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Shading corals and deploying more heat-resistant species across the Great Barrier Reef on an as-yet untested scale could buy the world heritage site another two decades, according to a study led by Australian government scientists.

The scientists said combining “life support” interventions such as cloud brightening – which involves spraying sea water to make low-altitude clouds more reflective – with better management of a coral-eating starfish could help delay “precipitous declines” caused by global heating.

But the scientists said it would only be effective if strong global action was taken to rapidly cut greenhouse gas emissions.

The study, published in the journal Royal Society Open Science, presumed the new and mostly untested technologies could be deployed on an unprecedented scale.

Coral reefs around the globe are considered to be among the ecosystems most at risk from the climate crisis.

The study’s lead author, from Australia’s national science agency CSIRO, said the results in the face of global heating were “confronting” but showed there was a way to buy the ecosystem some time if the technologies developed as hoped.

“If the reef needs to be put on life support for a while, then these interventions are how we might go about doing that,” said Dr Scott Condie, a CSIRO senior principal research scientist.

“This is a way of sustaining the health of the reef until we can implement effective global action on climate change.”

Scientists in Australia are working on a $150m government-backed program to develop and deploy a range of technologies and measures to protect the reef.

For the study scientists ran computer models with different combinations of approaches to see which would keep coral cover at the highest levels.

Dr Ken Anthony, a co-author of the study and associate principal research scientist at the Australian Institute of Marine Science, said: “Corals are to reefs what trees are to forests. If you lose the framework then you are saying goodbye to all the species that rely on them.”

Scientists from CSIRO, the Australian Institute of Marine Science, University of Tasmania, University of Queensland, Southern Cross University, Great Barrier Reef Marine Park Authority and University of Sydney contributed to the research.

The study presumed that the world would take strong action to reduce emissions, using a scenario where global temperatures rise about 1.8C from current levels.

With no interventions at all, the models suggested average coral cover across each of the Great Barrier Reef’s 3,753 individual reefs would fall to just 3% by the year 2070.

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Combining three approaches would deliver the best outcome. Controlling the coral-eating Crown of Thorns starfish, shading reefs and developing more heat tolerant corals saw a 53% rise in coral cover, compared with taking no extra action.

The results of the modelling, the authors said, suggested these gains delayed the “precipitous decline” of coral cover by about two decades.

Anthony said the suite of approaches could be likened to a “healthcare strategy” to manage climate change which was like a “systemic disease” for the reef.

“But you don’t give up on the patient. If you have comprehensive healthcare and you do the best with existing and new interventions and ramp those up, you can buy the reef some time.

“The key message here is that there are no solutions without mitigation.There is a limit to how far we can take this.”

Climate change is widely acknowledged by scientists as the greatest threat to the future of the reef.

Ocean heating has triggered three major mass bleaching events since 2016. Bleaching weakens corals and can kill them if temperatures stay high. Excess heat can also kill corals outright.

The latest 2020 bleaching event which affected reefs along the entire 2,300 kilometre length was the most widespread on record.

Dr David Wachenfeld, chief scientist at the Great Barrier Reef Marine Park Authority, described the event as an “urgent call for help.”

In 2019 the authority downgraded the reef’s long term outlook to “very poor” for the first time.

In the research, the authors admit the assumptions they used in their modelling about the effectiveness or scale of some of the interventions were optimistic.

One approach being developed are artificial structures placed around the base of reefs that help stabilise coral rubble that juvenile corals can grow on. This could help on a more local scale.

But the modelling assumes deploying these structures could be done at a scale of 100 hectares per year, which the authors say “is orders of magnitude larger than any past deployment.”

Condie said some of the assumptions about how quickly technologies could be developed and deployed were “aspirational” and others were possible “if you were prepared to invest enough”.

In another example, the modelling assumes shading the reef through technologies such as cloud brightening – which has undergone an early trial – could reduce temperatures across the entire reef to the equivalent of 1C for a month.

But the research says “major uncertainties” remain in the “efficacy and cost-effectiveness” of these technologies.

Prof Terry Hughes, director of the ARC Centre of Excellence for Coral Reef Studies at James Cook University who has been monitoring and researching changes to the reef caused by global heating, said: “I think this research tells us that interventions won’t get us there and we have to deal with the root causes – greenhouse gas emissions.”

Hughes said it seemed “implausible” that shading reefs could ever deliver cooling to levels modelled in the research.

“As the authors say themselves, they are modelling something which is orders of magnitude more than current interventions.

“I am not saying don’t investigate these, but as the modelling shows there is no reef-scale intervention that we could actually practically deploy that would make a difference.

“This is a general comment and not in relation to this paper, but are we buying time for the reef or are we buying time for the fossil fuel industry so that its inevitable decline is just postponed?

“A more rational approach should be to stop the emissions.”



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