Climate crisis puts half of coral reefs at risk by 2035

Half of the world’s coral reefs are threatened by 2035 if nothing is done to mitigate the climate crisis.

That’s the alarming finding of a new study published in PLOS Biology Tuesday, which found that 50 percent of reefs could face “unsuitable” conditions in just 13 years.

“While the negative impacts of climate change on coral reefs are well known, this research shows that they are actually worse than anticipated due to a broad combination of climate change-induced stressors,” lead author and University of Hawaiʻi (UH) at Mānoa Department of Geography and Environment in the College of Social Sciences PhD student Renee O. Setter said in a press release. “It was surprising to find that so many global coral reefs would be overwhelmed by unsuitable environmental conditions so soon due to multiple stressors.”

The fact that coral reefs are in trouble is not news. The climate crisis is currently considered the greatest threat to the world’s reefs, and 14 percent of them were lost because of it between 2009 and 2018 alone. According to the Intergovernmental Panel on Climate Change, even limiting global warming to 1.5 degrees Celsius beyond pre-industrial levels would still see 70 to 90 percent of tropical reefs wiped out.

The new study builds on these earlier warnings by considering how multiple stressors might interact to harm a reef, instead of focusing on just one factor.

“We know that corals are vulnerable to increasing sea surface temperatures and marine heat waves due to climate change. But it is important to include the complete anthropogenic (environmental change caused or influenced by human activity) impact from numerous stressors that coral reefs are exposed to in order to get a better sense of the overall risks to these ecosystems,” study co-author and associate research professor at the Hawaiʻi Institute of Marine Biology in UH Manoa’s School of Ocean and Earth Sciences and Technology Erik Franklin said in the press release.

The five stressors the research team considered were

1. Sea-surface temperature

2. Ocean acidification

3. Tropical storms

4. Land use pressures

5. Human population pressures

The research team was interested in when one or more of these pressures would generate unsuitable environmental conditions. This means that the reef ecosystem’s health would degrade considerably, but the species calling it home wouldn’t necessarily become locally or globally extinct. To find out, UH Manoa-based team ran different models based on different emissions scenarios considering the impacts of one or multiple stressors.

In a worst-case, business-as-usual emissions scenario, they found that just one stressor would push half of reefs into unsuitable conditions by 2050. However, if multiple stressors were considered, half of reefs would reach that point by 2035. For a best-case emissions reduction scenario, the difference was still stark. Looking at just one stressor would see 41 percent of reefs facing unsuitable conditions by 2100, but considering multiple would see 64 percent of reefs reach that point by the century’s end.

For the worst-case scenario, predictions were even more dire for the mid and end point of the century, with 99 percent of reefs facing unsuitable conditions due to at least one stressor by 2055 and 93 percent of reefs threatened by two or more stressors by 2100. All of this means that scientists and conservationists need to act faster to save the world’s coral reefs.

“Prior studies have indicated the projected dire effects of climate change on coral reefs by mid-century; by analyzing a multitude of projected disturbances, our study reveals a much more severe prognosis for the world’s coral reefs as they have significantly less time to adapt while highlighting the urgent need to tackle available solutions to human disturbances,” the study authors concluded in their abstract.

While the paper is global in scope, it also has important local consequences.

“This has great implications for our local Hawaiian reefs that are key to local biodiversity, island culture, fisheries and tourism,” Franklin said in the press release.

The team next hopes to study the impact of the climate crisis on individual coral species to determine which are more vulnerable.