Global Challenges UOSM2010 John Shepherd: Climate change science summary

hello my name is John Sheppard I’m from the National oceanography centre at the University of Southampton and I’m going to be talking to you about climate change which I call the factor 40 problem I want to explain to you what’s happening with the climate why it’s happening and at the end what we can do about it the overview of the talk is shown here I will start by reviewing for you some of the basics of climate science particularly the energy balance and the greenhouse effect itself I go on to talk about climate change in the past what we know about natural variability of climate which is of course substantial and then go on to review the science of climate change and discuss whether or not it’s still controversial next I want to talk about climate change in the future so I’ll give you some of the latest results from the fifth assessment of the Intergovernmental Panel on Climate Change published this year and the prospects to the end of this century to 2100 and indeed beyond and then finally I want to talk about dealing with climate change responding what can we do about it how big is the problem and what are the possible responses and there are really three mitigation adaptation and geoengineering perhaps this slide summarizes most of what you need to know about the climate system on the left-hand side you can see incoming solar radiation ultraviolet and visible light from the Sun coming and warming the earth as it receives its energy some of it is reflected by clouds but most of it is absorbed by the atmosphere the land surface and the oceans and on the right-hand side you can see the outgoing radiation from the warm earth all warm bodies give off infrared radiation I do you do everybody does all the time and as the earth warms up it gives off more infrared radiation and in fact if it’s out of balance it will continue to warm up until it is emitting enough radiation to balance that which is received this is what we call the energy balance of the climate system and it is the fundamental process that controls the temperature of the planet and of course what we have done with greenhouse gases is interfere on the right hand side of that diagram to make it harder for the energy to leave the earth and that’s like turning off the tap that’s draining your bath it fills up in this case the earth gets warmer until the heat energy is able to get through the barrier of the atmosphere and escape to space now there are of course natural greenhouse gases as well as those that we’ve created the most important one is water vapor without water vapor the earth would be about 30 degrees cooler than it is and that means it would be pretty much all frozen that’s very important because there’s more water vapor when the planet gets warmer and that means that we have a feedback process that I’ll talk about later but also water vapor is controlled by natural processes by evaporation from land and ocean surfaces and also by condensation clouds and rain remove water vapor from the atmosphere and provide a natural control on its level so that we can’t change the amount of water vapor in the atmosphere by very much directly carbon dioxide is different it doesn’t have the same natural controlling process that water vapor does and although it is both natural and a man-made greenhouse gas it is part of the natural carbon cycle that operates really rather slowly compared with the water vapor cycle and that turns out to be important too and then there are other greenhouse gases such as methane and nitrous oxide that can be very important in circumstances but which I won’t talk about much in this talk some important features of the natural carbon cycle are shown on this slide here and the bid I want you to focus on is the three numbers golden yellow gigatonnes GT is scientist shorthand for billions of tons of carbon in this case and as you can see we have roughly the same amount of carbon as carbon dioxide and other compounds in the atmosphere in the living biosphere shown in green and in the surface ocean shown in blue and these are the three big reservoirs that exchange relatively rapidly and form the fast acting part of

the natural carbon cycle and that number in the atmosphere is 700 now maybe a little bit more it started about 500 we have already added about 200 billion tons of carbon to the atmosphere now the climate system if it were simple would be easy but it’s not simple it’s not just the black body in a laboratory or even a black body in space the climate system is quite complicated it includes things like water ice clouds vegetation all of these things and some of these processes cause feedbacks and a feedback is when we make a change to a system and the system responds in such a way as to either to amplify or diminish the change that we made and some of the changes are negative feedbacks that diminish the change and the basic one is the simple fact that we get more thermal radiation from a warmer surface that is the fundamental feedback that stabilizes the climate system but we also have positive feedbacks the water vapor feedback that I mentioned before we have more water vapor when the planet gets warmer and that increases the greenhouse effect we have what we call the ice albedo feedback albedo is a scientist fancy word for reflectivity ice and snow reflect a lot of incoming radiation and as the planet warms we have less ice and snow on the surface and that means less radiation is reflected that means we have another positive feedback and there are also feedbacks in the carbon cycle that are actually less well understood than the other two and all of these act to amplify the response of the climate system to any change that it suffers and they actually enhance what we call the climate sensitivity the amount that the planet will warm for a change in forcing or a change in greenhouse gases in the atmosphere positive feedbacks don’t