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The Earth’s natural radiation cycle has been disrupted over the course of
the last century by volcanic eruptions, consequently worsening climate change.
Volcanoes such as Mt. El Chichon and Mt. Pinatubo both had eruptions in the
later 20th century with significant climatic consequences. The Mt.
Pinatubo eruption of 1991 is one of the greatest examples of this, as it
scattered ‘an estimated twenty million tonnes of sulphur dioxide and volcanic
ash particles’ (Wolfe, 2000). This sulphur
dioxide reacts with water vapour in the stratosphere producing volcanic
aerosols. In fact, the eruption of Mt. El Chichon in 1982 produced aerosols
that ‘enhanced optical depth by up to 0.3 within limited areas of the eruption
hemisphere during the first year’ (Mass & Portman, 1989, p. 568). This meant that the
earth’s albedo increased due to aerosols and more solar radiation was
reflected, ultimately cooling the globe and presenting a powerful short term
change upon climate. The northern summers of 1992 and 1993 had the coolest
global average temperatures of the period from 1986 (Jones & Viner, 2000) displaying the
abnormal consequences on climate provoked by the Mt. Pinatubo eruption even so
much as a year after the eruption occurred. These cooling effects show the
incredible impact volcanic eruptions have upon climate change by diminishing
the most impactful climate forcing of the last century. Moreover, these
volcanic aerosols heat the stratosphere ‘by absorbing both solar and
terrestrial radiation’ (Robock, 2000, p. 191) and the disparity
between stratospheric and tropospheric temperatures amplifies the jet streams
in the tropopause. This in turn causes a ‘pattern of tropospheric circulation,
resulting in winter warming of Northern Hemisphere continents’ (Robock, 2000, p. 191) and imposes a
positive feedback upon climate by heating up large sections of the earth’s
surface and atmosphere. They can also have a devastating effect on habitats as
well as forests by destruction due to acid rain. This combination of different
types of feedbacks occurring is why volcanic eruptions hold such significance
regarding climate change.

The natural carbon cycle is a big contributor towards climate change
throughout the past century. The cycle has amplified the effects of human driven
carbon dioxide emissions; posing as a positive feedback when considering ocean
capacities to hold carbon. It has been observed that ‘warmer ocean waters will
hold less dissolved carbon, leaving more in the atmosphere’ (Riebeek,
2010, p. 5)
and ensuring that our atmosphere’s rising temperature is furthered by the
abundance of carbon dioxide and water vapour. Both radiative forcings trap
infrared radiation and ensure less heat is lost through the earth’s cooling
process. Ocean’s warm further due to the net warming of the globe and this in
turn results in even less carbon absorbed and more water vapour emitted, initiating
a cycle of warming that is orchestrated through the natural carbon cycle and
would hold far less impact without a natural driver. It can be argued ‘the
release of just 2% of the carbon stored in oceans would double the amount of
atmospheric carbon dioxide’ (Houghton, 2015, p. 34) showing how
impactful altering the oceans carrying capacity can be towards climate change. Also,
carbon dioxide causes soils to ‘release trapped carbon dioxide or methane into
the atmosphere’ (Riebeek, 2010, p. 5) solidifying the
natural carbon cycle’s dominating nature when contributing towards global atmospheric
warming. Rising heat temperatures increase ‘fire frequency and insect
infestations’ (Riebeek, 2010, p. 5) and when trees
eventually perish due to burning or decay even more carbon is released and left
to manifest in the atmosphere. These additional processes display natural
causes to global warming from multiple perspectives and how intricate these
combinations of cycles can be; seriously affecting both human driven climate
change and natural changes also. The impact upon human climate change is what
makes these natural drivers so important over the last century. Human carbon
emissions have increased dramatically over the past one hundred years and when
coupled with natural drivers have changed the climate entirely; damaging
habitats and completely altering atmospheric greenhouse gas concentrations.

