Weather And The Oceans
Kat - What can actually affect the temperature of the sea? Is it strong sunlight or motion? How does the sea change its temperature?
Emily - The sea changes it's temperature very slowly because water has a large heat capacity. That's why these sea surface temperatures have this long time scale effect on the weather. That's why sea surface temperatures tend to vary very slowly over the time scale of months, whereas the weather changes very quickly over days or hours. It's that slow change in the changes of the oceans that causes the slow variability in the atmosphere.
Kat - I tend to think of the sea as a big homogenous mass of water. But if you could see it and see the different temperatures and currents and saltiness, what would our global oceans look like?
Emily - There are different temperatures and salinities throughout the ocean, and in fact the whole overturning circulation of the ocean.
Chris - The Gulf Stream for want of a better word.
Emily - Exactly. The Gulf Stream is driven by changes in density caused by changes in the salinity of the water and changes in the temperature of the water.
Chris - So adding a while lot of fresh water from the North Pole because of the melting of the Arctic ice sheets is actually quite a major issue then?
Emily - Certainly. In terms of over-circulation and in terms of thermohaline circulation it would certainly be an important issue.
Chris - Is there evidence that it's on the down turn because recent research shows that it may have reduced by some 30 or 40%?
Emily - Well there was some recent research that came out at the end of last year suggesting that there was observational evidence that that circulation had been slowing down. Indeed, if you do model predictions of the next hundred years or so, then you do predict a slow gradual decrease in the speed of the over turning circulation.
Chris - And just very briefly, if that does occur, how much heat does that give to the UK and what are the consequences for the UK's climate?
Emily - Well that's quite difficult to say. I'd like to stress that people may have seen the film The Day After Tomorrow but the actual chances of the whole Gulf Stream shutting off quite unlikely. But the Met Office has done a calculation with an imaginary situation. They've tried shutting it off. What they found for the UK was that the temperature was going to drop by four degrees or so. But I'd like to stress that it's unlikely.