necessarily lead to a runaway process like when you get feedback on an amplifier and it howls that is a runaway response and that it’s not necessarily going to happen the main thing is that positive feedbacks make the system more sensitive and one of the most important additional parts of the climate system is clouds now clouds are very tricky we all know that if a cloud crosses the Sun on a sunny day it will cool down and it’s colder at night than it is during the day and we also know that during the night if there are clouds we’re unlikely to get frost because clouds also prevent heat from leaving the earth so they act both to cool the planet and to warm the planet depending on the latitude the time of day the time of year and the type of clouds so clouds are very tricky especially because we’re interested ja tenant not just in the difference between those two large numbers the warming and the cooling effect but also in how that will change as the temperature changes now to move on to climate in the past George Santayana said that those who are ignorant of history are condemned to relive it I’ve paraphrased that by saying that those who are ignorant of the past are condemned to misunderstand the future the climate has changed in various interesting ways in the past and unless we understand that we’re unlikely to make very accurate predictions for the future now in fact over a very long time scale climate has been really rather stable the earth is about four-and-a-half billion years old and for most of that time for almost all of that time we know that there has been liquid water on the surface of the planet and we know that from geological evidence from the existence of sedimentary rocks that were laid down in water and for liquid water to be present on the surface the temperature has to be somewhere between let’s say zero and forty or fifty degrees centigrade it can’t be much outside that range and that is quite a narrow range compared with what it could be and it’s existed for four-and-a-half billion years that is remarkable but within that climate has also changed from time to time particularly we have had in the last few million years a continual sequence of ice ages and relatively warm periods such as the one we are still living in the Holocene that has lasted for about the past 10,000 years when the climate has been remarkably stable but when an ice age ends the climate changes rapidly what we call a deglaciation or termination of the Ice Age we can see

the temperature change by several degrees over a period of a few thousand years and that is a very large and very fast change of the natural system and the evidence from the past suggests that the climate has varied a lot in the past and so future change is unlikely to be gradual or steady either and that’s illustrated in this slide from Richard Ally’s book the two-mile time machine which shows the well-known covariation of carbon dioxide in atmosphere in the red and the temperature in Antarctica shown in blue now this is a remarkable correlation it’s one of the tightest correlations between two natural variables that I have ever seen quite extraordinary and it is unthinkable that there is not a causal relationship between them in fact there’s a very interesting causal relationship because warming causes co2 to rise but increased co2 also causes further warming so we have here a closed cycle of positive feedbacks that are causing these to vary in lock step over very long periods of time and what you can see on this slide where by the way now is on the left hand side and the past is on the right hand side which is the way paleo climate scientists tend to plot things because deeper in the core means further in the past what you can see on this slide is that at the end of the ice ages we have these very sharp rises of both carbon dioxide and temperature that are almost completely synchronous and in fact during an ice age we have even greater variations this slide is taken from ice cores drilled in on the Greenland ice cap also from Richard Ally’s book and it shows the really quite extraordinarily rapid variations that have happened during the past 100 thousand years the last glacial cycle those are changes of several degrees occurring over a decade or possibly even less and that is quite remarkable now we believe that those changes are associated with the ocean circulation this slide shows a cartoon of the overturning circulation the deep ocean circulation of the world ocean and what you can see is warm water coming from the south going north up the Atlantic reaching the high latitudes near Greenland and up into the Arctic becoming cooled becoming denser and sinking and going back down south and if that deep thermohaline circulation is interrupted then it causes a major change in the regional climate at Greenland and that we believe is what is causing those rapid changes this circulation actually transports one petawatt of heat up into the north atlantic and most people don’t know what one petawatt of heat is so I will tell you that it is roughly the output of 1 million nuclear power stations it’s a lot of heat and if you shut that off it makes a big difference least in the North Atlantic region so the ocean circulation is important too well given that natural climate variability exists is it a source of comfort can we say that climate has changed a lot naturally and so the present changes must also be natural unfortunately not that’s like saying the last nine times the fire alarm went off it was a false alarm so this one must be a false alarm too not a safe assumption can we say that climate has changed so nothing we can do will make much difference unfortunately not quite the reverse in fact what we see from the record of the past is that the climate is actually very sensitive to quite small changes those ice ages are paced by small changes in the orbit of the earth around the Sun that affect not the amount of sunlight that the earth receives but its distribution with the seasons with summer and winter time of year that small change has triggered those major changes of climate so we’ve see that it’s very sensitive and the mechanisms of this are understood in general but not even in full detail yet and it is entirely possible that our present-day climate models which are of course based on our best current understanding of the system may not yet be sufficiently sensitive they don’t react quite so much or quite so fast as the real climate system which is rather more volatile than our models seem to be so it’s entirely possible that future changes will be greater than we think

