*Transcription by Oscar A. Escobar* *Central Florida. Gt. - May 18, 2016*
*The original you tube video:* *https://www.youtube.com/watch?v=GoGZrwzWHJI* *Video Abstract:* Published on Dec 15, 2015 Various parts of the world have “dimmed” and “brightened” at times, as measured by surface solar radiation records, and some of that is clearly related to pollution patterns. But new data suggest an additional mechanism is at work. That something is whitening global cloud-free skies and changing the way that solar radiation reaches Earth’s surface. A provocative new analysis, presented in this briefing, points to a likely cause—an unintentional geoengineering experiment. Participants: Charles Long, Senior Research Scientist, Cooperative Institute for Research in Environmental Sciences at the NOAA Earth System Research Laboratory, Boulder, Colorado, U.S.A.; Martin Wild, Professor, ETH (Institute for Atmospheric and Climate Science), Zurich, Switzerland. PDF slides for Martin Wild's Power Point presentation: *Global Dimming and Brightening Decadal changes in sunlight at the Earth's surface* http://fallmeeting.agu.org/2015/files/2015/12/Wild-slides.pdf PDF slides for Chuck Long's Power Point presentation: *Evidence of Clear-Sky Daylight Whitening: Are we already conducting geoengineering? * *Chuck Long (NOAA ESRL GMD/CIRES) Jim Barnard & Connor Flynn (PNNL*) http://fallmeeting.agu.org/2015/files/2015/12/Long-slides-.pdf *(00:00) **(Moderator):* Hello welcome to our 11:30 press conference: *A**ccidental Geoengineering.* Our speakers are Chuck Long, Senior Research Scientist at the Cooperative Institute for Research in Environmental Sciences at the NOAA Earth Systems Research Laboratory in Boulder Colorado. And Martin Wield Professor at ETH Zurich. And there is a press release at the back of the room. *(00:27)* (*Martin Wild speaking*): Ok... good morning everybody! I would like to give some background information about the phenomenon which has recently gained considerable public and scientific attention. The so-called phenomenon of global dimming and brightening. Which relates to the recognition that the sunlight that we receive a the Earth’s surface it's not stable over the years but undergoes substantial decadal changes. *0:55 *And to understand this phenomenon a little bit better... I would like to start looking into the global energy balance of the Earth... as shown on this picture with the sun as the ultimate energy source for the climate system. Not only for the climate system but also to all life on earth in general. *Sun **light** that goes into the climate system heats **the earth’s **surface. This heat is emitted back into space in terms of thermal radiation, but only a part of it makes it to space, a considerable part of it is absorbed in the atmosphere, which is the so-called greenhouse effect*. And anthropogenic climate change, first of all, can be viewed as a change in these fluxes through anthropogenic activity. On the one hand through an increase in greenhouse gases, which further traps the amount of emission of thermal radiation into space… (garbled)... but also by perturbing the amount of sunlight that we receive at the earth surface. And this is caused by air pollution and related particles in the air, tiny particles which we call aerosols which can modify the sunlight. *(**2:16**)* But do we have any evidence that these solar fluxes have really also been changing, not only the greenhouse effect and greenhouse gases influence fluxes. And indeed there is evidence from the long-term observational records at the earth’s surface, as shown here for a composite of records from Europe, which show strong month decadal variation. This record shows the sunlight at the Earth’s surface from the 1940’s to near present, and what we see here is that we have strong multi-decadal variations. *(**2:52**)* We have a period where sunlight has decreased from the 1950’s to the 1980’s. With a period which we call *“**dimming** period”* and a more recent recovery, which we call*“brightening period”* where the sunlight at the Earth’s surface has recovered and we have again more sunlight that makes it through to the earth's surface. *(3:17) *So... What could be the reason for these variations? An obvious reason could be that the output of the Sun has been changing. And the Sun indeed has some variation in its activity, as seen in the variation in sunspot numbers which have an 11 year cycle and which vary the output of the energy that comes out from the Sun. However these variations are much much more a smaller than we see… the variation that we see at the earth’s surface, and they also not correlated with the variation at the earth’s surface. *(**3:52**)* So basically the Sun cannot explain the dimming and brightening phenomenon. That means if it's not the Sun, it must be the atmosphere that plays a role in (the) modification (of) the sunlight that gets through to the earth's surface. And the atmosphere has indeed... undergone substantial changes in the last decades, particularly in terms of air pollution in the atmosphere. And we show here sulfur emission as a proxy of air pollution from the 1950’s to 2000. And we see a strong increase in air pollution from the 1950’s to the 1980’s. And then we have a... turning (of) the trend and the decrease in the more recent years. And this decrease is partly related to the numerous air quality measures that have been implemented to reduce the air pollution... which has resulted in a reduction of air pollution. If we compare that