Increasing concentrations of carbon dioxide and
other trace gases in the atmosphere, largely as a result of human
activities, are expected to cause a significant increase in the
earth's temperature over the next several decades. The increase
would entail major ecological, economic, and social consequences.
The likelihood of such global warming is high, and its causes seem
to be fairly well understood. The emission of these gases into the
atmosphere, therefore, should be monitored carefully and probably
should be reduced considerably in order to prevent serious harm to
human welfare. While the harmful effects would not be great in the
short run, it would be extremely unwise to postpone serious efforts
to limit the build-up of most of these gases. While "it may be too
soon to start implementing drastic measures for either limitation
or adaptation, . . . there is an immediate need for adoption of
measures that ensure that the world is better prepared to respond
to climatic change."
The concentration of carbon dioxide in the
atmosphere by 1985 had increased by about 25 per cent since
pre-industrial times. It is likely to increase by a further 40 per
cent by the year 2050 if present trends in energy use continue; by
80 per cent if energy use accelerates. The additional warming
effect of other trace gases, especially methane, nitrous oxide, and
the so-called chlorofluorocarbons, is expected to be about equal to
that caused by carbon dioxide. (The chlorofluorocarbons are also a
principal cause of the depletion of stratospheric ozone, discussed
below.) The expected climatic change would exacerbate the problems
of drought, desertification, deforestation, and soil erosion and
worsen the prospects for sustainable agriculture. Another
consequence of global warming would be a higher sea level, which
would profoundly influence habitation patterns, agriculture, and
industry, particularly in river deltas, flood plains, and other
low-lying coastal areas.
While most of these effects are expected in later
decades, already in by the 1990s the increased climatic variability
required a greater buffer capacity in food supplies than has been
considered necessary in the past, at both national and
international levels. In later decades adjustments of rainfed
cropping patterns, extension or modification of irrigation systems,
or changes between major land uses (e.g., arable use versus grazing
or forestry) may be necessary.
Although the forces driving global warming are
now broadly understood, its precise regional distribution and
environmental impacts are not. Concerted efforts by the
international scientific community will be necessary to clarify the
prospects. If things are allowed to go on as at present, the world
might in a few decades have to adapt very rapidly in the face of
catastrophic change. But immediate measures to slow down the
buildup of greenhouse gases would reduce the warming and its
undesirable consequences. The 1987 Montreal Protocol on Substances
That Deplete the Ozone Layer and the 1989 Helsinki Declaration on
the Protection of the Ozone Layer8 are steps in that
direction. They call for drastic cuts in production of fully
halogenated chlo-rofluorocarbons (CFCs), which are greenhouse
gases, by the end of the first decade of the 21st century.
Carbon dioxide is responsible for about 50 per
cent of the greenhouse effect, so major attention should be given
to strategies that would limit or even reduce its emission. The
strategies include increased energy efficiency and modification of
technologies in ways that lead to reduction in the use of fossil
fuels. The preservation of forests, especially the tropical
forests, is also essential.
About two thirds of the global carbon dioxide
released by human activities arises from the combustion of fossil
fuels. They released about 5.3 billion tons of carbon in 1986. In
addition, deforestation, land exploitation, and burning of other
components of the world's biomass currently release 2 to 3 billion
tons of carbon annually, nearly 80 per cent due to deforestation.
Annual emissions of carbon dioxide from fossil fuel are projected
to contain about 7 billion tons of carbon in the year 2000, between
10 and 14 billion tons in 2030, and between 13 and 23 billion tons
in 2050, depending on the rate of growth in the demand and supply
of fossil fuel energy.
The developed market economies of North America,
Western Europe, and Japan produce 49 per cent of global carbon
dioxide emissions, the economies of Eastern Europe 25 per cent, and
the developing countries 26 per cent. In addition to the enormous
use of fossil fuels in the industrialized countries, virtually all
production of chlorofluorocarbons takes place in these
countries.They have the major responsibility, therefore, for
devising ways to limit the output of the greenhouse gases. Although
they have reached initial agreements to reduce the production of
chlorofluorocarbons in order to preserve stratospheric ozone, very
little has been done to reduce or even to slow the growth of
CO2 emissions.
In view of the opposition to nuclear power,
adjusting the world energy mix to environmental concerns will be
difficult unless technological breakthroughs can provide benign,
economically competitive alternative energy sources and/or
radically improve energy efficiency. Such developments can be
expected in the long term at best, and adjustments in the medium
term will by necessity be limited to greater reliance on the less
malignant energy sources.
Vigorous application of the following policies to
reduce carbon dioxide emissions could limit global warming to a
rate that would make the necessary adaptation of global economic
activity relatively manageable:
(a) Reduce fossil
fuel use through increases in end-use energy efficiency;
(b) Shift the fossil fuel
mix toward natural gas. For the same energy output the combustion
of natural gas produces about 57 per cent of the amount of carbon
dioxide produced from coal, and the combustion of oil produces
about 83 per cent. Available technologies and reserves favour such
an adjustment, particularly in the electric power sector;
(c) Replace fossil
fuel combustion with alternative energy technologies;
(d) Eliminate net forest
loss by more careful management of development in forest areas and
by large scale reforestation;
(e) Remove carbon
dioxide from the flue gas of thermal power plants for disposal in
the deep ocean. They account for 15 per cent of carbon dioxide
emissions.
The first four of these measures can serve more
than one environmental and economic purpose. Even if the worst
scenario does not come about, the world would benefit in other
respects by taking these measures now. Other greenhouse gases that
could be controlled to varying degrees, based on present technical
knowledge, are methane, nitrous oxides, and tropospheric ozone.
Priority should be given to detailed studies of the sources of
these gases, their interactions in the atmosphere, and technologies
that would reduce their emissions.