rather than less now what is happening to the climate one thing is certain and even the dissenters now agree that the world is getting warmer this slide shows several climate records of from the thermometers that have been measuring temperatures for a little over a hundred hundred and fifty years and a reconstruction of those by the berkeley earth’s surface temperature project in grey and then the convention estimates in red green and blue which you can see on the right hand side of the diagram and what you can see is that everybody including the dissenters who felt that they would get a different answer actually agree not only that the climate is getting warmer but they actually agree on the fine detail of the way that that has happened so that is something that we don’t need to dispute any further in fact if we look at the last thousand years for which of course we don’t have thermometers it’s quite miraculous really that we know anything about temperatures in the past but that information comes from proxy records like tree rings and measurements made in ice cores and all sorts of ocean cause that sort of thing these proxy measurements also show that climate has been relatively stable for as I said the last 10,000 years and even for the last thousand years they don’t all agree with one another as you can see on this slide but broadly speaking there have been relatively minor changes of a fraction of a degree centigrade over the last thousand years and then a sudden rise since the Industrial Revolution that you can see on the right hand side the other thing we know is that carbon dioxide in the atmosphere is increasing this is a famous slide from the measurements made at Mauna Loa in Hawaii by charles david keeling and his successors and they show not only the steady and inexorable rise of carbon dioxide but also that tiny seasonal variations caused by photosynthesis and respiration of plants mainly in the northern hemisphere and last year carbon dioxide reached 400 parts per million for the first time and so it’s now off the scale even of this graph that was drawn a few years ago that is also not in doubt and we also know by analyzing the isotopes the different chemical forms of carbon that it is caused by the burning of fossil fuels and not by some other cause so we know that it’s increasing and we know why and that is quite unprecedented this slide from the previous IPCC report shows carbon dioxide over the last 10,000 years and as you can see it has a displaced zero at 250 in the bottom left hand corner and the level has varied between 262 280 a very small change one or percent or so over 10,000 years and then in the last hundred years it’s gone shooting up and continues to do so and is now actually off the scale of this graph to so that is quite unusual now we know that carbon dioxide is a radiatively active gas that it means that it will cause a greenhouse effect and we know that because it absorbs thermal infrared radiation and that was discovered more than a hundred years ago and that’s actually how its measured in the lab and up mount Aloha if you want to know the carbon dioxide in your room then an infrared gas analyzer is probably the instrument you would use because of that fact that means that it absorbs infrared in the atmosphere that means it will increase the greenhouse effect and contribute to global warming and we can calculate that it was first done in the 19th century by swedish physicist svante arrhenius his paper from 1896 is available on the web you can download it and read it it’s a remarkable piece of work to have done the to have obtained the results that he did with very limited resources and a pencil and paper and no computers is quite extraordinary his answer is actually quite close to those that we get from big computer models these days what that means is that the effects of carbon dioxide can be modeled in simple models in complex models in whatever sort of model you want and we can try and find out how good are those models this slide again from the IPCC shows a whole range of models all the yellow Wiggly lines are the results from a

bunch of different models and they don’t agree about the legals because there is no way that they could we can’t give them enough information about the initial conditions of the system to enable them to do that it’s a chaotic system and it varies a lot depending on the starting point but the general features are quite well represented and the models agree quite well between each other and you can see the average of the models since the red line and you can also see the average of those observations in the black line and what you can see is that on a multidecadal timescale over 20 or 30 years they vary together very well on shorter time scales from year to year and even from decade to decade there are Wiggles that the models cannot and do not explain and are not expected to explain and we can also see the effects of major volcanic eruptions shown by the vertical lines for a gung el chichon and Pinatubo which caused a sharp cooling followed by a recovery over a year or two of the temperature back to the trend so we know by doing these simulations of the past that the models are capable of reproducing the changes of the real climate system and that gives us some confidence that we can