 I'm Dan Lund from the University of Bristol in the UK. I'm a paleo-climate scientist, so I'm interested in past climate change and the relevance that that has for future climate change. And I'm also a fan of J.R.R. Tolkien's work. Well I guess ever since I've been a child I've been really into those Tolkien books. I've probably read them tens of times if not more. And I think the stories have always really grabbed me. They're very exciting. They're extremely well written. And also one of the things that's really fascinated me and actually one of the reasons I got into this is that there's a huge back story as well. You have for example The Hobbit and The Lord of the Rings, but behind that there's a whole mythology that's only just hinted at really in those books. And then you can go as deep into it as you want because there are, his son Christopher Tolkien actually published a lot of his works posthumously. And those you can look at now and that includes a lot of the back story in there. For example lots of maps of Middle Earth that aren't actually in the original story. And it was those maps that enabled us originally to actually model the whole of Middle Earth because actually for in The Lord of the Rings itself a lot of the action only occurs in a small part of the world like equivalent to the size roughly of Europe. But obviously if you're going to simulate the whole climate of the world then you need a lot more and we were able to use those maps for that. Actually it turns out that Tolkien's world was not necessarily a sphere like our Earth and in fact he's a little bit vague on this subject but probably he originally intended it perhaps to be a flat circle in fact. And so that did cause us some problems actually because the climate model that we used is basically fixed. It assumes that you've got a spherical Earth. And so we had to take a few sort of artistic liberties with that in that we mapped this flat Earth onto an actual sphere. So it's not, what we did probably wasn't entirely correct if you like but it was the nearest approximation that we could do to what Tolkien originally intended. Ok well, so we actually simulated because the only maps that I could find that covered the whole of Middle Earth or the whole of, well actually it turns out again it's a bit geeky but it turns out that the whole world is called Ardur and Middle Earth is actually only a small part of that and actually the only maps that I could find of the whole of Ardur that were drawn by Tolkien were actually of probably what they called the first age or the second age which was prior to the drowning of Númenor. So actually if you look in the paper I show a map of the whole of the world of Ardur and in there you'll actually see for the Tolkien geeks out there there's actually, Númenor is actually part of that so we weren't actually technically simulating the climate of the Lord of the Rings but maybe a few thousand years beforehand but probably that didn't affect the climate hugely I expect. The way that we actually went about simulating Middle Earth or the climate of Middle Earth was we had two starting points. One was a climate model which we needed and that's something that we use a lot here in the department of Bristol so actually one of the things that I do is I'm a palier climate modeler and one of the things I do a lot with the climate model is actually simulate the climate of millions of years ago and so millions of years ago the continents are in different positions and so it's something that I'm actually quite used to is adapting these models for worlds that are quite different from the earth that we live in today and so we used a climate model and we used a model that was developed at the UK Met Office about a decade ago or more but it's actually quite a good model and it was actually used and featured in the most recent IPCC reports so in some ways although not state of the art it is a current model that's being used for science. So we have a climate model, we have some experience at adapting these climate models to different worlds so the next stage was then knowing what the world actually looked like, Tolkien's Middle Earth and to do that I actually found some maps, went back to some original maps that Tolkien had drawn and also some reinterpretations of those maps by some other workers and then literally because they weren't published digitally what the model actually needs is literally a string of numbers that defines where the continents are, how high the mountains are and how deep the oceans are almost like in a sort of a spreadsheet if you like of going along the longitudes of the earth and down the latitudes of the earth so that was the starting point that I needed but all I had was some maps so literally what I did was I took some tracing paper and traced those maps and then scanned them into a computer and actually coloured different regions depending on how high they were or how deep they were according to these maps so if there were mountain ranges that were indicated by Tolkien then I'd set those blue for example and other different heights, different colours and then I was actually able to read that file in to a computer programme and then reinterpret those colours as different heights and generate a file that is needed by the climate model to define where the continents are, how deep the oceans are, how high the mountains are etc so that was a starting point in the model and this is what we call boundary condition file or input file to the model of where the continents were and how high the mountains were and that was the starting point and then literally it's really a question of just pressing go and seeing what happens although there's a few other sort of decisions that we have to make so for example one of the things that we have to tell our climate model now it's not the case with all climate models but we have to tell the model how much carbon dioxide there is in the atmosphere and so we had Tolkien never discussed the CO2 levels in Middler so this was an assumption that we had to make and actually we considered this for some time and thought we could take something similar to perhaps pre-industrialisation on the earth but then we thought well no that's probably wrong actually because dragons like smorg and the activities of the wizards and sauron for example may well have raised the CO2 level on Middler and so we actually set quite a high CO2 level which is actually similar to the level that we might expect in the middle of this century perhaps if emissions continue unabated as they are so that's another decision we had to make we had to also say something about what the soils were like in Middler so we took soils that were perhaps typical for those of the present day and these are all things that the model doesn't actually predict itself but are things that you have to tell the model so once we'd made some of those decisions it was literally just a question of pressing go and crossing our fingers and we did that and it actually turned out that about a week into the simulation so this is a week of model time if you like which takes a few hours on the supercomputer so a few weeks into the run actually the climate suddenly became unstable and actually generated a super green house climate and we had temperatures of more than 100 degrees C in the oceans and actually that's obviously completely unrealistic Tolkien never discussed temperatures like that in his books and also we know that that's not physically realistic and actually that's something that can happen in any climate model so that it can go unstable if the physics in the system are not able to cope if you like with some of the boundary conditions that you've given to the model and in particular one of the things that can happen is if the slopes in the ocean are too steep for the actual resolution of the model or the resolution of the physics that you put or not the physics that you put in the model but the resolution of the model actually that can cause these instabilities and actually when we do our past climate simulations going back millions of years this is something that we'd seen before happening in the model and actually it's something we know how to deal with and actually all you have to do is smooth some of these very steep changes in the depth of the ocean or in the heights of the mountain and sort