For years, the United States' National Oceanic and Atmospheric Administration (NOAA) has categorized coral reefs at five levels of concern — from "No Stress" to the most threatened "Alert Level 2." But disturbing reports of record-setting temperatures recently prompted NOAA to add three new higher warning levels to their system.

What's happening?

NOAA's Coral Reef Watch assigns a warning level based on degree heating weeks (DHWs). The DHWs signify how many weeks a reef has been subjected to temperatures above the normal maximum. And while the prior rankings gave the highest threat rating to 8 DHWs or above, new data from the northern hemisphere showed several places surpassing 20 DHWs, as the Guardian explained.

The high DHWs lead to excessive amounts of coral bleaching, which is often fatal for reefs and the life they support. 

"We are entering a new world in terms of heat stress where the impacts are becoming so pervasive that we had to rethink how we were doing things," said Coral Reef Watch director Dr. Derek Manzello, per the Guardian. "When you exceed a DHW value of 20 it is analogous to a Category 5 cyclone, with unbelievably severe, drastic damage. It's the worst-case scenario."

Richard Leck of WWF-Australia agreed. As he told the news outlet, "What this new system shows is that ocean temperatures and the risks to coral reefs are literally off the charts … global heating is impacting our oceans in the here and now in ways unimaginable only a decade ago."

Why is coral bleaching so concerning?

Essentially, coral bleaching causes corals to starve, which is bad news for the 25% of all marine life and the 500 million humans who depend on corals for survival, according to U.S. government agencies. 

But perhaps even more concerning is the fact that human-induced global heating is making the issue worse. With temperatures rising and weather patterns changing because of pollution, the world's oceans are growing far too hot, far too quickly. 

According to Professor Tracy Ainsworth of the International Coral Reef Society, severe heat events were rare even just a decade ago. "But now we don't just talk about bleaching events, but mortality events — and that's what this change represents," Ainsworth told the Guardian.

What's being done?

Because the primary cause of coral bleaching is global heating, it's crucial to take steps to reduce your daily pollution. 

From opting for public transit instead of driving, to minimizing your food waste, to skipping toxic chemical pesticides and herbicides (which often end up in the ocean) in your garden, there are a number of concrete actions that you can take. And when it comes to protecting the ocean, it's important to choose an ocean-friendly sunscreen.

There are also several organizations working hard to combat bleaching, such as the reef restoration and research group Coral Gardeners.

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