Experts Debate Climate Change Science, Policy

Experts Debate Climate Change Science, Policy



all right so I talked about why climate change concerns me and I like to begin with this plot this is something of an iconic plot and it shows the temperature of the last 150 years measured by thermometers on the surface and this is year on this axis running for the last you know hundred 20 years and temperature anomaly which is the departure from the mean and what it shows is that temperatures been going up and it's been going up by about 0.74 and there's some error bar of course there's uncertainty now if this is all we had you would have to be very skeptical wait I doing something what oh really all right let me switch to is that better I was the clicker that's weird all right I've never heard any to that before all right this is the important point if this was the only thing we had there are lots of ways these data could go bad and so what scientists do is we look for what's called coherence we want to follow our Concilium lots of different words for want to find lots of data that are independent that tell you exactly the same thing so if you ask the question why are scientists so confident the earth is warming it's because we have lots of data we have surface thermometers they show temperatures warming we have satellites you can measure temperature from a satellite that shows the earth is warming glaciers are melting sea ice is receding we know ice melts reliably at 32 degrees Fahrenheit so with a warmer planet you expect to see less ice and indeed we do ocean temperatures we're not talking about the surface that's included in the surface thermometer record we're talking about the temperature the bulk of the ocean that's going on and finally sea levels rising and the best part about this is this creates this really integrated system it all fits together perfectly so for example glaciers so glaciers are receding our glaciers are melting and now that water's running into the ocean that's causing sea-level to go up in addition ocean temperatures are increasing on ocean temperatures increase water like most things expands and that causes sea levels to go up and so it all fits together it's this coherence of data and even if any one of these data sets is wrong it really wouldn't affect your confidence because we have so much other data that suggests it's warming and because of this the IPCC calls this unequivocal which means essentially beyond doubt and so for example professor Lindsay will be talking after me he wrote in a Wall Street Journal op-ed there is general support for the assertion that global average temperature anomaly has increased about 1.5 degrees Fahrenheit since the middle of 19th century so essentially nobody argues this and again I don't want to waste too much time on this I want to get to the interesting thing but the key thing to look at is look for coherence look for lots of evidence supporting a point and you'll clearly see why scientists are so convinced that the mainstream view of climate science is right so the real question I want to address here is this question of how much does carbon dioxide warm the climate this is really the key question and it's not a question of does carbon dioxide warm the climate I think professor winds and I will agree it does it's a question of magnitude a question of how much it warms the climate and we're going to talk about here is this question of climate sensitivity it's off that's often referred to as climate sensitivity and that's and we're going to use a standard measure which is how much warming would occur if we doubled carbon dioxide okay and so we're gonna go through the math and we do a very simple calculation that indicates that we might be screwed all right so we start off with the equation that I suspect professor wounds and Waffen should also show you so there's really no debate about this and this is a design I use the slide and presentations at NASA headquarters so you know it can't be very complicated and so he's so TF which is the final temperature this is how much warming you get if you double carbon dioxide now T I is how much warming you get if you add carbon dioxide the atmosphere and nothing changed so so no changing clouds no change in humidity the atmosphere no change in ice no change in the lapse rate which is the temperature structure everything remains fixed and so let's go to the source dick Linton's Wall Street Journal op-ed it is generally accepted that a doubling of carbon dioxide will only produce a change of about two degrees Fahrenheit if all else is held constant and again that's that term right there so we can convert to degrees Fahrenheit to 1.2 degrees Celsius and we know what this term is right here now the key part of this is if all else is held constant now it turns out that all else has not held constant and the things that change are this F right here and that stands for feedbacks so let's talk about what a feedback is and and what this does to the what this does to the problem all right so start off with let's say you add some carbon dioxide the atmosphere now fessor wins and I agree that if you did nothing else that would give you about a degree at one point two degrees of warming but other things do change so we know for example and I'll show you some data showing this in a second that as the surface warms the atmosphere becomes more humid now water itself is a greenhouse gas so the increase in humidity causes additional warming and that additional warming causes more humidity and that causes more warming so you have this infinite loop that goes now a lot of people think because the loop is infinite it has to imply a runaway that the warming has to be infant that's not right if you remember back to you probably 9th grade math you can have infinite series that converge on a finite number and that's essentially what's happening here so you get additional warming from this water vapor feedback let's go back to our equation and what you see here is that if F is greater than 0 then this number is less than 1 and you're dividing by number smaller than 1 and the final temperature is greater than the initial temperature and we call that positive feedback where these processes are amplifying the warming for carbon dioxide and if F is less than zero then this number is less than this number and you get a negative feedback and that means that the feedbacks tend to damp out damp out the effect all right so let's go to let's let's look at what F is in a little more detail so we can essentially write F which is the total feedback as the sum of various feedbacks that are operating this first one is water vapor so WV stands for and that's the one I just talked about is the earth warms the atmosphere holds more water and that it gives you additional warming and so you'll hear a lot of people say if you read the blogs that there's no evidence for this it's just assumed by the models or it's hypothetical in fact that was true twenty years ago but we now have data and so let me show you some data that I think is actually quite clear all right so this axis is temperature surface temperature and that's the black line and this is surface temperature this is of the tropics and there's a reason for that which I can explain if someone's really curious and so you can see the temperature the tropics of the last eight years has been going up and down these are mainly and so events El Nino La Nina so there's a big wad anemia of that right here and you know you can sort of pick out other little events the temperature goes up and down the red line is water vapor and this is measured by a satellite that's one of the red lines the other red line is what we call a reanalysis system and I won't go into the details of that but feel free to ask me if you want and what this shows in duck there's even a little lag this is the timescale for water vapor is a timescale for temperature you see the water vapor actually even lags the temperature by a few weeks which shows that water vapor is reacting the surface temperature services or changes in water vapor you see the water vapor follows a surface temperature exactly I mean this is really you know next time a skeptic tells you that the water vapor feedback is you know doesn't exist or it's purely hypothetical you know you can you have a decision whether you can believe them you can believe your own eyes it's quite it's quite clear that water vapor follows temperature now we can then put this into a radiative transfer calculation because we know the spectroscopy of water vapor very well it's like we don't spectroscopy with carbon dioxide and so you can get a number in these units and the unit's appropriate for the equation I gave you point-six and so we can fill in the first term zero point six and what we do now is we're gonna go fill in all the rest of the terms and we'll see what we end up getting all right now I'm not gonna go into great detail about the other two let me go back for a second so this is the lapse rate feedback it's a negative feedback that simply reflects the fact that a warmer atmosphere radiates energy more if you took physics you might remember Sigma T to the fourth so that's essentially what the lapse rate feedback says the ice albedo feedback is ia and that simply reflects the fact that if you melt ice ice is very reflective so as ice on the planet goes away the planet actually absorbs more solar radiation and that's a positive feedback and so we can actually put terms on this and again these are based on data you can estimate these from satellite data and this is a negative feedback that offsets about half of the water vapor feedback and then the I saw beto feedback is a small positive feedback it's big in the Arctic but the Arctic doesn't cover a huge region of the globe so when you average globally the isobutyl feedback is sort of a it's not terribly important so we get to the cloud feedback and in many respects this may be where professor winds and I disagree most vehemently on the cloud feedback so let's talk about clouds and I'll give you a little primer about clouds okay so there's a little puffy trade cumulus maybe and clouds do two things to our climate the first thing clouds do is they reflect solar photons back to space so that orange beam is some sunlight comes in hits the cloud and goes back out and that effect tends to cool the climate so in that way clouds cool but on at the same time clouds absorb infrared radiation emitted by the surface upwelling that would escape to space and because clouds are colder remember Sigma T to the fourth clouds emit less radiation and so they also tend to warm and the net impact of clouds is the difference between these two counteracting effects now in today's atmosphere clouds tend to cool so clouds are cooling by about twenty watts per square meter so it's actually quite a big amount but don't get confused of the elementary grad students take of confusing the magnitude of a functionalist derivative just because cool now does not mean that that the derivative of the function is also cooling and in fact as the climate warms we really don't know what's going to happen do clouds cool more that would imply a negative feedback or do clouds cool less that would imply a positive feedback so as before let's go to the data let's see what the data tell us and this is some work I've recently done and this is so and this axis right here is how much energy clouds trap and this comes from measurements of an instrument called series which is flying and now on the NASA Terra satellite and I'll see you some reanalysis data and then this is global average surface temperature anomaly so these are anomalies deviations from average at the average all this data at the zero zero and what you end up seeing is first off there's no strong trend in this so you don't see clouds actually changing a whole lot as the climate warms yeah so the number doesn't actually seem to change but we can do better than that