clouds are absolutely critical to the earth's climate system along with the particles that form those clouds and the reason is that we actually understand the greenhouse gases rather well so for over one hundred years now we've known the radiative effect of say adding carbon dioxide to the atmosphere so carbon dioxide acts as a blanket and it traps some of the outgoing heat that's that's trying to get away from the earth's surface and we're actually very happy there's carbon dioxide in the atmosphere because otherwise the atmosphere the planet would be too cold and life wouldn't exist but the problem is that we're adding c o two to the atmosphere and thereby warming up the planet beyond where we've sort of evolved to be at the temperature that we're sort of used to not only us but the other life forms on earth so we know that we're adding carbon dioxide of the atmosphere we know that this is having a warming effect and this was all worked out all of the radiative transfer was worked out over one hundred years ago and most people understand that this is sort of a well understood part of the earth system and most people understand that adding c o two has has effect that that we call global warming what a lot of folks don't know about is the role of particles in the role of clouds so human activities at the same time as putting out c o two are also putting particles into the earth's system and you know these can be the particles that you see spewing out of a smokestack or coming out of the you know dirty truck in front of you as you're commuting to work and it turns out that those particles for the most part are scattering sunlight back into space before it makes it to the ground and you can most easily think about this is being in a city on a smog day or a hazy day and you get this very diffuse light it's looking at the sun it's like looking through frosted glass in a bathroom and you can tell that not all of that sunlight is making it to you and so what this is doing is sending some of that sunlight back into space that would have otherwise made it to the surface to warm the surface another thing that we explore in the lab is that these particles act as the seeds that cloud droplets and cloud ice crystals form on and what it means is that as we as humans put more and more particles into the earth system we're changing the properties of the clouds in the earth's environment we're making more clouds we're putting them in different places different altitudes and different location because of the particles that we're putting in and if you've ever been out on a sunny day versus a day that has clouds you know that the cloud is going to intercept some of that sunlight coming in it's going to scatter it back into space clouds or in general sort of or a white high i'll be to always say effect and so they're going to send that sunlight back into space and allow it to the surface of the planet so what does this mean for the climate system it means that we're doing two things we're doing the well known thing of increasing temperature by putting carbon dioxide greenhouse gases into the earth's system warming the planet up but then at the same time we're taking some of the sunlight out of the system because these particles we're putting in are sending solar rays back into space and the clouds that they're forming are also sending solar rays back where does it end up well it ends up that the greenhouse gases are winning the effect from the greenhouse gases is larger than the effect from the particles and from the clouds by several times and so we have a warming effect but we're not realizing all of the potential warming we could have because the particles in the clouds are keeping that down it's minimizing the  effect what's even more important for us to scientists is that we've known about the carbon dioxide the greenhouse gas effect for a long amount of time we've worked out all of the physics involved in that we understand the emissions of this material to the atmosphere really well we haven't had as much time understanding the cloud and aerosol system so they're much much more uncertain so for example there's this intergovernmental panel on climate change report that every four five years assesses the state of the earth's climate and how humans are impacting it and one of the things that they've noted is that although the earth's on cloud effects are smaller than the greenhouse gas affects there about four times as uncertain so what this means is when we add up all of the human effects on the earth system our certainty of that is really set by a lack of understanding of the aerosol and cloud effects until we understand ourselves and clouds we're not going to figure out the climate system on its own particles themselves are are rather complex in the earth system because they're better very heterogeneous it's a term that we use to say that they're not the same depending on where you are in time and in space and in altitude they change on a daily basis depending on what's being produced you can think about this in the case for wildfire producing a smoke cloud you know one day the fire hasn't started so there's none of these particles a few days later the fires in full swing and you're getting a ton of particles and then maybe the fire's been put out and you've got the smoldering going on with a little bit of particles being produced and that's just one simple example but if you think of the earth's atmosphere as a whole particles are very heterogeneous they may appear in one location the wind may blow them out of the way