A litany of ocean threats

20 December 2012

Interview with

Mark Spalding, The Nature Conservancy, John Bruno, University of North Carolina and Chapel Hill, Enric Sala, National Geographic

Helen: Last time on Naked Oceans Sarah looked into the history of the oceans - and now I'm looking to the future, and what lies ahead.

With unfolding exploration in the marine realm, scientists today understand more than ever before about what lives there and how this immense, complex system works. These are undoubtedly exciting times. But we also have a clearer picture than ever before about how much the oceans are threatened by human activities. Geologically speaking, life on earth comes and it goes, but in terms of the impacts we're having on the oceans, over time scales that matter to us, the next few decades could be crucial.

Gravity ocean mapI've been chatting with various people who've appeared on the Naked Oceans over the past 2 years, to find out what they think might lie ahead. I started by them which ocean threats they think will be of greatest concern in the years to come.

Mark: It's the litany of threats is huge in the marine environment, as it is everywhere I suppose. We try and summarise them into local threats, sediments and pollution, and the bigger picture threats of overfishing everywhere. And the biggest threat of all which is climate change and its ramifications. Those are the big ones for me. Certainly I think climate change is the spectre hanging over all of this, frightening us all.

Helen: Mark Spalding there, from the Nature Conservancy, raising the issue of climate change in the oceans - something that's on the minds of everyone I spoke to:

Here's National Geographic Explorer in Residence, Enric Sala:

Enric: Warming and acidification of marine water is something that is so huge and affects the entire food web from the microbes to the top predators to whale sharks, polar bears.

Helen: In one of the first episodes we made of Naked Oceans, we spoke to John Bruno from the University of North Carolina at Chapel Hill, back when he'd just written a review paper in the journal science about the impacts of climate change on the oceans. When I caught up with him again recently, he had been looking at the latest projections for climate change and ocean warming from the upcoming fifth assessment report or AR5 from the UN's Intergovernmental Panel on Climate Change, or IPCC. The report looks at how warm the oceans are likely to get by 2100 based on different future emissions scenarios:

John: And the projects are really frightening. So we are very plausibly looking at 2 to 3 maybe even 4 degrees Celsius of warming in tropical areas. I've known that but somehow I'd got it in my head that we were only going to see a half a degree or a degree Celsius. I think reefs could handle that. Four degrees, it's just so extreme. That's more than ten degrees Fahrenheit, that would absolutely devastate not just reefs but all kinds of tropical ecosystems, terrestrial and marine. And that is becoming a really plausible scenario just based on our recent greenhouse emissions rates and the fact that those emissions have actually been accelerating in the last few years. Climate change is something that I'm more and more concerned about, and of course not just the temperature but also the other side of that coin, the acidification problem.

Helen: And that acidification problem is looking to be a really big one. Already, the oceans have become 30% more acidic since the dawn of the industrial revolution because much of the co2 emitted by human activities has been absorbed into the oceans. Impacts on marine organisms that live inside calcium carbonate skeletons is already being detected most recently among sea butterflies - the flocks of tiny molluscs that flit through pelagic waters and are a vital food source for many other animals including fish and cetaceans. In parts of the southern ocean where natural upwelling exacerbates falling ph, the shells of sea butterflies are already starting to etch and corrode away. 

Warming seas and acidification aren't the only knock on affects of climate change that we are likely to see unfolding - there are a couple of other issues that don't get a lot of attention at the moment but could get much worse in the future:

John: There's two ancillary affects of climate change and gas emissions that a lot of people are arguing aren't getting considered. One is UV. We were making progress on UV and that seems to be stalling or reversing, so Carlos Duarte for example is arguing that UV is a big cause of invertebrate and vertebrate larvae mortality in the plankton. 

And the other big one of course is the affect of temperature on oxygen concentration. So the big thing that's going to happen when the oceans warm is that they hold very little oxygen, so the warmer the water is the less oxygen it holds, the higher the metabolism of animals, and therefore they need more oxygen and those tow things really coincide to kill animals above 31-32-33 degrees Celsius. And that's going to eb somple mortality not some kind of indirect process like coral bleaching or disease enhancement. So that's a really big concern that never gets talked about as well.

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