you can all you can look with your eye but people who do you know Chi by eye and science typically get where they deserve so let's do some statistics on this and we can put a best-fit line through this and you get you get a value of about 0.15 these are the two sigma uncertainties and you can do statistics you say there's an 80% chance that the slope through this is positive so this means is that it is borrowing the parlance of the IPCC these data suggested is likely that the cloud feedback is positive and again our best bet is 0.15 so if we go back to our equation we can we can plug 0.15 in but before we do that let some X interest of time I'm gonna skip ahead a little bit all right so we go here so so here's our climate sensitivity are here here's the value we just derived so you have these numbers up you get this and we'll plug this into our equation and what do we get for a doubling of carbon dioxide 2.7 degrees Celsius and if you had some uncertainty as I pointed out there's a lot of uncertainty in the cloud feedback I derived and if you put that on something you pretty much get the canonical IPCC range of the double carbon dioxide you get four point five degrees of warming now one point I want to make this was not derived from a model this was derived from data and I'll come back to that point repeatedly so get used to it but the other point I want to make is if this is all we had we wouldn't have great confidence against scientists look for Castilian so we want to look for all we want to look for lots of data that support what we think is happening so let's go to the ice ages ice age is another great example of climate change and so here's our favorite equation and we know a few things about the ice age first of all we know the ice ages are about five degrees colder maybe five to eight but five in the context of this calculation is conservative and we know how that we know how the ice ages were different there were big ice sheets and the ice sheets tended to reflect sunlight back to space if you averaged that over the globe the ice sheets reflected about three and a half watts per square meter we know there were less greenhouse gases in the atmosphere the last glacial maximum and those allowed about 2.6 watts per square meter of energy to be radiated in space we know the planet was dry or that minute was dustier and these aerosols also reflect sunlight back to space and so we know what we are what are called climate forcings and we know when the climate forcings work and so we can calculate what Ti is if there are no feedbacks we know the four things that are no feedbacks it's trivial to calculate what the temperature change would have been all you have to do is know the spectra of the atmosphere and we know that we know the spectra of the constituency atmosphere extremely well and so you have to out these two are known you can solve for F and you get four zero point five eight if you remember we got zero point five five the last one and and in climate change that's identical so the ice ages feature the same climate sensitivity as we derived from the Latin the last ten years of data and let's go further two points isn't enough we need lots of data to confirm this so let's go back let's look at the 420 million years now it is difficult but you can infer how carbon dioxide varied over the last half billion years similarly you can infer how temperature varied and if you do that you see temperature and co2 are generally correlated now there are obviously things other things going on continents are moving asteroids are hitting the planet volcanoes are going off so carbon dioxide not the only thing driving climate the carbon dioxide and climate are associated in times when climate carbon dioxide is very low you usually have ice when carbon dioxide is very high you usually don't have ice and so you can use these data and they inferred that climate sensitivity greater than 1.5 degrees C has probably been a robust feature of the Earth's climate system over the past 420 million years now I actually could go on believe it or not and show you more examples of data that show that climate sensitivity is you know in the canonical range of two to four degrees but but it was time I won't I won't continue to go on let's definitely go to another question which is how much warming are we going to experience because at some level no one really cares about the past you're interested in climate change for the future and so let's sort of go through a quick calculation that doesn't require a climate model so we have an estimate of what we think climate sensitivity is and again there's a mountain of data to support this given carbon dioxide reaching 500 to 900 parts per million in the century it's about 390 now so we know carbon dioxides you know approximately going to double may become close to tripling and also given that other greenhouse gases are also increasing we know methane methane sort of flat but other greenhouse gas is also increasing ozone is certainly increasing tropospheric ozone things like that we can therefore expect several degrees Celsius warming okay and again this is not a model calculation this is based on data and an estimate of how much carbon dioxide is going to go up now this happens to agree with models and this by the way is why I believe models not because I have some religious belief in models but because the models agree with the data I believe in data first models come second that the models look good if you compare the models to the data and all the things I've looked at I won't show nice lies but perhaps I will in my rebuttal the models look great models do quite a good job of simulating things now it's not to say you can't find some statistic where the models don't do well that's pretty easy so this is sort of interesting I did some googling on Professor linson before this and I found this sort of interesting thing to see what does what what does he said about warming I thought this kind of missions this is about betting on climate change and apparently professor Linden said at one point that he'd be willing to bet that it was cooling in 20 years and it turns out that when a paul i mean anybody would take that bet that's a I would bet anybody that's gonna be warmer in 20 years and it is now and so blog or contacted linson he would only take 50 to 1 odds that temperatures are going down so he obviously agrees temperatures are going up and that's consistent I should point out that's completely consistent with his view that carbon dioxide warms the planet so there's really no disagreement there between the two of us but all the sort of interesting was the magnitude so he professional Vincent offered a alternative net which was that if the warming of the next 20 years was less than 0.2 degrees he would win if the warming was greater than point 4 degrees he would lose and there'd be no payout for warming from zero point two to zero point four and he wanted two to one odds so this was twice as likely as that and I sort of started I saw that I start struck I sort of say what did the IPCC models show and that's basically what it is so apparently at least when that was written he was unwilling to put any money on the fact that the IPCC models were overestimating climate change and so and so perhaps there's less disagreement between the two of us on future warming maybe there's agreement lies elsewhere I'd be interested to see his talk okay now and ago I will say again two-to-one odds it seems he views warming up here to be twice as likely as warming down here all right so let me tell you bout why I'm concerned so I've sort of shown you data about the warming is no concern is fundamentally a moral judgment let me give you some idea of why I think we should be very concerned about warming of a few degrees and you're probably seeing there and say a few degrees who cares doesn't sound like a lot but this is a really interesting plot and these are model runs and sort of different colors show a range of model predictions you see the models pretty much agree with our back-of-the-envelope calculation I predicted a few degrees of warming and sure enough you see the models predict a few degrees of warming and this shows or the historical record I know there's a lot of debate this is going out I'm not having good luck today the equipment another you know there's debate down here about their births I know I'm just trying to get the laser pointer and I can see the laser pointer this is just not but the point the point I want to bring is this seems period right here this is a period called the Little Ice Age little ice age is about one degree cooler than it is now and I'll think about that for a moment one degree doesn't sound like a much not much but one degree cooling is enough to make the earth go into a region that people refer to as a little ice age your intuition about what's a big change which is based on local conditions one degree change here doesn't change much but in the global average one degree is a huge change if you cool the planet by one degree you enter a little ice age now another thing is this is about the amount of warming we've had since the last ice age about five or six degrees now think about how different the planet was during the last ice age and that was only five six seven degrees cooler than it is now so you have to look at temperature increases of a few degrees very seriously if we get if we have warming's of say three or four or five degrees it's going to be a different planet you know we're not gonna be living on the same planet and you might say you don't care about that well that's you know that's a moral value judgment I can't argue with that but I do care about that and that's why I'm concerned oh the other thing I'll just say very quickly it's kind of funny to see how people look at climate change before and after so this is a quote from Vladimir Putin Russia is a northern country if temperatures get warmer it's not that bad we could spend less on warm coats and you think about a global warming you know great it's like you think barbecues and go to the beach but in reality things aren't that bad this is after the heatwave they had this summer practically everything is burning the weather is anomalously hot what's happening with the planet's climate right now needs to be a wake-up call to all of us climate change is not all fun and games it's not short sleeves and barbecues it's drought it's forest fire I looked up the weather forecast for Moscow during this and the forecast was smoke I've never seen that let me think about that smoke that's what climate change is it's not it's not great things so um Susan how much time Jeff from okay good all right so I want to talk a little bit about skeptical science because you can't understand the debate unless you understand the context of this now this is a memo that was written by some cog at Brown & Williamson late 60s doubt is our product since it is the best way of competing with a body of fact that exists in the mind of the general public it is also the best way of establishing a controversy and you know you think about all the memos are written I'm quite certain the person that wrote this at the time didn't realize that there'd be books written on it merchants of doubt quite an excellent book doubt is their product and it's completely established through the release of tobacco documents they knew cigarettes were killing people they absolutely knew in fact they knew it before the Surgeon General had proven it and yet they they embarked on a policy of debating the science to produce doubt that was their strategy and so let me give you an example of what the tobacco strategy would look like so when it comes to tobacco the facts aren't all in science can't tell us how cigarettes cause cancer they can't give us the mechanism they can't tell you how many cigarettes you need to smoke before you get cancer they can't tell you why some lung some smokers get lung cancer and others don't