Harmful Effects Of Ozone Layer Depletion
The Earth’s atmosphere is made up of different layers. The layer
closest to the surface is called the troposphere which extends from the
Earth’s surface up to about 10 kilometers. The ozone layer is
located above the troposphere in the stratosphere (10 Ian to about 50
Ian high). Stratospheric ozone is Earth’s natural protection for all
life forms, shielding our planet from harmful ultraviolet-B (UV-B)
radiation. UV- B radiation is harmful to humans, animals, and plant
life. The ozone layer is being destroyed by certain industrial chemicals
including ozone depleting refrigerants, halos, and methyl bromide, a
deadly pesticide generally used on crops. Ozone depletion damage gets
much worse when the stratosphere is very cold. This has been the case
for the past two years, causing extensive ozone depletion. This past
winter, ozone depletion reached the most severe levels ever recorded
over the Northern Hemisphere. Western United States ozone levels also
continue to drop 3- 4 per cent per decade. Even if all of our
efforts to stop harmful emissions are successful, the ozone layer is not expected to begin recovery until around 2020 at the earliest. Ozone depletion occurs in many places in the Earth’s ozone layer, most severely in the Polar Regions. NOAA scientists have travelled to Antarctica to study the ozone depletion that has been occurring there since the late 1970s. In 1986, soon after the reported discovery of the ozone hole, Agronomy Lab (now ESRL) scientist Dr. Susan Solomon led a team of 16 scientists, reached to the conclusion that human- produced trace gases containing chlorine and bromine were causing the ozone hole. This unique record from the South Pole station clearly shows the annual development of the spring time Antarctic ozone depletion over the past two decades.
Ozone and the NOAA
Ozone depletion at the South Pole can also be viewed from another
perspective through the images created from data collected by the NASA
TOMS satellite, and the NOAA SBUV-2 instruments aboard NOAA satellites.
Continued surveillance is necessary in order to verify the expected
recovery of the ozone layer. Arctic Ozone Significant depletion also
occurs in the Arctic ozone layer during the late winter and spring
period (January – April). However, the maximum depletion is generally
less severe than that observed in the Antarctic, with no large and
recurrent ozone hole taking place in the certain industrial processes
and consumer products result in the atmospheric emission of
ozone-depleting gases. These gases contain chlorine and bromine atoms,
which are known to be harmful to the ozone layer. These gases eventually
reach the stratosphere, where they are broken apart to release
ozone-depleting chlorine atoms. Methyl bromide is another important area
of research for NASA scientists.
Primarily used as an agricultural fumigant, it is also a significant
source of bromine to the atmosphere. Although some ozone depleting gases
also are emitted from natural sources, emissions from human activities
exceed those from natural sources. NOAA researchers regularly measure
ozone depleting gases in the lower and upper atmosphere and attempt to
account for observed changes. As a result of international regulations,
ozone depleting gases are being replaced in human activities with
‘ozone-friendly’ gases. The world’s population is a stakeholder in
decisions that limit the emissions of ozone depleting gases. In 1987,
the international community put in place a treaty known as the Montreal
Protocol on substances that deplete the Ozone Layer. Since that initial
treaty was ratified, periodic assessments and updates have been
conducted. The Protocol success has derived in part from these
scientific updates on the science and observation of ozone depletion
made over the past 15+ years. Global Dimming “Each year less light
reaches the surface of the Earth.
No one is sure what’s causing ‘global dimming’ or what it means for
the future. In fact most scientists have never heard of it. But it has
become a cause of concern today and several scientists are working on
it.” What is global dimming? Global dimming is the gradual reduction in
the amount of global hemispherical irradiance (or total solar
irradiance) at the Earth’s surface or in other words the reduction of
heat reaching the earth is known as Global Dimming. Causes and Effects
.. Though the actual cause of Global dimming is yet to ascertain yet
some scientists think that it’s nothing to do with changes in the amount
of radiation arriving from the sun, Although that varies as the sun’s
activity rises and falls and the Earth moves closer or further away, the
global dimming effect is much, much larger and the opposite of what
would be expected given there has been a general increase in overall
solar radiation over the past 150 years.
