very slow.
Water vapour is also a greenhouse gas, but it condenses as clouds and
does not accumulate in the atmosphere.
Of all the greenhouse gases, CO 2 is the one which contributes most
to the greenhouse effect related to human activities, the anthropogenic
sources, due to the considerable quantities emitted. In addition, since
emissions of this gas are also increasing steadily, it plays amajor role in the
future risks of climate change.
The impact of greenhouse gas emissions on climate change
We have only recently become aware of the risks involved in climate
change. In 1988, a decisive step was taken with the creation of the
Intergovernmental Panel on Climate Change (IPCC), on the joint initia-
tive of the World Meteorological Organisation (WMO) and the United
Nations Environment Programme (UNEP).
The first IPCC report led in 1992 to the adoption of the 'climate'
convention, currently ratified by 189 countries. The second report was
published in 1996, before the signing of the Kyoto Protocol. The third
report, published in 2001, led to the adoption of control measures and
sanctions designed to ensure effective application of the Kyoto Protocol
[19]. The fourth report, published in 2007, confirms and improves the
main conclusions of the previous report.
Over 2000 scientists from154 countries participate in the IPCC studies.
Wishing to reach a consensus of opinion, the IPCC has remained prudent
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