and why some smut non-smokers get cancer think of all these things we don't know how can you possibly try to link cigarettes with health impacts and you can't tell me any of those things you know the mechanism you have nothing and the answer is that by focusing on things we don't know you obscure what we do know and even though these are all true I don't know how many cigarettes you have to smoke before you get cancer I don't know why some people don't get cancer and other people do but I do know that if you smoke cancer you increase your chance of gaining these diseases and so this doubt strategy is incredibly effective and I'll just this is funny so I'll go over it I saw the New York Times the tanning indoor tanning Association tried to adopt the doubt strategy tanning continence the New York Times tanning causes melanoma hype and they go on to say recent research the benefits of moderate exposure sunlight outweigh the hypothetical risks surprisingly there's no compelling scientific evidence that tanning causes melanoma and you know this is wrong but again they're trying to introduce reasonable doubt and and it's time to rethink sunbathing find out more at sunlight scam calm and a few months ago I was trying to update my slides I went to sunlight scam calm and it was gone and so I did some googling and every once in a while the universe meets out some well-deserved justice and this is one case indoor tanning Association settles FTC charges that it deceived consumers about skin cancer risk from tanning so doubt is their product and you see this in tobacco you see this in tobacco secondhand smoke you see this an ozone depletion you see this in acid rain I I'm the parent of two five-year-old so I'm very familiar with debates over vaccine if you listen to the debates about people who say you shouldn't get your kids vaccinated it's the doubt agenda tanning beds quite ridiculous and now climate change and so let's go through what I mean ok I'm on time let me go through what I mean when I talk about the uncertainty agenda or the doubt agenda when it's applied to climate change so I googled professor Johnston and I found this document he'd written global warming advocacy science a cross-examination and I just want to highlight a few points a what do we really know about global mean surface temperatures and can we really be so sure at all the purported warming trends and then you go to the next page see the existence of significant alternative explanations for 20th century warming so these arguing is that the climate is not warming and the warming is natural and this is what a lawyer does and a lawyer a defense lawyer does not look for coherence they don't want to look for an argument that completely makes sense instead they're trying to make lots of arguments because a defense lawyers product is reasonable doubt it's exactly the same strategy that tobacco companies use and that's essentially what's being involved here and I give professor Johnson credit he didn't try to hide this he you know he calls this a cross-examination you know I want a lawyer cross examines people he's not looking for both sides of story he wants the he wants the person to say what they want what the lawyer wants to hear and and so you know this is you know climate change skepticism as it's generally practiced is one of the defense attorney agenda one of doubt is their product and and so you know I don't know what fresher lenses going to say you know and his arguments tend to be better than most skeptics but you know during my rebuttal I'll try to bring up points that I think support this all right so let me just finally uh I'll sum up following elements that should provoke suspicion all right so you're gonna hear a lot we talked to skeptic you hear a lot about model bashing models don't do this models don't do that well let me show you I didn't talk about models in my talk and maybe I mentioned once or twice but it's data data is what carries a day and data is why scientists believe climate change is an issue alarmist elitists and Al Gore anybody who talks about alarmist elitist Rob gore is not interested in serious discussion you're essentially using rhetorical rhetorical tools and try to paint your opponent as biased err confused and you know that's not when I hear that I kind of turn off um conspiracies people that invoke conspiracy theories what that really means is nobody believes what they're saying and the conspiracy theory is there to explain why nobody agrees with them so if somebody walks into a room and says you know gravity doesn't work you know a bunch of physicists will laugh at them and so they have to generate a conspiracy theory about why they're being laughed at and so when people would vote conspiracy theories like scientists are just chasing grant money I mean there's no evidence for that I mean I'd like to see some evidence that that's actually the case and there isn't any evidence because it's a conspiracy so so you know a citing natural variability without a mechanism natural variability is not magic pixie dust there is a physical mechanism for every climate change and you have to determine what that is and so people that say natural variability but they don't cite a mechanism you should view them very suspiciously not cause for alarm this is not a scientific argument it's a value judgment and absolute uncertainty no error bars the IPCC is a very upfront about the uncertainty you can say they don't you don't agree with how they do it but for example the iconic statement that the warming is 90% we're 90% sure it's due to humans 90% in it I mean so we're Ted there's a 10% chance that maybe the warming's not due to humans and so you know you can argue that the least they do that skeptics rarely give you error bars they they believe what they say and so I'll be interested to hear you know in future in French lenses talk if he's willing to give some uncertainty you know how sure is either he's right and and you know if he's not if he's a hundred cent certainties right that's suspicious and so I'll sum up there know itself six you know nine minutes for my rebuttal thank you [Applause] [Applause] okay thank you pleasure being here I'm going to stay here so I can see at least what my slides say but I think I'll stick to the format of only casually responding to guilt by association and so on leave it to you to decide and I'll give my own view of how you approach science and this issue what I've come to realize is most people including policymakers don't actually know what the debate is about will will see a number of the points that end who referred to as he said there's no general disagreement on but it's equally true they are not germane for the concern that you have and that's I'll try and clarify that in this talk you know Andy sort of was on both sides of this but I think some of you may be surprised to hear that the debate is not about whether it is warming or not or even about whether man is contributing some portion of whatever is happening and here we agree the issue is how much and is it a matter or should it be another concern now unfortunately a lot of the confusion is not simply the lay public forum but it is the bulk of time who have made it sound as though the question is is it warming and so people without looking at the data or looking at the scale use that as a basis for their decision here are a couple of statements and again Andy has covered some of this ground a doubling of co2 by itself only gives limited warming all models project more warming because they require a positive feedback this is something and he went over that is required in order to be small warming now let me clarify something positive and negative feedback is not a statement of cooling or warming a positive feedback takes whatever change you're trying to impose on the system and amplifies a negative feedback resistance chain it happens to be the case that most well-designed systems including your body temperature of characterized by negative they maintain a certain stability the second thing is if one assumes all warming over the past century is viewed to greenhouse forces then the derived sensitivity to a doubling of co2 is less than indicated the way you make models consistent Concilium for whatever phrase and he wishes to use with the positive feedbacks is by introducing other negative forces like aerosol which are fundamentally unknown and the people who are the experts in aerosols warts rodent and so on recently written on this thing that allows for virtually any range of temperatures consistently given the above and here I will use the word alarming because one has to distinguish between small and large changes that you may be personal choices but that it's settled science should be offensive to any sentient individual and that despite the fact that this is not emphasized by the Intergovernmental Panel on Climate Change I agree with Andy on the notion that models are not our only tool even if it were true it depends on the models being objective and not arbitrarily adjusted they are however models are not our only fool one good thing that models do is show why they get the results they get so sometimes it's hard to beat through and the reasons involve physical processes that can be independently assessed by both observations and basic theory and here I would differ with India I think many of the results are suggesting that the MA so exaggerated warning trying to show some of these results even without the scientific breakdown there are reasons why and here it's interesting with come to rather different conclusions from and beyond this why you should be suspicious about the presentation of the law first of all the claim of incontrovertible 'ti is far more suspicious than the claimant out arguing from Authority is commonplace in this field and obviously you should look with the scientific great data and reasoning and even elementary logic more to the point this is something Andy does not start abusive the term global warming is generally done without either definitional quantification we'll come back to that and you touched on this but I think it pays to have a better idea of what's going on there is also something that Andy did in terms of consistency many of the phenomenon he referred to including ice glaciers and so on the Moscow fires are complex phenomena having many many causes to identify phenomena with multiple causes the global warming or even as proof of global mania that the of initio and certainly again something you've seen many times the conflation of the existence of climate change which after all is unquestionable always return without for agenda climate change is of course misleading there are some salient points by definition nothing in science is incontrovertible and especially in a primitive and complexity of life science climate incontrovertible 'ti longs to religion or it's referred to installment value of authority in a primitive Masuda sized field like climate is a dubious value said this already respect to the last item however the situation may not be as difficult as it sounds you do have a way as layman of checking science so for instance this letter appeared last spring in science and it was signed by 250 members of the National Academy most of the signers had no background in climate science there were the usual suspects while early which seems lighter George would weld on Kennedy shell in Cooper but a few were indeed active into difference to the signers now here are two of the assertions of course you can't read this letter here but let's focus on these assertions natural causes always play a role in changing Earth's climate but are now being overwhelmed by human increased changes and warming the planet will cause many other climatic patterns to change it speeds unprecedented modern times including increasing rates of sea-level rise and alterations in the hydrologic cycle now one of the signers was a colleague of mine Paul wood and here's what he