The coral reefs necessary for the survival of half a billion people are very likely doomed to disappear due to global warming, even if the objectives of the Paris agreement are respected, according to a study published on Tuesday.
With an average temperature rise of 1.5°C compared to the pre-industrial era, the most ambitious goal of the Paris agreement, more than 99% of corals would be unable to recover from marine heat waves more and more frequent, estimates the study published in the journal PLOS Climate.
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And with a warming of +2°C, their mortality would be 100%, according to researchers who used a whole new generation of climate models analyzing the oceans at a resolution of 1km2.
“The stark reality is that there is no safe warming threshold for coral reefs
,” which are home to a quarter of marine life, said lead author Adele Dixon of the University of Leeds.
"Even 1.5°C is too much warming for ecosystems on the front line of warming
," she told AFP.
The 2015 Paris Agreement aims to limit warming to well below +2°C, if possible +1.5°C.
14% of corals have disappeared
Faced with the multiplication of heat waves, storms and floods on a planet which has so far gained around 1.1°C, the threshold of +1.5°C has de facto become the main objective.
But it could already be reached around 2030, according to the latest report from UN climate experts (IPCC).
In a previous report from 2018, the IPCC predicted the disappearance of 70 to 90% of corals at +1.5°C, and 99% at +2°C.
Too optimistic estimates, according to the results of the new study.
"Our research shows that corals around the world will be even more at risk from climate change than we thought
," said Adele Dixon.
After a bleaching episode related to the increase in water temperature, reefs generally need at least ten years to recover, if all other factors (water quality for example) are
"optimal"
, notes Maria Berger, another author of the study.
But the warming which multiplies the sea heat waves makes this recovery time impossible.
"We estimate that at +1.5°C, more than 99% of coral reefs will be exposed to intolerable thermal stress, and 100% at +2°C
," she told AFP.
Due to warming and pollution, 14% of corals disappeared between 2009 and 2018, turning underwater landscapes vibrant with color and life into cemeteries of bleached skeletons, according to recent research.
Australia's Great Barrier Reef has suffered five major bleaching events in the past 25 years.
And according to a study by experts from the US Oceanic and Atmospheric Administration (NOAA), not yet published but obtained by AFP, the Great Barrier Reef was the victim in November and December of a new heat wave. unprecedented.