That means something must have happened to the Earth’s atmosphere to
stop the arriving sunlight penetrating. The few experts who have studied
the effect believe it’s down to air pollution. Tiny particles of soot
or chemical compounds like sulphates reflect sunlight and they also
promote the formation of bigger, longer lasting clouds. “The cloudy
times are getting darker”, says Cohen, at the Volcani Centre. “If it’s
cloudy then darker, but when it’s sunny things haven’t changed much.”
Global dimming creates a cooling effect that may have partially masked
the effect of greenhouse gases on global warming. Fossil fuel use, as
well as producing greenhouse gases, creates other by-products. These
by-products are also pollutants, such as sulphur dioxide, soot, and ash.
These pollutants however, also change the properties of clouds.
Clouds are formed when water droplets are seeded by air-borne
particles, such as pollen. Polluted air results
in clouds with larger number
of droplets than unpolluted clouds. This then makes those clouds more
reflexive. More of the sun’s heat and energy is therefore reflected back
into space. It is currently thought that the effect of global dimming
is probably due to the increased presence of aerosol particles in the
atmosphere. Aerosol particles and other particulate pollutants absorb
solar energy and reflect sunlight back into space. The pollutants can
also become nuclei for cloud droplets. It is thought that the water
droplets in clouds coalesce around the particles. Increased pollution,
resulting in more particulates, creates clouds consisting of a greater
number of smaller droplets, which in turn makes them more reflective,
therefore bouncing more sunlight back into space. Clouds intercept both
heat from the sun and heat radiated from the Earth. Their effects are
complex and vary in time, location and altitude. Usually during the
daytime the interception of sunlight predominates, giving a cooling
effect; however, at night the re-radiation of heat to the Earth slows
the Earth’s heat loss. The impacts of global dimming itself, however,
can be devastating. Millions from Famines in the Sahel in the 70s and
80s .
The death toll that global dimming may have already caused is thought
to be massive. Research Climatologists studying this phenomenon believe
that the reflection of heat have made waters in the northern hemisphere
cooler. As a result, less rain has formed in key areas and crucial
rainfall has failed to arrive over the Sahel in Northern Africa In the
1970s and 1980s, massive famines were caused by failed rains which
climatologists had never quite understood why they had failed.
The
answers that global dimming models seemed to provide, the documentary
noted, has led to a chilling conclusion: “what came out of our exhaust
pipes and power stations [from Europe and North America] contributed to
the deaths of a million people in Africa, and afflicted 50 million more”
with hunger and starvation. Billions are likely to be affected in Asia
from similar effects. Scientists said that the impact of global dimming
might not be in the millions, but billions. The Asian monsoons bring
rainfall to half the world’s population. If this air pollution and
global dimming has a detrimental impact on the Asian monsoons some 3
billion people could be affected. It is also concluded that the
imbalance between global dimming and global warming at the surface leads
to weaker turbulent heat fluxes to the atmosphere. This means globally
reduced evaporation and hence precipitation occur in a dimmer and warmer
world, which could ultimately lead to a more humid atmosphere in which
it rains less.
This phenomenon of ‘global dimming’ is now being accepted as a
reality by scientists the world over. Some of them believe that this may
help in protecting the planet from global warming, according to a
report in the Nature. There’s massive evidence that the world is indeed
getting warmer. But it’s also getting darker. In fact, many scientists
believe that global dimming puts the brakes on the warping of our
planet.
Without global dimming, global warming would be much, much
worse! And there’s no telling which will win in the end, heat or cold.
Roughly speaking, global dimming is faster and heftier, while global
warming is slower and more gradual. Somewhere down the line, there could
be a threshold, a point where Dimming beats Warming or Warming beats
Dimming. Whosoever be the winner the sufferer is the human being. NOAA
researchers from several laboratories have participated in all of these
scientific updates and have also been active in preparing outreach
documents to communicate the science of ozone depletion to the public.