সেউজী ধৰণী
Global
Warming --- a threat to the mankind
Compiled by
Sameena
Taskin Sadiq*
Introduction
With the advent of civilization man has adopted modern scientific methods
to monopolize the management of all natural resources. This managerial
capability has brought him to the brink of unprecedented environmental problem.
Unplanned urbanization and industrialization have been adding more problems to
the environment daily. Two human activities --- the burning of fossil fuels and
destruction of forests have resulted in increasing carbon dioxide concentration
in the atmosphere. After World War II, the burning of fossil fuel in the world
increased many folds. Similarly, over exploitation and unplanned destruction of
forest also increased to a great extend. Due to these human activities our
ecosystem gets disturbed and many environmental problems arise. Global Warming
is one such problem and most modern attention to this problem is now begun with
discussion of depletion of Ozone layer. Ozone is a molecular form of Oxygen.
The Ozone layer is a relatively thin strata of these molecules set in the lower
portion of the Earth’s stratosphere. Depletion of the Earth’s Ozone layer has
resulted in a large increase in Ultra Violet Radiation reaching the surface of
the earth that caused many health problems. The United Nation Environmental
Programme (UNEP) has therefore, identified Global Warming as a great threat to
the mankind and rightly chosen a slogan “Global Warming: Global Warning” to
alert the human race. In this project work, therefore, an attempt would be made
to understand what global warming and ozone depletion is and how these happen
as well as their remedies
Global Warming
Global warming is the term used to describe a gradual increase in the
average temperature of the Earth's atmosphere and its oceans, a change that is
likely to be changing the Earth’s climate forever permanently. While many view
the effects of global warming to be more substantial and more rapidly occurring
than others do, the scientific consensus on climatic changes related to global
warming is that the average temperature of the Earth has risen between 0.4 and
0.8 °C over the past 100 years.
How the Earth Become Warm
The life on Earth depends on energy from the sun. About 30% of the
sunlight that beams towards the Earth is deflected by the outer atmosphere and
scattered back into space. The rest reached the green planet’s surface and is
reflected upwards again as a slow moving energy called infrared radiation. As
it rises infrared radiation is absorbed by some gases like water vapour,
carbon-di-oxide, ozone and methane which slow the escape process of infrared
radiation from the atmosphere. Although these gases make up only about 1% of
the Earth‘s atmosphere, they regulate the climate of the planet by trapping
heat and keep the Earth atmosphere warm enough for inhabitation. This process
of warming is similar to that of a greenhouse atmosphere where plants are
grown, especially in the winter. The glass panels of the greenhouse let in
light but keep heat from escaping. This causes the greenhouse to heat up and
keeps the plants warm enough to live in the winter. As the process of warming
in a greenhouse and the Earth is similar, the phenomenon of keeping the Earth
warm is called Greenhouse Effect and the gases that trap heat are called
Greenhouses Gases.
Importance
of Greenhouse
The greenhouse effect is important.
Without the greenhouse effect, the Earth would not be warm enough for
inhabitation. This phenomenon of warming was discovered by Joseph
Fourier in 1824. Later, scientists found that in the absence of the greenhouse
effect, the Earth’s average surface temperature of 14 °C (57 °F) could be as
low as −18 °C (−0.4 °F) where no vegetation is possible . But if the greenhouse effect becomes stronger, it could make the Earth
warmer than usual. Even a little extra warming may cause problems for humans, plants,
and animals. Scientists
have observed that the increased volumes of carbon dioxide and other greenhouse
gases released by the burning of fossil fuels, land clearing, agriculture, and
other human activities, are believed to be the primary sources of the global
warming that has occurred over the past 50 years. Many scientific observations
recorded that the average facade temperature of the globe has augmented more
than 1 degree Fahrenheit since 1900 and the speed of warming has been almost
three folds since 1970. Scientists are now of the opinion that lacking of big
curbs in greenhouse gas discharges, the 21st century might see temperatures
rise of about 3 to 8 degrees.