with the sunlight we get at the earth’s surface... it fits very well. That means... we have increasing air pollution we have a decrease in the amount of sunlight at the earth’s surface, and as soon as we have this decrease in air pollution we have a recovery again of the sunlight. *(5:16) *And how can we explain this variation… this mechanism? These aerosols, these tiny particles in the air... they can scatter and absorb the sunlight that comes through the atmosphere and thereby reducing the amount the goes at the surface. But also they can change the properties of clouds in that polluted clouds, which is a bit counter-intuitive, become brighter; as we can also see for example from satellite pictures, more reflection of solar radiation back to space in polluted clouds. And the polluted clouds... they can also stay longer in the air because their droplets are smaller and therefore do not precipitate so quickly. That means we have brighter and longer living clouds and this also shields the sunlight from coming to the earth’s surface. *(**6:07**)* So what does this all mean, for example, for global warming? What is the relevance of dimming and brightening for global warming? I show here the temperature records of global *surfaces from the 1950’s to the to 2000’s, and what we see here is...* *that during this dimming period we can also cause this accidental* *geoengineering period where **we** increased air pollution* and thereby reduced the amount of sunlight that came through to the earth's surface. *W**e see that the warming is* *very modest. So it seems that this dimming* *or **this... **un-intentional geoengineering* *has depressed global warming during this period. When we stopped doing* *this**geoengineering... and more sunlight comes again trough to the earth's surface you see that that temperature has been rising much more rapidly, due to the* *additional sunlight that gets to the earth’**s** surface in addition to the underl* *yin**g* *greenhouse effect which causes this warming*. *(**7:12**)* *Recently I started also to look at the asymmetric hemispheric pollution, because it's quite interesting to see that this global air pollution which we show before... this **the** black curb here… is mainly found on the northern hemisphere **(blue curve)**. On the southern hemisphere we have and an order of magnitude less pollution and we also do not have this trend reversal in the recent years. So when we compare now the temperature and the warming rates on the northern and the southern hemisphere… we see that on the northern hemisphere we have a very strong… even a reduction in surface temperature during the dimming period... and then strong... very strong warming in the brightening period, whereas on the southern hemisphere the more pristine southern hemisphere we have a gradual increase in the warming.* *So you could also see this as a geoengineered world, and this as a non-geoengineered world.* *(8:13)* And I published this in a recent paper that is currently available online for early view on on on the website of the Wires Climate Change. And I would like to, before I stop, also to briefly mention some other environmental issues where global dimming and brightening plays a key role, for example... It has a strong impact on the intensity of the water cycle, because during the dimming period we have less and less energy that comes... arrives at the Earth’s surface, and therefore less and less energy to drive the global water cycle, which resulted in a speed-down or attenuation of the global water cycle. In the more recent brightening period, there has been more energy available again to drive the water cycle and therefore also led to an intensification of the water cycle. *(9:05) **I'm coming from Switzerland and in Switzerland we have great concerns about our glaciers because they are retreating, but we have noted that this retreat only started during this brightening period. Before **when we had this **the dimmin**g** period, the reduction in sunlight prevented the glaciers from being melted.* *(**9:27**)* There's also a strong impact on the growth of the biosphere... because the biosphere needs sunlight for the photosynthesis. So if sunlight changes that impact the biosphere and furthermore... the plants particularly like diffuse light and diffuse light has been particularly strong during this dimming period. *(**9:53**)* On a more applied level… dimming and brightening have also had an impact on the growing market of solar power generation... because of course this substantial changes in the solar resources affect the productivity of renewables. *(**10:11**)* And with that I would like to end and if you are more interested in this subject I can suggest two papers... one is a popular overview paper I wrote on the topic of global dimming called “*Enlightening Global Dimming and Brightening”* in the Bulleting of the American Meteorological Society. And the second paper is.. The “*Latest (a status) on Dimming and Brightening”, *and in particular discusses its impact on the global... on global warming and this is the paper that has just been published online and it's open open access. Thank you very much. *(**11:17**)** (Chuck Long speaking)* Thanks Martin... that was a wonderful overview of the dimming and brightening phenomena and a little about ‘why we should care’. *My talk is a little bit about a subset of that... and the idea that yeah... we might be actually conducting some unintentional geoengineering here.