‘Reefs as we have known them will not survive anywhere’

Himanshu Nitnaware (HN): How worrisome is the scale of the event with over 80 per cent of coral reefs bleached?

David Obura (DO): This is the strongest heatwave experienced by corals globally, the fourth since 1998. These global mass coral bleaching events have in the past resulted in about 15 per cent of all corals dying each time. After each event some coral recovery happens, but there has never been enough time and recovery ability to get back their earlier state. So, we are observing progressive loss of corals in almost every coral reef region around the world. Within the next few decades, it is predicted that these heatwaves will happen less than two to five years apart, which, of course, means it is impossible for reefs to recover, and we are seriously concerned that reefs connected across basins as we have known them will not survive anywhere. Individual reefs and some resistant regions will remain with coral reefs, but most will transition to novel ecosystems dominated by algae and other invertebrates and/or microbes

HN: Are such events getting frequent and severe?

DO: With warming temperatures, bleaching events have increased in frequency, duration and in terms of geographic extent. The Indonesian-Philippine region (containing the most diverse and vibrant reefs globally in a sub-region called the “coral triangle”) is the last region that does not (yet) show major declines in reef health at regional levels, but individual locations and sub-regions are being impacted already. Many regions were thought to be refuges as they did not bleach during the first and the second global bleaching events, but inevitably, with the amount of immediate and committed warming being imposed by fossil fuel use and economic growth globally, the tolerance thresholds of most regions have been exceeded to date. For example, the Great Barrier Reef did not bleach until the third global bleaching event (2014-17), and was lauded as “too big to fail”—this is not a typical display of short-sighted, short-term hubris in this era of catastrophic global change. But in the third global event its thresholds were exceeded spectacularly, rolling from one sub-region to another. And with committed warming—unless we go to zero emissions as fast as possible, to remain within 2oC warming, and ideally return to 1.5oC warming or below—even the Indonesian-Philippine region’s limits will be exceeded. Many studies and evidence are in agreement—they are synthesised in the IPCC reports in particular, as well as in IPBES (though with less focus on climate change impacts).

HN: Are the corals able to recover from bleaching?

DO: The recovery of reefs from bleaching and mortality is impeded by increasing temperatures, accumulation of other pressures, and insufficient recovery from prior events such that the recovery ability is undermined. At the level of individual corals some adaptation is being shown in that corals alive now are not bleaching at temperatures that induced bleaching and even mortality in 1998. But this is because the susceptible corals have been eliminated, and those that survived and reproduced have some capacity for adaptation to changing conditions. But all evidence suggests that the degree of warming is likely too fast to keep up, and anyway, so much genetic diversity has been lost by elimination of the weaker corals (individuals, population and species) that they will likely experience genetic bottlenecks, which raise extinction risk. My own view is that most coral reef regions are committed to crossing a tipping point within the next 20 years, if they have not done so already. It’s certainly not nice to be a voice that says it. But we have to face the facts to minimise damage and bring forward the best possible future outcomes.

This interview was originally published in the cover story Fading reefs in the November 1-15, 2025 print edition of Down To Earth