of smooth over the topography in some way and then actually we did that a couple of times and then the model became stable again and we were able to simulate about 70 years of climate on Middle Earth before we ran out of before we were spotted running these simulations on the university supercomputer at which point we decided to stop so actually the original idea became as part of a proposal that I put in to the Natural Environment Research Council or NERC which is the funding body for most of the environmental science that happens in the UK and I submitted a project to them to look at the climate of millions of years ago on our Earth, nothing to do with Middle Earth and in particular we were looking at a time period called the Cretaceous which is about 150 to about 65 million years ago and that project was all about trying to understand if we can use some of these past time periods to say which were actually very warm and were like greenhouse worlds with very very high CO2 and the project was really to look at those and see if there's anything we can understand from those climates that could inform our own future climate and so that was the aim of the project but with all proposals for projects to the Natural Environment Research Council you have to submit what they call an impact plan which is a way that you're going to communicate your research to it can be the general public it can be users of climate research like industry, commerce or it can be policy makers for example so we had a few ideas for that for example we said that we would commission a painting of the Cretaceous world and the future world perhaps that could hang in a gallery in Bristol as a way of communicating our science to the general public we said that we would organise some meetings with policy makers to discuss our findings about the sensitivity of climate in the future that we found out about from these past climate models but the other thing we said we'd do for communicating with or for engaging with the general public if you like was to do these Middle Earth simulations but it was not funded in any way so we didn't request any money if you'd like to do these simulations I essentially carried them out in my spare time in fact I was amazed actually it was mainly because I spent so much time doing these past climate works actually in the end I was able to pretty much finish set up the simulations in one evening although it was very long it was more like an evening in the morning because I got quite into it but basically it wasn't a huge amount of work but it was in my spare time it wasn't funded but I did run the simulations on the university supercomputer which is free to use by members of the university for research purposes so if you accept that this is research purposes then I think the university would be very happy with what I did so I didn't tell anyone I was doing it actually but I did get to a point where I thought maybe people who were trying to discover a cure for cancer or something might get a bit annoyed that I was running middle earth simulations that was always the idea really for this work was to communicate with the public about climate science we didn't really want it to be purely a fun exercise if you like just about middle earth and so originally I envisaged this perhaps being a page on the university web page where we mentioned something about the middle earth simulations and then talked a bit about our own work on past climate simulation but actually the more I got into it the more I realised there was actually a potential to do more than that and actually write something a little bit more substantive and I can't remember at what point but at some point I had the idea of actually writing almost a mock paper about these simulations and in fact in some ways it grew and grew I originally intended it would be quite short but in the end I think it's one of the longest papers I've ever written and so and actually one of the real challenges was going especially maybe because the format was in the format of a scientific paper to actually get in the mindset of writing this for a non-climate scientist audience if you like and so I wrote a first draft of this paper and I actually sent it to a few friends and family and they basically just tore it to shreds because they said we don't understand this what do you mean by this, this doesn't make any sense and actually that was hugely useful and I think made it a really big difference and I think was one of the main reasons that it was picked up on by the media was because actually the written work the paper that went with it and the press release had all been looked at by friends and family and had gone over it with a critical eye and so actually I did find that quite challenging writing for a non for it was sometimes difficult to know whether you were writing for a Tolkien fanatic audience or your climate science colleagues or you know joe blogs on the street but in the end hopefully we got the balance between those three so one of the things I was interested in when I was looking at the simulations was thinking we had this climate prediction for Middle Earth but looking at it I wasn't sure of what that climate really meant in some ways like you have a certain temperature and a certain rainfall but I thought a really useful way of interpreting that the model output really was to ask the question what some of these places in Middle Earth how their climate resembled places in our Earth and so for example I chose a few places in Middle Earth so we started off with the Shire with its rolling hills and you know it's a very green very nice part of Middle Earth and so I thought well what is the model predicts the climate of the Shire how does that compare with the real Earth and in particular I knew that the recent film had been a lot of that have been or if not all have been shot in New Zealand and so I was very interested as to whether the right choice had been made and whether the Shire's climate really was like that of New Zealand for example so I actually made a map of the world our Earth and highlighted all those regions that had a climate similar to that of the Shire and so we found out for example that there were parts of New Zealand that had a climate very similar to that of the Shire but actually they were nearly all in the south island and it was apparently the film was filmed in the north island so it was out by a few hundred miles maybe and also we found out that the parts of the UK were very like the Shire and actually there apparently I haven't this was only from reading something on the internet but apparently Tolkien envisaged the Shire as being similar at least to parts of the UK and in fact we found that Leicestershire and Nottinghamshire do have a very similar climate to that of the Shire if you believe the climate model it turned out that Belarus was probably the country that had the climate most similar to that of the Shire but then also if you after doing the Shire were obviously interested in other places and in particular we thought well Mordor is a very well known part of Middle Earth it's where the evil Sauron lives it's very black and desolate and so we tried to find places in the real Earth that were like Mordor and actually somewhat to my delight we found that Los Angeles in the US had a climate almost identical to that of Mordor also parts of Australia I think Alice Springs and also had a very Mordor like climate and a few other places in various parts of the world so that was a bit of fun really sort of putting the climate results of Middle Earth into a little bit of context in our Earth at the time when I did this England were actually down under in Australia playing cricket against Australia and I thought and actually one of the test matches that we lost was almost right bang in the middle of the most Mordor like climate so I think that almost certainly explained our whitewash by the Aussies this year a good question is what it actually is a climate model so a climate model is a piece of or the usual use of the word for climate model is a piece of computer code a list of instructions to a computer that encapsulate our very best understanding of the way that the atmosphere of our planet and the ocean work in a physical sense so there are actually some very well-defined equations of motion of the atmosphere and ocean