Causes of
Global Warming
There are three primary greenhouse gases which are responsible for global
warming. These are: carbon dioxide, methane, and nitrous oxide, all of which
naturally exist in the earth’s atmosphere. These three gases are required to
regulate the atmospheric temperature of the Earth. However, the problems arise
when there is a surplus of these gases in the atmosphere. As their atmospheric
levels increase, so does their ability to trap heat resulting in a rise in
global temperature. Carbon dioxide is released into the atmosphere by the
combustion of solid waste, fossil fuels, wood and wood products. Methane
emissions are a direct result of the production and transportation of coal,
natural gas, and oil. The raising of livestock and the decomposition of organic
waste also contribute to the amount of methane emitted into the atmosphere.
Nitrous oxide emissions are a result of agricultural and industrial activities
as well as the burning of solid waste and fossil fuels.
There are
also greenhouse gases which do not occur naturally. These are generated by
human activity. Examples of these gases include; chlorofluorocarbons found in
refrigeration devices, hydrofluorocarbons, and perfluorocarbons. Each varies in
their heat trapping ability and combined with those gases originally present in
the atmosphere; serves to retain a sufficiently larger amount of heat then
would naturally be retained.
Effect of Global Warming
Global warming over periods of time has many implications for natural
ecosystems. If the earth's warming trend continued into the next decade the
earth may enter a period of climate change unlike any of the past. Analysis of
temperatures shows that the earth has warmed an average of 0.5 Celsius over the
past 100 years. This is due to the increase in greenhouse gases. In 1990 the
IPCC concluded that if human activities contributing to the greenhouse effect
are not checked, the global temperature will be 3 Celsius before the end of the
next century. A climate change of this amount has not occurred since the last
10,000 years ago.
There are numerous effects of global warming. Ecosystems will be
destroyed as a result in the increase in temperature. Hence many animals that
live in cold temperatures will disappear. As a result of global warming many
regional and seasonal variations will occur. The land in the north will become
instable due to the permafrost layer decaying. Other problems may be loss of
winter, increased disease and pest infestations, urban smog, and summer heat
stress. Droughts, forest fire hazards and intense storms will occur as a result
to shifts in winds and rainfall patterns. Higher sea levels as a result of
water's thermal expansion and large masses of ice melting. Insect pests will
migrate faster with increase of climate and then will attack more trees and
plants because of larger numbers. Fish will be affected because of the increase
in temperature will change migration routes. As a result of climate change many
habitats will change and disappear because they cannot survive in warmer
temperatures. Hence many animals will die as a result of their environment
disappearing. The frozen north will be less frozen because of the permafrost
melting. There will be an increase in icebergs because of increased glacial
flow off land. People have effects on their health, they will experience heat
stress, warmer winter will be less cold and therefore fewer cold related
problems, disease will increase in warmer temperatures. Food prices will
increase as they become less populated because of the heat. These are just a
few of the numerous effects global warming has on the earth.
Mitigation
There are many things that can be done to reduce global warming and insure
the earth stays inhabitable. People can become aware of the problems and lower
the emissions of greenhouse gases. They can use their vehicles less because of
the burning of fossil fuels. Buying of goods that are eco-friendly is helpful
to reduce greenhouse gases. Recycling not only cuts down on waste but also
products made from recycled materials require less energy to make. Similarly, the
governments must play a major role in the reduction of global warming. Some
plan may be developed to fight global warming with the following aspects:
1. Limiting and
reducing greenhouse gases
2. Anticipating
and preparing for global warming
3. Improving the
ability to predict and understand global warming.
The Energy Efficiency and Alternative energy act has also been
established in some countries to stop and prevent global warming. Programmes
like plantation of trees that can survive in warm temperature is also
helpful. Zoning by law can forbid
construction where floods are likely to occur. Framers try new crops that can
survive in warmer temperatures.
However, developing countries find it difficult to reduce their use of
fossil fuels and natural resources such as forests, because this is their only
way out of poverty. Therefore agreements have to be made so that developed
countries share their new technology and provide financial help to developing
countries to help them reduce their emissions. These are just some ways in
which world is adapting to fight with global warming. However, far more needs
to be done to our world and allow life to continue the way it is now.