use them for predictions of the future so just to summarize the climate facts the things that we know beyond reasonable doubt that for all practical purposes can be regarded as effectively certain atmospheric concentrations of carbon dioxide are increasing and it’s due to the burning of fossil fuels the world is warming and it’s warming at a rate which is quite unprecedented in human history and that co2 is a greenhouse gas that is likely to cause such warming and the rate of warming is consistent with the changes in carbon dioxide concentration that we have observed we can build and test climate models against the past and we find that they are capable of explaining what has happened the explanation is in fact complete and sufficient and we do not need an alternative explanation and indeed no alternative explanation exists if it did we would have a problem because we would have two explanations for the same thing and that would be a problem I think that that is a very consistent story and I would ask what more can one reasonably ask for now if you are skeptical about climate change if you wish to dissent from the mainstream view of climate scientists worldwide then you need to choose one of the statements on this slide to disagree with and explain why you disagree with it and explain the consequences of that and then we can have a discussion about whether or not that is a serious problem but unless you have an alternative explanation for one of these facts then the conventional explanation stands unchallenged so is the science of climate change still controversial well the answer to that is yes but not in the way that climate dissenters normally assert the evidence for human influence is very strong indeed the Intergovernmental Panel on Climate Change conducts a process of synthesis and review that is the biggest and most rigorous collective review of scientific evidence ever undertaken in any field and there is no need for an alternative theory and no evidence in support of any credible alternative but there is a lot of misunderstanding and misinformation and there are climate skeptics funded by interest groups that create the appearance of controversy which is fueled by the false balance of the media where for every person who says one thing you have to have somebody to disagree with them if you want to know more about this controversy then i recommend the book the merchants of doubt by Naomi Oreskes which analyzes what has happened in climate change and another number of other controversial issues where science and scientific evidence were extremely important another thing that is worrying a lot of people at the moment is whether or not the warming has actually stopped now it has slowed down in the last 10 to 15 years and that is shown on the left hand slide which shows five different records of temperature for the last few decades and as you can see since 1998 which was according to some of those records the warmest year on record the rate of rise has been relatively slow and that has led some people to claim that the whole climate science is wrong and that there is some fundamental problem in fact that’s probably not the case the right hand slide shows some work by Foster and Rance Dorf in which they allowed for the

effects of variations in the solar cycle in the El Nino Southern Oscillation which is a well-known periodic phenomena between the atmosphere and the oceans and volcanic eruptions and they showed that once you have allowed for those effects the rise continues without any evident pause and since that work there have been additional analyses not only of temperatures in the Arctic where the observations are relatively sparse but also of the apparent recent increase in heat uptake by the oceans so there is no evidence from the recent pause that anything is fundamentally wrong there are a number of factors that appear to have contributed to this the real climate controversies do exist but they’re mostly about uncertainties particularly in relation to those feedbacks that I mentioned and particularly in relation to clouds which has been ever since the beginning and is still the most difficult process to represent well in climate models there are also uncertainties about the feedbacks in the carbon cycle that I mentioned that we don’t understand as precisely as we should we also don’t fully understand the precise magnitude of natural effects such as solar variations these effects of solar variations do seem to be a little bit larger than we might have expected and we don’t know why that is and we don’t quite understand the precise extent to which climate change is natural or anthropogenic although it’s very clear that it’s primarily caused by man one of the big uncertainties is the rate of melt of ice sheets and the consequent rates of sea level rise that will occur as the planet warms work is ongoing and is improving those estimates but they are still very uncertain we know roughly how much sea level rise to expect but not how fast it’s likely to happen and the existence and the primary causes of climate change caused by man are not really in any serious doubt if you want some reliable information I do recommend that you go to a website called real climate where climate experts not only post analyses of controversial subjects but also respond to questions and either read or watch Richard Ali’s TV program made for the public broadcasting service in the USA called Earth the operator’s manual both the video and the book contain a wealth of information by a true expert and that is Richard alley on the right-hand side there he’s a glaciologist which is why he has a furry hat and is peeking out from under a glacier now to bring things up to date in 2013 the IPCC produced its latest report and I’ve put some quotations from that report on this slide here I’m not going to read them all out but it is clear that human influence on the climate system is real and substantial we have seen