they may be produced at one point in time and not another point in time even more complicated is that different particles have different effects on the earth system we've talked about clouds a little bit they may be very good at forming clouds or they may have no effect on cloud formation and so that's one effect they can have the other is that they have certain properties in terms of interacting with solar radiation and what i mean by this is that you can think of particles like sulfate particles that might come out of a smokestack organic particles that might come out of a forest setting and those tend to be very good at scattering solar radiation they're very good at offsetting this climate effect by sending solar rays back to space there are other types of particles things that we call black carbon sometimes that are called soot and this is the material that would come out of that dirty truck that's in front of you as you're commuting to work and  the name implies they're very dark they're very absorbing they actually trap that solar energy they're very good at intercepting it and holding it in the earth's system so they're actually a warming agent there like a greenhouse gas it turns out that there's a lot more of these sulfate in organic particles that are scattering radiation back into space than there are so particles that are absorbing it so aerosols are a net cooling effect but there are certain particles that act as warming agents and working out that exact balance is one of the things that we have to do as climate scientists to figure out what the aerosol effect is we're going to be running an experiment to show how critical small particles aerosols in the atmosphere are for the formation of clouds to demonstrate that we're going to make a cloud and we're going to do it in this little jar right here so to get started this is going to mimic a cloud that's going to form over a body of water like an ocean so that you can see the bottom of this has a bit of water in it so you could pretend that we're going to make a cloud over the ocean off the coast of boston or something like that normally clouds form by convective activity the surface of the earth heats up the air is somewhat warmer and then it moves upward in the atmosphere and as it does that the relative humidity increases the temperature decreases you hit one hundred percent relative humidity and your club forms unfortunately i am not tall enough to lift this quickly enough to get a cloud to form in it so instead what we're going to use is a pump to drop the pressure in this and mimic that cloud moving up with that air moving up and forming the cloud in the atmosphere and you can tell the pump is on because when i put my finger over this little filter right here you'll hear a slight sucking noise and that's the pressure in the jar dropping which is going to be akin to this moving up in the atmosphere and i can hold my finger over this for quite a bit of time and you won't see anything happening in the jar inside there's no cloud forming and the reason that there's no cloud forming is that this little he's right here is actually a filter so it's taking all of the particles out of the atmosphere before they make it into the jar so this jar right now is only air there's no particulate matter in it whatsoever as the pressure drops the relative humidity is going up quite a ways it probably is reaching one hundred ten one hundred twenty percent relative humidity humidity that you would never hear on the nightly news and yet there's no cloud that's forming so what we have to do is introduce particles into this jar to get the cloud to  form we're going to do this with a common household match and you can imagine that this is going to mimic a process like burning down a forest wildfires that's going to add particles to the atmosphere so we first light the match and then to get the particles to form you'll see the smoke come off in just a moment so here's the smoke we let it into the jar the jar now has particles inside of it and when we do that the cloud can form on the particles that we put into it will let the relative humidity go down and the cloud goes away there are still some particles in there though and so another cloud will form on the particles that are left over we can let somewhere into the jar and yet more particles will form on a cloud you'll notice that the club becomes thinner and thinner each time because we're removing particles every time i open this up and they're pumped away so obviously this is a high tech cloud chamber this is not something that we can use to produce laboratory quality data instead what you see behind you is one of our high tech chambers this is something where we have very precise control over temperature and relative humidity and this instrument is able to figure out the size of the cloud droplets that are being produced and the numbers that are being produced we can also add specific particles to it for example if we're interested in biomass burning we don't have to use a match we can put particles in there that have been burned for material that we're interested in or we might be interested for example in a dust storm and we're able to put mineral dust particles into this and see what their cloud new cleaning potential is and so instead of having the the water in the bottom of the jar the water is actually in one of these jars and it's constantly fed through this unit and what you can see on the screen here are the number of droplets being formed versus the cloud particle size in this case so this is how many