Just a year ago, the colors were bright under the waves. Now the Maldivian reef is dead, the coral killed by the pressure of rising ocean temperatures.

What is left is gray, a scene repeated in reefs around the world.

Coral reefs are areas underwater where small creatures live. The coral is hard material formed on the bottom of the sea by the skeletons of those creatures. Usually brightly colored fishes swim among the coral.

The world has lost about half its coral reefs in the last 30 years. Scientists are working to prevent their destruction. The health of the planet depends on it.

"This isn't something that's going to happen 100 years from now. We're losing them right now," said marine biologist Julia Baum of Canada's University of Victoria. "We're losing them really quickly, much more quickly than I think any of us ever could have imagined."

Scientists say global warming is causing the rising ocean temperatures.

Global warming is the heating of the planet, which most scientists say is caused by harmful carbon dioxide and other greenhouse gases released into the air by human activities. The gases trap heat on the planet and its oceans, causing temperatures to rise. Even if global warming stopped now, scientists still expect that more than 90 percent of corals will die by 2050. Without serious efforts to help the coral, there is the risk of losing all of them.

"To lose coral reefs is to fundamentally undermine the health of a very large proportion of the human race," said Ruth Gates, director of the Hawaii Institute of Marine Biology.

Why are coral reefs important?

Coral reefs support a fourth of all marine species, as well as half a billion people worldwide.

The reefs produce some of the oxygen we breathe. They serve as barriers, or walls, to protect coastlines from the storms. They provide billions of dollars from tourism, fishing and other trade. They are also used in medical research for cures for diseases including cancer, arthritis and infections.

"Whether you're living in North America or Europe or Australia, you should be concerned," said biologist Ove Hoegh-Guldberg, at Australia's University of Queensland.

"This is not just some distant dive destination, a holiday destination. This is the fabric of the ecosystem that supports us."

"Bleaching"

A temperature of just one to two degrees Celsius, can force coral to expel the algae that live there. This leaves their white skeletons uncovered. It is a process called "bleaching."

When the water cools, the bleached coral can recover. But when the water rises in temperature, the coral will die.

Sixteen percent of the world's corals died of bleaching in 1998. The problem became much worse in 2015-2016. That is when the El Nino, a natural weather pattern, warmed Pacific Ocean waters near the equator. The bleaching continues today, even after the El Nino ended.

While stories have been written about damage to Australia's famous Great Barrier Reef, other reefs have also suffered, from Japan to Hawaii and Florida.

Julia Baum, the University of Victoria biologist, said the central Pacific has been hit the worst. She has been working, there on Kiritimati, or Christmas Island. For ten months between 2015 and 2016 the water temperatures were warmer and 90 percent of the reef died.

Now the U.S. National Oceanic and Atmospheric Administration scientists are predicting another round of increased ocean temperatures starting next month.

They say models show the return of bleaching in the South Pacific soon, along with the possibility of bleaching in parts of the Indian Ocean. It might not be as bad last year, but it could damage reefs that are still hurting from the last two years.

Some help ahead

Last month, Ove Hoegh-Guldberg helped start a program called 50 reefs. The program wants to educate the public on the issue and to protect the reefs from pollution, overfishing and coastal development.

Other scientists are working on experiments they hope will stop the possible final disappearance of corals.

"We've lost 50 percent of the reefs, but that means we still have 50 percent left," said Ruth Gates, who is working in Hawaii to breed corals that can better withstand increasing temperatures.

She is also trying to "train" corals to survive rising temperatures. Gates says it is time to start "thinking outside the box." In other words, it is time to come up with creative ways to help the coral.

I'm Anne Ball.

And I'm Kevin Turner.

Anne Ball adapted this story for Learning English from the Associated Press report. Hai Do was the editor. We want to hear from you. Write to us in the Comments Section and find us on Facebook.

marine – adj. of or relating to the sea or the plants and animals that live in the sea

undermine – v. to make (someone or something) weaker or less effective usually in a secret or gradual way

proportion – n. an amount that is a part of a whole

dive – v. to jump into water with your arms and head going in first

fabric – n. material or the basic structure of something

algae – n. simple plants that have no leaves or stems and that grow in or near water

equator – n. an imaginary circle around the middle of the Earth that is the same distance from the North Pole and the South Pole

breed – v. to keep and take care of animals or plants in order to produce more animals or plants of a particular kind