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What causes climate change?
I. Natural causes of climate change:
o Solar variation
Solar radiation is so important to Earth’s climate that cha nges in sunlight
could bring about changes in climate. These changes could occur over long
or short time frames. The sun was born 4.55 billion years ago; the star has
been very gradually increasing its amount of radiation so that it is now
20% to 30% more intense than it once was. Whilst, Earth was about the
same temperature back then as it is today due to CO
2 levels were much
greater. The resultant greenhouse warming made up for the lower portion
of solar radiation. The average solar radiation reaching Earth has
revamped only partly during the past few hundred million years.
Sunspots refer to magnetic storms that appear as dark, relatively cool
regions on the sun’s surface -represent short -term r adiations in solar
radiation. Sunspot activity varies on an 11 -year cycle. There is a closer
interaction between Sunspot and Solar radiation. The y both increase when
one rocket. The proportion of solar radiation that reaches Earth’s
atmosphere is known as Insolation. The rate of insolation is affected by the
number of clouds, dust, ash, and air pollution in the atmosphere. Rapid
alters in insolation can also be caused by volcanic eruptions and asteroid
impacts.
o Milankovitch cycles

Significant variations in the amount of solar radiation striking the planet
can be the result of differences in Earth’s position relative to the sun. The
Milankovitch theory describes three variations in Earth’s position relative
to the sun:
(1). Eccentricity: How elliptical the planet’s orbit is .
(2). Obliquity : The angle of Earth’s axis of rotation.
(3). Precession: The amount of the Earth wobbles on its axis of rotation.

The superimposition of these three variations results in a variation in
climate pattern of about 100 000 years. Scientist have shown that the
climate in the past several hundred thousand years, and particularly glacial

advances of the Pleistocene Ice Ages, has been closely associated with the
100 000-year pattern of these Milankovitcch cycles.
o Plate tectonics
The movements of the continents and the processes that cause them are
described by the theory of plate tectonics . Because plate movements
determine the shapes and sizes of continents and ocean basins, plate
tectonics can have a long term effect on climate. When all the
continents are joined into one supercont inent, as they were 225 million
years ago (MYA), most of the land are a is far from the oceans, and a
harsher continental climate dominates. But when the continents are
separate, as they are today, ocean currents are better able to dist ribute
heat because more of the land surface is near an ocean. This results in
less extreme global and regional climat e. Plate motions also reinforce
Milankovitch cycles. If continents are located near the poles, and the
amount of solar radiation reaching the poles is low, snow and ice will
accumulate, which is favorable to pl anetary cooling and perhaps the
initiation of an ice age. Plate tectonics cause geologic act ivity that, in
turn, influences climate. When limestone or other carbonate rocks push
up to form mountain ranges, or when tectonic ac tivity lowers sea level
so that more carbonate rocks are exposed, t hese rocks undergo a
weather ing process that releases the greenhouse gas CO2 into the
atmosphere. But if plate tectonics processes cause the sea lev el to rise,
carbonate breakdown decreases. Plate tectonic movements cause mos t
volcanic eruptions. These can have short – or long term ef fects on the
climate. The aerosols released by the 1991 eruption of Mt. Pinatubo in

the Philippines reduced global insolation by 5% and decreased average
global temperature by about 0.9°F (0.5°C) the following year. As a
re sult, the United States had its t hird wettest and coldest summer in 77
years . In addition, extremely rare, but incredibly large, eruptions of
flood basalts produce very fluid lava that covers millions of square
miles ( km) with extremely thick flows. These violent eruptions propel
ash, dust, and aerosols into the stratosphere, block sunlight, and cause
global cooling. Conversely, the eruptions release CO2, which causes
greenhouse warming. If the basalt eruption is rich in sulfur gases, the
sulfur combines with water vapor to produce sulf uric acid haze. Sulfur-
and nitrogen oxide gases in the atmosphere combine with water vapor
to form sulfuric and nitric acids, which later fall as acid rain , rain that
is more acidic than natural rainwater. Acid rain can damage plants and
dissolve shells and have many other negative effects. Similarly,
asteroid impacts can cause climate change as enormous amounts of
particles are thrust into the air and block sunlight, leading to global
cooling. On the other hand, sulfur gases, CO2, and water vapor are
green house gases that cause global warming. Mass extinctions are
possible results of asteroid impacts or flood basalt eruptions.
II. Human causes of climate changes