said in a recent paper in general of climate and repeated just the week ago in the departmental lecture the syntax is of course convoluted as it usually it remains possible that the database is insufficient to compute mean sea level trends with the active sea necessary to discuss the impact of global warming as disappointing as this conclusion may be and so when you hear anyone speak about sea level rise accelerating doing anything else there's no basis for it in the current measurements they are sets which cannot be directly compared but all I'm saying to you is if you go to the scientific literature and look at it carefully you often see that the authoritative assertions are no more credible than the pathetic picture of the polar bear that accompanies the letter now global warming what is it what are we talking it actually refers to a fairly obscure statistical quantity globally average temperature anomaly well this is as you take a given station you have a time series the temperature you take let's say 1952 1918 front of that robbery look at the deviation of that average each year and just plot the deviations each station and an average deviation now it's a quantity that is hardly causing climate change so you have to be very careful when somebody says look this major I say to curtain there was only five degrees change in this quantity this puppy is a small residual it's not a force but when you come to look at it it depends on and so Pacific fatal oscillation it depends very much on the fact that the climate sense system is never an equilibrium the oceans are always carrying heat to and from the surface where it's below the surface it's not affecting the surface budget directly into the surfaces are equilibrium and so you do have insult you do have a ND statement to justified to cause for it is nonsense of course we know numerous causes and we speak about them in the normal phenomenology but it's the fact that it's small and the error bars are large that means the quantity can be readily abused now the last time somebody actually showed what was done around 1990s saw him stand watch lawrence livermore and what he showed here were the points that go into this quantity namely the temperature anomaly and individual stations it's the average of these as a function of time that is the graph of temperature and the show now what he is supposed to look at when you look at the graph well I suppose the first thing to look at another coordinate axis you know you don't do so the scale here is each unit is two degrees centered okay and what you're seeing is fundamentally on this scale there are roughly as many stations that have negative anomalies each year as positive event coverage of that and indeed when you average these it confirms that you get a little noisy line that is hoping around zero now how did that become the graph that I showed very easy unfortunately like garnish what's happened here to the graphics I'm afraid what was done I'll have to describe it by words is you change the intervals on this graph from two degrees the two tensors you stretch this graph out as a socket so that now looks and with its tense of the degree change instead of the normal variance about two degrees ah here it is if you look here and again I am wondering do I have anything doesn't show the oh yeah here use the pointer so here you have the usual picture but if you look this is minus point two and point two this is two and two okay so give you a sense of this this is something that appears in the Boston Globe every day what they show is the temperature I don't know okay you have the blue bars and they show for each day the high and low temperature of the day you then have the dark gray Center which is the average high and low for today then you have the light gray bars which are much bigger they go from the record high to the record low of the day and what you see is of course there's an increase in temperature after all you're going through winter summer it's April and if you look at the record highs they come from all over the past and the record lows as well in this case the record low is 1909 record high was 1974 but the day that they published this and then you have that red line in the middle just for perspective the thickness of the red line represents the range of global mean temperature anomaly that's in the perspective your experience the only reason I mentioned that is people readily say I agree the earth is warming and you may and you may have good reason for it but it can't be a personal experience because your personal experience is huge compared to the scale of the change okay so the claim that the earth has been warming and there is a greenhouse effect and that man's activities of contributors are in fact trivially true statement they are not argued they're basically and they also have nothing to do with the policy issue of whether we should be worried regardless I haven't feel that they are nonetheless as you know frequently trotted out as evidence and supportive of treating them as an alarming issue the issues that are essential and here one of them we agree on one has not been mentioned the magnitude of the warming you expect and the relationship of warming of any magnitude to various projected apostrophes that are presented now when you get to the catastrophic picture forest fire and so on you're guilty of what sometimes is referred to as the prosecutors fallacy what that confuses is the near certainty that if a shoots be there will be evidence of gunpowder on a stag with the assertion that if C has evidence of gunpowder in his hands and C shot clearly the second does not follow with global warming the line of argument with many of these events creating sea ice and so on is even sillier announced for something like this the Wall Street Journal article they kept up some dirt leaving an indent in the ground into which a Rockefeller and he tripped on this rock and bumped into C was carrying a carton of eggs he fell and broke then if some broken eggs were found it showed that they picked up some dirt which would be bad enough in terms of logic but these days we go even further and decide the best way to prevent broke broken egg system and dirty now there are some problems with the science and he keeps referring to data and this is a field where the data is really hard and I'll show you some examples where we can be absolutely confident the data is wrong data is not a gold standard in this field it's not like going to the National Bureau of Standards and ISPs it's now and looking at some precise measurement their measurements fairly slow you will not have been Climategate you know various biases feeling temperature anomalies I found this in some ways to be a complicated at the coalition because small temperature changes are not abnormal and the claimed changes are consistent with low climate sensitivity but the public has been misled to believe that whether it's warming or cooling is a matter of vital importance so tilting the record is not so much important to the science but to the public perception also there's a tendency in this field who hear the word validation a lot of data is being analyzed with the aim of supporting rather than testing martyrs and that certainly been my experience serving on the IPCC in the National Climate Assessment Program it's also evident in recent scandals concerning Himalayan glaciers area here's an example of where I know the data of something in the data is wrong and that's a little bit surprised but you know again it shows there are ways of doing that so for instance there is one thing that is well understood in ecology dominated by Convention and the temperature tends to have to be approximately following something poking moist doesn't have to be exactly but it's roughly in one consequence that is robust is all temperature changes have to be about two to three times larger at just point to this event you find the pointer again in what is called the upper troposphere than they are at the surface what these four pictures are are for climate models that in fact show this and this sense the models have to be bred they show different sensitivity but they all show this hot spot the hot spot is not a sign of greenhouse it is a property of basic physical property of the moist adiabat the trouble with it is that the observations here are missus trends as a function of altitude are shown by the solid wall and they don't show the surface warming much less than the upper troposphere the only thing one can say from this is basic physics that is widely accepted says that either this data must be wrong or this data must be wrong or both are wrong but we know something is wrong in this picture if it turns out this data the upper part is correct then it says that the surface trend this is basically since 1979 has to be reduced now you say can that happen there's ample reason to believe it has interesting because there are all sorts of Corrections of five all sorts of scandals all sorts of other things going on but the data itself is not something rock-solid as Andy and I agreed sensitivity is a crucial issue and as he said it refers to what you expect in equilibrium from the doubling of co2 it's terribly important to say in equilibrium because the more sensitive your climate is the longer it takes reach equilibrium by time you get to some of these really large outliers it takes centuries the problem with using paleo data is it assumes you know what Klaus the climate room and it is certainly not in the case of last glacial maximum a change in the global mean it is the Milankovitch orbital hypothesis it doesn't operate by changing the mean it operates by changing the insulation of high latitudes that summer with very little change then even you also can't test models by comparing models with models they're not facing business could skip this these are statements that the IPCC claims are authoritative they have been endorsed by National Academies and numerous professional societies but again you have to look at these endorsements here's a recent letter signed by the presidents of both the Royal Society and the National Academy of Science I think it tells you a lot about the current state of the science again you can look at it your leisure if you wanted but let's focus on a few sentences the first one is however as your editorial is responding to an editorial the financial crimes acknowledges neither recent controversies nor the recent cold weather negate the consensus among scientists something unprecedented is now happening the concentration of carbon dioxide in the atmosphere is rising and climate change is occurring both need to human actions note that this statement seems to go well beyond the IPCC statement they claim that only more than half the temperature change over the preceding 50 years but the attributed commands of with aerosols included in order to cancel much of the excess warming the models produced were over the assumptions underlying this claim namely that the models adequately dealt with natural internal variability have been shown to be false to say they acknowledge the phenomena and so fatal oscillation and the assumption that they had was crucial to their conclusion of course one could carefully parse the sentence from Greece and Cicero perhaps what they meant is there was increasing co2 you demand that there was warming due to this though it might only be a small part of the already small observed warming but this is what they meant then the statement is trivial and suggests no basis for a law however there is no doubt that this is not what they intended the reader to infer they then continued uncertainties in the future rate of this rise stemming largely from feedback effects on water vapor and clouds our topics of current research who would guess from this throwaway comment that feedbacks are a critical issue without strong causative defects there would be no pause for long and no need for action what recent cicerone