As the metaphorical canary in the global warming coalmine goes, the planet’s coral reefs are hard to beat.

Swathes of corals in all tropical basins have been hit by the longest mass bleaching event yet recorded that kicked off in 2014 and ended, at least officially, in June.

Fossil fuel burning is firmly linked to rising ocean temperatures that push the corals into a stress reaction – they expel the special algae that give them their colour and most of their nutrients. It’s not certain death, but it can take five to 10 years for even the fastest growing coral species to fully recover.

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On Australia’s Great Barrier Reef, one research group found the abnormally hot conditions that caused corals to bleach in 2016 were 175 times more likely under today’s climate than one that hadn’t been loaded with extra carbon dioxide.

In 2016 about 30% of all corals on the reef died. In 2017 James Cook University’s Prof Terry Hughes estimates another 19% died.

And all this as global warming reaches just 1C. What happens to coral reefs at 1.5C of warming – the target set by the United Nations Paris climate agreement? Or higher?

It’s under this stark reality that a group of 18 mainly Australian scientists and reef managers, including those in government agencies, have waded in with a controversial proposal in an article in the science journal Nature Ecology and Evolution.

Existing conservation approaches, such as improving water quality around reefs and imposing restrictions or bans on fishing, are not working, the article says.

Instead, the scientists argue: “New and potentially riskier interventions must be implemented alongside conventional management efforts and strong action to curb global warming.”

Those interventions include “assisted evolution” – a suite of techniques that have been commonly used in commercial settings (think of selective breeding in plants and livestock as one example) but are now being considered as a way to develop coral species that have better tolerance of the heat extremes that reefs are increasingly facing.

Another idea is known as “assisted gene flow” – and involves essentially moving coral larvae or corals that can cope with higher temperatures into areas where current coral species are dying.

Much further down the track, the authors also suggest developments in synthetic biology where beneficial genes are either created or selected from the same species.

Across all these methods, the authors write there are multiple issues, some ethical and some practical, that need to be much better understood. But the time to start is now.

For example, physically moving coral species could see dangerous pathogens hitching a ride. Or, once in place, transplanted coral could simply die because of a lack of adaptation to local conditions.

How do you select which species to “save” and which ones to discard? With those decisions, also come knock-on effects of the multiple marine species that rely on those coral habitats.

How would the public react to an “artificial reef” or the inevitable claims that scientists are playing God?

It could all get very messy and very costly.

Several leading scientists I’ve spoken to say a key danger in advocating technological fixes is that it could be an excuse to ignore what everyone agrees is the main game – cutting greenhouse gas emissions as quickly as possibly.

The lead author of the new article is Dr Ken Anthony, a principal research scientist at the Australian government’s Australian Institute of Marine Science.

Anthony accepted that some in the science community could see the pursuit of unconventional methods as a tacit admission of defeat on the emissions front.

“But we need a philosophy where we don’t just give up,” he told me. “We do need two balls in play. We need to fix climate change and the more we can mitigate carbon, the better the chances that these things will work. It is not an either, or, situation.

“But we agree it’s controversial to talk about this … We have to start looking at the reef in an objective way. How can we protect habitats that protect species?”

We need to find solutions, but I don’t think growing corals is part of that Terry Hughes

James Cook University’s Prof Terry Hughes, a director of the Australian Research Council Centre of Excellence for Coral Reef Studies and also the convenor of the national coral bleaching taskforce, is deeply skeptical about the viability of many of the proposed techniques.

In particular, whether corals are developed in laboratories or are physically transferred from one location to another, the physical placement of corals on reef structures is “extremely expensive”.

He said: “I actually see this problem we are now facing – with back-to-back bleaching events on the Great Barrier Reef killing about half the corals – that this is more a governance problem. What’s broken is not so much the corals – they don’t need fixing – but the legal frameworks, the politics and the institutions.

“We need to find solutions, but I don’t think growing corals is part of that. I think it’s about changing people’s attitudes and behaviours and getting carbon dioxide emissions down by transitioning away from fossil fuels as quickly as possible. Without that, nothing else really works.”

People are now operating under the terms that everything should be on the table Ove Hoegh-Guldberg

On this point, AIMS’s Anthony is in agreement. “The better outcome we get in terms of carbon mitigation, the better chance we stand with conventional and these new interventions,” he says. “I can’t imagine having success where you don’t have both. As I said, you have to have two balls in play and if you drop either of them, then it could be game over.”

Dr Mark Eakin, coordinator of Coral Reef Watch at the US government’s National Oceanic and Atmospheric Administration, thought it was “responsible and necessary” to have open discussions about alternative strategies.

“Corals and coral reefs are now at a critical juncture,” he told me by email. “Conventional conservation measures alone are no longer enough. We need to be looking at all of the tools in our toolboxes.”

But critically, Eakin added: “The biggest danger of moving in this direction is the potential that some will see this as being a way to engineer our way out of the problem — using it as an excuse to not act on the rising CO2 that is the ultimate cause of the problem.”

Prof Ove Hoegh-Guldberg, a leading marine biologist and director of the University of Queensland’s global change institute, is a pioneer in coral bleaching research.

He told me there was a “movement sweeping the coral research community” in response to the massive and unprecedented bleaching at reefs around the world.

“The pace of environmental change is outstripping the natural ability of corals to keep up, and people are now operating under the terms that everything should be on the table. That’s reasonable.”

But he said each time the media reported on new technological fixes, there was a ripple effect among politicians looking for a way out.

“A solution might look good on paper and yes, you can grow heat-resistant corals in a lab, but nobody wants to talk about the economics. Once you scale these things up, they can become very expensive.”

One study looking at marine restoration projects found coral reefs were the most expensive to restore, with costs as high as $1.8m per hectare (the entire Great Barrier Reef covers about 35m hectares).

Hoegh-Guldberg offered up a “back of the envelope” calculation on costs.

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The Great Barrier Reef is 40,000 sq km. If you were to grow a coral in a lab and transplant it every five metres at $5 each time, then this gives a cost of about $40bn, “and that’s just for one single species,” he says. Scale this up globally, and he says you easily get to costs in the trillions of dollars.

“We are in a desperate situation and we need to try all sorts of things because you don’t know what might work,” he says.

“But on the other hand, you can get distracted from the main game. The only economic way to deal with this issue is to reduce emissions and take up renewable energies at a furious rate,” he says.

“Clearly we have to think outside the box, but let’s not pretend the core issue is not reducing emissions. For coral reefs, it’s really the Paris agreement and 1.5C … or bust.”