 Hello my name is David Stevens and I do research in oceans and their impact on the climate system at the University of East Anglia. I guess as a scientist I like to do controlled experiments so you maybe change something and see how it responds but you need a control case. Now unfortunately we don't have a control case. You know we've only got the one planet and yet we are performing an experiment and I guess modeling is pretty much our only chance of trying to predict what might happen or understand what we are doing to the planet. A climate model is a mathematical description of the components of the climate system so the ocean, the atmosphere, the cryosphere and we use equations to represent those components and essentially we just solve those equations. I do find it amazing that you can set up a mathematical model of the earth and essentially do nothing but shine the sun on it and it produces a climate not unlike what we see if we can take measurements. The fundamental equations we use I guess go back to Newton's second law of motion so if you consider a parcel of fluid in the atmosphere or in the ocean then there will be forces on that parcel of fluid and those forces will induce an acceleration and that gives that parcel of fluid a motion and we can essentially solve for many many millions of parcels of fluid all around the earth and compute the winds in the atmosphere and currents in the ocean. My main interests are in the ocean and the oceans role on the climate system so I very much focus on trying to improve and understand the ocean component of climate models. The full models themselves are really really complex and understanding them is not really the kind of thing that a single person can do in isolation so climate modeling tends to be a team type activity. There might be a group working on the ocean, a group working on the atmosphere but then they'll come together and help build a single model of the entire system and then work together in terms of analyzing the results because the components are all interacting with one another. Let's start by just talking about what why you might even study the ocean. It's really important because it's enormous capacity to store heat. One of my favorite factoids for telling people about the ocean is the top few meters of the ocean have got the same heat storage capacity as the entire atmosphere above. So there's an enormous potential for storing heat or taking heat out of the atmosphere or releasing heat back to the atmosphere. So the ocean isn't a single monolithic slab of water. If you go to say the tropics the waters at the surface can be around about 30 degrees Celsius and yet if you go down to the depths at say four or five kilometers the waters can be say two degrees Celsius. So there's an enormous differential in heat between the surface ocean and the deep ocean. So that leads to possibly the question of why is the water so cold at the tropics in the deep waters and where is that cold water come from and it doesn't take too much thought to think well actually it must have come from somewhere cold and there are movements in the ocean right down to the deepest parts of the water column which are transporting waters from the poles where water tends to sink gets very dense and sinks to the seafloor and then spreads out throughout the world's oceans and this transfer of cold water towards the warmer regions the equatorial regions and the associated warm water flowing from the surface from the tropics towards the poles provides a heat transport so the ocean is transferring heat from the equatorial attitudes to the polar attitudes. So this flow of warm water at the surface towards the poles and cold water at depth towards the equator produces a transfer of heat from the equator towards the poles and it's this transfer of heat plays an important role in keeping our planet at the temperature and the regions of our planet at the temperatures that we live in. I'm not talking at all about global warming here just how the climate system maintains itself in a fairly equilibrium state I mean there are some there is some variability on top of this but the basic mean state is set by some of these processes. People have for many years thought about what would happen if this overturning circulation we talked about earlier particularly within the Atlantic shut down that transports an awful amount of heat northwards towards the high latitudes in Europe. There's been less focus on the southern oceans and yet there is an overturning circulation associated with the southern ocean and the waters around Antarctica and it often seems very remote and we thought what would happen if that shut down would it have an impact and how global would the impact be felt. So we did some similar experiments where we released a significant amount of fresh water in the southern oceans to mimic carving or melting of the ice sheets to look at the impact that might have on the planet as a whole and there were some surprising findings right through to impacts in the northern hemisphere. So you know the Antarctic being a long way away doesn't mean so you can ignore it and the any problems that might occur there and not our problem because you know they potentially might be. I guess probably the key question at the moment is how will the ocean respond in a change in climate? Will it reduce the impacts of the global change we're seeing or is it reducing the impacts of the global change? What are the potential feedbacks could some regions see a faster change in climate some regions slower? We already know that the Arctic sees a much more amplified response to global warming than say the tropics. There are a number of ways of going out into the ocean and measuring the heat of the ocean or the temperature of the ocean. So the traditional method was to go along in the ship and then lower an instrument from the surface down to the seafloor and make a profile measurement of temperature. That's very expensive both in terms of people and monetary costs. Ship time is tens of thousands of UK pounds per day and then you have to man it and have trained scientists operating the instruments. More recently there's been a huge increase in the number of profiles of temperature in the ocean from something called the Argo network. So Argo is a network of floats and they do something rather odd for a float in that they sink. So they start at the surface and will sink to a depth of about 2,000 meters and then they move along with the ocean currents and after 10 days or so they can pop up to the surface and when they're coming up to the surface again they're measuring temperature and they speak through the satellite communications network and deliver their temperature data they've recorded and then sink back down to the depth again and then travel along. And there's about 3,000 of these in the world oceans and it's produced a real step change in the number of measurements we have of temperature profiles. Pre and post Argo is just the it really can start with contrast. So the temperature data we collect from the both ships and from the Argo program are useful to help us start off our forecasts of the climate system and in particular the ocean component. So to start a forecast we need to know the state of the system at one particular time and back in the 60s we had very few measurements of vast swathes of the ocean where there were literally no measurements ever been taken whereas since about 2005 there are measurements throughout the world's oceans pretty much everywhere there are very few regions possibly just the polar regions where measurements are sparse. So we use this this data to provide some starting point for our forecasts and that's called initialization. Initialized forecasts of ocean conditions have certainly got a much better chance of being more accurate now where we have all this data compared to the 60s. I originally trained as a mathematician and in my third year I did a course on mathematical modeling of the oceans. It was very theoretical and you looked at very idealized models that oceans were square basins and it was really focusing in on processes and I found that really really interesting so I went on and did a PhD in mathematical modeling of the oceans but the models became more complex and more realistic and eventually that led me to talking to observational oceanographers and I guess in the late 80s early 90s was a time when the models of the ocean were just getting realistic enough for observational oceanographers to really start to believe them and possibly even use them in planning their observational campaigns and so I started to work with one of the observational oceanographers here and actually even went to see a few times which was really well one exciting but two seeing the measurements actually collected at first hand you know really gives you I think a much greater insight into what's going on within the ocean and also an appreciation of what you're doing in terms of the modeling. This research cruise and they're called cruises. They're not necessarily a holiday but it was to the Antarctic and to the southern ocean taking measurements in the southern ocean it's about two months long but really enjoyable and really productive so I joined the ship in the Falkland Islands and then we sailed down to the Antarctic continent and then from there took measurements all the way up through the Atlantic to just off of Brazil so just near Rio de Janeiro but it really was you know mesmerizing it's absolutely beautiful pristine the wildlife is just incredible and you know we should make sure we shouldn't damage it. I think it's just a case of being in trying to engage and be open and be honest and I do try and get out and engage with the public so I go into schools and you know I try and give public lectures when there's good opportunities so most recently I did one to a group of old age pensioners in Norfolk in July so but again you know they were all really interested really engaged and it's good fun you know I really do enjoy trying to put over some of the science