• New research reveals the dire threat that climate change poses to coral reefs, one of the most important ecosystems in the world.
  • Within 20 years, 70-90% of coral reefs will likely die. By 2100, there could be few to none left.
  • Photos show what vibrant reef systems currently look like, and what could happen to them in the future because of climate change.
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Coral reefs are dying.

Between 70% and 90% of all reef systems could disappear within the next two decades because of pollution and climate change, according to new research.

That projection, which researchers from the University of Hawaii Manoa presented at annual Ocean Sciences Meeting last week, suggests that by the end of the century, there could be few to no suitable sites for coral reefs anywhere in the world.

Coral reefs cover less than 1% of Earth’s surface, but they provide a home for over 25% of all marine life. Millions of people rely on them for food, medicine, protection from storms, and employment in tourism sectors.

But corals are highly sensitive to water temperature, and climate change is causing oceans to warm and become more acidic. Some studies suggest half of the world's coral reefs have already died.

The new research also found that by the end of the century, there will be very few locations where human efforts to restore coral habitats would be viable at all.

"Trying to clean up the beaches is great, and trying to combat pollution is fantastic. We need to continue those efforts," Renee Setter, the lead researcher on the project, said in a statement. "But at the end of the day, fighting climate change is really what we need to be advocating for in order to protect corals and avoid compounded stressors."

Here's what bright, biodiverse coral reefs look like, and the dead shells they could become.


Coral reefs are often considered "rainforests of the sea" because of the diverse array of creatures that live in them.

Foto: A green turtle swims through corals on the Great Barrier Reef off the coast of Cairns, Australia on October 25, 2019.sourceLucas Jackson/Reuters

Australia's Great Barrier Reef is the largest and most extensive reef system in the world. But half of it was killed off in two consecutive years of coral bleaching in 2016 and 2017. It's currently facing another.

Foto: Soft yellow corals in the Great Barrier Reef.sourceLucas Jackson/Reuters

In 2016, one-third of the 3,863 reefs in the Great Barrier Reef system went through a catastrophic die-off after an extreme heatwave. A bleaching event the next year devastated even more reefs; the cumulative effects have killed an estimated half of the Great Barrier Reef.


The new research projects that reefs could cease to exist by the end of the century if ocean warming continues.

Foto: Blue staghorn coral in the Great Barrier Reef showed signs of bleaching on October 25, 2019.sourceLucas Johnson/Reuters

The blue staghorn coral in the image is experiencing a bleaching event. When healthy, it ranges from vibrant turquoise to royal blue in color.

"The bright blue staghorn coral is not normally that color. It is fluorescing - another sign a coral is in distress," Lyle Vail, director of a research station in the Great Barrier Reef Marine Park, said in a statement from the World Wildlife Fund Australia.


As waters warm, coral loses the algae that lives in its tissue, provides nutrients, and gives coral its bright color — a process called bleaching.

Foto: A blacktip reef shark swims over dead coral off the island of Huraa on December 12, 2019, near Male, Maldives. Some parts of the Maldives are believed to have lost up to 90% of corals.sourceCarl Court/Getty Images

Bleaching doesn't completely kill coral, but it makes reefs vulnerable to toxic algae, disease, predators, and death.

Oceans also acidify as they absorb more carbon dioxide, and that causes bleaching, too.


Some estimates suggest that about half of the world's healthy reefs have already been killed in the last 30 years.

Foto: A gorgonian giant sea fan and soft corals on a rock in a coral reef on the Mergui Archipelago in Myeik, Myanmar.sourceSirachai Arunrugstichai/Getty Images

Runoff from agriculture and pollution from nearby cities pose additional threats to reefs.

Foto: A crown-of-thorns starfish feeds on a bleached, dead hard coral on a tropical reef. It's a predatory starfish that can damage the rest of the marine ecosystem.sourceRichard Whitcombe/Shutterstock

A proliferation of crown-of-thorns starfish in the Great Barrier Reef in 2018 was caused by nearby fertilizer runoff, which helped the starfish breed. Overpopulation of these predatory starfish can ravage coral reefs.

The coral, meanwhile, was experiencing bleaching events that made them weaker and more vulnerable to attack.


In the Pacific Ocean, overfishing has thrown food chains out of balance. The overharvesting of reef fish removes the natural consumers of some seaweed-like algae, allowing it to grow to levels that can smother reefs.

Foto: A commercial fishing net abandoned over a coral reef, at the Triangle Pinnacle in the Gulf of Thailand.sourceGuntaphat Pokasasipun/Getty Images

According to estimates from the World Resources Institute in 2011, 55% of the world's reefs are threatened by overfishing, with nearly 30% considered highly threatened.


Fishing boats also drag nets that entangle live coral and tear them away from their bases.

Foto: A large table coral off the coast of Indonesia.sourceSergeUWPhoto/Shutterstock

Boats' anchors can damage and destroy reefs, too.


Scientists and policymakers have tried to protect coral by banning sunscreens with toxic chemicals and encouraging divers not to touch reefs.

Foto: A large table coral is dying, possibly from disease, off the coast of the Solomon Islands.sourceEthan Daniels/Shutterstock

Some marine scientists are also trying to build reef "nurseries" from equipment like old ships or concrete blocks that young coral — usually raised in laboratories — can grow on.

Foto: A coral nursery on the coral reefs of the Society Islands in French Polynesia, May 9, 2019.sourceAlexis Rosenfeld/Getty Images

The researchers at the University of Hawaii Manoa attempted to map out future locations that would be suitable for coral restoration efforts

Foto: Hard corals bleaching on the rock underwater at a dive site in the Gulf of Thailand.sourceGuntaphat Pokasasipun/Getty Images

Their models took into account future sea-surface temperatures, wave energy, water acidity, pollution, and overfishing.


The study found that by 2100, there will be "few to zero" suitable coral habitats.

Foto: Shedd Aquarium coral research scientist Ross Cunning, right, and Amanda Weiler, Shedd's dive program manager, collect coral samples at the Yellow Bank coral reef near the Exumas Islands in the Bahamas.sourceZbigniew Bzdak/Chicago Tribune/Tribune News Service via Getty Images

The few sites that could support reef restoration were in Baja California and the Red Sea.

Foto: A bleached coral reef in Tahiti, French Polynesia in late May 2019.sourceLuiz Rocha, California Academy of Sciences

But even those are not ideal reef habitats because of their proximity to rivers, the study found.


"Honestly, most sites are out," Setter said in the release, adding, "by 2100, it's looking quite grim."

Foto: A 2017 photo provided by NOAA shows bleached coral in Guam.sourceDavid Burdick/NOAA/AP

Environmentalist David Attenborough spoke about his first time scuba diving in the Great Barrier Reef in a BBC interview: "Below me there was a wonderland — a coral reef. On it, there were fish I never dreamed of, with colors I could only imagine, and there were all these other organisms that I had never seen before in my life."

Foto: Fire corals are found on reefs in the Indian, Pacific, and Atlantic Oceans and the Caribbean Sea.sourceRainervonBrandis/Getty Images

Future divers, however, are unlikely to enjoy the same sights.