What is
Ozone?
Ozone is a
relatively simple molecule, consisting of three oxygen atoms bound together. It
is created when solar rays hit a molecule of O2 and causes it to
split apart. If one of these freed atoms hits another O2, ozone (O3)
is formed. Ozone is broken down naturally in the stratosphere by sunlight and
chemical reactions with compounds containing nitrogen, hydrogen, and chlorine.
In a normal atmosphere the ratio of ozone being created to ozone breaking down
remains fairly constant.
What is Ozone layer?
The ozone layer is a deep layer in the
stratosphere, encircling the Earth that
has large amounts of ozone in it. Ozone can also occur in small amounts at
ground level. Ozone's unique properties allow it to act as a protective layer
around the Earth. It acts like a sunscreen, filtering damaging UV rays. This
layer is thickest at the poles and thinnest at the equator.
Importance of Ozone layer
As was already stated, ozone is a protective layer
shielding Earth from harmful UV rays. In order to understand this concept one
must understand UV rays. UV radiation is a form of radiant energy from the sun.
Different forms are classified based on their wavelength and these are: gamma
rays, x-rays, UV, visible light, infrared radiation, microwaves, and
radiowaves. UV radiation is in three forms. UV-A (320-400nm) passes directly
through the ozone layer and is the least harmful; UV-B (280-320nm) is very
harmful and; UV-C (200-280nm) is the most harmful however, all of this
radiation is absorbed by oxygen and ozone. UV-B radiation is of most concern to
us on Earth. As there are factors which affect ozone there are also factors
which affect UV: latitude, season, time of day, altitude, cloud cover, rain,
and air pollution.
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| With the Ozone layer |
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| Without the Ozone layer |
However, when the balance between production and
destruction is disrupted then ozone depletion occurs. According to scientists
the amount of ozone present was constant until the late 1970's. The Antarctic
has been suffering severe depletion since 1979. The "hole" here
occurs during September and November. By the late 1980's ozone had decreased as
much as 60%. In 1987, 15% of the Southern Hemisphere was affected. In October
1992, total ozone loss was at 105 DU (Dobson Unit) over the South Pole. Ozone
loss connected with the Antarctic is now occurring over New Zealand, Australia,
South America, North America, Europe, and Russia.
Causes of Ozone Depletion
There are three main contributors to the
ozone problem: human activity, natural sources, and volcanic eruptions.
However, according to scientists, certain man-made chemicals are major
contributors to the problem. These chemicals are called Ozone-Depleting
Substances (ODS) and include many gases containing chlorine and bromine, such
as: chlorofluorocarbons (CFCs, substances containing chlorine, fluorine and
carbon) used in refrigerators and blowing agents for foams; the
"Halons", used for firefighting; methyl bromide, used in agriculture.
Since the Second World War, CFCs have been widely employed, mainly because they
are chemically inert and, as a consequence, non toxic and extremely stable.
CFCs do not dissolve in rain: after several years, carried by the winds, they
reach the stratosphere without being modified. Here their molecules are broken
down by the intense UV light, and free chlorine atoms are created by this
degradation. Each chlorine atom can destroy several thousands of ozone
molecules before being removed from the atmosphere: chlorine is a catalyst for
the ozone depletion. Bromine (e.g. from
methyl bromide, used by farmers as a fumigant) is even more effective than chlorine.
Moreover, there are dramatically different effects
depending upon its location. Near Earth's surface, where ozone comes into
direct contact with life forms, it primarily displays a destructive side.
Because it reacts strongly with other molecules, large concentrations of ozone
near the ground prove toxic to living things. At higher altitudes, where 90
percent of our planet's ozone resides, it does a remarkable job of absorbing
ultraviolet radiation. In the absence of this gaseous shield in the
stratosphere, the harmful radiation has a perfect portal through which to
strike Earth.
