Earth is likely just a decade a way from hitting 1.5°C of global warming — and scientists say it will be "catastrophic" for coral reefs
The United Nations has warned the continued use of fossil fuels is hurtling the planet to 1.5°C of global warming, relative to 1850-1900 levels, a threshold that will result in "unprecedented" extreme weather events. According to new research, climate change will also result in coral bleaching that will be "catastrophic" for reefs, and potentially, the marine life that live around them.
Bleaching can occur from a change in ocean temperature, pollution, overexposure to sunlight and low tides. Any of these influences can stress coral and causes it to release the algae that live in its tissues. The loss of algae, corals' primary food source, causes the coral to turn white and makes it more susceptible to disease.
Reefs are "among the most biologically diverse and valuable ecosystems on Earth," serving as a vital resource for an estimated 25% of all marine life, which depend on reefs for their life cycles, according to the Environmental Protection Agency. Roughly half a billion people also depend on reefs for food, coastal protection, tourism and fisheries' income.
But as climate change continues to negatively impact the planet, it will "overwhelm" those reefs, researchers said, and almost none of them will be able to escape a grave scenario.
The latest study, published in PLOS Climate on Tuesday, focused on thermal refugia, areas of coral reefs that can maintain the temperatures that coral reefs need to survive, even as nearby ocean temperatures increase. Presently, about 84% of reefs are thermal refugia and have had enough time to recover between heat waves that bleach, and kill, coral reefs.
Once the planet hits 1.5°C of warming, researchers said, just 0.2% of Earth's thermal refugia will have enough time to recover between extreme heat events, and more than 90% of those reefs will suffer "an intolerable level of thermal stress." At 2°C, researchers found, no thermal refugia will remain, and all coral reefs will be exposed and vulnerable.
This study was published the same day that other researchers concluded that marine heat is the "new normal" for oceans.
The only areas researchers believe might be able to survive the 1.5° threshold are small regions in Polynesia and the Coral Triangle where lower rates of warming are anticipated. But even those regions would no longer be suitable if Earth hits 2°C of warming.
"Our finding reinforces the stark reality that there is no safe limit of global warming for coral reefs," lead author of the study Adele Dixon said in a statement.
And the world may just be years away from watching this unfold.
The U.N.'s Intergovernmental Panel on Climate Change (IPCC) said in August that the world is likely to hit the 1.5°C of warming threshold in the early 2030s. As the IPCC explained, global warming of 1.5°C will result in more frequent and more intense extreme heat events. It usually takes coral reefs about a decade to grow back and be fully functional again after a severe coral bleaching event, but under the predicted climate scenarios, they will not have enough time to recover.
Humans' excessive rates of deforestation and overuse and burning of fossil fuels, which greatly contribute to greenhouse gas emissions and heat within Earth's atmosphere, are the primary driver for the anticipated outcome of global warming.
The researchers proposed some measures that can be put into place to help the ailing reefs, including removing stressors such as fishing and tourism, and helping coral migrate to more suitable environments. But they added that such measures may only be beneficial in the short term, and that the true culprit — global warming — must be addressed, and quickly.
Scott Heron, a physics professor at the ARC Centre of Excellence for Coral Reef Studies in Australia, said that the study confirms that people must urgently take "significant action" on greenhouse gas emissions.
The Paris Climate Agreement has the majority of nations committed to staying below the 1.5°C level, but researchers of this study said that limiting global warming to that change "will not be enough to save most coral reefs."
"Coral reefs are important for the marine creatures that live on them and for over half a billion people whose livelihoods and food security rely on coral reefs," research supervisor Maria Beger said. "We need to not only deliver on Paris goals - we need to exceed them, whilst also mitigating additional local stressors, if we want children born today to experience reef habitats."