my name is dan said so and where i'm a professor of atmospheric chemistry at mit and we're here today talking about climate change and geo engineering climate changes is now rather settled science in the sense that we've known about the addition of carbon dioxide and other greenhouse gases to the earth's atmosphere for a number of years it's actually been known for over one hundred years some of the first work on greenhouse gas warming dates back to the eighteenth fifty's when a pair of scientists did the sort of seminal work the first work on understanding how things like c o two in our atmosphere could warm the climate sunlight as it comes into the planet can be can make it to the surface of the earth warm the earth up and then as a result the planet gives off some heat so that heat is then absorbed by these greenhouse gases in the in the earth's atmosphere and some of that heat is then transferred back to the surface of the planet you can sort of think about it like a  blanket on top of the planet so that some of the heat that it's giving off that would otherwise make it to space makes it instead it is transferred back to the planet and warms the planet and so this is actually a good thing if we didn't have greenhouse gases in our atmosphere the planet would be below zero degrees c blue thirty two degrees fahrenheit and it would be frozen it would be a big snowball and so we should be thankful that there are some greenhouse gases there thanks to tyndall and rainiest we understand this concept and we have for some time now the problem is that over the last few hundred years really since the industrial revolution we've been burning fossil fuels we've been burning trees we've been burning all kinds of different materials and we've been putting c o two into the atmosphere we've also been emitting other greenhouse gases things like methane and nitrous oxide which act in very much the same way and so as these rise in our atmosphere we see a corresponding rise in temperature of the planet and this is been called everything from climate change to global warming but the end salt is the same which is the planet is warmer now than it has been in many thousands of years and we have much more of these greenhouse gases so current estimates are that there's something more than forty percent more c o two in the atmosphere than before the industrial revolution started and so that's not the whole story of climate change there's other things that we as humans are doing to the atmosphere that are changing it one of the most important is something that we study in my  group which is the human addition of particles to the atmosphere and so this is pretty easy to imagine if we were any of us is commuting to work today there was probably a big truck that went by and it was spewing some smoke out and so it's easy to understand that we as humans are effect we're putting particles into the atmosphere and so those particles act in a very different way with respect to the solar energy that's coming into the planet most of the particles that we as humans are putting into the atmosphere reflect  sunlight back into space you can think of them acting sort of like a sun shade or an umbrella you know if you're out sitting at the at the beach during the summertime and you're getting a little too hot you might put that umbrella out and it would reflect some sunlight back away from you and you wouldn't warm up as a result and so the particles that we're putting into the atmosphere do that they also have a secondary effect and that's that they act as the seeds on which clouds form so if you go out today in you look at a cloud you're seeing droplets or ice crystals in the atmosphere and at the heart of each one of those droplets rays crystals is an aerosol particle one of these small particles and some of those droplets and ice crystals are there because they're forming on particles that we as humans put into the atmosphere and so those clouds as anybody that's gone out on a cloudy day understands are going to reflect sunlight back into space before it strikes the planet and so the planet as a result is not going to be as warm it's not going to capture as much energy as a result and so we have these two sort of heating factors we have greenhouse gases that are warming and we have clouds and particles that are cooling and the reason that we talk about global warming is because the greenhouse gases are winning out we've put some particles into the atmosphere and created some clouds as a result but they're not offsetting all of the global warming that's going on because of the greenhouse gases and so we still have this imbalance this warming and we've actually been doing a reasonably good job of cleaning up particles due to human emissions we don't nearly cause as much pollution now from particles as we used to and we have not been doing the same thing with c o two so c o two sort of rising particles are holding steady or even going down and so we're seeing more and more and more warming is as a result and so this is the world that we live in we're already some thing like a degree warmer than we were before the industrial revolution and we're probably locked into more than that already  due to the c o two that we're going to continue to emit into the atmosphere due to fossil fuel burning there's no prospect of really sort of turning off fossil fuel power plants or or turning in all of our gasoline powered cars airplanes or shipping in the next few years so you can imagine that we're already locked into more warming than we've talked about already this this one degree and so when it comes to policy a lot of experts are talking about you not wanting to go over two degrees warming and when i say two degrees i'm talking about degrees celsius so degrees fahrenheit as we use in the united states are something more than that and so you know policy experts want to sort of lock into to two degrees centigrade of warming we're probably already past that we're probably already locked in the emitting more c o two than is going to be sustainable it at a two degree level of warming and so as a result people have started talking about some of the options that we might have for  drawing down that c o two or for somehow altering masking the temperature rise of the planet and so the term that has been used quite often is geo engineering in some circles it's not a very popular term and i would agree with this because engineering has a certain amount of certainty to it and what i mean by that is that i think when when we think about engineering we think about solving a problem or or or making something where there's a high degree radiation or changing and these are probably not as as catchy a phrase but but they're more correct they're more correct for what we're trying to do and so geo engineering