Doomsday Clock: The Countdown For Coral Reefs

By, Kira Coley, ECO UK Correspondent

Generating an estimated $29.8 billion per year from fisheries, tourism, and coastal protection, coral reefs are one of the most important ecosystems on Earth. And now, the latest climate research suggests they are soon to become one of the most endangered. New climate model projections developed by scientists at the University of Miami, NOAA Atlantic Oceanographic, World Wildlife Fund, and United Nations Environment provide a coral bleaching “doomsday clock” and reveal which of the world’s underwater cities will be the first casualties of climate change. Governments and conservationists must act now to reduce emissions and prioritize the protection of reefs that may still have time to adapt to the inevitable warming seas.

There is no news in the fact that climate change is bad for coral reefs. Between 2014 and 2016, the world witnessed the longest global bleaching event ever recorded. In the end, 90% of the Great Barrier Reef was hit by bleaching and over 60% of its coral was killed in some areas.

Jerker Tamelander, head of the UN Environment Coral Reef Unit, explains: “We’ve left many reefs more vulnerable by subjecting them to a lot of direct stress. We fish too much, we take out herbivores that are needed to keep algae under control, and we subject coral reefs to nutrient pollution from land and wastewater. It’s pretty clear that these direct stresses make coral reefs less capable of meeting the climate change challenge.”

Doomsday Clock: The Countdown For Coral Reefs 1

“To help coral reefs cope with climate change, we need to manage the direct stresses and bring them to sustainable levels. We have failed to do this partly because we’ve failed to consider the full societal and economic cost of reef loss. There are now some tough decisions to make, and we have a lot of work ahead. The macroeconomic equations of entire countries need to change just as much as the local management on the reef itself.”

Marine Protected Areas (MPAs) include almost a quarter of all coral reefs in the world; however, many are not effectively managed. While most MPAs tackle the fisheries issue, rarely do they address multiple stresses and land-based sources of pollution.

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Coral reefs are especially vulnerable to climate change because they are easily affected by temperature changes. When sea temperatures warm, the algae that give coral its bright colors leave their host, causing the coral to look white and making it much more susceptible to starvation and disease. Photo credit: © Cat Holloway / WWF.


Scientists hope the new climate model projections will help resource managers better target management to reduce pressure on these vulnerable— and valuable—ecosystems.

“If we are to better target our management efforts, we need to first understand which reefs will be exposed to the changes in temperatures leading to coral bleaching and also when they will be affected. Before now, this information didn’t exist. This data is now in the public domain so it can be used for conservation and management planning. The projections also add serious weight to the already large body of evidence that climate change represents a grave threat to coral reef ecosystems and the goods and services reefs provide human communities,” said Tamelander.

Scientist were surprised by the enormous variation in the projections. And now, for the first time, they are able to answer important questions: What does the future hold for your local reefs? Are there any important differences in your region or country that can help prioritize management efforts?

Tamelander explains, “Reefs that are quite close to each other can face a very different bleaching future. The data shows us that, very soon, some reefs will be affected by coral bleaching every year. If we make all our management investments in those areas, we may lose our investment. On the other hand, some reefs in the same region may not experience these conditions until decades later. These are the areas flagged as conservation priorities because they have the time to adapt to the inevitable climate change, to continue to provide ecosystems services and can reseed degraded areas.”

Predicting the Fate of the World’s Corals

The new study shows that, on average, the world’s reefs will start suffering annual bleaching in 2043. About 5% of reefs will be hit a decade or more earlier. Reefs in Taiwan, around the Turks and Caicos archipelago, will be among the world’s first victims to annual bleaching. Around 11% will be hit decades later, including those off the coasts of Bahrain, Chile, and in French Polynesia.

There are several factors that influence when a reef is likely to fall victim to bleaching. Firstly, some areas are predicted to heat up faster than others— this is driven partly by our climate system and by oceanographic conditions. Another factor is the level of temperature variation to which coral reefs are naturally exposed and have adapted to. Reefs that experience less fluctuations in temperature over the summer are likely to be more vulnerable than those that are regularly exposed to a bigger temperature range.