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The El Niño
Southern Oscillation periods have greatly affected both surface and ocean
temperatures and have contributed to multiple aspects of climate change ‘as part of a naturally-occurring cycle’ (Met Office, 2017). The
cycle consists of an alternating El Niño and La Niña, in which the eastern pacific warms and cools,
respectively. The El Niño of 1998 saw unusually large surface and water
temperature increases and these alterations are known to directly affect global
precipitation. In 1997-8 Peru received ’16 times the average rainfall’ (Bayer, 2014) and furthering this,
it is said that ‘long-term trends in
the amount of precipitation have been observed over many large regions from
1900 to 2005’ (Jenkins, 2009) spanning almost the
entire of last century and the ENSO cycles make a significant contribution to
these trends. This evidence shows how impactful the effects of the oscillation
cycle can be towards climate change; natural disturbances lead to direct
consequences upon land and sea level conditions through precipitation but also
atmospheric pressure. This in turn leads to drastic changes in climate, after
all ‘ENSO is by far the dominant feature of climate variability on inter-annual
timescales’ (Jenkins, 2009) and this supports
the idea that these periods are natural cycles dictating climate change over
the past century. However, one must question the extent to which this evidence
supports the impact on climate change of these natural cycles. One could infer
that the fluctuation of these cycles lacks absolute dominance concerning change
climate in the long term as the opposing cycles slightly rectify the heat
changes caused by one another. Especially as the oscillations can be predicted
and thus ‘impacts
can be anticipated and decisions can be made to mitigate adverse effects’ (Met Office,
2017). Human driven forcings
such as carbon dioxide concentration increases have had harsher impacts on
global climate and are increasing hugely despite worldwide efforts to dampen


Human driven carbon dioxide and
methane emissions can be argued to be the biggest cause of climate change over
the last century. Experts have stated that ‘the global atmospheric
concentration of carbon dioxide has increased from a pre-industrial value of
about 280 ppm to 379 ppm in 2005’. This shows the recent period of carbon
dioxide progressing from a positive feedback to a positive forcing – stretching
as far as since the industrial revolution began. The absolute growth of
emission concentrations is why human driven forcings are so dangerous for climate;
they don’t fluctuate like many natural processes and are not designed to retain
order within the climate system. This huge increase in carbon dioxide causes
unparalleled changes in atmospheric temperature, consequently heating the globe
in massive proportions. Methane is even more efficient as a positive radiative
forcing and if it becomes as abundant as carbon dioxide it has the potential to
be just as dangerous towards climate. Humans are contributing to methane
emissions mainly through agriculture and gas leakage. The evidence of global
climate impact is compelling; Russia experienced ‘a persistent heatwave
combined with extensive wildfires’ that ‘led to an estimated 55000 deaths’ (Houghton,
2015, p. 2).
This is just one example of ‘extremes of weather and climate’ (Houghton,
2015, p. 2)
that have been inflicted upon numerous continents due to global warming. Since
1980, society began to recognise that human activity was a leading cause of
climate change and many have been campaigning for increased global action. In 2001,
the IPCC could no longer avoid the possibility that ‘most of the observed
warming over the last 50 years is likely due to the increase in greenhouse gas
concentrations’ (IPCC, 2001, p. 10). Communities did
indeed act on these statements combined with targets set at the Kyoto protocol
to reduce greenhouse gas emissions. Yunnan, China have introduced biogas
generators and ‘over 50 such systems’ have ‘considerably reduced local firewood
consumption’ (Houghton, 2015, p. 319). This implies that communities
have started to act and recognise that this is necessary in preventing more
dangerous climate change. It takes an extremely impactful factor of climate
change for civilisations to impede their own lifestyle for the good of the
climate and this is exactly what human greenhouse gas emissions are prompting
globally. Therefore, it can be argued that human greenhouse gas emissions are
the largest contributor to climate change over the last one hundred years.


Human CFC emissions are depleting
the essential ozone layer extremely fast and contributing hugely to global
warming as well as exposing damaging radiation. These CFC’s were once seen as
useful, ‘non-toxic and non-flammable’ (Houghton, 2015, p. 50) hence were
widespread throughout industries especially ‘throughout the 1980’s’ (Houghton, 2015, p. 50). This was a harmful
decision by humans; mass producing a damaging greenhouse gas for industrial
gain is an unnecessary and long lasting contribution to climate change; CFC’s
remain in the atmosphere for ‘100-200 years’ (Houghton, 2015, p. 50). The chlorine in
these greenhouse gases can destroy huge proportions of ozone layer that
actively absorbs ‘solar ultraviolet radiation’ which ‘would otherwise be
harmful to us and to other forms of life’ (Houghton, 2015, p. 50) showing how we are
incidentally affecting multiple life forms spanning across the surface of the
earth. The sheer danger of these specific greenhouse gases is displayed through
the international decisions to replace them with HCFC’s and HFC’s, compounds
which are still damaging greenhouse gases. In fact, HCFC’s are such a strong contributor
to global warming that in Copenhagen in 1992, it was agreed ‘HCFC’s would also
be phased out by 2030’ (Houghton, 2015, p. 52). Humanity has
therefore been contributing heavily towards ozone depletion and surface
warming; repeatedly replacing the more dangerous compounds with alternatives
that are still harmful. Thus, consistently impacting climate change to a much
greater extent than any natural cycle.

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