Another unaccounted for climate variable: Airplanes make existing clouds brighter

From STOCKHOLM UNIVERSITY and the department of negative feedbacks comes this surprising finding that says not only do contrails add reflectivity for incoming solar radiation, they also increase reflectivity for other nearby clouds.

Jet contrails as seen by satellite. Credit NASA Langley Research Center

Jet contrails as seen by satellite. Credit NASA Langley Research Center

Clouds may have a net warming or cooling effect on climate, depending on their thickness and altitude. Artificially formed clouds called contrails form due to aircraft effluent. In a cloudless sky, contrails are thought to have minimal effect on climate. But what happens when the sky is already cloudy? In a new study published in the journal Nature Communications, scientists at ACES and colleagues from the UK show that contrails that are formed within existing high clouds increase the reflectivity of these clouds, i.e. their ability to reflect light. The researchers hope that their discovery offers important insights into the influence of aviation on climate.

“Normal contrails are the stripes you sometimes see behind high-flying aircraft. Lots of times these contrails disappear fairly quickly. Other times they stick around for a while, and even spread out, sometimes considerably. There has been a lot of work done to find out how these form, and what kind of climatic effect they have – which is estimated to be rather small. Figuring out what kind of effects airplanes have while flying through clouds that are already present in the atmosphere has been much more difficult,” says Kevin Noone, Professor at ACES.

The researchers used a combination of flight tracking data and satellites equipped with sensitive lasers for detecting small changes in cloud optical thickness, i.e. the degree to which a cloud prevents light passing through it. When they looked at flight tracks from Honolulu to LA and Seattle to San Francisco, they found a significant increase in the optical thickness of the clouds close to the flight tracks compared to those further away. In other words, the clouds close to flight tracks were more reflective or “brighter.”

” Such effects only occur in certain latitude bands, so aircraft flying on polar routes in the Northern Hemisphere and close to the Equator are unlikely to produce these sorts of clouds. The most important areas are in the Northern and Southern mid-latitudes. Work is in progress to calculate the climatic effects of the changes we’ve observed,” says Kevin Noone.

###

The paper:

Aviation effects on already-existing cirrus clouds

Matthias TeschePeggy AchtertPaul Glantz & Kevin J. Noone

Determining the effects of the formation of contrails within natural cirrus clouds has proven to be challenging. Quantifying any such effects is necessary if we are to properly account for the influence of aviation on climate. Here we quantify the effect of aircraft on the optical thickness of already-existing cirrus clouds by matching actual aircraft flight tracks to satellite lidar measurements. We show that there is a systematic, statistically significant increase in normalized cirrus cloud optical thickness inside mid-latitude flight tracks compared with adjacent areas immediately outside the tracks.

Introduction

Air traffic is known to have an immediate and noticeable effect on clouds in the upper troposphere. New clouds that form due to aircraft effluent are called contrails1, 2, and may develop into more persistent and widespread contrail cirrus. Boucher3 was the first to realize that aviation might have a strong influence on the occurrence rate of cirrus clouds. Previous studies of contrail optical properties are either based on passive remote sensing in which contrails are identified as linear features in scenes of brightness temperature differences4, 5, 6 or modelling studies in which contrails are formed when favourable meteorological conditions are reached7. The life cycle of contrails and aviation-induced cirrus, their radiative forcing and feedback on natural clouds have been studied by treating them as an independent cloud class in a climate model8. The study by Iwabuchi et al.9 is the only one so far that has used height-resolved observations from space-borne lidar measurements to investigate the physical and optical properties of contrails. In their approach, the authors used passive MODIS (moderate resolution imaging spectroradiometer) observations to identify contrails for a subsequent detailed analysis of CALIOP (cloud-aerosol lidar with orthogonal polarization) observations.

In general, aviation-induced clouds (that is, contrails and contrail cirrus) have been found to be optically thin10, 11, and their climatic effects have been estimated to be minor4, 12, 13, 14, 15 even when considering their entire life cycle8, 16. The effect of contrails embedded in natural cirrus is a mechanism that currently has neither been studied nor assessed for its radiative effect on climate8,15, 16, 17.