that have been known for several hundred years and actually you can write down the very fundamental equations actually on a single piece of paper solving them is a lot harder and that's actually what a climate model does is it solves these fundamental equations of the atmosphere and ocean along and but in addition to that has some other components which try and replicate parts of the Earth's climate system that actually the model can't fully resolve because of its resolution so when I talk about the resolution of a climate model what do I mean so what I mean by that is the way that the climate models work is that they divide the world up into a series of boxes so it's very like Lego if you like so you can imagine sort of building up Lego and each one of those Lego blocks represents perhaps a box in which the climate model has a value for temperature it has a value for the amount of air or water within that box it has a value for how fast the air or water within that box is moving and how much moisture is contained within it if you've if it's the atmosphere so you can imagine you've got sort of this matrix if you like surrounding the world of these boxes that go up in the atmosphere down in the ocean now the model can't actually tell you anything about the climate on a scale that is smaller than one of these grid boxes and so what that means however these grid boxes typically are maybe the very highest resolution models are perhaps the order tens of kilometres but most models you're talking hundreds of kilometres so there are lots of processes in the atmosphere in particular that actually occur in reality on a much smaller scale than that for example clouds themselves are much smaller than the size of one of these grid boxes and so we have to make approximations to how some of those processes work so a typical climate model is made up of approximations to some of these what we call sub grid scale processes along with the solving these equations of motion in the atmosphere and ocean and also the model that we used contains a representation as well of vegetation at the surface so one of the nice things we were able to do with this model was actually predict the vegetation in Middle Earth as well so that is when I say a climate model that's what I really mean is a representation of a very best understanding of the physics and biology and chemistry that occurs in the atmosphere and the ocean and what the model can tell you tell the model what these fundamental equations are and then the other thing you have to give a model is what I talked about earlier these boundary conditions like how high the mountains are how strong the sun is how much carbon dioxide for example there is in the atmosphere and then you also have to give the model what we call an initial condition so that is a representation of what the atmosphere and ocean are doing right at the beginning of your simulation and that might be that you have a completely stationary atmosphere for example no moisture in the atmosphere, no clouds you might have a completely stationary ocean and then the model will take that initial condition and by solving these equations of motion and these approximations these sub grid scale parameterizations will basically move forward in time gradually evolving the temperature, rainfall wind speed, humidity cloud cover and evolve those by solving these equations of motion it will go out it will carry on doing that forever actually until you stop it the model that we use has a resolution such that for example if you take the UK as an example there are about six boxes six of these boxes that cover the UK and there is one for example which is the size of Wales and so if you're thinking about middle earth that is I actually have no idea I don't want to get it wrong so for the talking geeks I don't want to get it wrong but anyway they're probably more needy than climate exactly so one of these grid boxes is about the size of Wales for example so what that means is that the model cannot tell you about the weather at a particular location at the size of a city for example or a town so what the model can't tell you is what the climate is like in Brie or what's that oh yeah minus Tirith or someone like that or one of the other cities in middle earth like Rivendell for example but what it can tell you is something about the average behaviour over a larger area for example the size of Rohan or Gondor or something like that so that we have much more confidence in the model's more larger scale regional predictions than we do in the simulation of just one of these grid boxes for example and certainly not on the scale of a town or a city like Brie or minus Tirith an interesting place in middle earth is somewhere called the Greyhavens which is just on the west coast of middle earth and it's a place where in the books it turns out that the elves when they leave middle earth and go back to their homeland if you like they set sail from the Greyhavens and go west to their own country and actually some of the main characters in Lord of the Rings actually not elves but Frodo and Sam and apparently also Gimli and Legolas also set sail for the west and actually we found that one of the reasons they might have set sail from the Greyhavens is actually it turns out our model predictions was that we had very strong easterly winds that is blowing towards the west at the region of the Greyhaven so that explains why they left from there and not for example further south from somewhere in the west of Gondor for example another place that we looked at was Mordor and actually it turned out that Mordor was very desolate so the model actually predicted that very very little vegetation would grow there which is very similar to what it says in the books it was also extremely dry and very hot so that was one of the places that we did look at whereas it turns out that also similar to the books actually Rohan was very vegetated there were trees throughout the region and actually it turns out that there is somewhere in the books Tolkien makes reference to the fact that in the old days it was possible for a squirrel to travel from the north of Middle Earth to the south and actually we found because our model is akin to most vegetation models of real climate models if you like actually only simulates natural vegetation and so it can't predict for example how humans are going to deforest the world and so actually what the model predicted was sort of a potential natural vegetation if you like which is very much in agreement with Tolkien's indication that originally Middle Earth had a lot more trees whereas compared to the books now there are for example in parts of Rohan there's lots of grass and it's there isn't trees but the model predicted trees there and we say that is actually must have been because of what we call anthropogenic interference which is basically a climate model that speak for the horsemen of Rohan chopping down trees Saruman almost certainly affected the vegetation around Isengard I expect and so that again is something that can't be predicted by our model so we just predicted the potential natural vegetation it's certainly possible that there's a lot of discussion in the Lord of the Rings book about the Ents moving and actually so these are the trees moving actually in the books it says that they were looking for their wives and that they travelled vast distances and actually what our work perhaps suggests is that perhaps the real reason they move was that they were trying to move to more climates that were more suitable for them to flourish and grow so we certainly found and actually in the real world there are in our earth there are cases and it's something that's predicted by models where trees will actually move in a similar way to the Ents did but they will be moving in response to climate change rather than looking for their wives it is incredible actually the way that a lot of the model predictions actually were in agreement with what some of the things that Tolkien mentions in his books and I think like you say a lot of that was because Tolkien was such a careful scholar if you like and he took such great care with these stories if you like to make them as in depth if you like and it wouldn't surprise me actually if he spent some time thinking himself about the climate of his middle earth one of the things we