o G r een h ou se ga ses
Like natural processes, human activities remove carbon from
reservoirs where it has long been sequestered a nd send it into the

atmosphere. Fossil fuel burning, the most dominant among these
activities, releases CO2 that had been stored in the Earth for millions
of years. Burni ng rain forest to create agricultural or ranch lands, a
technique known as slash- and – burn agriculture that occurs in the
tropics, releases the 34 Climate CO2 stored in forests. Deforestation
also decreases the amount of CO 2 that is absorbed from the
atmosphere by plants. Other types of vegeta tion, such as crops and
grassland, are much less efficient at removing CO2 from the
atmosphere. Like CO2 levels, methane levels have been rising
precipitously for the past century as human populations have exploded.
About 60% of the methane that enters the atmosphere now c omes from
human activities. Rice production, which feeds a large percentage of
the Earth’s people, contributes the largest share of methane production.
Another source, the gas passed by farm animals, may seem laughable,
but its impact is highly significant due to the e normous increases in
meat pro duction in recent decades. Storing li quid manure in tanks at
massive livestock factory farms causes more methane to enter the
atmosphere (although dry manure sitting in a fiel d does not). Methane
also comes from de composition in landfills, waste treatment, and the
incomplete burning of rain forest materials. Other greenhouse gas
levels are also increasing because of human activities. Concentrations
of ozone in the troposphere, where it is a pollutant and greenhouse gas,
hav e more than doubled since 1976. Tropospheric ozone is created by
the action of sunlight on nitrogen oxide and hydrocarbon pollutants
su ch as the carbon – and hydrogen- based emissions from car exhaust.

Nitrous oxides (NO and N2O) are themselves greenhouse gases that
come from the burning of fossil fuels, forests, and crop wastes, and
al so from the manufacture and use of fertilizers. Chlorofluorocarbons
(CFCs) are extremely pot ent greenhouse gases in the troposphere.
They also destroy the ozone layer in the stratosphere. CFCs are
primarily responsible for the springtime ozone hole over Antarctica.
Although CFCs were once widely used, production peaked in 1986,
and the chemicals are now being phased out. Nevertheless, they will
continue to act as green house gases for several decades until solar
radiation breaks them down in the atmosphere. Their cur rent
substitutes, HFCs, are also green house gases, but they have less heat
trapping ability. Sulfur hexachloride (SF6) is an extremely potent
greenhouse gas t hat is manufactured for industrial uses.
o Land use changes
When people change the way they use the land, they may inadvertently
alter their climate. The most dramatic example of this is the urban
heat island effect , the phenomenon whereby urban areas are ho tter
than the surrounding countryside during the day and especially at
night. There are two causes of urban heat island effect: The first is
excess heat generated by the running of engines and given off by
buildings, among many other sources. The second is the lower albedo
of man -made surfaces, such as concrete and asphalt, when compared to
natural surfaces. Man -made surfaces store the solar energy that strikes
during the day and rerelease it into the atmosphere at night. This is
why nighttime temperatures over cities have risen dramatically in the

past few decades. For instant, in the desert city of Phoenix, Arizona,
the nighttime low temperature rose more than 10°F (6.5°C)
Land use changes can alter climate in other ways. When forests are
converted to farm s and ranches, the rates of albedo and
evapotranspiration are lower, and the balance of water and heat are
thereby altered. Climate patterns are changed: Often the region
becomes drier. Urbanization also changes albedo and lowers
evaporation in the urbaniz ed area; it reduces precipitation over the city
but increases it downwind between 1948 and 2005. The temper ature
differences between urban areas and the surrounding countryside a lso
make the weather over cit ies more variable, with more storms and
more dry spells.
o Global dimming
Human activities cause climate to cool because atmospheric pollutants
block sunlight. Still, scientists have found that global dimming has
been counteracting some portion of global warming. As air pollution is
reduced, the effect m ay likely be a further increase in global warming.

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