are actually saying is that we don't know if there is a problem a third statement they made is our academies will provide the scientific backdrop of the political and business leaders who must create effective policies to steer the world for the low-carbon economy recent cicerone are saying that regardless of the evidence the answer is predetermined if governments want carbon control that is the answer the academies will provide now it argued that nothing to better epitomize the notion of science in the service of colleges something that unfortunately has characterized so-called climate science where do we go from here now I would suggest that since this has become a quasi-religious issue it's hard to tell my personal hope is that we'll return to normative science to try to understand how climate actually became certainly one step in this is our present approach of dealing with climate is completely specified by a single number globally average surface temperature anomaly that is forced by another single number atmospheric co2 levels for example but it could be see you know solar output as well clearly limits real understanding so does the replacement theory by model simulation and point of fact there has been progress along east and I would suggest none of it demonstrates a prominent role to co2 has been possible to account the disciple of ice ages simply with orbital variations it was were thought to be the case before global warming in tests of sensitivity independent of the assumption that warming is due to co2 which is a circular assumption show sensitivities lower than others show the resolution of the early faint son paradox which could not be resolved by greenhouse gases is readily resolved by thousands negative feedbacks and rendered impossible to solve if you have possibly lets you know we don't have time to go through this and it would be tough even for grad students but let's begin let's see what we mean by the feedbacks if you have a system that is unprepared then you have the balance between incoming solar radiation and outgoing thermal radiation if you then add greenhouse gases and look at it before it has time to be equilibrate what you will see is that the greenhouse gases limit the outgoing radiation because they admitted the colder temperatures and so in order to re-establish balance the climate system must warm if you have feedbacks then on top of this you will have additional feedback greenhouse absorption let's say water vapor or clouds and they interact with each other so you can't really look at them independently because water vapor feedback only works where you have clear skies then you get still less radiation so the idea is let's look at space and see for temperature perturbation how does the outgoing radiation respond if you find that you get more out while cooling their given temperature than zero now here and these showed something and this is this diagram I'll skip it you can compare this with observations but the crucial thing when Andy showed his radiation from Sirius and the trend analysis he did not look at lags and Wiens much of the outgoing radiation comes some things like volcanoes what I call non feedback cloud variations and so on so you have to emphasize the lags and separate when you do that there is an unambiguous negative feedback system shown by the red line when you look at the models of the same temperature they unambiguously produce positive feedbacks but the situation is a bit worse than that and you know you can see this here when you look at the data for the models the models have also to cloud variations that are not because you get values for the sensitivity that many cases don't look like what you get from running your models for long-term I addresses here the IPCC reports are sensitive to point three we get from the model twenty two point four the thing to remember is when you take the uncertainty in the radiation budget even in the models the range that you have at the 90% confidence levels range is all over the place this is not true for the observations for the observations the uncertainties leave even when you through the error bars the sensitivity tightly constrained the reason is this equation this equation is a fun equation you notice what happens when that people is one anyone tell me and anyone tell me what is the answer to this lunatic poster I am NOT asking you and I don't know about your head tell me no infinite infinite okay now that's the tricky part of this because it's saying when you have positive feedbacks and you're starting out as andy says you know around here you add a little bit and you're up here and a little bit more you're out of sight and so it's always extremely uncertain if you have negative feedbacks then you're in this part of the graph and it's tightly constrained in in other words it's the existence of positive feedbacks and models that leads to the uncertainty now recently there's been an observation and then data and data subject to all sorts of uncertainties but when one is talking about forcing of climate one is considering the flux of or radiative forcing now the thing about this flux is at the top of the ice where you can space the flux is the form of radiant visible but as you go down in the atmosphere biloba books remains reasonably constant that's what one means by non diversity what makes up the flux changes so at the surface the main component of the clothes is evaporation which is called the latent heat flux that is to say when you evaporate that is a change of state it involves energy now some scientists when sat all were looking at something that's commonly been reported that the models show much less change in precipitation when the temperature changes the nature things and precipitation and evaporation should be equal to the reasonably short constants so whence was actually thinking how to produce something more dramatic for climate wanted to say that maybe the model should be showing much bigger rainfall but he was ignoring the fact that this is a flux of here and in point of fact what Wentz was doing it was giving rough measurement of climate sensitivity sensitivity is a ratio of flux to temperature change let me do that more carefully let's call EC the change of evaporation with temperature and he uses units of percent change for degree now let's call CF the radiative forcing Q to a doubling of carbon dioxide that's three point six watts per meter squared let's call FL the heat flux associated with EC a percent change next point eight watts per meter square four percent change in evaporation as a result the climate sensitivity will be CF divided by F L so what whence it all found was it models evaporation changed between 1 and 3 percent or degree depending on the model for the observations the evaporation as confirmed by precipitation and they're independently studied from satellites gave you about five point seven percent change or degree if you calculate the sensitivity you get the model one and a half to four negative or observe you get point eight moreover you can consider if you read the subsidiary material that went supplied for his paper that point eight is almost certainly an overestimate of the sensitivity because as whence openly acknowledges when the observations differ too far from the models okay we can discuss some of the other points perhaps later I mean glaciers and sea level so on ocean are cases where you know for instance sea ice in the summer depends on winners much it more so than temperature one can go over all this collaborative evidence that and the invention and you'll see it quickly kind of falls away but we can leave that to Q&A I mentioned the early faint son I don't know if then did you know what his paradox is but just in case you're wondering about climate sensitivity the Sun is a star which brightens because a few billion years ago the solar output this on a certainly twenty percent less remember doubling co2 is a two percent change in the unit so here we have twenty most models would say the earth would be frozen solid infection ten times bigger and yet the geological evidence is the earth was not frozen and temperatures were not today's there have been 30 years of attempt resolve this paradox by asking for co2 methane or the gas is none of them what we recently showed is that but it's the right answer or not it's perfectly possible on any rate you now have some idea why I think there won't be much warming in the co2 and without significant warming it's impossible to fight how to pass the piece to such warmia I would even suggest that if you had significant warming it would still be extremely difficult connection I know some people will have class at 1 o'clock um and so if you do don't feel awkward about me easily and thanks a lot I turns out I've loved what I was doing debate in high school I was really good at flowcharting people's arguments I've apparently lost that my notes are a mess but obviously I can't respond to everything he said there are a lot of points we agree on and there are a few points we don't so I think I'll go just over a few points that I think maybe a different Turpin tation is in order first I just want to say one thing I was quite shocked when Professor Linton said that he didn't think data was the gold standard I mean if you say you don't believe models and you say you don't believe data what do you believe and and to some extent I think a nuanced version of what he said is correct you don't believe every data set because some data are wrong what you look for again is you look for lots of data sets that agree and if all the data shows the same thing you can be pretty sure that's right now if the data don't show the same thing then you've got a problem and then you have to decide which data set you believe it or not and hopefully I'll have time to get to that although I'm not sure I will the other thing I want to say I'm probably forgetting some detailed critiques is this question about no cause for alarm a fresher Lyndon repeatedly said that I think it's important to recognize that's a value judgment that's not a scientific judgment and you know before the lecture he was smoking and so you know that's a risk he's decided that that's a risk he's willing to take but not everybody would take that risk and so losing my voice when he says that there's no there's no cause for concern that's he's giving you his value judgment on that mm-hmm okay so I want to get to a few points and slides let's start off with no sorry about that it's a lot harder to prepare for rebuttal there's a prepare for your actual talk I just taught let's talk start off with the work he showed that the climate models were overestimating he actually didn't spend a lot of time talking about it but it's basically this paper and I know he's revised it I have not seen the revision so I've talked about this but this is a paper that he published in GRL about a year ago and was picked up he probably saw it on Fox News of The Wall Street Journal and and basically it's the argument that he gave very briefly that the climate sensitivity is very low and and there are a couple of problems with this this paper this work has been severely criticized in the peer-reviewed literature so the first thing is it only looked at the region from 20 North to 20 South and it turns out that clouds are important at all latitudes not just 20 or 20 South in fact you can't you cannot I would argue infer a climate sensitivity by looking at 20 North to 20 south so my analysis included all latitudes it was a global average I mean there may be a few degrees of the pole where the satellite doesn't go over but but not many I'll skip this plot alright and this has been very it has been criticized this is a paper that came out by Dan Murphy at the Irana me lab and he basically said the analysis of Lynch and Choi erroneously applies global concepts to a limited region I guarantee if I had published a paper and looked at 20 or 20 South he would be all over me about