While optically thick cirrus clouds have a net cooling effect on surface temperature, optically thin cirrus clouds, like greenhouse gases, can have a warming effect15, 18. Aircraft emissions and contrails at cirrus altitudes have the potential to either cause optically thin cirrus clouds to form (that would have a warming effect on surface temperatures) or increase the optical thickness of existing clouds (or induce new optically thick clouds), thus, causing a net cooling effect. Enhanced observations of the effects of aircraft on cirrus cloud properties are needed to help bound and quantify these possible effects.

The aim of this study is to test the hypothesis that contrails formed within natural cirrus clouds have no measurable immediate effect on cirrus optical depth inside and outside flight tracks in the upper troposphere. We combine data of aircraft flight tracks with spaceborne lidar observations to investigate the effect of aviation on the optical thickness of already-existing cirrus clouds. We detect a statistically significant 22% increase in normalized cirrus optical thickness in mid-latitude air traffic flight tracks compared with adjacent areas outside the flight tracks.

Approach

Figure 1 illustrates our approach. Typical flight tracks for connections between Seattle (KSEA), San Francisco (KSFO), Los Angeles (KLAX) and Honolulu (PHNL) are shown as thick coloured lines. CALIPSO orbits are indicated as thin grey lines in the figure. The inset shows normalized COT (nCOT; see below) at 532nm across each of the flight corridors between Los Angeles, San Francisco, Seattle and Honolulu. In cases 1 and 2 aircraft had passed the area <30min before the CALIPSO overpass. In case 3, CALIOP observed the location of the flight track before the passage of the aircraft. For these cases cirrus clouds were present at the flight level of the aircraft. For the cases 1 and 2 where the aircraft arrived before the satellite overpass, CALIOP nCOT was clearly larger for the inner part of the flight track compared with clouds present on either side—creating a ‘plane track’ signature caused by an embedded contrail or another effect on the cloud caused by the aircraft.

(a) Typical aircraft flight tracks (coloured lines) and CALIPSO satellite trajectories (grey lines for 16-day cycle, black lines for example cases). (b–d) Close-up of three example overpasses indicated in a with values of normalized cirrus optical thickness (coloured dots) and illustration of the inner and outer track (light and dark grey shading, respectively). White and grey dots in b–d refer to data that have not been considered in the analysis and do not fulfil the quality assurance criteria, respectively. Times of CALIPSO and aircraft overpasses are given at the bottom of b–d. Negative and positive time delay values indicate that the aircraft arrived at the scene before and after, respectively, the satellite overpass.

(a) Typical aircraft flight tracks (coloured lines) and CALIPSO satellite trajectories (grey lines for 16-day cycle, black lines for example cases). (b–d) Close-up of three example overpasses indicated in a with values of normalized cirrus optical thickness (coloured dots) and illustration of the inner and outer track (light and dark grey shading, respectively). White and grey dots in b–d refer to data that have not been considered in the analysis and do not fulfil the quality assurance criteria, respectively. Times of CALIPSO and aircraft overpasses are given at the bottom of b–d. Negative and positive time delay values indicate that the aircraft arrived at the scene before and after, respectively, the satellite overpass.

Discussion

Air traffic corridors are far more prevalent in the northern hemisphere than in the southern hemisphere, so we anticipate any climatic effects these embedded contrails may have will be more pronounced there. Even though cloudiness may already be changed by earlier aircraft, we can isolate the effect of a single aircraft on cloud properties. Since the effect of aircraft on cloud properties may well last longer than 30min the overall effect of air traffic on cloud properties may be larger than the values estimated here. Estimating the climatic effects of embedded contrails is beyond the scope of this paper; however, given the broad coverage of air traffic corridors in the northern hemisphere, embedded contrails as identified in this study are potentially an important and not yet considered contributor to the non-CO2 effects of aviation on climate17.

Further work will be needed to quantify the effect identified in this study. Initially, detailed radiative transfer modelling is needed to assess the impact of an increase in COT on the Earth’s radiative budget. From the modelling perspective, future studies will need to estimate the magnitude of the observed effect on a global scale and assess its contribution to the overall non-CO2 effects of aviation on climate. The increase in cirrus optical depth may result from the emitted soot in the first few seconds within the plume. Soot particles are not efficient ice nuclei. They rather form droplets when water saturation is reached in the plume and freeze subsequently20. Hence, the effect on the microphysics of the cirrus is an open question, and will require detailed microphysical modelling to address.

