ENVIRONmental POLLUTIION
The major environmental problem today is
global warming or
climatic change due
to accumulation of several gases like carbon
dioxide, and nitrous
oxide, Chlorofluorocarbons, along with water
vapour in the
atmosphere causing greenhouse effect and depletion of
ozone layer in
stratosphere affecting the several aspects of humanity
on planet earth.
Greenhouse effect
The earth receives energy from the sun,
which warms the earth’s
surface, as this
energy passes through the atmosphere, a certain
percentage (about 30)
gets scattered. Some part of this energy
is
reflected back into
the atmosphere from the land and ocean surface.
The rest (70%)
actually remains behind to heat the earth. In order to
establish a balance,
therefore, the earth must radiate some energy
back into the
atmosphere. As the earth is much cooler than the sun, it
does not emit energy
as visible light. It emits thorough infrared or
thermal radiation.
However, certain gases in the atmosphere form a
sort of blanket
around the earth and absorb some of this energy
emitted back into the
atmosphere. Without this blanket effect, the
earth would be around
30
o
C colder than it
normally is. These gases
like carbon dioxide,
methane, and nitrous oxide, along with water
vapor, comprise less
than one per cent of the atmosphere. They are
called “greenhouse
gases”, as the working principle is same as that
which accurs in a
greenhouse. Just as the glass of the greenhouse
prevents the
radiation of excess energy, this “gas blanket” absorbs
some of the energy
emitted by the earth and keeps temperature levels
intact. This effect
was first recognized by a French Scientist, Jean
Baptiste Fourier, who
pointed out the similarity in what happens in
the atmosphere and in
a greenhouse. Hence the term the “greenhouse”
effect. The
greenhouse effect is essentially a positive, life-giving
process that
maintains the earth’s temperature at levels tolerable by its
life forms.
This gas blanket has been in place ever since
the creation of the
earth. Since the industrial
revolution, human activities have been
releasing more and
more of these greenhouse gases into the
atmosphere. This
leads to the blanket becoming thicker and upsets the
“natural greenhouse
effect”. Activities that generate greenhouse gases
are called ‘source’
and those that remove them are known as ‘sinks’.
A balance between
‘sources’ and ‘sinks’ maintains the levels of these.
Humankind upsets this balance when new sources
that interfere
with the natural
sinks are introduced. Carbon dioxide is
released
when we burn such
fuels as coal, oil, and natural gas. In addition,
when we destroy
forests, the carbon stored in the tree escapes as
carbon dioxide into
the atmosphere. Increasing agriculture activities,
changes in land-use
patterns, and other sources lead to rising levels of
carbon dioxide,
methane and nitrous oxide . Industrial processes also
release artificial
and new greenhouse gases like CFCs
(chloroflurocarbons).The
resulting enhanced greenhouse effect is
more commonly
referred to as global warming or climate change.
240 Watt per m
3
Potential
Effects of Greenhouse effect or Global
Warming
Some potential
effects on agriculture and others
associated with
climate change are
listed in the following (From U.S. Climate Action
report). Therefore,
climate change is a threat to humanity!
1. Biomass
production- decrease in productivity of crops and
grazing lands directly
through changes in temperature and
precipitation,
frequency of droughts/floods and indirectly
through changes in
soil quality, pests, and diseases, shifts in
agro ecological
zones. Alteration in the species diversity and
die-back of tropical
forests and grasslands due to change in
the pattern of
rainfall etc.
2. Decline
in soil quality- due to decline in soil structure,
increased soil
crusting and compaction, accelerated soil
erosion, leaching
& acidification, salinization, and organic
carbon decline and
nutrient depletion.
3. Water
resources & quality- warmer climate will change
rainfall &
snowfall patterns leads to increased droughts &
floods, melting of
glaciers and polar ice sheets resulting in
accelerated sea-
level rise affecting freshwater resources,
coastal agriculture,
fisheries & aquaculture, forests, natural
ecological systems,
human settlements, loss of land due to
inundation &
erosion, salt-water intrusion, increased sediment
load, eutrophication
etc.
4. Air
quality- increase dust concentrations, greenhouse gases,
industrial pollution
etc.
5.
General – warmer and wetter climate will favour the growth
and spread of vector
borne diseases like malaria & dengue
affecting human
health increased frequency of storm and
other extreme event
caouse decrease in hydro-power
generation, loss of
infrastructure, tourism, disruption in
transport routes,
human settlements, industries, building
Impacts of Climate Change
C to
4
Impact of rise in temperature of 1.8
o
C
o
Forests
Coastlines
Biodiversity
Agriculture
Depletion of Ozone layer
The earth atmosphere is made of numerous gases. In 1983.
