Greenhouse gases arise from a wide range of
sources and their increasing concentration is largely
related to the compound effects of increased
population, improved living standards and changes
∈ lifestyle. From a current base of 5 billion, the
United Nations predicts that the global population
may stabilise ∈ the twenty-first century between 8
and 14 billion, with more than 90 per cent of the
projected increase taking place ∈ the world's
developing nations. The associated activities to
support that growth, particularly to produce the
required energy and food, will cause further
increases ∈ greenhouse gas emissions. The
challenge, therefore, is to attain a sustainable
balance between population, economic growth and
the environment.
The major greenhouse gas emissions from
human activities are carbon dioxide (CO2),
methane and nitrous oxide. Chlorofluorocarbons
(CFCs) are the only major contributor to the
greenhouse effect that does not occur naturally,
coming from such sources as refrigeration, plastics
and manufacture. Coal’s total contribution to
greenhouse gas emissions is thought to be about 18
per cent, with about half of this coming from
electricity generation.
The worldwide coal industry allocates
extensive resources to researching and developing
new technologies and ways of capturing greenhouse
gases. Efficiencies are likely to be improved
dramatically, and hence CO2 emissions reduced,
through combustion and gasification techniques
which are now at pilot and demonstration stages.
Clean coal is another avenue for improving fuel
conversion efficiency. Investigations are under way
into super-clean coal (35 per cent ash) and
ultraclean coal (less than 1 per cent ash). Superclean
coal has the potential to enhance the
combustion efficiency of conventional pulverised
fuel power plants. Ultraclean coal will enable coal
to be used ∈ advanced power systems such as
coal-fired gas turbines which, when operated ∈
combined cycle, have the potential to achieve much
greater efficiencies.
Defendants of mining point out that,
environmentally, coal mining has two important
factors ∈ its favour. It makes only temporary use of
the land and produces no toxic chemical wastes. By
carefully preplanning projects, implementing
pollution control measures, monitoring the effects
of mining and rehabilitating mined areas, the coal
industry minimises the impact on the neighbouring
community, the immediate environment and longterm
land capability.
Dust levels are controlled by spraying roads and
stockpiles, and water pollution is controlled by
carefully separating clean water runoff from runoff
which contains sediments or salt from mine
workings. The latter is treated and reused for dust
suppression. Noise is controlled by modifying
equipment and by using insulation and sound
enclosures around machinery.
Since mining activities represent only a
temporary use of the land, extensive rehabilitation
measures are adopted to ensure that land capability
after mining meets agreed and appropriate standards
which, ∈ some cases, are superior to the land’s premining
condition. Where the mining is
underground, the surface area can be
simultaneously used for forests, cattle grazing and
crop raising, or even reservoirs and urban
development, with little or no disruption to the
existing land use. In all cases, mining is subject to
stringent controls and approvals processes.
Fonte: http://www.ielts.org/pdf/115024GeneralTrainingReadingsampletask_−Multiplechoice.pdf
Considere as afirmativas que seguem.
I – O carvão limpo não é tão eficiente quanto o carvão normal.
II –O carvão limpo custa mais caro.
III – O carvão limpo, além de ser mais limpo, é mais eficiente.
IV – O carvão limpo pode melhorar a eficiência de conversão de combustível.
V – O carvão limpo queima numa temperatura mais baixa do que o carvão normal.
Assinale a alternativa correta.