right now sort of falls into three broad categories the first one is a rather sound scientific idea which is to find some way to capture the c o two that we've already put into the atmosphere to draw that amount of greenhouse gas down to a level that would have corresponded to something that we would have seen in pre industrial times go back to a climate that we've been in before and so that's one that's one idea the other two ideas play off of this idea that we get this negative climate effect from particulate matter in the atmosphere and the clouds that they form and so the other two ideas revolve around putting more particles intentionally putting more particles into the atmosphere and trying to use them to reflect more solar radiation back into space thereby masking this this temperature effect and the other idea is to put particles into the atmosphere and try to make them form clouds so that we get more of these bright white clouds that reflect radiation back into space and so in general those are sort of the three major ideas that are out there for geo engineering at this time and this has become rather mainstream i think that you know in the last few years  really be become convinced in the united states that climate change is happening that it is a problem and it's something that we have to solve and so we've started to think about what these possible solutions could be and so about a year ago the national academy of science and so this is a this is a nonpolitical body in washington d c it was actually first formed under the lincoln administration to tackle some of the big challenges that we have as a nation and bring together groups of experts to understand them and to make recommendations so a couple of years ago they convened a group a committee to look at geo engineering and they came up with two reports not just one which is kind of odd you normally think of writing reports and you know if somebody asks you for one you don't give them two for my students who would be like me asking for one term paper and i'm turning into but they had a very good reason for wanting to do this  and the reason is that they felt that carbon sequestration trying to remove carbon from the atmosphere was very very different than trying to put something in to the atmosphere to mask a temperature effect either particles or clouds and so they said we're not going to give you one report we're going to split it into two and we're going to address sort of sequenced ration ideas on one hand and we're going to address this idea of trying to change the reflectivity of the planet in the second report and i summary the they were very much more positive about the science of the c o two sequenced ration the reason for that is that it represents something that we know has happened in the planet's history we have been able to measure the rise in c o two in our atmosphere and we've been able to see what the climate state is as the c o two goes up in the atmosphere and so as a result they said that this is more of a sure thing that if we start to find a way to draw down that c o two  we can think of ourselves as running down that c o two ramp and running down that climate ramp back to where we were before and so the ideas for how to sequester that carbon are are varied and some of them are actually already in place right now  so they span from land management changes for example you could imagine growing more trees where there aren't trees and those trees are largely made out of carbon and they would be pulling carbon dioxide out of the atmosphere and turning it into a sequestered form in the in the form of those trees other ideas include trying to get more organic matter into soils modern farming practices tend to takes carbon out of soils which is then released into the atmosphere so ideas include trying to put that  material back into soil sequestering it that way probably the one that most people think about is sequenced ration of carbon by pulling c o two out whether it be at a power plant or just directly out of the atmosphere and forcing it back down into the ear so we remove natural gas from the earth all the time we pull out and so the idea would be if we burn that and we turn it into carbon dioxide maybe at the power plant we can just pull that out of the stack and will force it back down  into the ocean into one of these gas reservoirs or will force it back down into an oil well or something of that sort and so this is actually already in place there's places where natural gas is being removed and  used but it comes along with a lot of carbon dioxide that it's trapped with that carbon dioxide is even now as we speak being pulled out and put back into the wells and so this is a technology that really in place and something that we can sort of build on right now so this was the first national academy report and again just to reiterate they were very positive about this and the ideas that were there between land management changes and  things like pulling c o two out and putting it back down and trying to go back to an earlier state of our atmosphere something that that we know about the second report was much much more speculative and so this addressed this idea of  engineering something that's been more commonly or more more currently being called solar radiation management so the implication here is that we somehow manage the amount of sunlight coming into our planet the report actually didn't like any of these terms they didn't like the certainty of engineering and they didn't like the certainty that was associated with management and so they they termed this report modification as a term that we use for the brightness of our planet overall and so the report just said that we're going to try to modify it but tried to stay away from any certainty of what was going to happen and so broadly speaking that report falls into the two categories of things that have been proposed the first one which is to put particula matter into the atmosphere the second one which is to try to make artificial clouds so both of them draw from lessons that we've learned in our planet and as i mentioned as an atmospher chemist we do a lot of research in this area one of the reasons that we do a lot of research in this area is that it is so uncertain right now we don't know very well what we as humans have done to our atmosphere in terms of adding particulate matter and the effect that it's had on the radiative balance the temperature of our planet we know even less about how those particles are forming clouds we're still in the infancy of understanding which particles are the best at forming different types of clouds how they might change things like precipitation around the planet and how those might then affect the radio to balance the temperature of the planet as a result and so