Climate change is worsening heat waves in oceans. Here’s why that’s a problem

This summer has seen record-high temperatures around the world, but the damaging effects of heat do not stop at the water's edge. In Europe, the Mediterranean Sea has been experiencing elevated temperatures since May, with deadly consequences for delicate underwater ecosystems. Ali Rogin reports.

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  • Geoff Bennett:

    This summer has seen record high temperatures around the world but the damaging effects from the heat do not stop at the water's edge. In Europe, heat waves on land have led to heat waves in the water. My colleague Ali Rogin has more on this phenomenon which has existed for decades, but is only now gaining widespread attention.

  • Ali Rogin:

    Marine heat waves occur when ocean temperatures are higher than usual for at least five days. The Mediterranean Sea has been experiencing one since May, with temperatures five to nine degrees Fahrenheit higher than normal. That might not sound like a lot, but it's deadly for the delicate ecosystems that populate the sea. And experts predict there will be more damage before the summer is over.

    For more on these marine heat waves, I'm joined by Michael Jacox. He's a research oceanographer with the National Oceanic and Atmospheric Administration. Michael, thank you so much for joining us. What's causing these marine heat waves?

    Michael Jacox, National Oceanic and Atmospheric Administration: Well, marine heat waves can be driven by a number of different things, changes in the atmosphere, different weather systems can get a high pressure system in the atmosphere that reduces winds and mixing in the ocean, for example. So they do occur naturally, and can happen for a number of different reasons.

  • Ali Rogin:

    But part of this is because the oceans themselves are getting warmer, right? So the conditions that have existed for a long time, in terms of those weather systems are getting exacerbated by the fact that the oceans are simply getting hotter. Is that right?

  • Michael Jacox:

    Yes, exactly. So you've got even if these things happen naturally, you now have them occurring on the backdrop of a warmer ocean. So if the ocean warms by one degree than, you know, a three degree heat wave is now four degrees. And you've got this compounding effect that really amplifies the impacts of the waves.

  • Ali Rogin:

    Right. And so it becomes more palpable with every season. So to that point, when did the scientific community kind of become aware that this was a phenomenon that needed its own level of study and also needed its own name needed its own terminology?

  • Michael Jacox:

    Yes, the marine heatwave terminology really came around about a decade ago now, that sort of warm ocean temperatures have been studied in different forms for many decades. But some prominent events in the past decade, I think, largely driven by the heat waves on top of the long term warming, have motivated a whole lot more study on these events.

  • Ali Rogin:

    Absolutely. And these heat waves lasts a lot longer than heat waves on land, right?

  • Michael Jacox:

    Yes, that's right things in the ocean just evolved slower than they do in the atmosphere. So you can have events that lasts for anywhere from weeks to even years in some cases in the ocean.

  • Ali Rogin:

    Wow. And what kind of damage have you been seeing that these heat waves do to the marine life that requires these, you know, very specific kinds of temperatures to have a prosperous ecosystem?

  • Michael Jacox:

    Yes, so there's a wide range of impacts that that deserves. You can think of things like mortality and bleaching of corals, changes in the availability of food for different species which impacts their mortality, their survival and reproduction. These e-mails have been associated with blooms of toxic algae which can poison animals and make seafood unfit for human consumption.

    And also they've caused distribution shifts where marine species, there's these heat waves that come along and they look for favorable conditions elsewhere and they can be found 1000s of kilometers away from where you normally expect them.

  • Ali Rogin:

    And do you expect dynamics like that to continue? I mean, we're seeing temperatures rising all over the world with no sign of progression. Is that going to be the case with marine heatwaves?

  • Michael Jacox:

    Yes, certainly, you know, there's the long term trends and on top of this, we're going to have the natural variability. So we should certainly expect to see more of these impacts in the future.

  • Ali Rogin:

    Very sobering stuff. Michael Jacox with the National Oceanic and Atmospheric Administration. Thank you so much for your time.

  • Michael Jacox:

    Thanks, Ali.

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