Finally tonight, a look under the sea. Coral reefs are a crucial part of the marine ecosystem,

providing habitats for all sorts of marine life and protecting coastlines from storm damage.

But as Ali Rogan reports, scientists say rising ocean temperatures are posing a grave threat to the

future of the world's reefs.

The Maldiv Islands in the Indian Ocean are the picture of paradise.

But beneath the aqua blue water, there's a crisis unfolding.

Once vibrant, coral reefs have lost their colors in what scientists say is part of the

worst global bleaching event

on record, impacting more than 80 countries and territories.

A report from the National Oceanic and Atmospheric Administration revealed that 84% of the

planet's coral reefs have been hit.

The Smithsonian's Melanie Mcfield says the bleaching is triggered by prolonged exposure

to elevated ocean temperatures due to human-caused climate change.

It's very alarming.

So I think people really need to recognize what they're doing, you know, by the inaction.

You are, it's the kiss of death for coral reefs.

This is not the first mass event of its kind. It's the fourth known widespread bleaching of coral reefs.

But the troubling part, McPhield says, is that these episodes keep getting worse.

Coral reefs are known as the rainforest of the sea because of their biodiversity.

But scientist Mark Eakon says ocean temperatures aren't expected to cool anytime soon.

And until they do, the heat stress on corals could lead to permanent damage or kill the reefs altogether.

We just may never see the heat stress that causes bleaching dropping below the threshold

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