Conservation and Biodiversity
Why Oceans are Losing Their Color: Coral Reefs and Climate Change
July 21, 2025
If there is any ecosystem that can do it all, it’s the coral reef. After all, what other underwater habitat can support over a quarter of all marine species on Earth, protect our coastlines by absorbing 97% of wave impact, serve as a source of food for millions of human beings and thousands of other species, produce medicine and look amazing while doing it?
But despite everything coral reefs do for our planet, they are also one of the most vulnerable ecosystems on Earth. They currently occupy about 0.1% of the Earth’s surface area, and it is estimated that half of the planet’s coral reefs have been lost since 1950.
Climate change is the main culprit behind these worrying findings, and it is estimated that if global temperatures rise to 1.5º C above pre industrial times, up to 90% of tropical coral reefs may disappear by 2050. And with millions of tourists crowding these areas and using plastic materials that end up in our waters, our reefs are in more danger than ever.
That’s why every year during the third full week of July we recognize Coral Reef Awareness Week, which is dedicated to raising awareness for an ecosystem that does so much for us and our planet. Here are 5 major ways that climate change and pollution are impacting our coral reefs.
1. Flamboyant to Fading: Coral Bleaching
When you imagine a coral reef, you probably picture a stunning underwater landscape of vibrant colors and brilliant fish floating alongside them. The bright colors of coral reefs are their most recognizable feature, and unfortunately, as a result of climate change, these colors are fading.
The striking shades of coral are mainly produced by microscopic algae called zooxanthellae that live inside coral tissue. Coral is an animal and cannot make its own food, so it relies on zooxanthellae to turn sunlight into sugars through photosynthesis. A molecule called chlorophyll is what allows zooxanthellae to absorb light and gives them their distinct pigment. The coral also helps with this task by producing their own protein pigments that can absorb light for their microscopic partners, making their colors appear even brighter. In return, the coral receives 90% of the food made by the zooxanthellae.
But when the water becomes too warm, coral get stressed and expel the zooxanthellae in response. This causes reefs to not only lose their colors, rendering them a ghostly white in a process known as coral bleaching, but also their main food source, putting them at risk of starving to death if conditions do not change.
The world is currently in the midst of a fourth global bleaching event that has impacted nearly 84% of the world’s reefs between January 1, 2023 and May 31, 2025. As a result, in 2023, Jamaica was the epicenter of what was the most severe coral bleaching event in the Caribbean to date. Approximately 90% of the nation’s corals died in a two month span from September to October.
2. Acidic Waters
Ocean acidification is sometimes known as the “osteoporosis of the sea.” Just like the disease that weakens the bones of those afflicted, the increasingly acidic nature of our oceans as a result of climate change eats away at the skeletons and shells of various marine organisms, including coral.
Our oceans are becoming more acidic because of the increase in carbon dioxide being released into the atmosphere. Around 30% of this carbon dioxide is absorbed by the ocean, where it combines with water molecules to form carbonic acid. This weak acid then releases hydrogen ions, lowering the pH of the water and making it more acidic.
The reason this is so bad for coral reefs is because their skeletons are made of a material called aragonite, a form of calcium carbonate. In order to make this material, carbonate ions must be present in the seawater. However, carbonate ions bond with excess hydrogen ions as oceans become more acidic, leaving less of this vital mineral for the coral, which can result in their skeletons dissolving.
In the Caribbean, action is being taken to monitor this threat to coral reefs with an ocean acidification buoy that was installed in a coral reef in Puerto Rico in 2008. This buoy chiefly measures carbon dioxide levels in the air and water to monitor the acidity of the waters and help scientists and local communities find new ways to tackle this problem.
3. Extreme Weather with Extreme Results
Many of us are familiar with the devastation that hurricanes cause to thousands of communities on land each year. Just as vulnerable to these destructive storms are coral reef communities underwater.
The warming of the planet as a result of greenhouse gases affects the water cycle and changes weather patterns, leading to more extreme weather events. In the past 30 years, the intensity of cyclones has risen, particularly in the Atlantic Ocean and the Caribbean. As oceans warm, it is predicted that cyclones will become even more intense with higher wind speeds and heavier rain.
Coral reefs are expected to experience more physical damage as the intensity of these cyclones increases. In Southwest Madagascar, there was a decrease of up to 45.8% of coral cover at 19 sites between 2012 and 2015 as a result of cyclones. While the average coral cover increased to above pre-cyclone levels after 2 years, the increased frequency of such extreme storms holds worrisome connotations for the future safety of reefs around the globe.
4. A Plastic Parasite
Plastic pollution is another major concern for coral reefs. Scientists at the United States Environmental Protection Agency (EPA) found that microplastics, miniscule particles of plastic, can impact coral growth and adhere to their surface, making it harder for them to obtain food and even forcing them to expend valuable energy to remove them.
Most reefs on the planet appear to be impacted in some way by plastic pollution. A Nature study found that 77 out of 84 surveyed reefs in three separate oceans contained human-generated debris, including reefs previously thought to be untouched, with macroplastics accounting for 88% of this detritus.
These findings have inspired new potential measures for reducing plastic pollution, such as designating mesophotic, or low-light, reefs as protected areas and developing biodegradable fishing gear, but there is still a long way to go to fight this plastic problem.
5. Blocking the Sun – And the Future of our Reefs
As the Earth becomes warmer, you might find yourself reaching for sunblock more frequently for protection against the sun’s rays. However, though sunblock may prevent us from getting sunburned, it is actually doing harm to coral reefs.
Over 3,500 skincare products across the globe contain a sunscreen chemical called oxybenzone, or BP-3, that has been found to increase rates of coral bleaching, damage coral DNA, and lead to abnormal coral growth. Benzophenone-2, or BP-2, is a similar chemical that has been used since the 1960s that can kill juvenile coral.
These chemicals enter the seas when sunscreen washes off of swimmers as well as through wastewater. BP-2 is particularly concerning seeing as it is not removed from many municipal wastewater treatment facilities, allowing it to become particularly prevalent in Caribbean and Indo-Pacific waters.
These harmful chemicals exacerbate the effects of climate change on our coral reefs, resulting in bans on sunscreens containing these chemicals in places such as Hawaii, whose ban on harmful sunscreen chemicals went into effect in January 2021. Seeing as about 14,000 tons of sunscreen end up in our oceans annually, forgoing sunscreens with BP-2 or BP-3 is more important than ever.
What can you do?
To help protect the world’s coral reefs during Coral Reef Awareness Week and beyond, there are a few things you can do.
Firstly, check whatever sunblock you are wearing for harmful chemicals and try to swap it for ones that are mineral-based and do not harm coral.
You can also support EARTHDAY.ORG initiatives such as “Our Power, Our Planet” to advocate for a shift to renewable forms of energy and prevent the further release of greenhouse gases into our atmosphere, or sign the Global Plastics Treaty to help decrease plastic pollution around the globe.
Let’s return the favor to the coral reefs that do so much for us and our planet and take action to protect these biologically rich marine environments!
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