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 took inspiration from NASA’s mission to put an astronaut on the moon. But for Hoegh-Guldberg, the fine gray dust of the moon’s surface had nothing to do with the other world beneath the gentle waves of Queensland.
He remembers the copperband butterflyfish and its iridescent colors, whose beauty “defied logic,” as well as the “incredible” epaulette shark that uses its fins to walk on the seabed.
Today, however, diving on reefs comes with the burden of knowledge that Hoegh-Guldberg’s ten-year-old self did not have.
“Maybe my depression is because… I feel like I’m failing,” he told Guardian Australia in his home city of Brisbane.
The pioneering coral scientist looks at record temperatures in the world’s oceans in 2023 and takes it personally.
In what is becoming an all-too-regular occurrence, coral reefs like the ones he has spent his life researching are turning white in the Northern Hemisphere. He is nervous about what next summer will bring for the Great Barrier Reef.
“It takes 40 years of trying to get the science right to solve the problems,” he says. “And now that sea temperatures are literally going off the rails, it’s really starting to look like we didn’t do it.”
To any objective observer, Hoegh-Guldberg’s career has been anything but a failure.
A pioneer in the scientific understanding of coral bleaching, the University of Queensland professor has written more than 400 scientific papers. His work has contributed to the world’s understanding of the risks facing the ocean’s richest ecosystems – home to a quarter of all marine species – due to global warming.
Related: ‘Hope must be a strategy’: the scientist who refused to let the climate warmongers win
Hoegh-Guldberg began his PhD in California in the early 1980s, when reports emerged that coral reefs were turning white in large areas.
Was it a disease? Was it pollution? Was this caused by excessive sunlight? Did corals respond to a change in water salinity? “Everyone was speculating a bit, but no one had done the experiment,” he says.
In a series of what he calls “cooking experiments,” Hoegh-Guldberg took coral fragments and subjected them to different conditions in the laboratory.
What he and his colleagues discovered was that corals had a temperature threshold. Once these temperatures are exceeded, the corals begin to expel the tiny algae that live within them, giving the corals their color and many of their nutrients.
He first saw a major bleaching event for himself in 1994 in Tahiti. The reef was so clear that he could see the bleaching from the boat before he entered the water. Hoegh-Guldberg says locals told him they had no term in Polynesia to describe what happened.
Branded as an alarmist
As the 1990s drew to a close, more bleaching events were recorded and their severity increased. In 1998, corals around the world were bleaching.
“So the question is: How long will it take before this becomes a problem?” says Hoegh-Guldberg. At the time, he thought the answer might be a century away.
But he took the results of climate models and linked them to the temperature thresholds of corals.
Rather than a century or more, models suggested as early as the 2020s that some reefs could bleach six or more times per decade – a frequency far too high to give them time to recover.
“I thought I made a mistake. I didn’t believe it. I spoke to the climate people who supported me on the models. And yes, no matter how you look at it, by 2040…2050 you will be affected by bleaching events every year.”
It’s almost like getting an ulcer because you’re always on guard. That can build up over time and leave you a little depressed
Ove Högh-Guldberg
Hoegh-Guldberg wrote up the results in a paper. “Events as serious as 1998, the worst ever, 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 the conservative media labeled him an alarmist. He received threatening emails calling him a communist and saying they hoped he would die.
He felt empowered and confident in his science, but privately it affected him.
“It’s almost like getting an ulcer because you’re always on guard,” he says. “That can build up over time and make you a little depressed. I’m really a very optimistic person. But it does confuse you a bit, there’s no doubt about that.”
‘Could I have done something?’
In 2022, the Great Barrier Reef saw its sixth mass bleaching event. It was the first to occur in a supposedly cooler La Niña year and the fourth in six years.
“Could I have done something?” he asks. “You know, I could have glued myself to a fence somewhere?”
But the thought of turning to activism comes and goes quickly. He is more useful to the world, he says, as “the bald professor who comes along and talks about the details.”
Hoegh-Guldberg has spoken to governments and monarchs about the crisis facing reefs (both the literal kind, like the Prince of Monaco and current King Charles, and the figurative Sir David Attenborough). He has provided his expertise to climate lawsuits, to several United Nations climate reports and to government committees.
What gives him reason to remain optimistic, he says, is that some reefs around the world appear to be less exposed to global warming than others, thanks to the peculiarities of ocean currents. By focusing on protecting these reefs from other impacts, they can survive long enough for governments to reduce greenhouse gas emissions and stabilize temperatures.
“If you can do that, you start to maintain inventory,” he says.
Related: ‘Where did I go wrong?’ The scientist who tried to sound the climate alarm
However, he believes that if reefs are to be saved, it will take many generations for conditions to return to those he remembers as a child. “We have to look at this as a multigenerational response that we have to commit to,” he says.
As for the Great Barrier Reef, he believes the World Heritage Committee should have put it on a list of endangered sites, despite successive governments lobbying against it.
It is clear that the reef is in danger. “If it walks like a duck and it sounds like a duck…,” he says. “I think if you start playing with words, you’re doing a disservice to the debate.”
He says the Australian government is still showing a “kind of schizophrenia” by allowing new fossil fuel projects to proceed while claiming to be taking action on climate change.
“This is a planetary emergency,” he says. “This is so crucial for humanity. We will not live in bubbles in the future. You know, sooner or later we have to find a way to reconnect with nature.”
• In Weight of the World: The Burden of a Climate Scientist, we hear how three groundbreaking scientists made their discoveries, the personal toll it took on them, and how they remain hopeful during the hottest year on record. Experience the full series here