did do is we did place middle earth in our simulation somewhere similar to where Europe is in the real world and I think that's part of the reason why we get climate similar to that which Tolkien predicted because it's quite possible that he had the European region in mind when he thought about the extremes for example if you look at the climate of the Scandinavian country the north of the Scandinavian countries and right down to the south of Spain and North Africa it's quite similar to the sort of climatic range that Tolkien had in middle earth so yeah I think he probably was a very good meteorologist as well as being a very good linguist and actually one of the things that we I think the thing I got the most correspondence about after the work the most complaints about certainly was our pretty feeble attempt to translate our paper into elvish and dwarvish and in fact the way that I did that was I confess I just changed the font of the of the paper into elvish and elvish script and dwarvish runes and didn't actually change any of the words itself and so I got lots of complaints about the fact that I hadn't done that properly so for all those people I do apologise. I found something online where actually someone had done a real translation of the abstract of the paper into elvish but it's since disappeared I've never been able to find it since then so I don't know if it was in a dream or whether it was removed from the web but I don't think it's there anymore but I'm pretty sure that someone did actually go to the effort of properly translating the abstract of the paper into elvish so congratulations to them so another interesting thing that happened was just after the paper was published I actually got an email from an Australian geologist who'd done a lot of field work in Australia and one of the things we said in our paper was that one of the regions of our real earth that was very similar to the climate of Mordor was just very close to Alice Springs in Australia that was sort of one of the bull's eyes of Mordor climate if you like and I got a letter a week later from an Australian geologist so I was expecting him to be very rude for highlighting this but he said actually no it's actually completely true because just outside Alice Springs there is a region known as Mordor Pound because in the 70s some geologists were there and thought the climate and just the whole feel of the place was so like Mordor from Tolkien's books that they named it Mordor Pound so it was actually almost like art imitating life or life imitating art or the other way around I don't know probably from Tolkien fans the most common response that I actually personal response I actually got in my inbox if you like was about the translations being wrong I got I got a few people emailing me actually a few writers of their own science fiction or science fantasy where these were people who like Tolkien had invented their own world and for example had maps of their own planets and were asking whether I could simulate the climate of their made up world unfortunately I didn't think the university resources would extend that far but I did tell them for a small fee I would do it for them but no one got back to me unsurprisingly so that was also mentioned to me that we should try and do the game of thrones climate so that's something that may be under development in the near future I don't know and there's many examples that you could use from science fiction and science fantasy there's obviously lots of the planets from Star Wars for example or that you say game of thrones or several other places the Narnia for example you could imagine a climate simulation of Narnia as well so I've I've heard people say that it's it's interesting that Star Wars planets have the same climate over the whole planet over the whole planet I'm not sure that that is the case I know for example the ice world of Hoth certainly is cold everywhere but I would still imagine if it is if it's orbiting a if it is indeed a spherical world and orbiting a single sun we and didn't have a completely unusual orbit or acts of rotation we would expect it to still be warmer at the equatorial regions in the middle of the earth and it would be at the pole but it's certainly possible maybe it has some chaotic orbit and it's tumbling around and so that's why all parts of the planet receive on average throughout a year the same amount of radiation I guess maybe it is possible I don't know maybe I'll start the model running and I'll let you know so a question that many people have asked is how can a model that is really designed or people's view of it is that it's designed to simulate our earth how can that model also be used to simulate middle earth now the answer to that is that actually the core of the climate model itself is not our world is not a map of our world or is not tied in any way to our world but is actually just based on the fundamental physical principles physical rules that were found by Newton and others hundreds of years ago that we think or we have no reason to doubt and the evidence supports that that these rules hold everywhere in our universe and so actually if you those same rules could in theory be applied to any planet so actually the same core of the model that is used to do your weather forecast every morning could actually be used to simulate the climate of Mars for example or Venus it's the same underlying physics that controls the motion of the atmosphere and well on our planet of the ocean and so as long as we make the as long as we can accept that Middle Earth maybe obeys those same fundamental physical rules as well there's no reason we can't use this model in the same way that we could use it to simulate Mars or Venus or Earth to use it to simulate Middle Earth so long as we have those what we call these sort of rather peripheral things called boundary conditions which is really just a map of the world saying where the continents were and how high the mountains are and how deep the valleys or the ocean are so long as you have that information this same climate model can be used to simulate any planet in the universe and also and this is where it has relevance for my own work our planet at any point in the past going back millions and even billions of years another thing that we're often asked as climate scientists is how can we have confidence in the predictions of our climate models for example a prediction of what the climate is going to be like at the end of the century in the year 2100 and that is a crucial question that we all have to ask ourselves and one that we as climate scientists try very hard to address and answer and there are several ways that you can do that and the first one the first way that we do that is to try and build our climate models in such a way that they do represent the underlying physics chemistry and biology of these universal laws of physics chemistry and biology so we know that they are grounded in physical fact if you like the very core at least of these models and so that as a start gives us not confidence but gives us a good basis for these climate models the first thing that we can then do of course is to use our climate models to try and replicate the climate not of the future but of today and so or of the last 50 years for example and so for the last 50 years we have a pretty reasonable observational network meteorological stations around the world that have been recording temperature, rainfall and also since the satellite era we've got observations throughout much of the world not just where we have observational data meteorological stations, we have satellite data as well so we have quite a good what I would consider a very good understanding over a large part of the globe of what the modern climate is and so we can confront our model if you like with this present day test and use the model to try and simulate the present day climate or the climate of the last 50 years and we can run the model for let's say starting in the year 1800 and run it for 200 years up to the year 2000 and see how well it does compared with these observations of climate from around the world and that is the first test that any clock climate model must pass if you like to be able to satisfactorily replicate these observations now actually that is harder than you might think doing that for a number of reasons one