C.F.Schonbein first
discovered the presence of ozone molecules in the
central part of the
atmosphere between altitudes of 15-35 km (from
the ground level) in
the stratosphere and that it absorbed the harmful
ultraviolet rays of
the sun. The ozone layer by absorbing the harmful
ultraviolet rays of
the sun determines the temperature structure of the
stratosphere and
safeguards life on the planet. It is believed that for
millions of years the
atmospheric composition had not undergone
much change. However,
in the past half-century humans have upset
the delicate balance
of nature by releasing into the atmosphere
harmful chemicals
that are gradually destroying the lie-protecting
layer.
The WMO has played a major role in identifying
the problem
of ozone depletion.
The UNEP, United Nations Environment
Programme, initiated
the Vienna Convention, attended by more than
30 countries. This
led to the landmark protocol on Substances that
deplete the Ozone
layer, which was depletion of the ozone and called
Montreal. It listed
the substances, which cause depletion of the ozone
and called for about
50% reduction of CFCs by the year 2000.
Chloroflorocarbon or
CFC is said to be one of the main gases
responsible for the
depletion of ozone layer and greenhouse effect. It
is emitted mainly
from air conditioners, refrigerators and aerosols or
spray can
propellants. Another widely used chemical that is a threat to
the ozone layer is
methyl bromide. This can release bromide, which is
30 to 50 times as
destructive to ozone as chlorine. It is used as a
fumigant (fumes used
as disinfectants for control of soil-borne
pathogens) for soil
and commodities and as a transport fuel additive.
It has to be clearly
stated that the expected recovery of the ozone
layer would have been
impossible without the Montreal Protocol on
Substances that
Deplete the Ozone Layer (1987), which called for a
phased reduction of
all ozone depleting substances. .
Methane
Emission from Rice Fields
Wetland rice fields
have recently been identified as a major
source of atmospheric
methane. Methane is produced as the terminal
step of the anaerobic
breakdown of organic matter in wetland rice
soils. In a natural wetland, flooding a rice field cuts
off the oxygen
supply from the
atmosphere to the soil, which results in anaerobic
fermentation of soil
organic matter. Methane is a major end product
of anaerobic
fermentation. It is released from submerged soils to the
atmosphere by
diffusion and ebullition and through roots and stems of
rice plants. Recent
global estimates of emission rates from wetland
rice field’s range
from 20 to 100 Tg/year (IPCC 1992). The
current
burden of methane in
the atmosphere is is approximately 4700 Tg (1
Tg=1 million tons),
and the global annual emission is estimated to be
500 Tg with an
apparent net flux of 40 Tg/year. Continued increase in
atmospheric methane
concentrations at the current rate of
approximately 1% per
year is likely to contribute more to future
climatic change than
any other gas except carbon dioxide. Methane is
exclusively produced
by methanogenic bacteria that can metabolize
only in the strict
absence of free oxygen and at redox potentials of
less than- 150 mV. In
tropical flooded rice soils, where soil
temperatures are
25-30
o
C, methane production
is rapid in alkaline and
calcareous soils(may
start hours after flooding)and slow in acid soils
(formed five or more
weeks after flooding). Methane production is
negatively correlated
with a soil redox potential and positively
correlated with soil
temperature, soil carbon content, and rice growth.
Easily degradable
crop residues, fallow weeds, and soil organic
matter are the major
source for initial methane production. At later
growth stages of
rice, root exudates, decaying roots, and aquatic
biomass seem to be
more important.
Conditions favouring methane production and
emission in
rice
fields
• Anaerobic
conditions in wetland soils
• Disturbance
of wetland soil by cultural practices
favours
soil trapped methane
to escape to atmosphere through
ebullition
• Use
of organic amendments
• Application
of chemical fertilizers
Mitigation options
• Prevent
of submergence of rice fields where ever
feasible
without affecting the
rice productivity
• Increased
adoption of direct seeding (wet and dry seeding)
instead of
transplanting
• Crop
diversification in rice based cropping systems
• Water
management- intermittent drying and mid-season
drainage in
controlled water situations
• Growing
rice cultivars having traits with low methane
emission potential
• Use
of sulfate-containing fertilizer reduces methane
emission
• Minimization
of soil disturbance during growing season to
reduce escape of
entrapped methane
• Use
of properly composted organic amendments
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