* *For those of you who’**ve** read my talk abstract, the talk I am giving this afternoon... you know... yeah we do think we're doing this... and we're doing it with aircraft. So I'm* *going to explain a little bit about the sciences of why we think so*. I'm gonna talk about cloud free conditions… or what we named “clear sky”. So if you're gonna talk about cloud free, it's a good idea to talk about... what is a cloud. Because if you gonna be free of something you better know what it is. *(12:03) *So you can see this picture I'm using as a background on my talk here... is a little whiten-out so that the letters show up a little bit better... but this is the image that it actually came from... you can see there's nice white areas… the white puffy things here... that's what we call clouds, but you see there's blue parts of the image as well, and we tend to call that cloud free... depending on our conception of how blue it is, and where you draw the line... if you actually look closely here you can see there's some structure in the blue part. Where you actually draw the line between... OK... I'm gonna call that white enough to be a cloud and…. no that’s blue enough... I'm going to call it cloud free or clear sky... is not so well defined in our business. *(**12:47**)* But the point here is that… in what we call clear sky we do allow some amount of condensed water to be there, whether it's liquid, or ice or whatever... we still allow that to be under the lump we call clear or sky cloud free. And as our studies show the overall clear period seem to be getting a little whiter, and naturally as scientists we always want to know why. So in order to get into this and understand it we have to take a look at some of the... some of the components of what we're doing in this area. *(13:25) *One of the things is... when you have downwelling solar energy we actually divide that into two parts... *we call the shortwave “irradiance”*, and that is the part that comes directly from the Sun.. kinda like those bright light shining in my eyes right now... and we cleverly call that the “direct shortwave”. -Scientists... we're like that you know…- And then there's *the rest of the sky-light we call the “diffuse short wave”* and that is caused by scattering in the atmosphere. If you go up into space there is no diffuse... because there's no atmosphere... things up there to scatter the light... and the source of the diffuse light is what scattered out of the direct. So this is kind of important to our story here... how we got into… into discovering what was going on here. *(14:07) *So we published a paper a while back… where we showed that, as Martin has been talking about, *the all sky increase of brightening in recent times over the continental United States was about 8 watts per meter square **(8 Wm**2**).* But we also took a look at the clear sky part. In other words if the clouds hadn't been there what would’ve happened... and there was still more than half of the increase would have occurred had the clouds... had there not been any clouds over the United States. *At *the same time, *or*shortly before, there was a paper published that showed that the very same sites we used in our analysis, showed that there was a lessening of the aerosol loading at the same time. So this is well understood... *i**t’**s called “the direct aerosol effect”.* Martin had a nice little image there of it... because *if you decrease the aerosols what you're doing is decreasing the* *scatterers... so you should have an increase in the direct shortwave,* *because there is less particles that knock the light out of the way, and a decrease in the diffuse...* *because there's less light being scattered* into the diffused. *(**15:09**)* When we looked at our data... that's not what the observations showed. Over the period of time of the 12 years that we looked... the direct component did not change at all. All of the increase occurred in the diffused. So this goes directly against our idea of the direct aerosol effect. OK. That has presented us with something we actually loves as scientists! Something we don't understand. That's our business! Try to understand it. So we got a mystery here. This is a paper... where a figure from that paper shows the two components… the defused and the direct.. the direct is referenced to the right hand side. And this is the anomalies... which is you take the average of the entire data set from each site and you look at the difference... in that way puts it all in the same playing field... you can see *in **the diffuse we have four and a half wat**ts per square **meter **(4.5 Wm**2**)* *increase across the study years and virtually nothing in the direct. *So this is what put us on to this. *(**16:03**)* *OK. S*o... I have a mystery and need clues to solve it. One of the first clues is the answer to the question… Why is the sky blue and clouds are white? And you probably heard this before, but want to make sure we all understand and are on the same playing field here. *The molecular atmosphere without the aerosols, without the clouds… scatters blue light a lot more efficiently than red light*, so… OK. You look away from the direct... the sky is blue because there's a lot more blue light being scattered toward your eye, and very little of the direct. But clouds are white because you *scatter... *I mean white is the sum of all colors... so you're scattering all the wavelengths about equally to produce that white. This gives us a tool we can use here that I'll talk more about later on... but if you can... you