 

Full paper (open access) here: http://www.nature.com/ncomms/2016/160621/ncomms12016/pdf/ncomms12016.pdf

 

NOTE: Under no circumstances will we be discussing “chemtrails” on this thread. Any such reference to that subject will be immediately deleted. – Anthony

Advertisements

45 thoughts on “Another unaccounted for climate variable: Airplanes make existing clouds brighter

  1. Some people cannot understand why we get parallel contrail tracks, but this image shows why. The contrail is blown eastwards with the jet-stream, so the next track from the following aircraft (following a ground-track) is in a parallel position to the west. And sucessive aircraft, draw successive parallel tracks.

    From this we can see how long these contrails persevere. The original track these aircraft were following was down the Florida panhandle, but those contrails have been blown way out into the Atlantic. Depending on the windspeed at the time, that is a considerable persistence as a definable trail, let alone persistence as individual ice crystals.

    • If one is situate underneath a heavily used “flight corridor”, such as … from Chicago or Buffalo to Miami or Atlanta …… or from Boston or NYC to Dallas-Fort Worth or LA …. the bestest time to observe contrails is in the early morning hours EST, just before or just after Sunrise at your location.

      The air traffic in those “corridors” is extremely active “early of a morning” ….. and due to the angle of incident the “rising” Sunshine is easily reflected “off” the underside of said contrail and thus said contrails are readily viewable by an observer on the ground.

  2. Sometimes contrails do the darndest things that have nothing to do with weather or climate. Unless one considers that Climate Change is the Left’s new religion.

    Over Denver, November 29, 2014. Taken by me.

  3. The introduction to this piece begins with the statement ‘Clouds may have a net warming or cooling effect on climate’.
    I think the vagueness of this statement is at the core of the confusion over whether or not there is a positive or negative forcing as a result of the warming caused by additional CO2 in the atmosphere.
    Couldn’t WUWT, with its legions of mighty scientific intellects come to a definite conclusion on this…like once and for all?
    My opinion is clear. Clouds shade the land and the ocean, clouds are core participants in all forms of precipitation, clouds reflect incoming sunlight, clouds occur over the equatorial oceans at the genesis of Hadley Cells. No engineer could look at Clouds and conclude that they were anything other than ‘cooling’ agents…the only people who believe they have a net warming effect are doctrinaire Warmists…can’t we get over this mealy mouthed ‘may have a net warming effect’ nonsense?

    • I’m not a warmist. You have to consider clouds as a double sided mirror, the reflectivity will depend on optical thickness (think partially reflecting mirrors in optics). So at times they (the clouds) will create net warming and sometimes net cooling. I guess this study is about that.

      [Altitude of the cloud, type of cloud (ice crystals, vapor only, thickness) etc. .mod]

      • will create net warming

        Aaaauuuugghh!!!!
        That simple statement is the source of all the trouble. Clouds cannot create warming, it is physically impossible for clouds to produce net warming.
        What clouds do is to slow down cooling. An area which is cooling will cool to a lesser degree with clouds overhead. So we have a cloudy area (possibly at night) which is warmer than it would otherwise be. The clouds did not warm it, the clouds simply kept it from cooling more. But it still cooled some, the clouds did not warm it.
        Some people understand and say “clouds warming” as a sort of verbal shorthand, others do not know and come away with a total misunderstanding of what is happening.

        It might be wise to avoid the verbal shorthand to avoid conveying a wrong impression.

      • I do not know anyone participating is a serious scientific discussion that thinks that clouds are an energy source.
        If someone says they are wearing a warm jacket, or “This jacket makes me very warm”, there are about zero intelligent humans who think that means that the jacket is a heater.
        I think you scream in vain over a semantic snafu in your own head.
        Relax…have a cup of coffee.

        Just sayin’…and JMO.

      • TonyL and Menicholas
        At what point , idiots, did I say that clouds were a source of heat? NET WARMING. Means that the BALANCE of radiation coming in and radiation going out tends to hold the heat in.
        You are going to argue some point because I haven’t added details.
        I actually think that clouds are a temporary effect.
        Different clouds at different heights give different effects.
        Have I missed something significant? Or are you so wound up by the word ‘warm’ that you can’t think straight?