of them is the fact that this observational network itself is not perfect there are parts of the world where actually the coverage is not perfect and if you go further back in time over the last 200 years that observational network becomes more and more reduced another very important aspect is that actually our climate is what we our weather if you like is what we call chaotic and what that means is that very very small changes in the or a very small error if you like in our observation in our observational network that we used to initialize the model to start the model off 200 years ago means that actually just within a few weeks of the simulation it's quite possible for even if your model was perfect to actually simulate weather that was very very different from that which was actually observed at that particular time and so you get these random variations if you like in your climate prediction which are not because the model is wrong but just because because of the chaotic nature of the climate system that means and the classic example that's always given that if a butterfly flapped its wings in a slightly different way within a few weeks you could end up with completely different patterns of frontal systems moving across Europe for example and because of that a climate model is never going to be able to completely reproduce the weather of the last 200 years however when you average together all these weather events what you end up with is climate and what we think is if we also run lots of climate model simulations as well as and compare the average of those with the average of many years for example of observed weather we can get quite a good comparison between a climate of a model and the climate of the real world and compare those and so that is a fundamental test that we can use to test our climate models and no model is perfect, there are many models out there there are in the last IPCC report there are maybe a few dozen let's say climate models that took part in or contributed to the last IPCC report and not a single one of those reproduces these observations perfectly even to within a degree at any point on the world a single model has errors of at least one degree C at some point in the world however when you take for example the average of a lot of those climate of those climate models they actually approach much closer to the observations and so we have some confidence actually that the average of many models is doing a good job of predicting the present day climate and that gives us some confidence about the average predictions of many models as we go into the future and look at for example the climate of the year 2100 however it's not always the average climate that we might be interested in there's policy makers for example are much more interested in extremes and for example economists are more interested not in what the average climate model predicts but actually in what is the worst case scenario and so actually it can be that there are certain groups that are much more interested in the upper end of the predictions there are other groups that are interested in the lower end of the predictions so actually that's actually one of the beauties of the IPCC is that you get a whole range of projections that give us some idea of the uncertainty in our future climate projections and as well as looking at the observed record of the last 100 years or so one of the things that the group here at Bristol that actually is heavily involved in is actually testing our models not with the present day but going back further and one of the really important things about that is we're applying our models to the future so we're applying our models to a world maybe 100 years in the future where the amount of carbon dioxide in the atmosphere is projected to be maybe double what it is double or more than double what it is today and if we just look at the record, the observed record of the last 200 years the variations in CO2 over that are tiny and get nowhere near these high values that we're expecting by the year 2100 and in fact if you go the best records that we have of the amount of atmospheric CO2, carbon dioxide in the atmosphere actually from ice cores that you drill where you drill down into the ice on Antarctica and you can extract these cores going down several kilometres that actually give you a record from the bubbles that are trapped in the ice of ancient atmospheres and so with these ice you can go back nearly a million years about 800,000 years currently the deepest ice core we have or the deepest CO2 record we have tells us what carbon dioxide has done over the last 800,000 years and it turns out that actually we've already gone completely outside, way outside the natural range of variability of carbon dioxide over the last million years so in the last million years the amount of CO2 in the atmosphere with some numbers on it has varied between about 180 parts per million and 280 parts per million so you can imagine a window sort of varying between 180 and 280 parts per million we are now today at about 400 parts per million so we're gone completely outside that natural variability of the last million years if you look at the projections for the year 2100 if you look at business as usual for scenarios for example if we carry on burning fossil fuels at the rate we are now you're talking about potentially CO2 levels of the order of 1000 parts per million and so you're talking we've gone almost in order of magnitude outside the range of variability of the last million years and it turns out that actually if you're thinking about the CO2 levels that we have just today about 400 parts per million it turns out that you have to go back 3 million years to get to levels that are similar to we have today to get back to levels that we're talking about at the end of the century about 1000 parts per million you're talking about going back 50 million years before you encounter a world that is similar to the ones that we think we're approaching towards the end of the century what was the world like 50 million years ago when we had CO2 levels similar to what we're expecting in the year 2100 is what we call a super green house planet you had for example there was no ice anywhere on, no permanent ice anywhere on the planet so for example today we have huge ice sheets over Antarctica and Greenland which so for example over Antarctica you've got about 3 or 4 kilometres of ice over a huge area but there was that in a world with about 1000 parts per million or the world of this 50 million years ago we call the year scene there was no permanent ice that had all melted there were things that resemble palm trees in the region that is now the Antarctic peninsula and so you're talking about a planet which is completely different to the one that we experienced today you have extremely warm polar temperatures you have equatorial regions that were warmer than we have today but actually it turns out that the polar regions actually warm up much more than the equatorial regions and so this sort of diversity of climate that we have today will likely get less and less as we, if we approach a world of 50 million years ago and actually a really interesting question is well how do we know this, how do we know what the world was like 50 million years ago and that's a really good question and that's actually where paleo-climatologist passed people who study past climate past climates in particular and in particular geologists they for example one of the things they will do is they can go out on boats to the middle of the ocean and they will take a cora and they will drop this through the ocean to the ocean floor and then they will drill down in the ocean floor and extract sediments from the ocean bed and it turns out you don't actually drill too far down in some place in the ocean before you reach rock that was or sediments that were laid down actually 50 million years ago and trapped in these ocean sediments or forming parts of these ocean sediments there are actually tiny fossils of creatures that were living in the ocean at the time and what they can do they can extract these cores they take them back to the lab and they make various measurements on these fossils for example and there are various things that they can look at which we think correlate to aspects of climate like temperature and therefore