Running Head: CLIMATE CHANGE AND POSITIVE FEEDBACK
Climate change and positive feedback loops in the tropical rainforests
Meghan Burke
Running Head: CLIMATE CHANGE AND POSITIVE FEEDBACK
Introduction:
Rainforests are a crucial part of the Earth’s ecological systems. They provide a sink for
carbon dioxide in the atmosphere, creating a buffer for climate change. They also provide a
source of carbon dioxide, which is produced from dead plant matter. In addition to this, the
forest decreases the albedo of the earth and absorbs energy from the sun. This energy acts as
heat to transfer moisture from trees into the atmosphere and leads to increased local rainfall
which nourishes the forest. Climate change is affecting these components of the rainforest. It
creates positive feedback loops that harm this ecosystem and increase climate change. The
forests are such an important part of the climate system, that the effects that rainforests have on
climate and climate change has on the forests are significant and complex.
Running Head: CLIMATE CHANGE AND POSITIVE FEEDBACK
Rainforests play an important part in the climate system. Perhaps the most significant
role of the rainforest in climate is its role as a carbon dioxide sink. While they only cover about
6% of the Earth’s land surface, almost 30% of global soil carbon stocks are contained in their
soils (“H. Rainforest Role in the Carbon Cycle”) and 40% of the world’s carbon is contained in
the vegetation (Phillips et al., 1998). Furthermore, rainforests contain densely populated flora,
estimated to contain about half of the world’s plant species. Called the “lungs of the world,”
photosynthesis from these plants takes carbon dioxide out of the atmosphere while producing
more than 20% of the world’s oxygen (“Rainforest Facts”). These mechanisms help balance out
the increasing amount of carbon dioxide that is being released into the atmosphere from both
anthropogenic and natural causes. Scientists have estimated that rainforests absorb 4.8 billion
tons of carbon a year (Connor, “Revenge of the Rainforest”). This amounts to about 18% of the
world’s annual fossil fuel emissions, thus making a significant impact on how much carbon is
added to the atmosphere annually and buffering the rate of climate change. The amount of
carbon dioxide absorbed by the rainforests is second only to the oceans, which dissolve about
half of anthropogenic emissions that don’t remain in the atmosphere (University of Leeds, 2009).
Rainforests also contribute to global warming. While the large amount of vegetation
existing in the rainforest helps to absorb carbon, it also acts as a source of carbon. Dead leaves
fall from trees to the forest floor, creating layers of leaf litter. These leaves are decomposed by
microbes, which releases carbon dioxide into the atmosphere (Poppick, “Tropical Rainforests:
From Carbon Sink to Carbon Source,” 2011). This carbon dioxide contributes to local and
global climate change and conflicts with the rainforest’s role as a carbon sink, although the
amount of carbon absorbed by the rainforest is still higher than carbon released (Poppick), so the
rainforest’s main purpose in the carbon cycle remains as a sink. Other effects that dead, dying,
Running Head: CLIMATE CHANGE AND POSITIVE FEEDBACK
and decaying vegetation can have on the rainforest and climate are that dead foliage offsets
photosynthesis since dead leaves are leaves that aren’t photosynthesizing, and that the albedothe amount of sunlight a surface reflects- of the rainforest is increased. The former effect
contributes to warming while the latter has a more complex effect on the climate, both
counteracting warming and contributing to it.
The dark surfaces of the rainforest’s foliage increase the albedo of the earth, absorbing
energy from the sun rather than reflecting it. The rainforests have the lowest albedo of all natural
terrestrial surfaces, estimated to reflect about 14% of short wave radiation reaching the earth
(“Final: Methods and Effects of Tropical Rainforest Deforestation”). However, energy
absorption plays an important role in the rainforest ecosystem. The energy from the sun, as heat,
increases the evaporation of water in the rainforest and the transpiration of plants. The water
returning to the atmosphere creates local rainfall for the forests which is in turn used by the
plants for photosynthesis, creating a balanced, self-sustaining ecosystem. The Amazon
rainforest, for example, produces an estimated 50-80% of its own rainfall through this process
(Butler, “Climactic Role of Rainforests”).
Climate change impacts all of these natural cycles and mechanisms in the rainforest as
the average global temperature increases. The changes brought about by climate change create a
positive feedback loop- a system in which one change leads to another, which further perturbs
the original change- in the rainforest, causing temperatures to further increase as more
greenhouse gasses enter and stay in the atmosphere. Higher temperatures may actually decrease
rainfall, as they tip the balance of warmth being beneficial and warmth being detrimental. There
are many variables that can lead to less rainfall in the rainforest. Climate change affects the
amount of water that is evaporated, transpired through plants, and how much is able to be held in
Running Head: CLIMATE CHANGE AND POSITIVE FEEDBACK
the air. All of those will increase with increasing temperatures. Climate change will also
displace water in parts of the world due to its effects on extreme weather and climate systems
like the jet stream and El Nino/Southern Oscillation. Warmer ocean temperatures increase the
intensity and frequency of El Nino/La Nina, as well as the moisture in the air from increased
evaporation. In turn, this causes drought in rainforests around the world (Ponce, “The Facts
about El Nino”). Other effects climate change may have on the rainforest and climate systems
are not completely understood and are still being studied. However, the trend that is being
observed in the world’s rainforests is consistent with the predictions of drought and less rainfall.
In 2005, and again in 2010, the Amazon rainforest suffered two “once in a century” droughts,
causing the rainforest to release carbon dioxide and absorb less from the atmosphere
(Derbyshire, “Amazon Rainforest hit by Second ‘Once in a Century Drought’ in Five Years,”
2011).
Deforestation also plays a part in droughts because the decrease in plants decreases the
amount of moisture the rainforest holds, the rate and amount of photosynthesis, and increases the
albedo of the area which changes the local climate. Plants are killed during droughts due to lack
of water and collapsed root structures. Dead plants contribute to this feedback loop since they
release carbon dioxide as they break down and are incapable of photosynthesizing, which
decreases the amount of carbon dioxide removed from the air, increasing the greenhouse effect
and the temperatures. The disappearance of dark leaves, bodies of water, and damp terrain
increases the albedo of the rainforest, contributing to the positive feedback loop, as there is less
rainfall. The rainforest continues to die and more carbon dioxide is released into the atmosphere.
The combination of the increase in temperature and drought enable the forests to be more
susceptible to fires. The rate of forest fires increase, which further decreases the amount of
Running Head: CLIMATE CHANGE AND POSITIVE FEEDBACK
biodiversity and kills more of the forest. Forest fires also release aerosols into the air though,
which help play a small part in counteracting the warming. The aerosols, in fact, contribute to
both cooling and warming, and further effect the ecosystem, although minimally. The overall
effect of climate change is the death of the vegetation and subsequent dieback of the forests,
which contribute the positive feedback loop.
Climate change makes a significant impact on rainforests and the role they play in the
world’s climate systems. Warmer temperatures create a positive feedback loop, killing the forest
and further increasing the temperature. Along with this, there are other effects caused by climate
on the rainforest, and vice versa. Some of these effects are not yet completely understood, but
many will continue to have an impact on climate and rainforests.
Running Head: CLIMATE CHANGE AND POSITIVE FEEDBACK
A diagram that summarizes the main effects of climate change on the rainforest and the positive
feedback loop that is created as a result.
Running Head: CLIMATE CHANGE AND POSITIVE FEEDBACK
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Running Head: CLIMATE CHANGE AND POSITIVE FEEDBACK
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