Will melting ice affect ocean salinity?

Chris - Peter Haynes, when ice melts, it's adding fresh water to the ocean. So does this mean that progressively,as we go through climate change and so on, that the salinity of the world's oceans will change...do we think?

Peter - As always, there's a kind of complicated answer. Because actually, what we expect is that some parts of the ocean will get more saline and some parts will get fresher. I mean, the fact is that climate change is associated not only with more melting of ice, but also more evaporation. So where you've got water flowing out from melting ice sheets, the ocean will come fresher. Where you've got some more evaporation, like in the Mediterranean for example, then the water will get saltier. And of course, if you go to some point in the ocean, what you see is some subtle combination or of all of those processes that are taking place over the globe. And then, the effects are brought by the circulation to the place where you are looking.

Chris - When you add fresh water to saltwater, because they're different densities, that can have effects, can't it? Because I've seen quite a lot of speculation about the impact of the Gulf Stream and the melting of the Arctic pushing that backwards, and potentially making Britain colder through global warming because we lose that heat source that comes up the west coast.

Peter - Exactly that's right. At the moment, you get something called convection where heavy water, dense water sinks in the North Atlantic and Arctic ocean, and that happens in part because of salinity, which adds to the density. And if you were to kind of flood the top of the ocean with fresher water, then that combination of temperature and salinity, that determines density, may no longer give to sinking. Some part of the circulation system of the Atlantic is driven by this process. So there would be potentially a change, but I think the jury is still out on how likely it is to happen. Another question would be when would it happen? There's a lot of discussion written about tipping points. I mean, that's another favorite idea in climate science at the moment. If you look at the list of tipping points, this is one which is sort of somewhat lower down the list. It's an effect which could happen, obviously would be potentially serious, but it's not one of the ones that is seen most imminent.

Chris - Thank you, Peter.