can look at the sky-light or the diffuse field, and look spectrally... look at a red… just a narrow band of red light, and a narrow band of blue light and take a ratio of that. Then the ratio for blue sky will be small... red over blue... because the red is a smaller amount, but for the white... as it gets whiter that it will approach one... and that's what we look. So if you have this... if you can do a red blue ratio and that increases over time... it’s a sign that the blue sky is getting whiter. *(**17:15**)* OK? The second clue we have to talk a little bit about is… how light is scattered in our atmosphere. *The molecular scattering we were just talking about... actually scatters light both forward and backward... about equally... and has to do with the relationship of the size... the size of the scatterer, in this case molecules **and**the size of the wavelengths that are interacting with it.* *Counter intuitively though if you have larger particles… larger scatterers... because of the way natural light kind of wraps around these things and goes forward in this size relationship regime.* Now if you get really big scatterers like a brick wall it's gonna just bounce and scatter off… but in this regime were talking about... where we have aerosols in and other things... it scares a lot more in the forward direction, a little bit in the back... so that's part of the story here. So... our hypothesis... we know that the aerosols decrease and therefore the down-welling total short wave is going to increase because of that. *(**18:07**)* But in order to account for what we observed, there would have to be a shift, from smaller aerosols to larger scatters... that scatter more in the forward direction... assuming that there's fewer of them as well, to make up that difference and keep it in the diffuse… because that's what happened... the increase in the direct that would have occurred just because of the aerosol loss had to be made up to scattered back out some way... and if you have a larger particles they scatter more in the forward direction and less in the backward direction. So. Per scatterer... there's actually more shortwave (that’s) gonna reach the surface from the Sun that way. So… OK. This is a mechanism you can do but what are these mysterious particles? *(18:48)* Well we did some detailed ready to transfer modeling, and there's one particle that is common in the sky that could do this... and that's ice crystals, small ice crystals. *So... if you have less of these aerosols from* *pollution that are put in there, more ice crystals could do this.* *Where* *did those ice crystals come from?* *There's also a well-documented increase in flight hours in the continental United States across the study period that we have. And what is it that jet**exhaust spits out?* *I**s... first of all small particles or chemicals that form small* *particles that can act as condensation nuclei for ice to form on and more* *importantly some water vapor. *Now if you've ever flown and paid attention to the flight information when they have it up on the screen, when you're up at altitude it's darn cold out there... minus 50-60 degrees. And the amount of water vapor that can exist without condensing in those conditions is very very small... dependent on the temperature. *So at minus 50 or minus 60 there's not a lot of water vapor up there... and so**if you put a little water vapor in... it makes a huge impact in changing the**relative humidity, because its relative to the amount of water vapor the air**can hold and so… you've seen this. You walk outside… you see a jet going*across the sky, you see a contrail behind it... then that contrail dissipates. *(20:06) **When the contrail* *dissipates... first of all, that's a mark that you are condensing ice up there... in* *the cold atmosphere, but when it dissipates it leaves the moisture there...* *and so now you've moistened this very very dry layer. If you keep that up... you get to* *the point where the ice crystals will persist and spread out, and this is that* *cirrus… sub visual cirrus haze that we’re talking about, that is doing our whitening that we are hypothesizing*. *(20:30)* So there is an instrument that can give us what we need need. We can go into the details here for the next half hour... or not. If you're interested in that later. But it's a... it's an instrument that sat right beside us… in a matter of fact it’s an instrument that they used to infer that the aerosol optical depth had decreased. But I'm going to use it in a little bit different way. It's (garbled) part of the measurement that they usually don't use, but it does provide this red and blue spectral diffuse light that we can use for this red or blue ratio idea. Now remember we said that across the study years... if this red to blue ratio increases... then that's a sign that we are whitening the sky, when we call it clear sky. And so we've managed to do this for one of our sites. The one in the central part of the of the United States is actually in Oklahoma, and we used two different ratios from this instrument. It’s nice to back things up, make sure you're not messing up with just one of them and in both cases we got the same result. There is, across the study years, a positive increase in this red to blue ratio, no matter how we look at it; and both of these results are statistically significant at the 95% level. So what this says is... this is not a definitive proof... but sure supports our hypothesis. *(**21:52**)* *So we have dry aerosols associated with pollution have been decreasing. This is* *has **been shown in many many ways… less sulfur outputs**and everything else. But the direct aerosol effect alone can't explain what we see in the observed direct and diffuse components. To that we need something else thrown in there... and small ice crystals do fit the bill right in our theories to to be able to produce this result.