you can reconstruct what temperature was like millions of years ago and if you just had one of these locations or one type of fossil or one type of what we call these proxies for past climates or past indicators of climate if you only had one of those you wouldn't have very much confidence in that but the point is we've now built up over many decades a whole array of evidence from all sorts of climate archives whether they're from ancient lake sediments ancient ocean sediments from ancient pollen that's formed parts of sediments or you've got ancient fossilized leaves and fossilized mammals and they all point to the same picture of this super warm greenhouse world 50 million years ago when we think CO2 levels were about a thousand parts million now one thing I should say is actually we have a very good record of how much atmospheric carbon dioxide there was going back a million years from the ice core records when you go back further beyond that it becomes much more uncertain we have to rely on indirect estimates of atmospheric carbon dioxide so when I say there was a thousand parts million carbon dioxide in the atmosphere 50 million years ago there are very large error bars on that but again we have more confidence in these records as we devise different ways of estimating the amount of carbon dioxide in the atmosphere and the more those different estimates agree the more confidence we can have in them and also we can test those same ways of estimating past carbon dioxide we can test them on the climate we have a million years ago and see if that agrees with the very robust records we have from ice core and it turns out that there are certain ways of reconstructing past atmospheric CO2 from looking at cores in the ocean that actually agree extremely well with the ice core record for the last million years and so we have some confidence that we can extrapolate those further back in time and it's those sorts of records that point to these very high levels of atmospheric CO2 large amounts of the carbon dioxide greenhouse gas in the atmosphere at the same time that we had these super warm climates as evidenced from the fossilized leaves and pollen and etc that we have from these paleoclimate proxies current present day CO2 levels have just recently hit 400 parts million there is some variation throughout the year so throughout the year and over the year we are bobbling in and out of 400 parts million but we have hit the 400 parts per million amount of CO2 in the present day atmosphere so a really good question to ask is what was the climate like the last time CO2 was about 400 parts million and it turns out that our best estimate so that it was associated with what we call the Pliocene time period so this was the mid Pliocene around about 3 million years ago and so an important question to ask is what was the climate like then and what do we know about the Pliocene 400 parts million world before I say that I should just make the caveat that the present day levels of CO2 of 400 parts million our present day climate has not yet adjusted to those high levels of CO2 so we have gone up unprecedentedly fast as far as we are aware from any point in the geological record any point there is no time in the ice core record of the last million years when CO2 has risen or fallen as sharply as it has in the last 100 years because of that climate there is some inertia in the climate system and the climate system takes some time to adjust to that and how long it takes is actually a point that is currently being researched in a lot of detail but one thing we are certain of is that the climate has not yet fully adjusted anywhere near to that 400 parts million levels of CO2 there are certain what we call feedbacks in the climate system that can take a long time to kick in actually it can take a long time for example for vegetation to adjust to a warmer climate and as climate warms vegetation changes and in many cases those changes in vegetation can then induce further climate change and can amplify that climate change we also know that in a warmer climate ice in our climate system is likely to melt and that itself also induces further warming because as ice melts it leaves behind a surface which is in general darker and therefore absorbs more light from the sun than it would have if the ice was there and you get these so called positive feedbacks that amplify the warming because some of these take a long time to kick in we are still adjusting to that 400 parts millions of CO2 so when I say what the Plyocene world was like 3 million years ago I am not saying that that is what the world is going to be like today what I am saying is maybe if we were able to equilibrate our atmospheric CO2 at 400 parts million which is actually looking because we would we would have to pretty much stop emitting CO2 tomorrow for that to happen and if we did go beyond that level of 400 parts million to reduce it back we probably have to implement some sort of geoengineering to draw back down that carbon dioxide and there are some proposals of ways you could do that but I won't go into that now but let's imagine for example we could maintain our atmospheric CO2 level at 400 parts million personally I don't think that's possible it may happen but what it's saying is in a few hundred years after that time what the climate would be like maybe like what we observe from these various reconstructions of climate 3 million years ago so with that caveat what was the climate like 3 million years ago well this Plyocene world one of the things we know about it is that sea level for example is probably about 10 metres higher than it is today what does 10 metres mean we're talking about inundation of many of the world's major cities we're talking about inundation of much of a lot of the crop land for example that we use to feed the population today a lot of the modern day population lives near the coast and those are obviously the ones that are going to be most greatly affected a 10 metre sea level rise is serious serious news for our planet let's make no bones about it and the Plyocene world with 400 parts million was we think a world with 10 metres higher sea level it was also warmer than today we have records of temperature from these sediments that are drilled in the ocean sediments on land that have accumulated in the lake beds for example and they also indicate a warmer world than we have today and actually the current best estimate is that it was about 3 degrees sea warmer on average over the world than we are today now to put that in some context the sea on average might not sound very much when you think like the difference that we have between winter and summer for example which is much greater than that however bear in mind that the last ice age when most of Canada and much of northern Europe was covered in kilometres of ice was actually as an average over the world only 4 degrees sea colder than today when you think about 3 degrees sea average warmer you're talking a complete change in the climate system on a really fundamental level and also a 3 degrees sea on average over the whole world means perhaps 10 degrees sea or 15 degrees sea in the polar regions and perhaps less in the equatorial regions so an average of 3 degrees sea actually has serious consequences globally a good question to ask is what are the models biggest weaknesses I said something about the strengths of the models and how we can test them and test how good they are by looking at present day observations and past observations for example but an important question is what are their weaknesses and there are several things and one of the things that actually the model turns out the models of relative weakness is actually in their simulation of extreme events so the models do what you could argue is a reasonable job of simulating average climate however if you were to ask a model how many what's going to be the magnitude or let's say what's going to be the change in the frequency of heat waves in the US in the next 100 years then that is going to be a question that's going to be very difficult for models to answer because in general not in all cases but in many cases they tend to underestimate the extreme event so they will underestimate the number of extremely cold days in any particular place and they will also underestimate the number of extremely warm