Effect of Ozone depletion
The effects of ozone depletion are not yet fully
understood, but we do know that they are potentially severe. Ozone, because of
UV radiation, warms the atmosphere, however because of the use of CFCs the
levels of ozone are declining and thus the stratosphere cools. Also, levels of
carbon dioxide are on the rise globally. This traps the heat in the lower
atmosphere and causes the stratosphere to become cooler. This increases the
chances of an Arctic ozone hole appearing. Ozone depletion may also affect
climate, indirectly, because of phytoplankton. If these microscopic marine
plants are destroyed levels of carbon dioxide will rise which will enhance the
greenhouse effect. Also, increasing levels of UV radiation will cause the
reactivity of potentially harmful substances to become enhanced. This radiation
has many effects on all living things. Some have the ability to adapt but some
are harmed by even a small change in UV levels. This radiation causes adverse
effects on humans and these effects are becoming worse as we spend more hours
in the sun. This exposure can cause skin cancer, eye damage and cataracts, and
immunosupression. Skin cancer is caused by too much sun. When a person sunburns
they are having an extreme reaction to UV-B radiation. The more sunburns a
person receives, the greater their chances of getting skin cancer. There are
two types of skin cancer: non-melanoma and melanoma. Non-melanoma skin cancers
are not lethal if treated whereas melanoma cancers are very dangerous. It is
expected that one is seven Canadians will get some form of skin cancer in their
lifetime. UV-B radiation also affects the eye. It can damage the lens, cornea,
retina, and the conjunctiva. An example of what UV radiation can do can be seen
through snow blindness. Another result of exposure to UV-B radiation is
cataracts. "Cataracts are a clouding of the eye's lens and are the leading
cause of permanent blindness worldwide." UV-B radiation also weakens the
body's immune system and this increases the chances of infectious diseases and
cancers. Researchers now know that autoimmune-deficiency syndrome (AIDS) can be
activated by exposure to UV radiation. UV-B radiation affects not only humans
but other living plants and animals as well. The problem for these populations
is that they cannot artificially protect themselves from these harmful rays.
Plants are a requirement for all forms of life because they are primary
producers of oxygen; they store carbon dioxide, and help prevent soil erosion.
With terrestrial plants the amount of UV-B radiation present can decrease
growth, photosynthesis, and flowering. Such adverse affects can profoundly hurt
the food web. UV radiation on freshwater and marine plants can also be very
harmful.
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Depletion of Ozone layer
How to fight against Ozone Depletion
The international community must work together in
the fight against ozone depletion. The first step in eliminating this problem
is for governments to recognize that there is a problem and that action must be
taken immediately. In 1977 the United Nations Environment Programme began
assessing ozone depletion. Two international agreements were reached in the
1980's: the Vienna Convention for the Protection of the Ozone Layer (1985) and
the Montreal Protocol on Substances that Deplete the Ozone Layer (1987). This
convention laid the foundation for the Montreal Protocol. The Montreal Protocol
was first signed on September 16, 1987 and it required that all countries who
signed to reduce CFC and halon emissions. The London Amendment, after the
Montreal Protocol, involved phasing out damaging CFCs and halons. At this time
methyl chloroform became a controlled substance, as did carbon tetrachloride.
This agreement had to be strengthened and thus came the Copenhagen Amendment.
This required that all signatories would phase out halons by 1994; CFCs, methyl
chloroform, and carbon tetrachloride by 1996 and; HCFCs by 2030. In order for
the Montreal Protocol to be a success it was a requirement that all nations,
both industrialized and developing, work together. The Interim Multilateral
Fund was created by developed countries to assist developing countries in the
fight against ozone depletion.
Summery
Global Warming and Ozone Depletion are not hard concept to grasp and it
is extremely important that all people be willing to understand this issue.
There are many things that can be done to reduce global warming and insure the
earth stays inhabitable. We must all take the time to educate ourselves and
others and make an attempt to help protect the environment around us. We may
not feel the harmful effects of what we are doing now, but if we do not take
immediate action future generations will suffer.
In
preparing this write-up various web sites on Global Warming and Ozone layer were
visited ---Authoress
*Student,
IVth semester (EC), Sikkim Manipl Institute of Technology (SMIT), Sikkim
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