(CNN) Climate change could destroy almost all of Earth's coral reef habitats by 2100, according to new research.

About 70-90% of all existing coral reefs are expected to disappear in the next 20 years due to warming oceans, acidic water and pollution, said scientists from the University of Hawaii Manoa, who presented their findings Monday at an ocean sciences conference.

"By 2100, it's looking quite grim," said Renee Setter, one of the University of Hawaii Manoa researchers, in a press release.

Some environmental activists and coral reef researchers have been working on coral restoration -- growing live corals in a lab, then placing them back into marine environments to try and revive dying reefs. But this may not be enough to save Earth's reefs, the researchers warned.

Photos: How are humans harming coral reefs? Also known as "rainforests of the sea", coral reefs offer spectacular sights, as well as supporting wildlife, providing food, jobs and coastal protection for an estimated 500 million people.



But human activities are threatening their survival. Scroll through the gallery to see how our actions are putting coral reefs at risk. Hide Caption 1 of 6 Photos: How are humans harming coral reefs? Rising temperatures: Man-made greenhouse gas emissions are making oceans warmer.

In hotter water, corals lose their algae coverings and turn white or "bleached". Bleached coral are not yet dead -- but without their algae they eventually starve. Hide Caption 2 of 6 Photos: How are humans harming coral reefs? Overfishing: The coral reef's inhabitants are its first line of defense. Fish eat some of the creatures that eat coral, while crabs and shrimp use their pincers to protect their coral homes. Fish also graze on seaweed and algae so that they don't grow to cover the reef.



Indiscriminate overfishing can disrupt these ecosystems, leaving the coral more vulnerable to predators. Fishing boat anchors can also scar and break the corals below. Hide Caption 3 of 6 Photos: How are humans harming coral reefs? Invasive species: Over the past 25 years, lionfish have colonized Atlantic coastal regions, from their native Indo-Pacific waters. It's thought they were released into the Atlantic by owners who no longer wanted them as aquarium pets.



With fewer natural predators, the species' new Atlantic populations are growing rapidly. They can eat and out-compete native coral reef creatures. Aquarium releases, aquaculture and fishing boats can all unwittingly introduce invasive species to delicate coral environments. Hide Caption 4 of 6 Photos: How are humans harming coral reefs? Acidification: Seawater absorbs our carbon dioxide emissions, which makes the oceans more acidic.



Corals, like many marine species, protect themselves with skeletons made from calcium carbonate. More acidic seawater makes it harder for corals to build new skeletons, and can even decompose existing skeletons.



Hide Caption 5 of 6 Photos: How are humans harming coral reefs? Pollution: Oil spills, septic waste and pesticides can also disrupt coral reef ecosystems.



Researchers at the University of Queensland, Australia, found that when corals are exposed to chemical pollutants over long periods, their resilience to other stresses - including higher temperatures and ocean acidification - may also decrease. Hide Caption 6 of 6

The new study mapped areas of the ocean that would be best suited to this type of coral restoration, taking into consideration factors like acidity, water temperature, human population density and fishing frequency.

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