* *Where does it come from? **Well... a**ir traffic over the USA and elsewhere, Europe and elsewhere has increased; and this is a mechanism that can produce the haze. We think it actually is... and it’s making, on average, the clear sky **whiter.**.. down across the decades.* *(22:38)* The manifestations of this, as Martin pointed out, redistributes the solar radiation in the way it reaches the surface. In this case because we're talking about the cloud free situation. And as Martin pointed out, plants like diffused light more than direct light, because you have less shading of the lower levels... all else being equal. And if you again... there's more forward scattering in this case... so if you actually increase the number of these crystals you could in a certain realm increase the amount of short wave that's reaching the surface through this mechanism, *up until the point where you're starting to get white enough that you'd start to call it a cloud and **then **you’re having multiple interactions which then decrease it… nullifies the forward scattering effect.* *But as far as climate change... we are changing the components of the climate system… by an activity associated with human industrial civilization.* *Here's another manifestation that... yes indeed... human activity can and is affecting the climate.* *So… unintentional geoengineering... if you look up the definition of geoengineering… it includes large-scale manipulation of parts of the climate system and the environment. And I believe this ice haze from jet traffic does satisfy that requirement. So... yeah we are.* So... thank you! *(23:58*) We’ll take some questions, and also want to point out if you're not... if you're interested... then later on... both Martin and I are giving some talks in the later session just right down the hallway here. Thanks! *(**Moderator** speaking)* Thank you! Are there any reporters in the room that have questions... please raise your hand and state your name and affiliation. *(24:22) (**Hi, I am David Appel from Yale Climate* *Connections**):* So... in terms of global climate models… What kind of global radiative forcing is this causing in watts per square meter? And are global climate models adequately taking this into account? *(Answer by Chuck Long):* By the traditional definition is based on human observations... part of that is that... by the time it gets white enough to be called a cloud... them it's going to have a major... as Martin pointed out with the global dimming and brightening... its gonna have a major significant noticeable impact on the total down-welling shortwave. This is not so much an impact on the total, as it is in the way it's reaching the surface. But that's in the solar side. There have been studies that show in the infrared side, the greenhouse side. This is part of that barrier up there that is preventing infrared from the surface to escape (?)... so much to space. So it is kind of a warming mechanism. *(25:28)* Now as far as global climate models though… *This very well-known scientist named Joyce Penner, who came and gave a talk at* *our institution, quite a while ago and she said... she was talking about this* *subject; and came to the conclusion that it was not so much an impact... but the* *question that was asked then was... but remember we're in a regime h**ere** that* *is dry...very dry, and if you put a little bit of water vapor… **it** can make a big impact.* *(**25:55**) *Global climate models… their vertical resolution high in the atmosphere is very large... so if you put that little bit of water vapor... but you spread it over half a kilometer or more… which is the resolution of the models there's no impact. But that's not the way this is happening. There's a study that was done actually... by a group from Wyoming... that studied these things and what they show… they were actually looking... they were using aerosol on... *so they're* *looking at the aerosol particles that... a**s** I said… jet exhaust puts it out. They… for many* *many years they look**ed...** up... at the flight altitude and they found these very thin* *layers of highly concentrated aerosols*. *But that's the point... the salient point* *is* *th**e**y’re** thin layers... they're not five hundred meters thick... so when you* *put that amount of water vapor in a thin layer it has a much much larger impact.* *And that's why the models can’t get this because they don't have that vertical* *resolution that actually adequately model this… so no, they can’t. They’re not getting this.* *(**Moderator** speaking)* Are there any other questions in the room? *(**27:08**)* *Hi, Jonathan Amos BBC news.