already a rise of about not point eight degrees centigrade and it is extremely likely that human influence has been the dominant cause of that warming moreover the global surface temperature is likely to change by a further four degrees in addition to that naught point eight by the end of the 21st century in a little bit less than a hundred years if emissions follow the highest of the assumptions made by the IPCC in their emissions scenarios and that is a very substantial change indeed roughly equal to the change in temperature between an ice age and a warm interglacial what the IPCC does is to start with emission scenarios in fact with concentration pathways shown in the small panel and there are four of them corresponding to low to medium and one high emissions pathway and these correspond to levels of carbon dioxide emissions that are shown in the big panel with the red line being effectively business as usual without serious attempts to reduce carbon emissions on the other hand the dark blue curve shows the effect of really trying hard to shift to a low-carbon economy and low carbon sources of energy and with that it is just possible to stabilize temperature within this century only just and if you look carefully you can see that by the end of the century we actually need negative emissions that means we need to take carbon dioxide out of the atmosphere again in order to achieve that stabilization that is a new result and a very worrying result because we don’t

actually know how to do that very well yet the temperature projections are shown on this graph here as you can see for that dark blue scenario temperatures are stabilized at about plus 2 degrees compared to pre-industrial because where these are relative to the north point 8 degrees that has already happened whereas for the red scenario they have increased a lot more and are continuing to increase substantially in fact there are a number of things that are changing and still changing by the end of the century and those include sea level sea level rise is likely to be something between a half a meter and one meter by the end of the century in addition to 20 centimeters that has already occurred and it depends of course on which of those emissions scenarios we follow and we do know that a lot of ice is quite likely to melt this slide shows the remnants of the Greenland ice cap during the last interglacial when the world was slightly warmer than it is today just over a hundred thousand years ago when most of that ice sheet had in act collapsed and not much ice was left and sea level was 4 to 6 meters above present much of that coming from Greenland some of it probably from West Antarctica the whole impacts of global warming are complicated and this slide from the stern review of 2006 shows the impacts in different sectors such as food and water ecosystems extreme weather and so on and basically whenever the arrows turn red that means people have problems and as you can see under 2 degrees some of the arrows are read by the time we get to four five and six degrees of warming just about everything is getting to be very difficult for some people somewhere and the oceans have an important part to play in all of this because the oceans are actually absorbing most of the heat over ninety percent of the heat actually goes into the oceans and so moderating climate change in fact it would be about double what it is now if it were not from the heat absorbed by the oceans they also maintain the global climate patterns including the warming of the North Atlantic by that conveyor circulation that I mentioned and they are absorbing much of the carbon dioxide and will absorb most of it eighty to ninety percent eventually and of course the sea levels are rising as the ocean warms and finally the oceans are becoming acidified because carbon dioxide is a weakly acidic gas and that is another problem not actually related to warming that I don’t have time to talk about today but I certainly hope that the world will not end in 2100 even though most of those graphs do the natural processes will sadly only remove carbon dioxide from the atmosphere very slowly in fact it takes many thousands of years and temperatures will continue to rise and will remain high for a very long time after the emissions have ceased that means we need to use long-term projections of climate change and we need to use simpler models such as the ones that I work on intermediate complexity climate models and the IPCC has now used these two to any assess climate change over the next 1,000 years they have some emission scenarios shown the top panel from more or less business as usual until the fossil fuels run out to a very strict conservation and transfer to a low-carbon economy shown in blue at the bottom and you can see the consequent air temperature change in the bottom panel not only does the temperature go way up to four five six degrees and beyond under that business-as-usual scenario but it stays there for a very long time not just one thousand years but several thousand years so that we are in fact making what is for all practical purposes and irreversible change to the climate system and that I think is very worrying another thing the IPCC has done for the first time is to try and assess our carbon budget it turns out because of processes that canceled in an interesting way that the temperature rise is roughly directly proportional to the amount of carbon dioxide that we have cumulatively emitted and that’s shown by the red blue orange lines that are overlaid on this graph showing the expected temperature change for different levels of total carbon dioxide emissions including of course some uncertainty bounds around