droplets are being made and this is how big those droplets are and right now we're just simply looking at the number of cloud droplets that are being formed in the ambient atmosphere so how many potential cloud particles could form in the environment that we're living in right now in the background behind you is a homemade cloud chamber something that we use for looking at the formation of ice clouds and that's maybe not surprising by the amount of insulation and duct tape that's on it but we can build something like this and make it specifically for  particular cloud type that we're really interested in which are cirrus clouds people know of these as being the very thin wispy clouds that you see especially on a clear day they're composed entirely of ice and they're existing high high in the atmosphere so many miles high you know sort of the type of pass through when you're out on a jet airliner we're interested in them because they are among the most uncertain parts of the climate system so i've already said that aerosols and clouds are uncertain within  and clouds one of the most uncertain things is the formation of these high altitude cirrus clouds they're very important for climate they tend to be the first clouds that solar radiation sees on its way into the atmosphere it means they're the first thing that can scatter radiation out of the air system  because they're very high they're also the last thing that the heat from the earth trying to get into space so they're the last thing that can sort of intercept that radiation and perhaps trap it send it back towards the planet they're actually so uncertain that there's debate about what forcing they have and what i mean by that is that there's debate about are they a warming agent for the planet or are they a cooling agent which of the things the interception of radiation or the trapping of earth's radiation is winning out and almost certainly that sign the warming or cooling changes depending on where these clouds are where they are in the atmosphere how high they are and all of these things are changing as humans change the particles that they're forming on and we're in particular very interested in some of the minor components of the atmosphere things like heavy metals lead that comes out of things in the past came out of touch with a lead that was used in gasoline now it's increasingly seen as a byproduct of coal combustion so there's a bit of lead that submitted when you burn coal and that finds its way into these particles and that lead is one of the key determinants in if something nuclear it's ice well if it forms these ice crystals that cirrus clouds form on or if it doesn't form the cloud and so we're keenly interested in how human impacts how small things small trace amounts of material that humans emit into the atmosphere can have on a cloud formation a vent or or the lack of a formation of  which is this huge lever arm in the climate system so another reason that cirrus clouds are so important is that they cover a huge fraction of the globe so at any one time it's thought that they cover maybe a third of the globe maybe even more than that and we don't tend to think about them because they're so high in the atmosphere that if there's a lower cloud layer they're invisible to us they're also very thin some of them are called sub visible and as the name implies we can't even see them they're so thin that we can look through them but we can see them with space based instruments like satellites to do some of our measurements we have to use rather exotic platforms so one of the things that we use is nasa research aircraft it's a b fifty seven it's actually an old air force bomber and reconnaissance aircraft that hast by nasa to do studies in cirrus clouds because it can get so high in the atmosphere and then stay there for a significant amount of time to do these measurements one of the things that's critical to understanding the earth's atmosphere is what we call the mixing state of particles understanding how one particles different from another how a special particle is able to for example nuclei to cloud whereas another particle that's very closely related isn't able to we have a couple of single particle and so what these are able to do is understand the chemical composition of particles on a single particle basis and so we use technology like this where we bring particles in one at a time we strike them with a laser and that laser is powerful enough that it bleats the particle that it essentially burns the material off and it creates ions and then we manipulate those ions within an electrical field and that allows us to say what the mass of each of those ions is which gives us the chemical composition of the particle it tells us is that mineral dust but not only that what type of mineral dust is it is a bio mass burning but not only that what's associated with the biomass burning what was the type of material that burned to create that particle this one built the prince investigator stan murphy and it was specifically built to go on research aircraft this one is a company that has built a single particle mass spectrometer so one thing that you can see is that it's somewhat smaller than the custom instrument and we sacrifice a bit of precision to do that so it's not specially built for our questions but it's much more in general useful and usually these are are much more useful to somebody that hasn't been working on an instrument like this for a number of years they're much more plug and play we do two things in this group so one of the things