Coral Reefs And Global Warming: There Is Hope


This literature review, meant for first year students studying climate change, focuses on the ability of coral reefs to survive global warming. Because of the recent temperature rise, coral bleaching has become more frequent and intense. Scientists are now focusing on the cause and effect relationship between warming waters and coral bleaching to devise methods for preventing mass extinction. The articles are structured beginning with an introduction to climate change and coral bleaching, followed by specific causes of bleaching (physical and biological factors, ocean acidification, and low oxygen levels), and ending with an analysis on the state of awareness that coral bleaching is connected to climate change. The Great Barrier Reef serves as a specific example of coral bleaching throughout the review to which newfound knowledge can be applied. Though scientists have a well-rounded sense of the causes of coral bleaching, there is still speculation as to the extent of the effects.


Recent research demonstrates how climate change causes surface water temperatures to rise, affecting coral reefs as they induce coral bleaching as focused on by this literature review for first year students interested in global warming. Coral bleaching causes coral to lose its photosynthetic organisms, losing all color, as demonstrated by the Great Barrier Reef after coral bleaching in 2016 and 2017. Scientists believe that bleaching will become more frequent and intense as temperatures rise, predicting a mass death of coral across the world. However, coral reefs have shown the ability to adapt given recovery time, and some are naturally tolerant to these conditions. Scientists have also found location and climate change specific factors, such as oxygen levels and acidification, that affect bleaching intensity. Discovering these causes of bleaching allows for a greater understanding of how to prevent bleaching, whether it is through using technology to alter shallow water conditions or using stronger species to help build up weaker ones. The articles provided in this literature review were chosen based on their unique views of how global warming has impacted coral reefs to provide a well-rounded analysis of the state of coral reefs in the context of global warming. With a bigger picture of climate change in mind, the research on the Great Barrier Reef can apply to other coral systems and vice versa, so that scientists can develop the best solutions for protecting these reefs and equip them to survive global warming.


Focusing on the big picture of climate change, Alan Buis explores how though a 1.5C increase in temperatures is inevitable, and has already happened in many places, limiting this rise makes all the difference in terms of survival. He believes if temperatures are allowed to reach 2C the impact of global warming could double in most areas, as seen by insect, plant, and vertebrate extinction percentage increases. If the temperature stopped rising at 1.5C, it could save sixty million people from drought and slow sea-level rise, allowing time for adaptation to the changing environment, according to Buis. With the threat of sea-levels on the coast, those species not able to migrate to different areas or adapt are threatened the most. Buis explains how coral reefs will likely decline 70-90%, becoming nonexistent at 2C, because they cannot migrate north. He supports this statement saying that coral reefs are susceptible to high ocean temperatures, increased acidity, and a decrease in oxygen levels which are all caused by climate change. Human health is also a major concern according to Buis, mentioning the effect on occupations, food, water, and the economy in relation to humanity’s ability to adapt. Through providing cause and effect relationships from around the world, Buis emphasizes the interconnected nature of climate change which is essential for a further understanding of global warming.

Knowing the extent of damage climate change will cause, Berly McCoy focuses on how global warming affects the Great Barrier Reef specifically.1 The 2016 Great Barrier Reef bleaching caused many scientists to question previous beliefs of global warming’s effect on coral reefs. McCoy describes how scientists thought coral bleaching was reversible, but they now predict more permanent results because of extreme temperatures. Coral bleaching occurs when photosynthetic algae living within coral leaves because of high temperatures, taking corals’ food source and color with it. It can be reversed over time as temperatures cool, and coral recovers. However, removed algae has been creating a covering over the newly formed skeleton of coral, causing it to lose strength, density, and calcium because of acid from the algae. The death of these coral reefs, she believes, would leave coasts unprotected, a high percentage of marine life without homes, and bring a harsh hit to the economy with the loss of tourism and fisheries. Ultimately, McCoy reasons that reducing the carbon dioxide emissions could help protect these coral reefs from completely dying.

Building on McCoy’s overview of coral bleaching, Charlotte Page identifies causes for this bleaching and how it can be prevented in the future to save other coral reefs, specifically the Great Barrier Reef. She believes it is important to examine both physical and biological factors that affect bleaching, so scientists are able to trace patterns of bleaching and locate areas that could become future centers for rehabilitation. Page explores why coral species respond differently to high temperatures by dividing these reasons into internal and external processes. Beginning internally, Page explains how each species reacts to extremities differently, so it is hard to predict which ones will respond positively or negatively. Tissue thickness is also a major factor as a thicker layer will increase the time it takes for nutrients to get in and out of coral. However, thinner tissue speeds up this process and ultimately benefits the coral. This knowledge opens the question of what physical factors cause this difference. Page lists cloud coverage, previous exposure, time to adjust, and rate of water flow as the main environmental influences. She explains water flow’s effect on tissue thickness saying a low rate of flow causes thicker tissue in coral. This statement is supported by a study that found a 25% decrease in respiratory and photosynthesis rates when there was zero movement in the water. On the other hand, she shows how high flow rates lead to thinner tissue and better bacteria in coral with the easy removal of toxins. Page believes that by picking areas with high flow rates, scientists can ensure success for if and when corals need to be rehabilitated.