these these ideas of changing these things have tried to draw natural examples from our past and one idea that has come about is to try to simulate volcanic eruptions and so for those of us old enough to remember  surface of the planet the next layer up is the stratosphere and so this material was lofted so high into the atmosphere it made it into the stratosphere and particles that make it into stratosphere can stay there for a very long period of time like a year and so  when those particles from mt pinatubo made it into the stratosphere the temperature of the planet dropped as a result by something like a degree and the reason was that those particles were were reflecting sunlight back into space and there's very famous incidence of this in human history in the eighteen hundreds cracker went off and we saw an even larger drop in the temperature of the planet and so we've seen these through recorded and even before recorded history where we can see the temperature of the planet dropping as a result of these particulate so the report acknowledged that you know this was the sort of you know scientific basis for this idea of geo engineering but the report and i am rather skeptical of this because volcanic eruptions are very different than what's being talked about so what we're talking about now is somehow trying to put material into our stratosphere and then keep that material there not for a year like a volcano might do but for decades or perhaps centuries and so this is very different than a volcano having a sustained amount of material and stratospheres is very different than the perturbations we've seen and so  the report is is skeptical in the sense that it's it hasn't really been proven what effect this would have on the planet moreover there are problems that are associated with volcanic eruptions that we have even been able to to measure since mt pinatubo one is that there was a huge destruction of ozone as a result of mt pinatubo so as soon as you put this material into the stratosphere ozone which we rely on to block highly energetic  rays from the sun of from coming in and causing things like like cancers was chewed up as a result of these particular being there the chemistry that was going on and so if we do this in in the stratosphere that is certainly going to be a result  there's other problems and one of them is that this simply would mask the temperature of the planet by reflecting sunlight going back into space but it wouldn't address the other aspects of adding greenhouse gases such as c o two to the atmosphere sosia to acts like an acid in the ocean and so there's been a lot of studies on the increased acidification of the ocean because of this increase in c o two the effect that it has a marine organisms things like corals and so if you're just simply masking temperature you're ignoring these other effects of greenhouse gases in the atmosphere it's a bit like breaking your arm and taking an aspirin the aspirin might make you feel better and in the short term but it certainly doesn't do anything about the other aspects of your broken arm and so the report notes this and this is certainly going to be a big concern another thing that that's a problem is that there's this implication that we have to get on to renewable energies things like solar cells and so if we start putting this material into the stratosphere we start diffusing radiation and what i mean by that is that the sunlight that's coming in is going to strike these little particles and be reflected off in all kinds of directions we're we're hoping that some of it goes into space so that it drops the temperature of the planet but it means that sunlight doesn't come down to the surface directly and that type of direct energy is what solar cells need to generate power so this diffuse radiation that's going everywhere means that our ability to generate power through solar cells drop so so you're almost cutting off an alternative technology that you need to get away from fossil fuels with this this effect of masking the temperature effect of the planet so there's these reasons and there's many many more as to why you would be very very careful about trying to do this and as a result the report is notably skeptical about it the other idea in this area is is to not necessarily just put these particles in to the earth stratosphere but instead put particles into the troposphere the part of the sphere that we live in and try to generate more clouds and again just to say this again anybody that's been out on a cloudy day knows that it's not going to be quite as hot you don't get the sunburn that you do on a sunny day you certainly don't see the bright sun coming in and you notice that some of the sun's energy is being reflected back into space and so the quote unquote  natural lesson that we've we've learned this from something called ship tracks and ship tracks are this idea that ships go across the ocean and they put particles out of their smokestack and you can see from satellites that sometimes as they go across there's these clouds that are being formed by those particles being put into the atmosphere and so the idea here is that we could try to do something like make artificial clouds as a result of putting particulate matter into the atmosphere and perhaps we tried to do this in ocean areas away from from people so that we wouldn't see this effect and so these types of ideas have been bandied about and one of the things that the report is very skeptical about and i am too i should take credit for my own skepticism is that when you change clouds you are going to change the precipitation of the planet and so for me personally this is a nonstarter so again you're simply trying to mask temperature you're not can do anything about greenhouse gases or ocean acidification but now you're also talking about changing the precipitation that we see on the planet and so what i mean by this is that if you start making clouds in regions that there weren't they're going to change clouds and particles downstream and so you could do things like create droughts in places that there weren't droughts before and some of the modeling studies that have looked at this suggest that you might create droughts in places like the amazon which is one of the places where we helped pull a lot of the c o two out of the atmosphere naturally into the amazon rain forest and create a lot of oxygen and so that type of thing could go on you could also create trench and floods in places that wouldn't normally get that much perceptive taishan and so by sort of playing with this thermostat you're having a lot of other undesired effects and so i often think of some of the invasive species that we've used in our environment where we think that we know what we're doing but we have these unintended consequences a