      • A double-sided mirror with the sun (about 5,800 K) on one side and the earth (about 15 K) on the other side. The net effect of clouds must be a lot of cooling due to reflected sun light. A cloudy day is much cooler than a sunny day and a cloudy night is only slightly warmer than a clear night.

      • A cloudy day is much cooler than a sunny day and a cloudy night is only slightly warmer than a clear night.

        in Maine in winter can be a very large difference between a clear and cloudy night with preceding day being the same patterns.
        clouds rolling in at night when daytime was lucky to have reached 10 deg F is a blessing.

      • Hey Alex, thanks for calling me an idiot. I was not talking to you, jackass.
        I was talking to the guy who screamed in the comment just above mine.
        You might want to develop some thicker skin, or at least try to look at the whole thread before deciding someone was contradicting you.

    • The paper is very interesting, in that it has, as its hypothesis, that contrails have no effect, based on prior results. This result is that the study disproves the hypotheses. On its own, not surprising on an intuitive level (the cloud-shade effect mentioned,) but by returning a statistically significant result, additional hypotheses can be built to quantify the effect in various contexts, and get to the specifics of when and how much these clouds increase albedo, or catch outgoing LW, or both.

    • “No engineer could look at Clouds and conclude that they were anything other than ‘cooling’ agents…”

      Therein lies your problem.
      You need to understand meteorology.
      Engineers don’t seem to on the whole.

      Question:
      Ever wonder why a cloudy night (in winter particularly) is warmer than a clear one?
      Hint: WV and H2O is a potent GHG.
      Ever wondered why sometimes (or perhaps even noticed) that a frost will melt once a clear spell is filled in with cloud.

      No?
      I’d suggest you open your eyes then.

      “….the only people who believe they have a net warming effect are doctrinaire Warmists…can’t we get over this mealy mouthed ‘may have a net warming effect’ nonsense?”

      No – as that MAY indeed be the case.

      • I see you only highlight the warming effect of clouds in the higher latitudes in winter as an example Toneb. I am a meteorologist and yes clouds keep winter time temps warmer than in clear skies in the mid to high latitudes. However, the reverse is true for summer where long sunlight hours would see solar input reflected back into space. Clouds also keep the equatorial tropics from overheating. Singapore (Lat 1 deg N) temperatures rarely vary outside 25-35 deg range. Also note how the hottest temp records in the world occur in the 20-35 deg latitude region. Why? Because this is the decent zone of the Hadley circulation where sinking air means clear skies and little cloud cover and lack of moisture in general. solar heating of the surface by day is largely unrestricted.

        I find it intriguing when I hear about how CO2 GHG warming will lead to a hot barren earth from some alarmists, yet in reality the opposite is the most likely outcome with larger areas seeing temps regulated by cloud and rainfall in the tropics and similarly colder areas towards the poles likely to see a more pleasant climate with a much more viable crop cultivation potential. I just don’t see where the catastrophic risk of warming a couple of deg C comes from.

      • Toneb, Overall clouds have a net cooling effect because the sun is very hot compared to the earth. A cloudy night can be warmer but only by a few degrees. A cloudy day is cooler by tens of degrees. The only way clouds could have a net warming effect is if clouds appeared mostly only at night so there would be little daytime shading. Obviously that is not the case.

      • Thanks Toneb.

        I think you’ve just proved my point about the power of doctrine over observation.
        You certainly illustrated your lack of comprehension ‘enthalpy’.
        Water Vapour is indeed the cardinal greenhouse gas…but water vapour also physically transports heat around the planet, clouds do indeed reduce cooling on a clear night…ever hear of dew?
        And that frost you noted melting…ever wondered what ‘frost’ is?
        No?
        I suggest you study some simple physics rather than repeating the mantras of post normal science.

    • I would have thought that the simplest estimate for summer in the mid latitudes should mean that increased clouds bring net cooling due to longer hours of sunlight being reflected back into space, but in winter the opposite is true. Increased cloud may lead to increased precip as well which would add to cooling in summer and reduce warming from increased cloud in winter.

      The tropics clearly regulate temps via cloud and precipation and stop very high max temps from occurring where the sun is more directly overhead and there is plenty of moisture.

      • I agree and would add that precipitation, especially in the form of snow at higher latitudes has the doubled effect of extending winter snow cover, and increasing albedo.