that you know that's irresponsible that's not science blah blah blah secondly if you look at the details it's actually a slide from the talk he gave not long ago he talked about lags he said I didn't take lags an account in the way the way professor Linden takes lags into account is it takes these changes and uses them in order to get around lags and what you notice if you blow this all right okay so so no no all right so this is a plot from his analysis and it shows that you use I mean I probably don't I probably I'm explaining it differently than he would explain it but this is what's in the paper and so it looks at these temperature increases and it looks at temperature decreases temporary increases are red and temperature decreases are blue and if you read the paper it says you know we take we want to look for places with temperatures increasing or decreasing by more than 0.2 degrees Kelvin and we're gonna look at it as a unit and that's in the paper I can I've got a PDF on my computer I'm sure he does now if you blow it up you see some really odd things in it you see what looked like some really arbitrary choices so for example he doesn't include that temperature increase yeah you talked about Lindsay and Choi he said as corrected by well I'm it's not published yet all right I'm gonna explain that why people don't believe this and this has published literature all right well I think it's important for people to see the criticisms it just because you've corrected them why did you publish this in the first place this is obviously wrong and people have to see why it's wrong look but I mean this is obvious look why did you pick they're warming to stop right there can you explain that well they picked a lot of places that you can't figure out why they picked the results they did so here why did they not extend that and I'll go over this quickly apparently professor Linden disagrees with me presenting this this is publishes his work he's done and this is why people don't believe his work you see that oh you see it where it goes over the top there now why would you do that you see here it doesn't quite go to the top and right and and so basically what they've done is imagine you have some data and you have a model that goes through the data and we but what you do is you go through and you pick the data you want and then you basically throw out all the other data and then you say well the models are wrong and I'm not the one and this is published I mean I could say well you're attacking him but this is actually in the peer-reviewed literature and let me quote what Kevin Trenberth wrote as shown here the approach taken by LC o.9 is flawed and as results are seriously an error their choice of dates is distorted the results and underscore the defective nature and their analysis and you know I apologize if I have this sounds harsh being a science is hard and you know people look at this and they say you know he's thrown out the data that doesn't agree with what he wants and I have another example of that actually so you say okay well that's one example but let's go on and talk about the hot spot stuff he showed I see the problem all right you that way yeah am i using up all my time probably all right so he talked about to say he's talked about the hot spot and what's important to recognize is that he there are actually several data sets there are several data sets that that you can use to determine the tropical upper troposphere and it is true the satellite and the balloon data show less warming in the upper troposphere than expected but regardless of what's warming the surface we agree that the upper atmosphere should warm faster should follow what we call a moist adiabat and if you're a grad student atmospheric sciences you will derive that but but he talked about basically I think he should one dataset which is a balloon data and the balloon data agree with satellite data but there's another data set where that people use wind data to infer the temperature and that's a straightforward analysis and that's this paper by Allen Sherwood and they showed that warming patterns are consistent with model predictions so so you have this thing we have three data sets you have the satellites and you have two different balloon radiosonde data sets and they don't give you the same answer now professor Winston didn't mention this data set but it's equally valid and and you know again if you're a defense attorney you don't show data which disagrees with your hypothesis and you know the key thing here is we don't really know what the trends in the upper troposphere are the satellite data are plagued with problems there's no question about that and you know future future science will will resort us all right I will end there [Applause] [Applause] you know you are finally reduced to a personal attack rather than work on the business there were numerous criticisms made of the paper by myself in Troy and we realized that many of them were correct and we spent a year correcting everything because we knew most of those changes as Trenberth had pointed out would not leave too terribly different answers and so virtually everything you said has been corrected and the answers that I presented here are specifically from the corrective work the use of tropics primarily is perfectly okay if you share the effect with others and there may be still other feedbacks but they establish a particular feedback with respect to the hotspot I I hope you understand something that Andy said because it's a very problematic issue in this field whenever you have a disagreement between model predictions and data you can be absolutely confident in this field that there will be somebody who will publish a paper saying we've changed the data and in this case you have what Andy calls a straightforward measurement of temperature I think a few people here might understand how it was done what Sherwood Nollan did was say there is a relationship between temperature gradients in the vertical or rather than the horizontal and wind shear changes in wind in the vertical so let us take balloon measurements of wind derive horizontal gradients of temperature and then use those to calculate temperature changes Christy has done this a number of other people have checked this the answers come out absurd but it gives you so much scope in its uncertainty remember uncertainty is something Andy throws at skeptics when you have this much uncertainty you can get any answer you want and so the answer was used to say the troposphere is actually changing much more than the direct measurements of temperature or radiance suggest who's using weak uncertainty to muddy the waters I know but I'm saying using wind to measure temperature I think Mike Garstang an old tropical meteorologist here smiling I mean this is an absurd way to do it we can get into that more in the question and answers portion of the debate now I have professor cannon it's impossible for me to move no no but I'm gonna put my thanks so this is an exciting day thank you all for coming and and thanks to two professor Winston and professor Destler for giving their informed cues and their passionate views I mean one thing I think this shows is that science is an intellectual endeavor but when you become committed to a point of view it becomes a passionate endeavor as well and the stakes are big here and I think there's no surprise that people feel passionately and think passionately on one side or the other I also would invite the law students to note the analogies that have been drawn by both our scientists to the legal process with the proponents of of anthropogenic climate change they need to do something about it cast as the prosecutors making prosecutorial errors and the and the defendants those that are skeptical of those claims being cast as defendants with a strong and capable representation by folks like my colleague Jason so what I'm going to do here is give outline a a policy approach assuming basically the science is understood by Professor Destler that is the question is what policy should we adopt in the face of potentially serious but uncertain adverse consequences from human induced climate change I'm gonna give an answer that's a conventional answer quite current in policy circles certainly not a consensus answer but it's one that should be familiar to most of you who who are familiar with these debates here the science doesn't drive the policy of course as both of our speakers have made clear but it certainly informs the policy and depending on which view the science that you accept you would be more or less concerned about future risks when we talk about a policy we talk about several components of policy I'll just roughly out long nose and get into the discussion we want first of all to set some sort of policy goal to orient our efforts we may set more specific objectives under that goal in the case of climate change those would be emission budgets or something of that kind to give us a concrete target to shoot at we'd want to select some instruments to use if we decided to reduce greenhouse gas emissions what instrument or instruments would be the best to do that and then we want some provision for monitoring and following the the the implementation of our of our policy to make sure that we were doing okay I think the right paradigm for making the initial decision that is what our policy goal should be is a risk management paradigm we could we try to do our best to assess the risks taking into account the uncertainties as we are able to understand them we make a judgement about what risks we are willing to accept and we work within that judgment to try to establish a policy that will limit risks to do that low information on costs and benefits is relevant and important to these judgments but I don't in the case of climate change they are determined to there should be determinative because there's such a huge range in estimates of both costs and benefits related to various climate options so we already know how to do risk management this is not a an arcane methodology we do it when we buy insurance we do it when we decide what the deductible and our insurance policy should be we do it when we decide to drive a car rather than walk and we do it when we decide how fast to drive the car particularly when we're going up twenty nine then we have to assess the risks that will be pulled over fine for driving too fast so this is not something that we're not used to doing the question here is whether the risks that are posed by continuing climate change under a business-as-usual scenario are acceptable to us or whether they are not and if they are not what should we do about it what changes should we make in the business-as-usual scenario which projects increasing greenhouse gas emissions over time what changes should we make to bring risks into the to a to a level where we would feel comfortable so accepting andy's view of the science i would characterize it generally as substantial risk that there are significant adverse consequences that will flow from continued warming and some risk of serious severe and irreversible consequences that may flow from continued warming i think that data that Andy and others are familiar wish shows that the likelihood of these impacts increases significantly when you move more than two or three degrees Celsius above pre-industrial levels the risks become more serious then that's about 3.6 to 4.5 point four degrees Fahrenheit that suggests the wisdom of limiting of of adopting a policy that would try to limit temperature increases increases in the earth's temperature to that two degrees three degrees Celsius rain right some people argue we should be even more aggressive and set a goal that limits warming to one degree Celsius I think we're right up on one degree Celsius already in terms of change that's already committed in the system and therefore I think that's not particularly feasible or useful as a goal and I don't advance