Can Deforestation bring down oxygen level?
by
Dr. Nitish Priyadarshi
Deforestation, or the removal of forests, is a major problem that has
devastating effects all over the world. Europeans began clearing forests
more than 500 years ago. The invention of modern machinery made the
process even easier. By the end of the 19th century, most of the
deciduous forest of North America, Australia and New Zealand had been
cleared. In the 21st century, tropical forests are being cut and burned
at alarming rates in South America and Southeast Asia. Asia as a whole
has already lost about 90 percent of its forests.
With forest resources--"the lungs of the Earth"-- under attack in many
regions, some have raised concerns about the planet's oxygen supply.
Oxygen is the most abundant chemical element, by mass, in our biosphere,
air, sea and land. Oxygen is the third most abundant chemical element in
the universe, after hydrogen and helium, but mainly in combination with
something else. The stuff is all around us but we don’t see it.
Chemically joined with other elements it accounts for more than a
quarter of Earth’s total weight and almost half the mass of the crust.
Free or dissolved molecular oxygen, however, represents only 0.01
percent of the total crust, hydrosphere, atmosphere, and biosphere taken
together. Only seven of every billion atoms takes the form of molecular
oxygen (O2), plus a neglible quantity as atomic or singlet O and ozone
(O3). If the atmosphere contained much more oxygen, it would be
inflammable. Remove oxygen and only anaerobic bacteria could survive.
How did plants come to alter the atmosphere? The key is the way in which
plants create their own food. They employ photosynthesis, in which they
use light energy to synthesize food sugars from carbon dioxide and
water. The process releases a waste gas, oxygen. Those of us in the
animal kingdom rely on oxygen to metabolize our food, and we in turn
exhale carbon dioxide as a waste gas. The plant use this carbon dioxide
for more photosynthesis, and so on, in a continuing system.
Oxygenic photosynthesis (synthesis by light) is by far the largest and
most familiar source of O2. Upon its introduction at precariously
trivial and fluctuating levels perhaps 2.8 aeons ago, oxygen began to
play a role in the evolution of life and earth’s surface processes.
After that, if not earlier, photosynthetic O2 and perhaps plate
tectonism joined sunlight, gravity, and water as lead players on the
evolutionary stage. Yet, for another 6 to 8 geocenturies it remained at
vanishing low levels as a result of reactions with a variety of reduced
substances.
Nor was oxygen-evolving photosynthesis the only source of oxygen.
Physical splitting of H2O by photolysis was probably the prevailing
initial process. Photolysis of CO2, as well as the release of oxygen
from the metallic oxides as a result of microbial processes and chemical
weathering, are potential but poorly understood sources.
On reaching present levels, perhaps 4 geocenturies ago, oxygen was still
consumed by new reduced volcanic gases, erosionally exhumed carbon, and
reduced matter in the hydrosphere right up to the present. Levels
fluctuate with rates of erosion volcanism, and deforestation. The
indefinite continuity of oxygen is not guaranteed.
Forests, a major source of oxygen to our atmosphere, are very important
to the world’s climate because they help in rain formation and absorb
carbon dioxide (CO2) from the air. As the forests disappear, the weather
will change, and some places will dry up.
There are many benefits that we get from our forests. Some of these
include cleaner drinking water, a home for plants and animals, economic
growth, clean air, recreational opportunities. Another most important
benefit we get from trees is called oxygen. If there were no trees to
give us oxygen to breath, we would not be able to live. Trees are known
as the oxygen supplier to our planet.
As vast forests such as the Amazon are denuded of their beauty and
natural resources, our atmosphere is also seriously altered. The forests
are stripped faster than they can be replanted, and when severely
depleted, photosynthesis is greatly reduced. No photosynthesis, no
oxygen. No oxygen, no life. But deforestation continues at a break neck
speed in many areas of the world.
