Coral reefs feed and shelter thousands of species of fish, buffer coastal areas against waves and storms, and support local economies through tourism and fishing.

But they’re increasingly threatened by a dramatic and destructive stress response known as coral bleaching. Bleaching occurs when prolonged exposure to warmer ocean temperatures and other stressors causes corals to expel their symbiotic algae, leaving corals’ white skeletons visible. (These algae give corals their color and nourish them through photosynthesis.)

Use the slider to compare bleaching projections for the 2030s and 2050s under a business-as-usual emissions scenario. Data source: WRI Reefs at Risk, adapted from Donner, S.D., 2009 study in PLoS ONE.

The map above shows the projected frequency of what the National Oceanic and Atmospheric Organization (NOAA) calls Bleaching Alert Level 2 Events for the 2030s and 2050s. (Specifically, it shows the percentage of years in each decade that these events will likely occur.) A Bleaching Alert Level 2 Event indicates intense heat stress and a likelihood that corals will die.

The brighter the color, the more frequently these events are likely to occur. So, that wash of yellow and green across the map? It signifies a dramatic rise in both the range and frequency of the most severe levels of bleaching if carbon emissions continue unchecked.

An analysis in the World Resources Institute’s Reefs at Risk Revisited report found that under a business-as-usual scenario for greenhouse gas emissions, roughly half of the world’s reefs could experience enough thermal stress to induce severe bleaching in five out of 10 years during the 2030s. During the 2050s, this percentage is expected to grow to more than 95 percent.

NOAA announced in summer 2017 that the third global coral bleaching event—the longest and most widespread so far—appeared to be on the wane. But it’s a temporary reprieve. As the map above reveals, things are set to get much worse.

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