 Sources and sinks of GHGs
Sources
The major anthropogenic (man-made) sources of
GHGs are:
 Energy production and industry
The anthropogenic activity producing the largest quantity of GHGs (particularly CO2),
is the production and use of energy. At least half of the warming that has already
occurred is due to CO2 and its contribution is expected to remain the same even
in the future.
Other significant sources of CO2 are: the burning of fossil fuels - coal,
petroleum, natural gas - for industrial, commercial, transportation, residential and other
uses. Small amounts of methane (CH4) are emitted during coal mining and the
venting of natural gas.
The production and use of CFCs and other
halocarbons during industrial processes also emits GHGs. The Montreal Protocol concerns
issues related to these substances.
Changes in land use patterns
Deforestation, biomass burning (including fuelwood) and other changes in land-use practice
release carbon dioxide, methane and nitrous oxide into the atmosphere.
Agriculture and livestock
Methane is released from rice cultivation and livestock systems; nitrous oxide is released
when nitrogenous fertilizers are used.
Waste
Methane is also released from landfills.
Sinks of GHGs
Sinks refer to 'storehouses' of the gases - places where they
can be sequestered.
The oceans are, perhaps, the biggest sink and contain
about 40 000 GtC (giga tonnes of carbon). By contrast, the atmosphere contains 750 Gt and
the terrestrial biosphere, 2200 Gt (IPCC 1996).
Vegetation
and soil also have the capacity to sequester carbon. Soils also remove methane to some
degree.
Atmospheric methane, however, is removed mainly by its
oxidation by the OH radical in the troposphere.
Halocarbons do not have any significant mechanism of
removal. They persist in the upper atmosphere (mid-upper stratosphere) for long periods
and break down in the presence of sunlight. Nitrous oxide may also break down in this
manner.
Regional distribution
of carbon dioxide emissions
It is ironical that the contribution of
developing nations to GHG emissions is less than half of that emitted by the developed
countries. The latter have been responsible for more than 60% of the stock of GHGs. Over
the last 100 years India has contributed only 2% of the total carbon emissions from fossil
fuel burning (Marland G, Boden TA and Andres R J. 2000).
References
Baumert
K A and Kete N. 2001
The US, developing countries and climate protection: leadership or
stalemate?
In Climate Issue Brief: World Resources Institute. Washington,
DC: World Resources Institute. 12 pp.
IPCC. 1996
Climate Change 1995: The Science of Climate Change
Cambridge: Cambridge University Press. 572 pp.
Marland
G, Boden T A and Andres R J. 2000
Global,
Regional and National CO2 Emissions
In Trends: a compendium of data on global change. Oak Ridge, Tennessee, USA:
Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department
of Energy |
