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 .. 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 .. 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.