A* essay answer for the exam question "Describe the 4 Natural causes of Long and Medium term Climate Change". This essay details the role of volcanic eruptions, cosmic collisions, variation in solar output and Milankovitch cycles in causing long and medium-term climate change.
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Describe the 4 natural causes of long and medium term climate change
One of the natural causes of climate change is super volcanic eruptions that result in the
release of large volumes of volcanic ash and dust in addition to gases such as water
vapour and sulphur dioxide. These enormous quantities of ash—1 cubic mile of volcanic
material in the eruption of Mount Pinatubo 1991—partially block the sunlight and
consequently lead to a global cooling. An example of this is the Mount Tambora
(Indonesia) eruption in 1815 that, according to many, lowered the global temperature
by 0.5°C. Furthermore, volcanic eruptions can also affect climate change on a longer
time scale because of the release of sulphur dioxide and water vapour. These two gases
combine and from sulphuric acid, which, due to their small size, can remain in the
atmosphere for many years. In addition, these small droplets act as effective reflectors of
sunlight and therefore further prevent the sun’s energy from reaching the earth’s
surface, leading to cooling over a longer time period.
Cosmic collisions are another significant natural cause of climate change, as before by
blocking out sunlight and resulting in global cooling. The impact of collisions of space
debris, particularly meteorites—up to 10m across– and asteroids—more than 10m
across— can throw up large quantities of upper atmospheric dust and debris. This
material, in large quantities can block out the sun’s energy for months and even years,
resulting in global cooling. It is believed that climate changes caused by a huge asteroid
impact was the cause of the mass extinction of the dinosaurs, which weren’t adapted to
the cooler, dark climate that limited the growth of herbivorous dinosaur’s food sources.
Additionally, variations in solar output are another natural cause of climate change. The
energy of the sun varies; it is not constant. Sunspots are darker areas on the surface of
Sun that increase solar output, particularly when in high numbers. The numbers of
sunspots increase and decrease over an 11-year cycle. A key example of this was a
period during the late 17th century when the sunspot activity was low and there was also
a period of cooling known as the little ice age.
The final key reason is the Milankovitch cycles, which are variations in the earth’s
elliptical orbit and tilt, occurring every 100,000 years. Over this cycle, the path of the
earth’s orbit around the sun varies from a circle to an ellipse, which changes the
distance between the earth and the sun and consequently the energy received from the
sun. The tilt of the earth, which changes over a 40,000-year cycle, also affects the
amount of energy received by the earth at different latitudes. For example, when the tilt
of the earth is greater—24.4°—areas like the tropics, which receive lots of energy, are
larger. Compared with this, other regions beyond the tropics are smaller. Overall, these
variations in the tilt and shape of orbit of the earth result in varying the amount of
energy received by different regions, thus changing the global climate.
All these natural causes cause climatic changes by either preventing the earth’s surface
from receiving the sun’s energy—such as the blocking of sunlight by super volcanic
eruptions and cosmic collisions—or by varying the amount received by different areas
as the Milankovitch cycle does. Therefore, lower levels of energy being received results
in the earth getting cooler as global temperatures drop and global warming occurring
when more energy is received. Although there are many significant natural causes of
global climate change, anthropogenic (human) activity is causing the enhanced
greenhouse effect (EGE) and the ‘hockey stick effect’ (since 1970) that is bringing the
world closer to the ‘tipping point’ when irreversible run away climate change will occur.
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