  4. You need specific atmosphere conditions in an area to have lasting contrails. You can evade these days by flying lower or higher in that area.

  5. You need specific atmosphere conditions in an area to have lasting contrails.

    Exactly. This is what so many fail to realise and start making stupid assertions about “abnormal” formations and the rest.

    Jet engines dump out enormous amounts of water vapour at elevated temperatures. This will initially condense under almost any atmospheric conditions. Then it will usually evaporate fairly quickly.

    Only when immediate humidity, temperature and pressure conditions are very close to cloud formation or already causing minimal cloud formation will this extra condensed water aerosol persist. Under these conditions it will either cause a persistent line of cloud in a clear sky or cause denser cloud in very light cloud conditions.

    • I have seen many a summer day ruined by the sky filling out with contrails that last all day reducing what could have been a warmer day. There is definitely by day a cooling effect from contrails in mid latitude summers.

    • Correct. But then why not demand all the elites stop flying jets? HAHAHA. Make them all use horse and buggy to get around.

  6. It seems beyond doubt that dumping both water vapour and condensation nuclei on a massive and increasing scale must have some effect on cloud coverage under certain conditions and thus on also when averaged over all conditions.

    since most commercial flights spend most time cruising in the lower stratosphere that is where the main effect will be. Stratospheric clouds tend to cause cooling , more flying causes cooling not global warming. Those flying should be claiming carbon credits for off-setting the effect of the “carbon” emmissions during the flight.

  7. “No engineer could look at Clouds and conclude that they were anything other than ‘cooling’ agents…”

    I see no reason to cast such generalities. What needs to be understood is that, in the context of climate change, “clouds” refers to changes in cloud cover no one cloud or the existence or not of cloud.

  8. Weren’t there noticeable effects after aircraft were grounded for 3 days, over the US, in the aftermath of 9/11? I was under the impression that some studies were done at that time. I didn’t see any mention in the article and it would seem to be relevant to this study, assuming the data exists.

    • Yes there was one study which did detect some warming due to lack of contrails but since no one knows what the weather would have been like anyway, it was inconclusive, though suggestive of an effect.

  9. My guess is that they produce a net cooling effect, but a small one, so nothing to worry about. I know where they’re going with this though. They are thinking geoengineering, which is a double-dumb idea, because it is completely unnecessary, so we’d be throwing money away, and environmentally dangerous, as are all their geoengineering fantasies.

  10. Contrails that grow larger rather than disappearing do this due to a rise in high atmospheric humidity. And yes, things like this do alter the climate to a degree and I would suggest it increases the effect of light rain which we call ‘drizzles’. I can’t prove this, I merely farmed for years and track the weather due to this.

    • This is a demonstrable effect. “Seeding” with emission nuclei can be observed around airports, and is frequently most noticeable during airshows when there is a lot of low altitude (3-10K ft) jet aerobatic displays. In my neck of the woods, a frequent Father’s Day (mid June) airshow would regularly produce cloud cover, and some years light rain late in the afternoon, when the jets started their routines. if the local humidity was high enough, common in June here.
      There is a “snow shadow” around Pearson airport in Toronto that regularly receives proportionally more snow during a snow event in the winter. This area is just slightly south and west of the airport (prevailing wind drift) and under the approach path of the most frequently (and heavily) used runways.
      Its pretty common in the summer especially, to watch jet contrails bloom in humid upper air to cover a significant proportion of the sky, as the day progresses.

  11. There has been a lot of work done to find out how these form, and what kind of climatic effect they have – which is estimated to be rather small.
    ===================
    that is unlikely to be true. the 911 attacks grounded all aircraft in the US for something like 3 days, and there was a statistically significant bump in temperatures over that time, as I recall from the literature on the subject.

    there is without a doubt a political interest in proving that jet contrails have no effect, which is no doubt driven be economic interests of various parties, so there are bound to be contradictory studies proving both points of view.

    However, contradictory studies only show that there is political and economic interests competing. Just because there is one study showing a positive effect, and another study showing a negative effect, you cannot conclude that the true effect is the average of the negative and positive effects. Unfortunately, this is the conclusion that people tend to form in their minds.

    The only reasonable conclusion is that the true effect may be positive or negative, and the effect may be large, but the size of the unknown also remains large.

