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The world's corals and coral reefs face severe degradation if global-mean temperatures rise 2 degrees above pre-industrial levels, an international study has found.

The study was published today in Nature Climate Change.

The study by a research team from Australia, Germany and Canada, looked at more than 2000 coral reef locations worldwide and projected how often these locations might face severe bleaching events due to increasing sea surface temperatures in the future.

The study revealed that only strong action to mitigate greenhouse-gas emissions plus an assumed ability to rapidly evolve will save some coral reefs.

Dr Malte Meinshausen co author from the University of Melbourne and Potsdam Institute for Climate Impact Research said " The findings revealed there was only a small window of opportunity to save at least some parts of the world's coral reef ecosystems from long-term degradation.’

“If we are not reducing greenhouse gas emissions rather swiftly, this already small window of opportunity will be effectively closing within a decade,” he said.

Coral reefs are the most biologically diverse ecosystems on the planet and provide critical services such as coastal protection, tourism and food to hundreds of millions of people worldwide.

Global warming and ocean acidification, both driven by human-caused CO2 emissions, pose a major threat to these important marine ecosystems.

“Our findings show that under current assumptions regarding thermal sensitivity, coral reefs will no longer be prominent coastal ecosystems if global mean temperatures reach 2°C above the pre-industrial temperatures,” said lead author Dr Katja Frieler from the Potsdam Institute for Climate Impact Research.

Professor Ove Hoegh-Guldberg, from the Global Change Institute and ARC Centre for Excellence for Coral Reef Studies at The University of Queensland said “The research used some of the most up-to-date models and sophisticated tools available.
 
The study involved scientists from Potsdam Institute for Climate Impact Research, Germany, the University of British Columbia in Canada and the universities of Melbourne and Queensland in Australia.

To project the cumulative heat stress at 2160 reef locations worldwide, they used an extensive set of 19 global climate models.

By applying different emission scenarios covering the 21st century and multiple climate model simulations, more than 32,000 simulation years was diagnosed.

Researchers said this allowed for a more robust representation of uncertainty than any previous study.