Coral reefs, home to marine life, could be wiped out even if climate goals are met: study

The coral reefs that anchor a quarter of marine wildlife and the livelihoods of more than half a billion people will most likely be wiped out even if global warming is capped in the Paris climate goals, researchers said on Tuesday. An average rise of 1.5 degrees Celsius above pre-industrial levels would prevent more than 99% of the world’s coral reefs from recovering from increasingly frequent marine heat waves, they reported in the journal PLOS Climate. At two degrees of warming, mortality will be 100% according to the study, which used a new generation of climate models with an unprecedented resolution of one square kilometer. “The stark reality is that there is no safe limit to global warming for coral reefs,” lead author Adele Dixon, a researcher at the University of Leeds’ Faculty of Biology, told AFP. .

“1.5°C is still too much warming for ecosystems on the front lines of climate change. »

The 2015 Paris Agreement enjoins nearly 200 countries to keep global warming “well below” 2C (36 degrees Fahrenheit).

But with more storms, floods, heatwaves and deadly droughts after just 1.1°C of warming so far, the world has embraced the treaty’s ambitious goal of a 1.5° limit. vs.

A landmark report released in August by the UN’s IPCC Climate Science Panel said global temperatures could hit the 1.5C threshold as early as 2030.

In 2018, the IPCC predicted that 70 to 90% of corals would be lost at the threshold of 1.5°C, and 99% if temperatures rose another half a degree.

The new findings suggest that these grim predictions were actually overly optimistic.

Marine heatwaves

“Our work shows that corals around the world will be at even greater risk from climate change than we thought,” Dixon said.

The problem is sea heat waves and the time it takes for living corals to recover, a healing period called “thermal refuge”.

Coral communities typically need at least 10 years to rebound, and that’s assuming “all other factors” — no pollution or dynamite fishing, for example — “are optimal,” the co-author said. Maria Berger, also in Leeds.

But increasing warming reduces the duration of thermal refuges beyond the ability of corals to adapt.

“We predict that over 99% of coral reefs will be exposed to 1.5°C intolerable heat stress, and 100% of coral reefs to 2°C,” Berger told AFP.

Australia’s Great Barrier Reef, the largest coral system in the world, has experienced five massive bleaching events in the past 25 years.

An unpublished study obtained by AFP, written by experts from the Coral Reef Watch Unit of the US National Oceanic and Atmospheric Administration, indicates that the Great Barrier Reef has again been in the grip of a wave of record heat in November and December.

The oceans absorb about 93% of excess heat from greenhouse gas emissions, protecting land surfaces but generating huge, long-lasting marine heatwaves that are already pushing many coral species beyond their limits. tolerance limits.

A single so-called bleaching event in 1998 caused by warming waters wiped out 8% of all corals.

Coral reefs cover only a tiny fraction – 0.2% – of the ocean floor, but they are home to at least a quarter of all marine animals and plants.

In addition to supporting marine ecosystems, they also provide protein, jobs, and protection from storms and coastal erosion for hundreds of millions of people around the world.

The value of coral reef goods and services is about $2.7 trillion annually, including $36 billion from tourism, according to the report.

Global warming, with the help of pollution, wiped out 14% of the world’s coral reefs from 2009 to 2018, leaving graveyards of bleached skeletons where vibrant ecosystems once thrived, recent research has shown.

Coral loss during this period varied by region, ranging from 5% in East Asia to 95% in the eastern tropical Pacific.

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