Dennis Allemand builds on a list of external causes of bleaching by adding ocean acidification as another leading factor in coral deaths. Before elaborating on ocean acidification, Allemand argues that working together with chemists, biologists, economists, and government officials is the most effective way of determining solutions for coral bleaching. This communication would ensure the best possible solution for the looming threats facing coral reefs. Allemand begins by exploring the importance of coral reefs as they relate to the economy and the ocean. He explains how they protect the coast and are a major source of tourism all while housing 93,000 species and covering 0.08-0.16% of the sea surface. However, he emphasizes the threat they face, including global warming and ocean acidification. Here, he emphasizes how though ocean acidification is not often mentioned in relation to coral bleaching, it is one of the largest impacts. As more carbon dioxide enters the water, the pH level decreases, making it harder for coral to obtain calcium needed for strength, hindering growth. Currently at 8.1 acidity Allemand predicts the pH level to decrease to 7.8 by 2100. He goes on to theorize solutions for this increasing acidity. He believes a repository of coral (consisting of high resistant species) could help rebuild reefs later on. This solution offers a unique outlook on how other coral species could be used to help protect reefs that are more susceptible to the warmer temperatures.

Just as Allemand focuses ocean acidification, Hannah Nelson adds the level of oxygen in the water to the list of causes. Nelson explains how not having enough oxygen, or too much, is detrimental to coral reefs and the surrounding ecosystem, affecting each species differently. She explains how many coral deaths are correlated to low oxygen levels in the water. When the water is deficient in oxygen, it is called hypoxia, and when it has too much, it is called hyperoxia. Oxygen is essential for every natural process coral undertakes, and Nelson describes how when one process such as photosynthesis is inhibited, others like respiration and calcification are as well. Related to Page’s research on tissue thickness, Nelson explores how it is associated with oxygen consumption and water flow rates. Faster rates mean thinner tissue and easier access to oxygen. However, when slow rates cause thicker tissues, it is harder for coral to take in the already the already low oxygen supply. Nelson expands on the causes of low oxygen saying that higher temperatures cause higher metabolic rates in organisms, increasing their oxygen demand. With less oxygen in the water but a higher demand, the supply of oxygen is quickly depleted. She emphasizes the urgency of controlling carbon in the atmosphere to prevent oxygen depletion and having more reefs monitored for oxygen levels, so scientists can learn more about how to combat low oxygen levels.

Whereas Nelson and the other authors focus on biological factors associated with coral reefs and climate change, Matthew Curnock presents an anthropogenic view, connecting how people view the threat to coral reefs as it relates to climate change. In order to prolong the lifespan of the Great Barrier Reef and other reefs around the world, it is important to foster support among the general public and make them aware of how climate change is threatening the reef. Curnock measures the support and knowledge of the threat global warming has on the reef by surveying 4681 tourists of the Great Barrier Reef through which he identifies emotional connection as the most effective means of gaining public support. The survey listed statements to both local and international tourists and had them rate their agreement with them and list what they believed to be the most important threats to the Great Barrier Reef. Curnock uses the results of this survey to provide evidence that many people do not associate climate change with coral bleaching. Because the Great Barrier Reef is a public landmark, Curnock argues it is easier to foster support for its wellbeing by raising public awareness of climate change. Simply stating facts increases doubt and is not intimate enough. He believes that to effectively gain support, information must be presented through reasoning and personal emotional appeals to foster concern and hope. Curnock provides ideas that could help encourage individual action: making small, life adjustments, providing hope and fostering pride, and setting easy objectives to reach. Through the use of this survey, Curnock was able to judge the extent to which people associated coral bleaching with climate change and better understand the best way to spark awareness and grow support.


The mass extinction of the world’s coral reefs is an urgent problem facing society today. Spreading awareness of this problem is essential to preventing it from happening. This awareness starts with a background understanding in how climate change relates to coral bleaching as well as learning more about the different causes of mass bleaching and how they can be combated. As the articles demonstrated, many factors both physical and biological are attached to why corals bleach. Buis provides a brief explanation of global warming and how it relates to the world and coral reefs as a whole, and McCoy builds on this basic understanding with her discussion of coral bleaching and the inner workings behind it. Allemand, and Nelson each provide different, concentrated views on what they believe to be the most important cause behind rising water temperatures including the interplay between biological and physical factors, ocean acidification, and oxygen depletion. Each of these studies culminate with Curnock’s study, showing a lack of awareness about climate change with a tourist survey. As demonstrated by the articles, scientists have discovered a significant amount of information about the causes of coral reefs. However, there is still more to uncover about the best ways to protect them in the future. Most of the research is theoretical, but scientists’ projections are hopeful. Through developing technology to protect vulnerable species and using strong coral species to rehabilitate the weak, they believe that coral reefs may be able to survive global warming.

09 March 2021
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