result and so my parents have had retired and they've moved away from the cold northern climate and they're in north carolina now and one of the lessons that was learned in the american southeast was with the kudzu vine and so this was something that we thought of in the eighteen hundreds and into the one thousand nine hundred as being this wonderful thing that animals like cattle would eat and it would protect the ground in avoid soil erosion and what's actually happened is that unintended it's grown completely out of control and it's caused much much more damage in terms of having to remove it than it ever did in terms of protecting soil or or feeding cattle and so this idea that we had back in the eighteen hundreds in early one thousand eight hundred about the effect that would it would have was certainly true it was one aspect of it but we didn't consider all of these other things and when it comes to these ideas of changing solar radiation around the planet i think that's the lesson that we really have to learn right now which is that we think we understand one aspect of how we might change the thermostat of of the planet with some future research it remains even that aspect of it remains highly uncertain at this point in time but we think we understand one aspect of it but we also are already have this idea that there's many many other aspects that that is going to propagate into that it's going to have other things that it's going to change the ozone level of the planet the precipitation of the planet where this particulate matter is going to go if it's going to create pollution or health effects in some other location we also know that it's not going to address other aspects of climate change such as the increase in c o of the ocean and so as a result at this time this is simply not something that we really should be exploring for me personally and i think for a lot of scientists today there are several nonstarters here you can think of it is the side effects being much much worse than the cure that we're proposing at this time and so while the reports and i myself are rather positive when it comes to carbon trying to draw carbon out and go back to an earlier climate state things like changing the particulate matter in the atmosphere changing the clouds in the atmosphere are simply knobs that we should not be trying to mess with this point in time  we just simply don't know enough about not only the effect of doing that but but the side effects of doing that which could be catastrophic and so for those reasons this this committee at the national academy separated this into two reports they recommended quite a bit think that you know we have some strategies to draw down c o two and try to tackle this problem moving forward but at the same time we should learn lessons from our own past i mention this idea of invasive species or or thinking that we are going to get one effect in getting something completely different which could have been more harmful than what we were trying to do at the beginning we need to keep that in mind and in this case especially when there's so many red flags so many warning signs so many things that this doesn't address that we should be very very methane is the second most important greenhouse gas in the atmosphere it is also the second greenhouse gas that we as humans or are augmenting or increasing in the atmosphere the ideas behind carbon ration are mainly aimed at c o two and not at methane the good news about methane is that it has a shorter atmospheric lifetime than does c o two so say that we put a lot of methane into the atmosphere right now it's a very potent greenhouse gas it's the second most important right now and we're going to see a temperature rise as a result the quote unquote good news about that is that it's removed rather rapidly so to undergo a number of chemical reactions and that methane will go away in the course of some years about ten years is what's commonly thought right now c o two on the other hand is much much more of a problem c o two has a much much longer atmospheric lifetime anywhere from hundreds to thousands of years for the effects of c o two once it's a minute to go away and so in the long run in the hundreds of years time frame which is the one that we're really concerned about you know in terms of melting ice caps and sea level rise and so on c o two is the bigger player that's the one that we really at this point in time have to be worried about and so carbon dioxide used to be about two hundred eighty parts per million of the atmosphere so two hundred eighty c o two molecules per million molecules and right now we've passed four hundred and so we've gone from this to a number to this four hundred number and so one of the aspects of climate change the degree or more of temperature rise that we've already seen is because we went from two eighty to four hundred and so we're already locked into more than that and the reason is that we don't have a switch that it's going to turn off coal fired power plants tomorrow we're not going to stop driving gasoline powered cars or flying airplanes tomorrow and so at least in the near term before we completely go to renewable sources of energy we're going to be emitting more c o two so we may go to four fifty or five hundred or six hundred parts per million and so that's going to lock us into a temperature rise of two or three or four degrees there's some uncertainty in all of these numbers and this is what we as atmospheric scientists are working on right now but the problem is there that you have a lot more c o two at some point in the very near future double what we started with in pre industrial times and that c o two is going to be in the atmosphere for hundreds or thousands of years and so to avoid again things like sea level rise or polar caps melting we need to find some way to draw down that c o two to whatever level we as a civilization decide is acceptable we may decide that we want to go back to two hundred eighty parts per million and we want to climb it like it was in the year seven hundred fifty before the industrial revolution we might decide that we're ok with where it is in two thousand and sixteen at four hundred parts per million and we're ok with the temperature that we've already got we may be comfortable with a little bit more maybe we can go to four fifty that's for us as a civilization to decide but nonetheless at some point in time we're going to exceed that number and we're almost certainly going to do it in the next few years whatever that that degree of warming is that that we're ok with as a society and then we're going to have to start thinking about how we're going to pull that extra c o two out of the atmosphere and where we're going to put it and that's the reason that we need to consider sequel st