* I just want to be clear… Can you detect the ice haze? I mean are there (?) other emissions or something like that, than can actually characterize it? *(27:21) **(Answer by Chuck Long):* We... yes... we did another paper because... we came up with the question... OK... along the lines of what is and isn't a cloud. We've developed a couple of techniques... both in sky imagery... which is based to emulate human observations, and then another technique that we develop that analyzes the time series of short wave solar radiation measurements to detect clear sky periods. And so the question is...what's our limit there. That's something we can look... we did a study using a very powerful vertically pointing Lidar... that can see these very subtle things. And so you can do that. Unfortunately when it comes to Lidar if you're going to operate them a lot... they have to be what's called ‘eye-safe’, so that if somebody is flying a plane over... they don’t blind the pilot by looking up to... have to be eye-safe. When they're eye-safe, they're less sensitive and they tend to be green lasers. Well solar radiation includes green light and it scatters into the barrel, and so (the) typical lasers... Lidars that we have... are not sensitive enough to see this, but if you have a powerful enough… or the right wavelength Lidars you can see this.. that’s one way to study it. Other than that… it's very difficult... because you're high in the atmosphere and these are so tenuous... it's kind of difficult to pick these things out otherwise. *(28:49) **(Moderator): *Are there any other questions in the room? *(29:00) **( Garbled.**.. **f**rom **Frankfurt, **German**y**): *The question is… you looked… you measured one site, that was Oklahoma... you looked at the air-traffic over the continental U.S. in some of your slides. Have you looked at areas where there is very little air traffic, to see if there are differences in your red blue ratios or in the whitening of the sky? *(**29:23**)** (A. Chuck Long):* Well there's lots of work to do. This is what we like to call in conferences… our preliminary results... Yeah! There's a lot of work yet to do. One of the things is this this MFR(?) SAR data that gives... its the only instrument I know of… that gives a spectral diffuse short wave, which we need for that red blue ratio idea. But it you have to be very careful. We are looking at something very subtle here, and so you have to make sure that you're looking through twelve years of data... you want to make sure that you using good, very good data for that; and that's manually intensive to do. So we are going to be looking… pursuing this at the other six sites that we had used. *(29:59)* Now in the paper where we looked at the broadband and show this... clear sky... on average four and half Watts per Meter square predicted increase. It wasn't the same at all the sites... and if you saw our map… you see there is... we have eastern sites and western sites... in and the amount of change would differed in... yes! Theoretically... the increase in that red blue ratio... should correlate with the amount of brightening, clear sky brightening that occurred at each site. And some of those sites... if you look at the… if you look at the U.S. air industry… some of those sites… there is not so much traffic lanes over top as others. And so we expect to be able to pick that out. But that's one of our questions we have. We haven't got the answer to that yet. But in science when you do something like this. You take a first crack at it to see what what you see. We're looking at yearly averages now. There's a lot of details yet to be looked at here... because you know 01 and 10 the average is 5. But 5 and 5 the average is 5. There's a lot of details yet... that goes into those averages we need to look at... but a very good question. *(31:06) **(Follow up question)* May I have a follow-up... I mean you stand here... and you put a slide up and say it's this haze or the whitening is caused by jet air traffic... but… *(C.L):*I said that's the hypothesis, yes. *(Q):* It’s the hypothesis?... You didn't say that, I think.*(C.L.)* I have it clearly on my slide that our hypothesis is this mechanism... you know... yeah! I mean that's how science works. You come up with a hypothesis... and it's very unusual in science when we can prove something is true. Usually what we do is we form a hypothesis and we try our best to prove it false. That’s our hypothesis. *31:48* (*Rick Levitt, freelance**)**: S*o I've got two questions… *(C.L)* Is he allowed to have two? (jokingly- laughter) One is on the infrared... I gathered that you are saying that a thinner layer of the small amount of ice or vapor has a bigger effect than the same… total column spread out... in terms of returning sho... long wave radiation? *(32:14)* *(A. **Chuck Long**)* Yes it does. There is a... real quickly... one of the biggest uncertainties in global greenhouse warming is cloudiness. Is it going to change? And if it does... how it's gonna manifest itself? If you have low level clouds... right?... They reflect solar radiation away... so that's a loss of energy. But they're warm... and so they still emit almost the same amount of infrared as the surface below them would, it's the amount... of infrared radiation that’s emitted is dependent on the temperature. If you have high clouds... you still... if they're optically thick… they're still reflecting away solar radiation, which is loss, but now they're radiating in the infrared and at much colder temperature. So you have to have a buildup of… of temperature below that cloud... in order to equal the same amount of infrared loss to the system. As you do... as you would, if the cloud weren't there. And so that's a warming influence. So high clouds tend to warm in the greenhouse effect. Low clouds tend to cool in the greenhouse effect. *(33:23) **(Rick Levitt)*: OK. And my other question is... which is kind of related to that... (garbled)... So, other than proving my childhood memories of bluer skies are accurate... What… what's the... you know... what’s the take home of this? It’s a little better for plants? And there is an effect on infrared... but is this a big effect? *(33:48) **(**A. Chuck Long**)* No... none of this because... again we're in a part... OK... there's several messages... it’s not a huge watt per square meter thing... though if you look at... if the clouds weren't there over... *an increase of four water meter squared per**decade is.. much much much larger than the projected increase due to greenhouse warming. They're talking about for wa**t**s per meter square… under certain scenarios… over forty or fifty years... this is in 10 years.