that importantly there are risks on the other side there risks that we will spend a lot of money pursuing such a policy and that it will turn out as as professor Linden has said that that warming is small or even non-existent and that we will have spent money or nothing there is also a risk that by entering onto a program like this we will create severe dislocations to the economy that will cause way more harm than we could be expecting to reduce through reducing the risk of climate change that's just the wisdom of waiting at least until we know more at least until some of the uncertainties that are clear from the debate are resolved and we assume that they will be resolved over time because we trust science and the progress of science and in the meantime we also may develop technologies that we don't have are not currently available in order to allow us to do reductions more cheaply than we are able to do them now and therefore avoid some of the economic risks how do you resolve this it's a matter of judgment in my own sense I think there are likely fewer risks to overreacting to the threat of climate change than there are in under-reacting and we can frame our policy in order to minimize the risks of overreaction to further protect our ourselves first dealing with the risks of overreaction the risks of engaging and an overly what turns out to be down the road and overly aggressive climate change policy will likely be easier to undo than the opposing risks why because we will have made investments and non-fossil fuel technology we decide those turn out to be not necessary we can disinvest we can phase them out we can reinvest and what presumably remain the the cheaper or more efficient fossil fuel alternatives we can also avoid serious adverse consequences to the economy that we don't anticipate but that materialize over time we can avoid those by building into our policy checkpoints and safety valves so if the price of carbon for example goes much higher than we anticipated with significant threat to the economy we can drop that price down or move back in other ways to avoid those serious effects so what about the other side the risks of under reacting to climate change if it turns out that we do have serious and irreversible impacts from ongoing climate change those are by definition irreversible they can't be undone and they present at least some of them present very serious difficulties and expenses in adapting and avoiding those impacts if it becomes clear if we wait and it becomes clear that yes I have five minutes and becomes clear that we have to speed along here the the then then it becomes the issue is sort of how quickly can react because there's such tie longtime legs in the climate system if we've already put the greenhouse gases in the atmosphere that are going to cause that it's very difficult if not impossible to correct for the in response to that new knowledge and prevent the irreversible or serious impacts from occurring effectively we will have locked in long term impacts so my conclusion I'm sure Jason will have another view of how you balance out that and clearly there are other factors to take into account this is a rough sense of how I think this kind of judgment would be made and some of the factors that go into it so the conclusion my conclusion is we should act to reduce greenhouse gas emissions consistent with the long-term goals of limiting climate change or limiting warming to the two or three degrees Celsius that I've indicated and I think we should be getting soon I mean soon I mean within five years sooner than two or three decades down the road and why is that because in the absence of a limiting policy our emissions will continue to increase there will be the in the concentrations of greenhouse gases particularly co2 in the atmosphere will increase and that increases the risks of climate change down the road and if we begin now this is a recent another National Academy of Sciences isn't always accepted as the gold standard but a recent National Academy of Sciences study showed that limiting warming within this two to three degree target range is feasible if we do begin now may be feasible if we do begin now likely feasible if we begin now for the three degrees but if we wait either those goals becomes not feasible we can't expect to be able to make them on reasonable estimates of our technological capability and development so that that commits us again to to expose us again to to further risk of climate change if we don't start to do something now now by saying start now I'm not saying you know blow the guts out of the economy I'm saying set a price for carbon I think that's the appropriate instrument either through a cap-and-trade program or through a carbon tax or carbon emissions tags and begin to ramp up that price so the economy can begin to respond and you do it you do it in a measured way so that you don't so that you minimize the the dislocation caused by the economy but you get on the road and create the institutions that are gonna be there if over time it becomes clearer still that the risks are real and serious the institutions that you can use to further advance the policy I have only a brief time I'm just gonna mention let me mention a geoengineering is an option here I think it should be considered carefully there's some collateral risk and they need to be considered but I'm not committed to reducing greenhouse gas emissions as the only way of limiting or controlling climate change if other useful and safe alternatives the final thing is of course the International setting the global nature of this many people argue with force and they're right that this is a global issue and they had a policy by the United States that substantially reduce greenhouse gas emissions would not be sufficient to make a substantial change at all in the worldwide trajectory for greenhouse gas emissions is that a reason for the United States not acting that's a close question to me and I think in the lines of at least 98 senators at one point that was a real question but I would I mean my my view would be let's start let's make a commitment let's make a modest commitment that could be followed by an increasing commitment and at the same time less aggressively engaged the world community hoping that our commitment and be some catalyst for further developments in the international setting but I'm also realistic enough to know that that may not happen if it doesn't we ought to adjust as part of our adaptive management we ought to adjust accordingly am i with in time Thanks thank you [Applause] I'm just gonna straighten up here I've entitled these remarks provisional some provisional remarks are an uncertainty and climate change policy and I very much have my economist hat on today and thinking about this problem it's true as Andy said that I have I'm wrong why I don't know if it's long but I pay for kicking around in the internet entitled a cross-examination of global warming advocacy science that's a bit more of a legal hat but of course it's caught entitled a cross-examination and you're all happy is happy to go and find that you can find it right away and google it and get me some more downloads and but you know all I tried to do in that papers look through the first learn a little bit more about climate science and then see if I could ask some questions and see if there were maybe questions to be asked of the version of climate science presented by the IPCC and that's all that paper does it asks questions can't answer questions good heavens I'm not a climate scientist like best ants ask questions that are not crazy and that are actually reasonably plausible and I think I have there's a very well known climate scientist at Georgia Tech and professor curry is one of the leading people in the world studying the relationship between global warming and hurricanes and she is I know means skeptic if anything she would be one of the sort of establishment climate scientists and recently on her blog that she just started up she thinks it may be something like the kind of cross-examination approach might be a way of giving the IPCC restoring some of the credibility that the AI she has lost as a consequence of climate game so in any event on to today's to talk what uh what's the why do I call provisional well because the kind of uncertainty when economists think about uncertainty they're used to thinking of terms of standard risk analysis the way actuaries do it you know the probability distribution over potential realizations of harm PIH eyes and then you can figure out things like expected harm and figure out how much you should spend to avert a particular amount of expected harm economists have come to think that with climate change we can't really do that because we look to the science and it seems like what we've got is what in economic terms is known as nighty and uncertainty we don't know the probabilities that different things might happen and we really don't know the magnitudes there are ways that economists have tried to esta toot them an estimate the magnitude of harm in the event of especially in the event of what really big catastrophic ly large temperature increases I'll show you what economists have done you won't be very impressed and you'll be probably pretty shocked to see what the state of the art is the state of the art is very bad oh that's what makes this a great problem and interesting from my point of view we don't know how to do this there is no accepted economic framework for dealing with what we call nighty and uncertainty which is a situation where we don't know the probabilities of harm we don't know the magnitude of harm in the event of in particular certain catastrophic climate change outcomes a catastrophic means a certain thing and economic land beings extremely large losses that occur with a very low probability now there are some problems with traditional economic analysis when you try to figure out how much to spend to avert a potentially catastrophic loss if people have what economists think are reasonably looking preferences basically people's preferences are such that they wouldn't spend an infant amount today to avert some kind of harm tomorrow and that seems like reasonable preferences because if you spend an infinite amount today to avert harm tomorrow it means you'll like terminate the present generation to protect the future that just doesn't make sense inconsistent if people have these reasonable preferences which end up with and traditional now now analysis is to spend an infinite price to reduce a catastrophic attention catastrophic risk even as the probability goes to zero well that can't be right Marty Weitzman is an economist up at Harvard generated that result in a paper relying on some work done it by a truly brilliant economist today Michael Schwartz who's now at yahoo.com and in any event he found this result in me gave a name to it but everybody looks at this and says well this is Ron we've got big problems we can't apply standard economic analysis to this problem so what do we do well we've got to figure this out this is probably one of the most interesting important problems in economics if we think we can use tools of economic analysis to provide some policy guidance and you know we've got to try to figure out this problem what's the problem potentially catastrophic loss low probability of harm but we don't even know the probability of harm we can't even really attach numbers to the probability of harm so I'll try to suggest during the quick talk today I'll talk a little bit about what actually has happened and there seems to be some hope that we can get a handle on this problem that maybe come up with some concrete policy recommendations so where does the probability of catastrophic temperature increases come from there are several papers now I think there's five or six in the literature row and Baker got this ball rolling there climate scientists at the University of Washington