Record-breaking ocean heat triggers massive coral reef bleaching

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• William Brangham:

  The temperatures of the world's oceans are quite literally off the charts. That orange line, that is last year's reading. The red line at the very top, that's this year's temperature readings.

  One of the most severe consequences of these warming falls on the world's coral reefs, which nearly a quarter of all ocean species rely on. According to NOAA, the National Oceanic and Atmospheric Administration, scientists issued a warning due to record-breaking temperatures in 2023 which accelerated the speed of the second largest mass bleaching event across the Atlantic, Pacific and Indian Oceans.

  For more on the global situation and what's at stake, we are joined by Julia Baum. She's a marine ecologist and coral reefs researcher and a professor at the University of Victoria in Canada.

  Julia Baum, thank you so much for being here.

  So NOAA just issued this report showing this widespread bleaching, which is a sign of distress in corals. We have seen reports over the years of declining health in corals. So how do you put what's happening now in the context of what we have seen before?

  Julia Baum, Marine Ecologist, University of Victoria: What we're seeing now is the fourth global coral bleaching event, as you said, and it's alarming and likely catastrophic.

  And what's particularly alarming about it is that, in the past, these bleaching events occurred a sufficient amount of time apart that coral reefs had a sufficient time to recover in between them. But now we're seeing these global coral bleaching events occur two within the past decade.

  So there was a mega event during the 2015-2016 El Nino that devastated coral reefs right around the world, including mass bleaching and mortality on the Great Barrier Reef and in many, many other locations. And coral reefs take many years to recover, so 10, 20, 30, 40 years to recover.

  So now to see another bleaching event that is very, very intense and widespread happening just eight years later is extremely worrying.

• William Brangham:

  So I mentioned briefly corals importance in the ocean ecosystem. I mean, we love them because they're not just what we see in Jacques Cousteau and David Attenborough documentaries. They are that, but they are also many other things.

  Can you sort of explain, remind us of their importance?

• Julia Baum:

  Absolutely.

  So I'm a marine ecologist, so, of course, I think about all of the wildlife that lives on coral reefs. And you already mentioned that a quarter of the world's diversity, different species of animals in the ocean live on coral reefs, which is completely astounding when you think about the fact that coral reefs cover less than 0.1 percent of the surface area of the world's oceans.

  But coral reefs are also extraordinarily important to people, so they are worth hundreds of billions of dollars every year. And that's through things like tourism, recreation, all of the coastal protection that they provide. So when we risk losing a huge proportion of the world's coral reefs, we're actually at risk of losing all sorts of other things that are vitally important to many, many people around the planet, especially those who live really close to coral reefs and rely upon them for either their sustenance or their livelihoods.

• William Brangham:

  When you look at the drivers of this warming ocean, climate change, El Nino, perhaps some other factors, what does your research indicate is most complicit in this problem?

• Julia Baum:

  Right.

  Well, it's climate change. So this is without a doubt driven by human-caused climate change. And so I want to link El Nino to that. Under climate change, El Ninos are now supercharged. And that means that they are occurring more frequently. They are at a greater intensity. So the magnitude of the heat stress that they unleash is a lot bigger, and they also can last for a much longer period.

  So, in the past, for example, you might have had some heat stress on an individual coral reef lasting for a couple of weeks. Now we see that type of heat stress lasting for many, many months, and that causes the corals to bleach and then eventually die. So they're becoming much more serious, and that's a direct result of climate change.

• William Brangham:

  We have seen over the past year all of these efforts to try to preserve the corals, pull them out of warmer oceans and store them in cooler tanks on land, sometimes cryopreserve these corals.

  What do you make of those efforts? And do you think overall they are going to be enough to save this ecosystem?

• Julia Baum:

  I think it's a tragedy that we are pushing to — coral reefs and coral reef researchers to that absolute extreme. That's a triage type of response. And it's a last-ditch response.

  Maybe it will make a little bit of a difference in some areas where it's being implemented, but it's not a solution that is going to save the world's coral reefs. And it's undoubtedly the only thing that is going to save the world's coral reefs at this point is a rapid reduction in greenhouse gas emissions. That is absolutely certain.

  Anything else that we do might help a few areas here and there. And, of course, that will be important in those areas where it helps. But if we are going to ensure that the world's coral reefs are still in existence in the coming decades, we have to rapidly mitigate climate change. There's no other way forward here.

• William Brangham:

  All right, Julia Baum of the University of Victoria in Canada, thank you so much for talking with us.

• Julia Baum:

  Thank you.