* *So it's a larger change. But as Martin showed, we're decreasing, increasing its a decadal thing rather than a hundred years phenomenon as greenhouse warming is.* *(34:24) *So... one take home is that… it is a part of our energy system. The part we're talking about here is clear sky. So… when you have clear skies this is re-partitioning the energy... but you're still getting roughly the same amount of energy to the surface. So it's not a big energy thing. *But what it is it's another indication that man* *can... and indeed is influencing the climate system. This is not a question. I mean it’s part of the problem... tha**t **the scientific community... we have convincing**people that man can do this in the greenhouse world. *I want to be very careful how I say this because i don’t... i don’t wanna... but part of it... *we know that part of the**problem that we have is... we're talking about some change of a couple of watts per meter square* *over fifty or a hundred years. It's pretty hard to grasp. But yeah we* *really doing… This is a more immediate thing and you can see this… walk outside...* *you know it's not difficult to study clouds... just walk outside and look up! **OK**?* *(**35:26**)* If you go walk outside... take a pair of sunglasses so you don't hurt your eyes, and make a habit of walking outside and hold your thumb over the Sun's disk. you will see a white area around the Sun. Some days that area is bigger, some days it's smaller, but that… that white area is caused by this forward scattering. You know you’re… scattering light out of the direct into the diffuse. And if you're standing to the side over here... looking this way (pointing)… well that's the blue sky... you're looking over there… if the sun is there... but if you look around the Sun... then you're in this forward scattering peak. The bigger that thing gets is an indication of the more of this haze that's up there. It’s one way you can tell it's up there. *(36:07)* So walk out in the morning... you'll see short contrails behind the aircraft that you see in the sky, and you put your thumb over the Sun and there will be a small white area around it. As that day progresses if it stays clear sky... and it's… and there's more jet traffic, you'll see the contrails hanging around for a longer amount of time, maybe even spreading out during the day and by the mid to late afternoon when you put your thumb over the Sun you'll see a bigger white disk. That's this... phenomena... that's... you can see this with your own eyes. *Now there's other influences, sometimes there's a larger scale air movement up there, so... sometimes the air masses are coming in that are more moist and sometimes more dry. So there is that influence. *But… walk outside look up... do this do it for a couple of months. Specially during the summertime, and you will see this phenomena. *(37:00)* (Moderator: I think we have aquestion from the chat. *This is from Harvey L.**)*:*Just to pin down the definition of accidental geoengineering. Are the**phenomena you both presented, different in some way from other human activities* *like automobile exhaust, biomass burning and the like?* *(37:19) **(**A**. **Chuck **Long): This particular phenomenon* *with aircraft is, because you have to deposit the moisture and the* *aerosols hi* *gh** up… where is dry and there aren’t a lot of aerosols up there. As far as* *generally brightening and dimming NOAA includes those things as well.* (Moderator: Thank you. Are there any other questions from reporters in the room?) *(*37:47) *I am Nicholas J… with Earth Magazine**):* With these... with the ice content would these most be closely related to things like cirrus clouds… If you had lump these in the cloud family? *(38:08) **(A. Chuck Long):* Yeah... the definition of cirrus... traditional definition is… a cirrus is “high ice clouds”. So these are high, there is ice but they're just not thick enough yet that we would call them a cloud. So, I label them an ice haze and that comes from the meteorological definition at the surface... of what is... what's the difference between a haze and a fog. Well if it's a haze they’ll gets thick enough that you can't see very far... they actually define it in terms of visibility and high-contrast... how far you can see. What a fog then is... just a cloud on the ground. So… But yes this is. There was a scientist many years ago named Ken Sassen, he was a Lidar scientists and he coined the phrase, I believe it may have been Kenneth that came up with this... but... he coined the phrase “sub-visual cirrus” to describe this haze things. Sub-visual meaning... if you stand here looking up and it’s still blue... you don't call it a cloud yet... but it's ice… so its cirrus like... I guess you would call it. End of conference. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/d/optout.