that and what that means is that if we want to stay within the normally accepted threshold of two degrees of warming compared to pre-industrial we cannot afford to burn more than about one thousand billion tons of carbon and we have already burned about half of that so if you accept that calculation we have used half our carbon budget and we have another half left to last us for the rest of this century and every other century Beyond and now and forever and that is a very challenging calculation so what about climate change in the future we need to factor stabilized temperature anywhere near that agreed level of two degrees we actually need to reduce global emissions enormously we need to reduce them in the first instance to about the level of the ocean sink which is running at about 2 billion tons per year and is likely to run that way for a while and that is actually to less than twenty-five percent of their current global level which is a massive challenge it’s a big hard and long term problem and big hard and long term problems are exactly the ones that are very difficult for politicians to deal with that’s why we’re making so little progress in fact I want to summarize for you the big picture and that is that we need to reduce our emissions by about a factor of four while the population is continuing to grow possibly by another factor of two by the end of the century and we have to allow for the fact that people in the developing world are trying to develop their economies and want to use more energy if they increase their energy use per head just to the level of the European Union let alone North America or Australia and if they do it using fossil fuels that would be a further factor of five of increased emissions going in the opposite direction to which we are trying to move if you multiply those factors together you can see that we need to decarbonize the economy of the world by about a factor of 40 and that’s why I chose the title for the slide it’s a factor 40 problem that we have to solve now Amory Lovins and co-authors many years ago now published a very inspirational book called factor for in which they argued that we could simply by doing things that we know how to do reduce our emissions by about a factor of 4 and I suspect they are not far from correct but that still leaves a mismatch by a factor of 10 and we have to ask ourselves whether there is really any hope of closing that gap and the only answer I can give you is maybe how might we do that what does it mean what we need to achieve is a fifty percent reduction in global emissions by 2050 and that means about two percent per year averaged over the whole world compared with about a three percent per year increase right now even more than that would need to be achieved by countries that have high emissions at the moment such as UK Europe and even more North America Australia and it would be even harder if we delay it turns out that a twenty year delay makes it roughly twice as hard to get those emissions down at the rate that we need and that means that it’s better to act early rather than to act late now there are ways of doing this reducing carbon emissions is commonly called mitigation and to do that we need energy conservation we need energy efficiency we need low carbon sources of energy and in particular we need to decarbonize the electricity supply and transport which will be very difficult renewable sources of energy are excellent for that but nowhere near enough just yet nuclear fission is familiar we know about it it exists it does have some safety issues but it does produce clean electricity and it does so in a way which is safe compared with some other forms of energy generation nuclear fusion thermonuclear power may eventually work it’s been coming for a long time but it probably will work sometime in the future but not in the immediate future by the middle of this century when we need it and hydrogen of course is often proposed as the solution to the problems but it’s only a carrier we can’t mine hydrogen it’s actually made from fossil fuels and the carbon dioxide goes into the atmosphere so we need a low carbon source of hydrogen and that probably means making it either from solar or nuclear power and almost certainly if we’re going to continue to burn fossil

fuels we will need carbon capture and storage to deal with the carbon emissions that they produce for some technologies we do know how to do these things this is actually the ship on which my grandfather ran away to sea early in the last century we know how to move people and goods around the world by sea using wind power and indeed possibly nuclear power but for aviation we have no way to power aircraft other than carbon-based liquid fuels and so that is a particularly intractable problem that needs a technical solution however we can ask if there is a way forward and I think there is and that is to develop and rapidly implement biofuels for niche applications in transport to decarbonize the electricity supply so that we can use electric vehicles comfortably and of course to use carbon sequestration and storage technology to clean up our continued use of fossil fuels this is going to take a long time it’s going to take several decades and so we need to start very soon rather than leaving it for very much longer and we could and should probably also actively research new things such as intervening in the climate system about which I’ll say a little bit more in a moment and finding ways to generate hydrogen from low carbon sources such as solar energy but there is no magic bullet and we need education and economic incentives and almost certainly regulation to make things happen one or other of these is not going to be sufficient it is possible to make hydrogen from solar power this is a slide of it actually happening in a lab in California and the technology works on the bench top but is not capable of large-scale application yet and we can use education to shift public opinion this slide was drawn by a class that my wife was teaching some years ago after a school trip to the zoo when she asked them to invent a low-carbon form of transport for school trips and they came up with the pedal bus which amazingly