Scientist branded an alarmist for revealing the fate of coral reefs

Ove Hoegh-Guldberg was only 10 years old when he first saw the Great Barrier Reef. That year, 1969, most young children around the world were inspired by NASA’s mission to send astronauts to the moon. But according to Hoegh-Guldberg, the fine gray dust of the lunar surface had nothing in the other world beneath the gentle Queensland waves.

He recalls the copperband butterflyfish, whose beauty “defies logic” and its fringed iridescent colors, as well as the “incredible” epaulette shark, which uses its fins to walk on the seabed.

But diving on reefs these days brings with it a load of knowledge that Hoegh-Guldberg didn’t have when she was 10 years old.

“Maybe my depression is because… I feel a sense of failure,” he tells Guardian Australia in his home city of Brisbane.

Pioneering coral scientist looks at record-breaking temperatures in oceans around the world in 2023 and takes it personally.

In the northern hemisphere, the coral reefs he has studied throughout his life are turning white in an increasingly commonplace phenomenon. He’s worried about what next summer might bring to the Great Barrier Reef.

“We’ve been trying for 40 years to apply science to solve problems,” he says. “And when sea temperatures literally go off the rails, it really starts to look like we haven’t done that.”

To an impartial observer, Hoegh-Guldberg’s career was nothing short of a failure.

A pioneer of scientific understanding of coral bleaching, the University of Queensland professor has written more than 400 scientific papers. Their work has helped shape the world’s understanding of the risks the ocean’s richest ecosystems, home to a quarter of all marine species, face from global warming.

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Hoegh-Guldberg was starting her doctorate in California in the early 1980s, when reports began to emerge of coral reefs turning white over large areas.

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Was this a disease? Was it pollution? Was it due to excessive sunlight? Were the corals responding to changes in the salinity of the water? “Everyone was kind of speculating, but no one had done the experiment,” he says.

Hoegh-Guldberg took a series of coral pieces in what he called “cooking experiments” and subjected them to different conditions in the laboratory.

He and his colleagues found that corals have a temperature threshold. When these temperatures are exceeded, corals begin to expel the tiny algae that live inside them, giving the corals their color and most of their nutrients.

The first time he saw a major bleaching event for him was in Tahiti in 1994. The reef was so bright that he could see the boat whitening before it entered the water. Hoegh-Guldberg says locals told him there was no term to describe what was happening in Polynesia.

Branded as an alarmist

Towards the end of the 1990s, more bleaching incidents began to be recorded, and their severity was increasing. In 1998, corals all over the world turned white.

“So the question is: How long does it take for this to become an issue?” says Hoegh-Guldberg. At the time, he thought the answer might be a century away.

But he took the output of climate models and matched them to the corals’ temperature thresholds.

Rather than a century or more, models suggested that by the early 2020s some reefs had bleached six or more times per decade; this frequency was too high to give them time to recover.

“I thought I’d made a mistake. I didn’t believe it. I talked to climate people who backed me on the models. And of course, no matter how you cut it, you’re going to have bleaching every year until 2040… 2050.”

Hoegh-Guldberg wrote up the results in a paper. “Events as violent as the 1998 incident, the worst on record, are likely to become commonplace within 20 years,” he wrote.

His findings were met with a storm of criticism. Some of his scientific colleagues thought he had gone too far, and he was branded an alarmist in the conservative media. He received threatening emails calling him a communist and saying they hoped he would die.

He was encouraged and confident in his science, but privately it affected him.

“It’s like you’re getting an ulcer because you’re always on guard,” he says. “This can build up over time and make you kind of depressed. I’m a really optimistic person. But it shakes you up a bit, there’s no doubt about that.”

‘Was there anything I could do?’

In 2022, the Great Barrier Reef witnessed its sixth mass bleaching. It was the first event to occur during a supposedly cooler La Niña year and the fourth in six years.

“Was there anything I could do?” He asks. “You know, maybe I got myself glued to a door somewhere?”

But the thought of turning to activism comes and goes quickly. He says he is more useful to the world as “the bald professor who comes in and talks about details.”

Hoegh-Guldberg has spoken to governments and royalty about the crisis facing reefs (both literally, like the Prince of Monaco and the current King Charles, and figuratively, like Sir David Attenborough). He has brought his expertise to climate court cases, many United Nations climate reports and government committees.

What gives him reason to remain optimistic, he says, is that some reefs around the world are less exposed to global warming than others, thanks to quirks of ocean currents. Focusing on protecting these reefs from other impacts could ensure they last long enough for governments to reduce greenhouse gas emissions and temperatures stabilize.

“If you can do that, then you start to maintain stock,” he says.

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But if the reefs are to be saved, he believes it will take generations for conditions to return to those he remembers in his childhood. “We need to think of this as multi-generational responses that we need to commit to,” he says.

He believes the world heritage committee should put the Great Barrier Reef on the list of endangered areas, despite lobbying successive governments against it.

Clearly the reef is in danger. “If it walks like a duck and sounds like a duck…” he says. “I think you’re not doing the debate a good service if you start playing with words.”

He says the Australian government is still displaying a form of schizophrenia in allowing new fossil fuel projects to go ahead while claiming to be taking action on climate change.

“This is a planetary emergency,” he says. “This is very important for humanity. We will not live in bubbles in the future. You know, we need to find a way to re-engage with nature as soon as possible.”

• In The Weight of the Earth: A Climate Scientist’s Burden, we hear how three pioneering scientists made their discoveries, the personal toll it took on them, and how they remained hopeful throughout the hottest year on record. Experience the entire series here