Earlier in Jharkhand forest played major role in balancing the
temperature difference. But now forest cover is rapidly depleting. Even
one of the biggest forest of Asia popularly known as Saranda Forest is
also decreasing many fold due to rampant iron ore mining in Jharkhand
State. Today the remaining forest areas are unevenly distributed. Bokaro
has only 4.4% of area under forest. Similarly Sahebganj has only 2.31%,
Dhanbad 12.72%, Deoghar 9.5% and Ranchi only 23.37% of area under
vegetation.
At the Survey and Settlement (1902-1910) the area under forests in the
Ranchi districts approximated to about 2,281 square miles, i.e. about 32
percent of the total land area of the district. At the Revisional Survey
and Settlement (1927-1935) this area shrank to about 1,956 square mils,
i.e. 27 percent of the total land area. Thus during a period of 25
years, 325 square miles of forests had disappeared. When the forests
were notified under the Bihar Private Forests Act,1946 and demarcation
was done only about 1,065 square miles were found under forests in this
district. Adding 213 square miles of reserve forests to this, the total
area under forest in this district came to 1,278 square miles. Thus in
course of a decade over 600 square miles of forests disappeared. Now it
has reached up to 23 percent and gradually decreasing further.
The unusually high concentration of oxygen gas on Earth is the result of
the oxygen cycle. The biogeochemical cycle describes the movement of
oxygen within and between its three main reservoirs on Earth: the
atmosphere, the biosphere, and the lithosphere. The main driving factor
of the oxygen cycle is photosynthesis, which is responsible for modern
Earth’s atmosphere. Photosynthesis releases oxygen into the atmosphere,
while respiration and decay remove it from the atmosphere.
Regarding percentage of oxygen present in the atmosphere in the
geological past, it was revealed that air bubbles trapped in fossilized
amber had been analyzed and found to contain oxygen levels of 38%. Yet
today it is well known that the average content of the oxygen in air is
only 19% to 21%. If we believe on the report of oxygen level in the
fossilized amber, it appears that since the early history of our earth
there has been a stunning decrease of 50% in the average oxygen content
of the air we breathe. According to other report, analysis of the air in
various parts of the world today reveals the frightening fact that the
oxygen content continues to decline. In fact in some of the larger and
therefore more polluted cities the oxygen levels have been measured at a
disturbing level of 12 to 15%. Scientists claim that anything under 7%
oxygen content in the air is too low to support human life, even for
short periods.
Historical trends, as explained in Atmospheric Oxygen, Giant Paleozoic
Insects and the Evolution of Aerial Locomotor Performance by R. Dudley,
JExB, show a high of about 35% just before the beginning of the Permian,
with a rapid decline to a low of about 13-14% near the beginning of the
Triassic, then a small spike at about 17% in mid Triassic, another drop
to about 14-15% early in the Jurassic, a sudden climb to about 21% by
mid-Jurassic, then a gentle climb to about 26% early in the Tertiary,
and a rather constant, steady decline to the present "20.9%."
Our planet’s future is under threat as cutting back tropical forests
we put our supply of oxygen gas at risk.
There is difference in opinion about oxygen depletion. Some scientists
believe that our atmosphere is endowed with such an enormous reserve of
this gas that even if we were to burn all our fossil reserves, all our
trees, and all the organic matter stored in soils, we would use up only
a few percent of the available oxygen. No matter how foolishly we treat
our environment heritage, we simply don’t have the capacity to put more
than a small dent in our oxygen supply.
But we can’t take any risk. If forest or plants provide oxygen, cutting
or burning trees is definitely going to affect the oxygen balance of our
atmosphere.
Sources:
Cloud,P. 1988. Oasis in space, earth history from the beginning. W.W.
Norton & Company, New York.
http://www.eia.doe.gov/cneaf/coal/quarterly/co2_article/co2.html
http://en.wikipedia.org/wiki/Oxygen
http://www.sdpo.org.uk/index.php?option=com_content&task=view&id=41&Itemid=61
http://www.columbia.edu/cu/21stC/issue-2.1/broecker.htm
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