days they will underestimate the number of torrential downpours that we have they will underestimate in general the amount of flooding for example models don't necessarily include flooding as an output but they will certainly underestimate the amount of extreme rainfall they may also underestimate the extreme wind events for example and a lot of this is actually related to the going back to this point about the size of the grid boxes that make up the model if you like and because these in theory the smaller that these grid boxes become actually the better that you would or the idea is the better that you'd begin to resolve some of these more extreme events so as you reduce the size of your grid cells for example you suddenly start to simulate hurricanes in the model typhoons which at a course of resolution the model is just not capable of resolving and so one of the ways that as modelers we're trying to address some of these weaknesses in the model about their prediction of extreme events is to try and make these boxes that make up the model smaller and smaller and that's why climate models become more and more expensive to run now it turns out that luckily computing power is getting increasing more and more as well and actually it turns out that it's almost constant through time how long it takes one single climate model to predict a year of climate for example so that is and typically that might be of the order sort of a day or something like that order of magnitude but that's because the resolution of these models the size of the grid boxes is getting higher in other words the boxes are getting smaller and smaller but the computer power is also increasing and so we're able to simulate sort of the same amount of time if you like with one of these models and so extreme events and we're trying extreme events is one weakness we're trying to address that partly by increasing the resolution of the models but also by improving the representation in the models of those processors that inevitably will occur at a scale smaller than one of these grid boxes just the scale of these grid boxes to just meters or so to be able to simulate some of the very fine scale eddys in the atmosphere for example and in my lifetime that's probably not going to happen given the current speed of increase of computer power and so there will always be some features of the climate system that we will have to approximate with what we call parameterizations that simulate these processes that occur on a very fine scale but one thing that we can do although we still need these parameterizations we can improve them we can try and make them a better representation of really what's going on and one way you can do that is to get more and more observations of the real world and to sort of try and get your parameterization to best match those observations that we have one of the real weaknesses of climate models at the moment is to do with their representation of clouds and we know that's a weakness but if we look at the future projections of the models the predictions for how cloud cover is going to change are basically all over the place so for most places in the world there is not good agreement between the models even in whether the amount of cloudiness is going to increase or decrease as we go into the future and that's because the models have very different ways of representing clouds and we don't know which one is right the important thing is that all of these representation of clouds in all the models do a reasonable job of simulating the present day cloud distribution but when they go off into the future they simulate something very different and that's why some of projections of the future are uncertain but a key point is that uncertainty is not a reason for complacency of you like or not doing anything about it and in fact in many walks of life the more uncertain you are the more risk averse you are and the more precautions you take and so saying that these climate predictions are uncertain is actually in some cases can be a reason for more concern because it means the change could be even greater than what the average model predicts if you like I heard someone say on the internet online talk and it could be you I'm not sure that the amount of power in the first climate model computer is 10,000 times smaller than your iPhone I do use that one because that was pretty cool so I'd love to hear you I don't know what the exact numbers are but I did the calculation for a lecture once but I wouldn't want to get it wrong if it was going to be I could say a bow I'll say a bow so one of the first ever weather or the first ever weather forecast that was carried out on a computer that I'm aware of was carried out by a guy called Charney he did a 24 hour weather forecast actually it took him 24 hours to do that forecast so it wasn't particularly useful but it turned out that there is some archive photography of what that machine actually looked like and actually it looks very similar to a modern day supercomputer it's about the size of a room it's got lots of leads everywhere and it's got a few people looking around technicians looking after it it actually looks very similar to a modern day supercomputer but actually if you work it out it turns out that in fact the amount of computer power in that first supercomputer that did that first weather forecast in the 70s your mobile phone has done that supercomputer and a modern day supercomputer is about 30,000 times more powerful than your mobile phone so there are many orders of magnitude that gives you a flavour of how supercomputing has moved on from the 70s just today so just in 40 years I'll say there's been a huge increase and along with that there's been an increase in the resolution and the amount of work or the amount of um how good this representation of many of these climatic processes are How did I first get into climate science well actually my undergraduate university degree was in physics and that was actually a four year course and in the first three years of that course it was we were doing thermodynamics and optics and quantum physics and laser physics and what have you but in the fourth year we actually had some options and you could go off and study general relativity or do more on laser physics but one of the options was on the physics of atmospheres and oceans and I thought that sounds interesting so I did one of my options in my fourth year of my physics degree was atmospheres and oceans and it was really then that I got interested in climate science and fluid dynamics really it was at that time and so I looked into PhDs that were available in that field and there were a few various universities and actually I was very really fortunate actually because I ended up going to Reading the University of Reading in the UK which I had no idea at the time when I was applying but actually is one of the world centres for meteorology and climate science research so I was really fortunate to be in an environment where there were a huge number of the lecturers were really were the world leaders in their field and also we had a fantastic group of students I was part of a cohort where we had a huge amount of fun but also we worked hard play hard and so my PhD was actually in when I first got interested in past climate change actually because I happened to end up doing a PhD on the dust cycle 20,000 years ago which was the last ice age so it turns out that there was lots of dust in the atmosphere in the last ice age and no one knew why and so part of my PhD was to try and understand why a cold climate should also be a dusty climate and so and then following on from that I got really involved in really interested in past climate science and well actually I had a year in France working in one of their climate institutes on a project that was actually funded by the nuclear industry and they were very interested in what the climate was going to be like in a million years in the future because on and tens of thousands of years in the future because they have, they're very interested in the safety of their the safety of their radioactive waste and they want to know that if they bury it in the ground that particular place is not going to experience extremes in climate so I was actually doing some million year weather forecasting but then after that I actually came back into