Yet, scientists warn that if the world fails to reduce greenhouse gas emissions, severe bleaching will occur every year on 99% of the world’s reefs within the century. Study leader Dr. Ruben van Hooidonk of NOAA and the University of Miami, said, “The biggest uncertainty in these projections lies in what we as humans achieve in terms of greenhouse gas reductions. Reefs can recover from bleaching, but when it happens every year there simply isn’t enough time. So, the reef condition, along with the goods and services they provide, will rapidly decline.” Tamelander comments: “We will lose many reefs, but they have been around for millions of years in different forms. I’m not so worried about the reefs, to be honest, I’m more concerned about us, the human race. All of the industries and all of the people that depend on reefs—they are the ones that are going to suffer.”

The Paris Agreement

The Paris Agreement’s aspirational target of limiting global temperature increase to 1.5 degrees provides a safer, but not an entirely safe, space for coral reefs. Even if emission reductions exceed pledges made by countries to date under the Paris Agreement, more than three-quarters of the world’s coral reefs will bleach every year before 2070.

Van Hooidonk explains: “Under the Paris Agreement, countries make ‘pledges’ called ‘Nationally Determined Contributions’ to reduce emissions and to re-evaluate their pledge in 2023 and every five years from then on. The best-case scenario is that countries make greater emission reductions than pledged. Of course, making these pledges become a reality is not helped by people calling climate change a hoax...”

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Coral reefs provide hundreds of millions of people around the world with food. Knowing when and where bleaching will occur could help governments, natural resource managers and conservationists make informed decisions on how and where to place conservation priorities. Photo credit: © Jürgen Freund / WWF.

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Photo: WWF's lead marine scientist, Gabby Ahmadia, surveys a reef in West Papua, Indonesia. Photo credit: © WWF-US / James Morgan.

Scientists are optimistic that, with the combined efforts of policy and technological advancements, countries can meet the emissions targets, but admit the timeline is going to be difficult for many.

A Future of Climate Change

If emission reductions exceed pledges made by countries under the Paris Agreement, coral reefs would have on average another 11 years to adapt to warming seas. Under this scenario, many high- and low-latitude reefs such as those in Australia, the South Pacific, India, Coral Triangle, and the Florida Reef Tract will have another 25 years, buying valuable time for conservation efforts. Regardless, even if the Paris Agreement is met, it will be too late for reefs near the equator.

Gabby Ahmadia, WWF co-author on the report, comments: “It is a little bit scary at this point. If we can buy time, then that will be critical until we can find some innovative solutions to this problem, which right now we just don’t have. But change is inevitable. We will have very different coral reefs in the future than that of today. There are some species of coral that are fast growing and provide much of the structural complexity reef fish need. These species are more susceptible to bleaching, so we will lose much of the structural complexity of the reef in many areas, greatly impacting reef fish populations and dependent human communities.” van Hooidonk added, “If we don’t greatly reduce emissions, climate change will lead to the decimation of coral reefs globally. It is my opinion that reefs will be severely degraded if we do not combat the issue at hand—climate change. Coral nurseries have been used to successfully restore some species to damaged areas, but it is a local solution to a global problem. So, can we save coral reefs? Yes, we can certainly save some reefs! But, we have to take climate change seriously. Besides political action, we all have to limit our carbon foot prints, and we need to do more than agreed upon in Paris if we want corals to thrive.”


Support for the study, entitled “Local-scale projections of coral reef futures and implications of the Paris Agreement” (stored at was provided by UN Environment, the World Wildlife Fund, NOAA’s Coral Reef Conservation Programme, the Atlantic Oceanographic and Meteorological Laboratory, the National Marine Fisheries Service via the PIFSC, USGS via the Pacific Islands Climate Science Center, Total Foundation, and U.S. National Fish and Wildlife Foundation.

The study was led by Dr. Ruben van Hooidonk and Dr. Jeffrey Maynard.

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