Environmental Engineering Reference
In-Depth Information
hillsides.
It is very difficult to estimate the full costs of such a storm. Deaths are relatively easy
to confirm but damage cannot readily be quantified. Most of these countries are relatively
poor, and roads, bridges, houses and utilities may take years to replace. Preliminary
estimates were of at least 11,000 deaths as a direct result of the storm and damage was
put at US$5 billion, but this is almost certainly an underestimate. Aid efforts started to
replace lost or damaged food supplies and housing in Honduras and Guatemala, which
were most severely affected.
Fortunately such storms are relatively rare in the humid tropics (see Chapter 7).
Nevertheless when and where they do occur, such as the Philippines, Vietnam and
Bangladesh, their consequences can be devastating. In many cases warning of the storm
is ineffective and emergency plans are limited, so the poorer sections of society suffer
most.
as less moisture is returned to the atmosphere, giving a positive feedback effect to higher
surface temperatures.
Less obviously, tropical forests may have an impact on the gaseous composition of the
atmosphere, which in turn can affect surface climate. As plants photosynthesize, they use
carbon dioxide from the atmosphere and therefore contribute to the balance of this gas. If
the forests are cleared, the subsequent vegetation growth is likely to have lower biomass
and so extract less carbon dioxide. Burning of the forest will directly add carbon dioxide
too. It has been estimated that if all the world's rain forests were burned between 1986
and 2000 the carbon dioxide concentration in the atmosphere would have risen by up to
20 per cent.
Methane is another greenhouse gas which would increase through forest clearance.
The main sources of methane are rice growing, biomass burning and cattle ruminating
(see Chapter 9). All these activities may increase as forest is removed, and methane is a
more efficient greenhouse gas than carbon dioxide.
These effects lead us to the largest scale of climate impact, as the addition of
greenhouse gases would add to global warming. Enhanced rates of clearance would
exacerbate the problem. General circulation models (GCMs) have been used to predict
what the impact of total forest clearance would be at both the regional and the global
scale. The consensus view is that the direct effects of deforestation on regional climate
may be large but the impact on global climate would be relatively small, perhaps
warming Earth by about 0·3° C.
FOREST MANAGEMENT
We have seen that tropical rain forests are rich ecosystems which are being threatened by
extensive clearance. At a local scale, the change in land use may benefit a small number
of individuals, but at a world scale we are facing a major crisis of the wholesale
extinction of species and habitats, which in turn may affect global climate. Can or should
anything be done about it?
Much deforestation takes place far away from the centres of national government. In
order to address the problem we have got to examine why clearance is taking place and