and they showed in a very elegant way the kind of economists like that's neat neat solution you don't need a model or crank through like a computer for this you can just solve it that if you assume a predominance of positive feedbacks in these models you're always gonna get the possibility some positive probability of really monstrous temperature increases bigger than like five degrees centigrade five eight ten twelve degrees centigrade so that we couldn't even understand what the world would look like that Dickinson had a graph up which showed you graphically what happens when you have uncertainty over the feedbacks and how then that is going to generate because they and you might remember that curve that went up very steeply as you went over to the right-hand side as f approached one when you start to have uncertainty and F gets big it just blows up the potential temperature increases now do we know anything we assume that we just don't you know won't have that good information about the feedbacks here's the quote from a very recent paper that came out in the Proceedings of the Royal Society by I think a colleague of Dickson família T and a guy our person for Harvard mater is a global climate know that feedback effects are crucial they observe simulation outcomes that are skewed to high temperatures hence the aerosol effect that all the models assume that cancels those the existence of fat tail fat tails we've all heard about from what the financial crisis how could that have happened Gary Gordon who's an economist at Yale says I added there's no way that could have happened that all the mortgage-backed securities could have gone tanked at the same time well it happened okay even though you had no probability attached to it it happened so something must have been wrong well Gary's running around trying to explain how well he wasn't actually wrong and it did happen but he was right which is hard to explain because it happened but he said it could in any of it the point here is this is the fat tail fat tail means there's more probability in these potentially big temperature increases than you need to think if you just Ted say normals based on other things and the existence of a fat tail is not an artifact of computational general circulation model simulation that will disappear with repeated Monte Carlo trials Monte Carlo trials you just run the models with different parameters and see what happened but rather an inherent consequence of the presence of positive feedback it's a very recent paper as they say PDFs probability that probability density functions with fat tails present formidable problems for conventional expected value cost-benefit analysis because the relatively higher probability of high cost outcomes and here they're talking about row and whitesman simple consequences that damage functions that is we're trying to estimate the damage from global warming because the damage from global warming is the benefit of while spending money to do things today to reduce the probability of that damage from happening will have unbounded expected value at all times and any practical policy designed to reduce the likelihood or consequence of lost probability outcomes must address not only the shape but its evolution over time now this is an interesting question what do we know what are we gonna learn over time and hopefully we'll learn something about the likelihood of these really catastrophic outcomes now and I think the OPCON conclude with this I think the optimal policy I think these guys are right that the optimal policy has to take into account our learning over time about the probability of these catastrophic outcomes well what are economists been doing we don't really know the harm from any we don't have very much information about the expected social cost of any change in temperature let alone a catastrophic one of eight or nine ten degrees centigrade Nordhaus is pretty much the state of the art here he's been doing this since well so long before this book came out so since the mid 70s that's 35 years he's a careful economist he builds models that try to take into account how markets really will respond to different changes in the environment and the policies that people interact in economists though can't predict very well anything that's relevant to this problem that's the bedroom example you think one thing economists predict is how people change adapt to changing prices well back in 1979 Nordhaus did a book really state of the art in terms of energy economics and predicted changes he was trying to predict how the demand for energy would change to try to respond to price changes which is a pretty basic economic question well I've got up here on the screen what the efficient forecast the market forecasts those are two forecasts that Nordhaus generated one assuming the market was efficient one assuming the market just was as it was and then over on the right-hand column these are 1979 forecasts are the actual oil consumption so what did he forecast 1985 a hundred one point or quadrillion btus would be consumed that was the efficient forecast eighty six point six point is compared for both years 1985 and 1995 which were his projections the projected demand under both the efficient forecast scenario and the market forecast scenario with the actual consumption the actual consumption was much much lower than both why he tried to figure out and use actual demand and supply elasticity's in the relevant markets but what economists cannot predict even in the short to medium term is how people will adapt to changing to large price changes okay but the same reason economists cannot predict what how we would adapt to large changes in climate now this cuts both ways you could say well hey we could have a pretty high carbon tax and people might adapt to that in ways that minimize the cost total cost of actually reducing and decarbonizing the economy that's possible but a corollary consequence is he also can't predict very well how people would respond to a completely different climate a much warmer climate take it again Nordhaus Nord houses model it's called the dice model it's probably much pretty much the state of the art and trying to think about the economic consequences of global warming where do his numbers come from numbers for what numbers for the economic consequences of global warming what's it gonna cost and therefore what should we spend today to try to prevent it here's what he says necessary use subjective or judgmental probabilities and analyses of climate change that is not real frequentist probabilities because there aren't any forced historical observations or limited historical observations we can't estimate the economic impact of the three degree rise in global temperature from historical data because nothing resembling this kind of global change is occurring what have worked researchers rely on a variety of techniques including personal judgments betting markets and surveys of experts as recently as 1995 virtually all the economic numbers for the costs and benefits of climate change were based on surveys of economists so what do we get he went out and surveyed people and said what what's what do you think the probability is of a catastrophic change in temperature that would cause a 30% decline in global GDP forever that's a that's ramping us back a at least a better part of a century in terms of economic conditions that's what he did he did this survey people gave them their king about the likelihood of this and then what did he do well then he and his co-author to come up with the social cost of carbon assume that came up with an estimate for the global damages from this in their estimate of the global damages from a two point well now three point zero degrees centigrade warming the total damages they estimated were going to be one point five percent of GDP continued forever but one point oh two percent of that GDP loss or sixty eight percent of the total that they published in the book which is the gold standard for coming up with these numbers is due to survey based catastrophic impact scenarios it's based basically on nothing nobody has any experience with this and if you survey a bunch of economists and ask them what's gonna happen based on stuff they do know about there's enough problems with that let's ask a bunch of economists what's gonna happen when the climate changes by three degrees centigrade which is something they have no knowledge of I don't how what are they gonna do they're gonna heard they're gonna try to guess what other people are gonna say and then you try to say what other people are gonna say so you don't look like what look like you're an outlier and a crazy person or an idiot so that's actually there's a big literature on that so and by the way we all have to remember when the Civil War started and Sherman was asked how long it was gonna last he said this is gonna be a long and bloody war that's felt last four years at the time when everybody in the North said this is gonna be short but over in months they thought Sherman was crazy I guess he wasn't so anyway how can we think about policy with this kind of fundamental uncertainty here's one interesting idea set out by this in this recent paper by of a hot oven and Deutsch it's possible to determine this is mathematically all the combinations of f1 flocks and positive feedback to give certain probabilities of a temperature increase below a set amount so in other words if you threatened if you set a threshold for the temperature increase then you could basically figure out all the different parameter values of Lycia stuff for flocks and feedback to get you a probability that are consistent that give you a probability below that then if you know the cost of the policy options that are available to lower either the emission rate or reduced the feedback parameter I think this is an interesting issue because it goes to land-use patterns it goes to a lot of things that we have control over change the feedback parameter then you could design an optimal economic policy do I know if this is true or not I don't know if this is true these are two climate scientists who came up with an interesting policy recommendation here's what I'd be more concrete about and finish with what do we know we know that all population projections of global population generated by United Nations and tourist groups over the last thirty years have been wrong they have vastly overestimated population increases in population growth why have they been wrong they have failed until now recently to understand the enormous Lea powerful relationship between education levels especially educational levels of women and ovulation growth rates as operates the fertility rate in other words if you want to do what if you want to if you really care about future generations if you want people to be wealthier and healthier and you want to see a decrease in global population by the end by 2100 which is now seriously talked about by demographers what do you do you spend your money today to educate women in developing countries it's not real complicated you generally increase education levels but it also is consistent with governance structures that treat women and men equally and of course in the world today that is certainly not true that every governance structure representative system that we have in existence today would even come close to agreeing with that goal so what do you do you spend money today to maximize I think economic growth to specially increase developing countries by increasing education levels and you try to minimize vulnerability to climate change no matter what the cause is climate change anthropogenic or non anthropogenic and there's things we can do that really would have concrete concrete impact and minimizing vulnerability and climate change especially in developing countries but also in the United States and other developed so that's it

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