Coral reefs have had a rough run over the past two years.

Climate change has ratcheted up ocean temperatures and El Niño helped kick them into overdrive in parts of the world. All that heat kicked off what has been a major coral die-off around the globe.

Coral bleaching alert levels over the past 30 days. Image: Coral Reef Watch

While El Niño has passed its peak, scientists have warned that the global coral die-off, known as coral bleaching, is still far from over. What began in 2014 is projected to continue through this year and even into early 2017.

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This is the third global bleaching event on record. The others were in 1998 and 2010, both El Niño years. El Niño, which is marked by warmer than normal waters in the tropical Pacific, has certainly played a role. The steady background creep of ocean warming due to climate change, however, is also an important factor. More than 90% of the accumulated heat due to climate change is ending up in the oceans and its effects are being acutely felt.

"We are currently experiencing the longest global coral bleaching event ever observed," Mark Eakin, the Coral Reef Watch coordinator, said in a statement.

The prolonged exposure to high water temperatures has left many reefs in critical shape. The warm water causes corals to expel the algae they rely on to grow, leaving ghostly white skeletons in the place of thriving coral communities.

Coral bleaching forecast for March-June. Image: Coral Reef Watch

The Pacific Ocean has been the epicenter of the global bleaching event and Christmas Island has been the tiny bullseye of that epicenter. The 150 square mile island sits right in the middle of the El Niño-warmed waters.

Coral there have been subjected to some of the most stressful conditions anywhere in the world. Specifically, El Niño sent water temperatures as high as 88°F, or about 6°F above normal, in the region. That extended period of stress had already killed off a wide array of corals when Kim Cobb, a coral expert at Georgia Tech, visited the reef in November during peak El Niño heat.

And though waters are cooling as El Niño ebbs, Cobb is expecting to see even more devastation when she returns to Christmas Island next month. She's using crowdfunding for the trip because of the rapid response nature of the work and the wealth of information she and other scientists can learn from.

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"I call it the data collection opportunity of an academic career," she said. "How this reef evolved through this mega El Niño (represents) this incredible opportunity because we know we may face more extremes in the future."

The data Cobb plans to collect will provide valuable insight into which corals survive this extreme heat event. With climate change expected to keep warming oceans, those types of insights could be key to conservation efforts, not just at Christmas Island but around the world.

And while Christmas Island should experience a reprieve with oceans returning to normal temperatures around the region later this year, other areas will continue to feel the heat. The odds are increasing for a La Niña event later this year. While that means cooler-than-normal waters for the eastern and central tropical Pacific, it ramps up temperatures in the western edge of the basin around Indonesia and the Papua New Guinea.

That area is known as the Coral Triangle, an ecologically crucial spot for coral, fish, turtles and other sea creatures. It's already under threat from the current global coral bleaching event and could face even higher risks if La Niña materializes.

This article originally published at Climate Central here