I am told actually exists in the Netherlands for taking the kids to school we do also need economic incentives and people often say that dealing with the climate change problem will [ __ ] the world economy Nick Stern’s review reached the opposite conclusion and carbon tax is at the level that would make an enormous difference to the profitability and competitiveness of renewable sources would certainly not [ __ ] the economy in the anytime in the near future in fact it’s the the amounts of taxation if you decided to use a carbon tax that are needed are really quite modest and of course if you introduce the new tax you could make it revenue neutral you could replace other taxes such as for example v80 which so far as i can see achieved no useful purpose at all other than to raise money could replace it rather than being additional to it and this would simply shift the balance of advantage between different forms of energy generation in a way that would favor low carbon sources but ideally of course this should be done internationally and at the moment there is little sign of international agreement on anything so radical we can also do things ourselves Al Gore produced a list in his book the inconvenient truth which I was surprised by when I read it because it didn’t include all the things that I thought were really important so I’ve added them here in red these are the ones that really make a difference for most of us most of the people that I work with and live with the biggest change we could make is actually by flying less and possibly by buying a smaller vehicle and a more efficient vehicle and then driving less far and using public transport those things are relatively easy to achieve and would make a big difference but there are a lot of other things on the list that you can use and for individuals to make a difference what about this idea of geoengineering about intervening to change the climate system try and modify the climate change that we are causing well if we continue to fail to get to grips with this problem it is possible that later in the century we may have to contemplate scary ideas such as this and there are actually two ways of doing it one is to try and increase a little bit of reflection of sunlight and the other is to find ways to actually take carbon dioxide out of the atmosphere and both of those are practically possible but not

economically affordable on the scale that is needed but research on these is probably wise in case we need them later in the century so to try and bring this all together and talk about the day after tomorrow is it already too late I don’t think it is two degrees or so of warming is now almost certainly inevitable but we can certainly still avoid + 4 + 5 + + 6 degrees and we almost certainly should can local action help yes it is it’s essential and unless we in the Western world put our own house in order we have little hope of persuading people in the developing world to take the difficult decisions that are needed to prevent global emissions going too far and what is the best solution there is no single magic bullet to solve this problem there is no get-out-of-jail-free card we need all sorts of technologies horses for courses and frankly I think we should forget arguments about whether nuclear is better or worse than wind power we’re going to need all the possible contributions that we can think of and we’re going to need them as much and as soon as we can afford and engineer them we in fact have four different possible responses to climate change what i call the fourfold way they are mitigation to reduce emissions possibly geoengineering to reduce the amount of climate change adaptation so that we suffer less from the changes that nevertheless occur and finally of course simply accepting the impacts the suffering that goes with them and those impacts and that suffering are most likely to be felt by the most vulnerable people in society and the most vulnerable people in the world and it is for them that we need to take action so we need to remember that increasing energy efficiency and using renewables of vital that decarbonizing the electricity supply is especially important my particular slogan is no combustion without sequestration but it doesn’t seem to have caught on yet we need to recognize that transport and especially aviation are among the most intractable problems and we may need to reserve biofuels and possibly continued use of fossil fuels for a long time for those purposes carbon offsets are a step in the right direction but far from a complete solution but delay will make things much harder and uncertainty is in my view not a valid reason for doing nothing rather uncertainty is a reason for taking precautionary action if you are convinced that an irreversible and undesirable change is going to be caused by what you’re doing now and finally the climate records of the past suggests that change is unlikely to be steady and that we should be prepared for a bumpy ride now this is not a problem for the far future this is a problem for people like my grandson’s shown in this slide who with a little bit of luck may still be alive in 2100 there are people now alive who are going to have to deal with the consequences of what we do now and it is in their interest that we need to act Albert Schweitzer said that man had lost the capacity to foresee and to forestall and that he would end by destroying the earth now I think he was pessimistic I do not think we have lost the capacity to foresee I believe that that is what the IPCC has been doing for us what the climate scientists do what we have been doing in this lecture this afternoon whether or not we have the capacity to forestall those changes I not so sure but I certainly hope that we will not end by destroying the earth so it’s a big problem can we fix it I’m afraid the answer to that can only be maybe and if we need try much harder than we have so far thank you very much you