Climate change could wipe out almost all coral reef habitats around the world by 2100, according to research released Monday.
The bleak outlook forecasts that warming oceans and rising seas could have a devastating impact on ocean ecosystems, suggesting that efforts to restore dying corals will likely encounter difficulties as global warming continues to wipe out habitats that could once support healthy reef systems.
"By 2100, it's looking quite grim," Renee Setter, a biogeographer at the University of Hawaii at Mānoa, said in a statement. She presented her findings at the annual Ocean Sciences Meeting, which is being held through Friday in San Diego.
Setter and her colleagues simulated ocean environments in which coral reefs currently exist based on projections of sea surface temperature, ocean acidification, wave energy, pollution and fishing practices. They found that by 2100, few to zero suitable habitats for corals are likely to remain.
"Honestly, most sites are out," she said in the statement.
The few sites that could support reefs by the end of the century include small parts of Baja California in Mexico and the Red Sea, according to the researchers.
The research shows that corals are most vulnerable to changes in their environment driven by human-caused greenhouse gas emissions. Greenhouse gases, such as carbon dioxide, trap heat in the atmosphere, increasing global surface and ocean temperatures. And when carbon dioxide mixes with ocean water, the resulting chemical reactions make the water more acidic.
The combination of warming seas and ocean acidification is already threatening coral reefs around the world, causing the ecosystems to undergo so-called bleaching events.
From 2014 to 2017, about 75 percent of the world's tropical coral reefs experienced warm conditions severe enough to trigger bleaching events, according to the National Oceanic and Atmospheric Administration. And in 2016 and 2017, about half the coral in Australia's Great Barrier Reef died after record heat triggered mass bleaching.
Coral bleaching occurs as a response to abnormal environmental conditions, such as cooler- or warmer-than-usual ocean temperatures, or when oceans become more acidic. When stressed, corals expel tiny photosynthetic algae that live in their tissues, causing the vibrant marine invertebrates to turn completely white.
Bleaching events don't necessarily kill the corals, but the reefs become particularly susceptible to disease, and as oceans continue to warm at an accelerated pace, many reef systems are under siege.
In addition to driving tourism and boosting local economies, coral reefs are an integral part of ocean ecosystems, supporting hundreds — and sometimes thousands — of fish and other marine species. In a 2017 Deloitte Access Economics report, for instance, the Great Barrier Reef off Australia, a designated World Heritage Site, was valued at $56 billion.
Beyond climate change, coral reefs are also under threat from illegal fishing, coastal development projects and pollution.
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Setter said that efforts to clean up pollution in the world's oceans and projects to restore at-risk reefs are essential but that ocean ecosystems will continue to decline if the root causes of climate change are not addressed.
"Trying to clean up the beaches is great and trying to combat pollution is fantastic. We need to continue those efforts," she said in the statement. "But at the end of the day, fighting climate change is really what we need to be advocating for in order to protect corals and avoid compounded stressors."