  12. Contrails generally form close to the tropopause and this is the reason why they are mostly seen in mid-latitudes rather than the tropics or polar regions. Commercial jet aircraft routinely cruise at 35-40,000 ft which is where the tropopause is in mid-latitudes. In the tropics, the tropopause is normally well above 50,000ft and at the poles around 30,000 ft or lower.

    During my fast-jet flying career, the lowest I ever encountered contrail formation was 26,000ft during a particularly cold winter.

    • … the lowest I ever encountered contrail formation was 26,000ft during a particularly cold winter.

      Something like the same phenomenon happens at ground level. One of my friends moved to Saskatchewan and observed that, when a group of cars left a stop light, they would be enveloped in an instant fog bank.

      I would suppose that the difference is that contrails last a while whereas cartrails dissipate more quickly.

  13. Here’s a clear, unambiguous opinion.

    The overall effect of all clouds together is that the Earth’s surface is cooler than it would be if the atmosphere had no clouds. link

    One reason things are confusing is that two sets of wavelengths are involved. Downward radiation is in the visible spectrum. The upward radiation is long wave infrared. The two wavelengths react quite differently with clouds. Visible light tends to reflect with little heating of the clouds. Infrared tends to heat the clouds which then reradiate in all directions. Some of the infrared then returns to the planet and causes a bit of warming.

    Unsurprisingly, James Hansen doesn’t think vapor trails are a problem.

    “Aircraft are likely to be a significant factor in future climate, but probably not via their contrails,” Hansen told me. “I think our main concern about aircraft will be their CO2 emissions, not contrails, which are a pretty small climate forcing.” link

    There, that’s your morning chuckle.

  14. So some clouds have a warming effect and some other clouds have a cooling effect. The real issue seems to be what net effect clouds have.

  15. Hey Leonardo, you hear that? Your jet-setting from one alarmist global warming conference to another is helping to cool the planet. Please make sure everyone knows about this new finding, proving that your hundreds of thousands of miles of jet travel, far from constituting the hypocrisy that you have so often been charged with, is actually helping the cause that you so fervently believe in! (Then you idiots can stop hounding the rest of us for flying where we actually need to go.)

  16. Anthony, I hate to pick, but you are misusing “effluent,” as in: “Artificially formed clouds called contrails form due to aircraft effluent.”
    The most common use of “effluent” is to describe the discharge from a sewage factory. The more common word for discharge from a fuel combustion engine is “exhaust.”
    Words matter, and unless we skeptics are precise, the Alarmists will tear us apart with glee. (Well, they do anyhow, but we shouldn’t give them ammunition to use on us.)
    Just my $0.02 (or less).

  17. Last week, on my drive to work, (it was very humid after the tropical storm passed) I saw a very unusual sight…the vapor from the evaporative cooler of the Fort Myers water treatment plant made a plume of steam that went up and created a thunderstorm.
    i have a video i shot, if anyone who knows how I can post a short video from my phone on here. It is very interesting…you can see the plume going up and become a cloud with a top to about 15,000′ or maybe 20,000′. I did not stick around to see when it started to rain out from it…it looked like a funnel cloud from a distance.

    • In other words, all it took was a tiny bit of extra moisture from a cooling tower, and a small one at that, to make a cloud that ascended right up a few miles.

  18. What do we want to breathe in an Atmosphere without CO2 and O2?

    How will the plants survive without getting CO2 from air?
    How will humans and animals survive without plants as food and Oxygen (O2) to breathe?

    #Geoengineering: #FAQ about #CO2!
    http://geoarchitektur.blogspot.com/2016/06/questions-and-answers-about-co2.html
    http://geoarchitektur.blogspot.com/2016/06/chemtrail-desublimation-trail.html
    http://geoarchitektur.blogspot.com/2016/04/sublimation-desublimation.html
    #SRM #HAARP #water

    Please learn about #Desublimation #Condensation!

    Desublimation is the KEY to understand Solar Radiation Management (SRM) and what Chemtrails basically mean!

    http://geoarchitektur.blogspot.com/2016/06/chemtrail-desublimation-trail.html
    http://geoarchitektur.blogspot.com/2016/04/sublimation-desublimation.html
    http://geoarchitektur.blogspot.com/2016/04/wolkenkunde-nephology.html

Comments are closed.