that we do is development of instruments custom instruments for what we need to do so this would be an example of a custom single particle mass spectrometer something that built for a specific task and we've modified this one and used it largely for doing cloud studies so it's very precise it has very good resolution right now we're trying to get funds to build a small version of this instrument these big research aircraft are going away so we want to build this and put it on a u a b which is this new generation of technology we've got the new platforms there's no money for us to build this instrument for you right now you know agency after agency says that's not in our budget right now this experiment is called electrodynamic balance and in a way i like to call it our anti gravity chamber so we put a single particle so one particle at a time is trapped in here and it has a small electrical charge on it so say that it has one positive charge on it we have an electrode on the bottom that's positive an electrode on the top that's negative and what happens is that that particle experience is a force upward in the electrical field and we very precisely tune it to offset gravity so the particle is perfectly suspended in the electrical field versus gravity and it's held there the record that we know of is that there was a particle that was trapped in this for something like three weeks for experiments to be performed on so it was sort of levitated anti gravity for three weeks and we're actually using this to understand cloud formation under very radical conditions very low temperature conditions for example clouds that would form around other planets like mars venus exoplanets so we can do in a chamber like this the questions that often comes up when you talk about clouds and climate change is can you use clouds to offset climate change so as soon as you say that particles and clouds are a cooling effect and they offset some of the global warming from greenhouse gases it's sort of natural to say well why don't we make more particles and more clouds and there's actually a lot of reasons why we should not be doing that when it comes to making more particles one of the things that we found out of her recent years is that particles have an incredible health risk associated with them so a lot of childhood asthma a lot of cardiopulmonary diseases are completely correlated with the amount of particles that somebody inhales over their lifetime so simply making more particles doesn't really make sense because we would have an incredible loss of  human life the next step that people go to as well maybe we could tailor make clouds and put them in some part of the atmosphere to send solar energy back into space before it makes it to the surface of the planet and there's actually quite a following of this it's sometimes called geo engineering this had to have a rather bad connotation of manipulating the climate system and so it's been resurrected as something called solar radiation management meaning attempting to control the sun's rays coming to the planet  unfortunately the people that are proponents of this don't mention a lot of the side effects are the things that aren't addressed by this so for example if you put particles or clouds high in the atmosphere we already know from things like volcanic eruptions that this has an incredible bad impact on atmospheric ozone for example they represent sites in which ozone loss can take place and we know after volcanic eruptions that it was own goes down as a result of having those particles in the atmosphere and so this would be a side effect of trying to put particles in clouds into the atmosphere to offset solar radiation and it's certainly something that we've only now begun to recover from from from the c f c s the chlorofluorocarbons that were depleting ozone in the one nine hundred eighty s and ninety's so that would be one side effect another is that by putting particles in and clouds into the atmosphere you're not addressing the problem of rising c o two so that warming is still taking place in the atmosphere  still building up in the atmosphere and so you're addressing not anything like the ocean acidification issues that go along with having this increase in c o two and so that's something that's very often not talked about from my standpoint as somebody that works with particles  clouds the thing that doesn't make sense to me the reason that this is so illogical to me is that we've already talked about how uncertain the effect of particles and clouds is if you go to these things like the i p c c report which say that particles and clouds represent four or more times the uncertainty of greenhouse gases the solution of somehow tweaking particles in clouds to offset greenhouse gases is sort of like using the course knob on an old stereo system to tune something as opposed to the fine knob we know the effect of c o two very well we understand its role in the climate system that's the knob that you want to tune to tune out a temperature issue you don't want to use the thing that you don't understand to do that so simply saying that it has a negative effect that as a cooling effect isn't enough you have to also ask yourself do we understand it well enough that we could actually get some kind of a measurable effect of the magnitude that we want and  simple answer to that right now is no the reason that we're doing so much work in this part of the field is because we don't understand it and so it doesn't represent a mechanism that we can simply use to tune climate to our liking