the past climate realm and came here to Bristol doing some research and then from then on it's just really carried on from then there are many many fascinating questions one of the key ones actually is relates to an apparent discrepancy that we have in our ideas of what climate was like in past super greenhouse climates like the Eocene 50 million years ago the picture that we get of climate from the geological record so from sediments in the ocean from like I said before fossilized leaves and fossilized pollen etc etc and the predictions for those climates that we get from models and it turns out that actually the models in general don't warm enough compared with the data that we have from the geological record so actually there's this and it's coming closer as the years go by the models and the data some of the data is reinterpreted perhaps as saying maybe it wasn't quite as warm as we thought or at least the uncertainties when you take into account the full range of uncertainties of some of these geological indicators we think well maybe there's some error bars on these estimates of past temperatures but even when you take those into account it still turns out that the models don't quite warm enough when we give them the amounts of carbon dioxide in the atmosphere that we think we're around at the time in particular they don't really warm up enough towards the polar regions so they warm up enough in the equatorial regions and the middle attitudes but in the polar regions they're really not quite warming up enough and so that's a big challenge actually for the modelling community and it's one that's been around actually for decades in fact and we're doing some work here at Bristol that's trying to address that by looking at the full uncertainty range of the model predictions and actually we're finding some very fruitful results from that in particular one of my colleagues Professor Valdeys has done some really fascinating work where they've taken instead of taking just one model prediction they take many model predictions all from one model vary some of the uncertain parameters within this model and make many predictions of what the eocene world for example 50 million years ago was like and some of those actually do match the data and so we are making some progress in terms of understanding this model data mismatch so that is one of the challenges in past times another relates to the fact like I said when we the models don't get enough warming when we put in what we think is the right amount of carbon dioxide now actually as I was saying before to get a handle on how much carbon dioxide there was 50 million years ago is a real challenge and there are many different ways that we try and do that but they're all indirect measurements well they're not really measurements they're indirect indicators for example one of the things you can do you can look at fossilised leaves and look at the size of the pores the stomata in these fossilised leaves and it turns out that that is a very strong indication if you look at experiments in modern greenhouses for example of how much carbon dioxide there was in the atmosphere and so you can get things from that you can get indicators by looking at how acidified the ocean was millions of years ago by looking at various measurements on the shells of ancient fossils and like I said when they agree you get some confidence but the error bars are still really huge so actually when we have a climate model and we're trying to simulate the climate 50 million years ago we don't know still how much carbon dioxide we should be putting in the model and obviously the more we put in the more it warms up and eventually you get to a point where you might agree with some of this polar data but by then you're quite often at CO2 levels that are much higher than what we think we're around so I think one of the challenges is this model data mismatch really in these deep time millions of years ago climates is still a major challenge but we're doing a lot of work on it and we're making some progress I think at the moment it's unequivocal that the amount of carbon dioxide in the atmosphere is increasing and is increasing fast and is increasing faster than it ever has in the past and that is also unequivocally due to human activities so burning of fossil fuels land use change et cetera so we have a definite increase in the amount of greenhouse gases in the atmosphere and it is also to the best of our understanding of the way to the best of our understanding of physics and chemistry and biology that that and our understanding of the way that radiation works and the way that radiation from the sun and emitted by the earth interacts with these molecules of carbon dioxide in the atmosphere that that will cause a warming the uncertainty that comes in in terms of future climate prediction is actually how much warming that will cause there are uncertainties associated with that for example and in particular associated with how parts of the system will react parts of our climate system will react in a warmer world so for example how will cloud cover change how will vegetation change in the future how will the wind patterns change and how will that affect the distribution of heat throughout the atmosphere and how will ocean circulation change so there are some uncertainties but it's unequivocal that there will be some warming in response to that CO2 change and we have a range through the intergovernmental panel on climate change we have a group of climate models that represents as a global community our best understanding of how the climate system will work and so that spread of future predictions if you like is a very good indicator of our best estimate of how the future climate is is going to respond under various scenarios of future increasing CO2 levels now the really important and that as scientists is almost as far as we can go what we can say is that this is what we think is going to happen to the very best of our scientific understanding and this is the uncertainty the range in those future projections there are also as climate scientists that's what we can do there are then various other people scientists and economists who can work on what is going to be the impacts of those climate changes so for example how much is that going to affect flooding how much will there be predicted changes in rainfall how much is that going to affect flood risk in various parts of the world how much is our predicted temperature changes how much is that going to affect drought and population movement and that is going to be applied due to additional heat waves in the future for example there are there are scientists working on those problems as well where the scientists stop and the policy makers begin is then what should we do about that and that in some ways is actually the most important question is what as scientists we can present our best understanding of what is going to happen but it's the policy makers who need to make that decision about what they're going to do about it it's it's my feeling that in the presence of uncertainty we should always take a conservative approach with a small c in that you must plan for the future and you should plan for the worst case scenario in some ways or you should certainly take into account the worst case scenarios in your future planning you should also consider of course the lower projections as well but we must consider that full range of uncertainty and it's up to the policy makers to make that decision and actually it's up to them to balance you know we have a global economy what do we spend our money on do we spend it on adapting to climate change do we spend it on moving to renewable energy so that we omit less CO2 do we spend it on something completely different like trying to cure malaria those are the really big questions for today's society and as climate scientists we can present all the evidence we have and we can be as honest as we can about the uncertainty in our projections and then it's up to the policy makers to act on that and do the best thing for our global society and global community and it is my hope that they do the right thing so stuff about the drowning probably might get into the for the top weeks they can revel in all this I sort of got carried away that's why I took it in it was my fault I accept full responsibility