If global temperatures continue rising, virtually all the corals in the Atlantic Ocean will stop growing and could succumb to erosion by the end of the century, a new study finds.
The analysis of over 400 existing coral reefs across the Atlantic Ocean estimates that more than 70% of the region’s reefs will begin dying by 2040 even under optimistic climate warming scenarios.
And if the planet exceeds 2 degrees Celsius of warming above preindustrial temperatures by the end of the century, 99% of corals in the region will meet this fate. Today, the planet has warmed about 1.3 degrees Celsius over preindustrial temperatures.
The implications are grave. Corals act as the fundamental building blocks of reefs, providing habitat for thousands of species of fish and other marine life. They are also bulwarks that break up waves and help protect shorelines from rising sea levels. A quarter of all ocean life depends on coral reefs, and over 1 billion people worldwide benefit from them, according to the National Oceanic and Atmospheric Administration.
To predict how corals will fare in future conditions, scientists analyzed corals that grew over 10,000 years ago across the Caribbean, including those off Barbados and Costa Rica, and those off the Florida Keys.
Many of the ancient remnants are now on islands in places where tectonic activity uplifted and exposed the seabed. These landscapes allow scientists to gather data that is impossible to get from living corals without damaging them.”The reefs have changed so much that they’re not even slightly doing what the reefs of the past used to do,” said Alice Webb, a coral reef ecologist at the University of Exeter and one of the authors of the study, which was published Wednesday in the journal Nature.
For thousands of years, corals — which require shallow water with access to sunlight to thrive — have grown vertically to keep pace with rising seas, generally maintaining a close link between reef height and sea levels.
Understanding the historical balance between growth and erosion is crucial for predicting how coral reefs might change in the future, Webb said.
But today, the climate is changing too quickly for corals to easily adapt, and the relationship between reef growth and the rising sea levels “is essentially broken,” said Chris Perry, a coral reef geoscientist at the University of Exeter and lead author of the study.
In the Caribbean, corals have been especially hard hit by recent years of severe heat stress and disease outbreaks, which can be exacerbated by warmer temperatures. About 60% of the studied reefs near Florida and nearly 40% of those near Mexico have “basically stopped growing,” Perry said. “We’ve seen off-the-scale warming, the magnitude and longevity of which has never been seen in the region.”
The world seems to be on track to cross the warming threshold that the study indicates would imperil corals. According to the most recent report by the Intergovernmental Panel on Climate Change, limiting global warming to 2 degrees Celsius would require an “unprecedented” uptick in efforts to cut back greenhouse gases.
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