Do jet contrails impact weather at the ground?
5$\begingroup$ This seems like two separate questions - a fact-based assessment of whether the weather on the ground changes with the presence of contrails; and a question about whether a specific conspiracy theory is true or not that would be better suited for Skeptics (which they have already addressed). $\endgroup$– Greg HewgillJun 24, 2015 at 20:36
9$\begingroup$ The TL;DR is "Yes, but in a way that's useless to conspiracy theorists -- they're cirrocumulus clouds by another name" $\endgroup$– UnrecognizedFallingObjectJun 24, 2015 at 22:20
$\begingroup$ A treasure trove for you: Climatology and Aviation (Joint Session between the 10th Conference on Aviation, Range, and Aerospace Meteorology and the 13th Conference on Applied Climatology) $\endgroup$– user2896Jun 26, 2015 at 1:08
2$\begingroup$ During the 9-11 groundings, the skies over the US were reported to be unusually clear. As flights resumed, sky conditions returned to their previous patterns. The conclusion drawn from these observations was that contrails have a tendency to increase cloud cover via a sort of "seeding" effect. $\endgroup$– Anthony XJul 4, 2015 at 4:46
Based on past observations and a study led by Patrick Minnis from NASA, contrails could result in increasing the temperature over the ground by 1°C every 30 years over the US.
From a study by German researchers Ulrike Burkhardt and Bernd Kärcher, the effect of contrails is comparable in other areas with a similar level of air traffic.
Because the air traffic is said to be about to increase very quickly, the effects of contrails on the temperature may increase too.
Contrails and natural cirrus: So similar that studies are difficult
Contrails are like cirrus, and actually some just become persistent cirrus. Sometime it's difficult to tell which one is a condensation trail, which one is a natural cloud. This makes more difficult the study of contrails effects, and introduces many uncertainties that need to be reduced:
The current studies take into account only the young contrail-cirrus, because they are still relatively easy to differentiate from natural cirrus, due to their linear shape. Most aged contrail-cirrus are not differentiable and are not counted as aircraft generated. This means the current results potentially under-estimate the effects of contrails.
Pertaining to the discussion, contrail-cirrus as clouds:
- Induce a cloud-feedback, i.e. the coupling between cloudiness and surface air temperature.
- Induce a radiative forcing, they increase the portion of the energy not re-emitted to space. The quantity is expressed in mW/m².
Increasing the air temperature has a link with increasing ground or oceans temperature, but the two notions mustn't be mixed. However cirrus are suspected to play a role in the global warming, because they could introduce a positive feedback into this warming.
Study: Coverage and effects of contrail-cirrus
Global radiative forcing from contrail cirrus published in Nature in 2011 was a study to evaluate the contrail-cirrus coverage, and its impact. Conclusion:
Aviation makes a significant contribution to anthropogenic climate forcing. The impacts arise from [...] and from changes in cloudiness in the upper troposphere. An important but poorly understood component of this forcing is caused by ‘contrail cirrus’—a type of cloud that consist of young line-shaped contrails and the older irregularly shaped contrails that arise from them.
The estimated effect is depicted on this map (mW/m²) from the study:
Net effect of contrails (CIC) warming compared to other aviation factors of warming:
Study: Effect of contrail-cirrus on US climate
NASA conducted a study in 2004: Patrick Minnis, J. Kirk Ayers, Rabindra Palikonda, and Dung Phan -- Contrails, Cirrus Trends, and Climate.
This study was analyzed in Science Daily: Clouds caused by aircraft exhaust may warm the US climate:
Using published results from NASA's Goddard Institute for Space Studies (New York) general circulation model, Minnis and his colleagues estimated contrails and their resulting cirrus clouds would increase surface and lower atmospheric temperatures by 0.36 to 0.54 degrees Fahrenheit per decade.
Aviation radiative forcing in 2000: An update on IPCC (1999)
This study was included in a new one by R. Sausen et al. in 2005. It shown the radiative forcing by aircraft could have been slightly underestimated:
Source: Aviation radiative forcing in 2000: An update on IPCC (1999) - R. Sausen
The US surface temperature is increasing by 1°C every 30 years: I would say this is very significant for plants, life, water cycle, oceanic currents, etc.
Also look at @Simon good answer about the increase of the difference between night and day temperatures, by more than 1°C, during the 3 days civil air traffic was forbidden on September 2001. This increase seems to confirm contrail-cirrus limit cooling on night time.
3$\begingroup$ Hmm... That estimation seems a little dubious, since total global warming from the mid 1800s to the present is estimated at around 0.6 degrees C, IIRC. 1C per 30 years would definitely be very significant, but it also seems very dubious (unless maybe they're talking about increasing average temperatures in a few particular places by that much, rather than global average temperatures.) $\endgroup$– reirabJun 25, 2015 at 5:30
2$\begingroup$ @reirab Note that the total temperature of the system doesn't change - the only effect is that heat from the atmosphere moves closer to the surface, effectively. It makes the surface temperatures higher, but the higher altitude temperatures lower. $\endgroup$– LuaanJun 25, 2015 at 8:25
1$\begingroup$ @Luaan The total temperature does change since it is not a closed system. If it were closed, I would agree but the Earth receives and loses an enormous amount of energy each day. Change either of those (reflectivity or total albedo for incoming, temperature gradient and absorption for outgoing) and the total energy in the system changes (if "Earth" is the system you are talking about). $\endgroup$– SimonJun 25, 2015 at 11:36
1$\begingroup$ @Simon Yes, but that's not the kind of system the report is talking about - they did not monitor the global change (if any), just the local impact. We're really talking about the specific study mentioned in the answer (the 2004 one), not Earth's temperature balance as a whole. The absorption of IR in water doesn't differ between regular atmospheric humidity and outright clouds - the only thing that changes is the albedo, and that should be higher for the cloud-scenario. So it's colder up, hotter down. But maybe I'm just reading that wrong. $\endgroup$– LuaanJun 25, 2015 at 11:43
$\begingroup$ You should change the first paragraph to mention lowering atmospheric temperature as well. As is, it implies that contrails generally contribute to global warming but actually if you look at the numbers it actually counters global warming (it contributes to global cooling). The rest of the answer is excellent though $\endgroup$ Jun 8, 2016 at 6:26
In the days immediately following the Twin Towers 911 attacks when there was no air traffic, a study found that the difference between night and day temperatures was greater and that day time temperatures were around a degree higher.
The idea about conspiracies to modify weather and chemtrails is well and truly shown to be complete nonsense - just Google for it.
3$\begingroup$ So, there was a statistical evaluation of some temperature difference, and the statistics used "the days immediately following the Twin Towers 911 attacks", that is, at most 3 samples. Ok, I do not even need to know what the values were compared to. That's not even valid nonsense! $\endgroup$ Jun 25, 2015 at 4:18
8$\begingroup$ While the 'results' of the study seem expected (there are far less contrails in the CONUS at night than in the day, so the daytime shading effect almost certainly outweighs the nighttime reduction in radiative cooling,) I must agree with Volker that 3 days is hardly statistically significant when studying weather. Literally a single low pressure system would be sufficient to make far more difference than what this study found. In the portion of the CONUS East of the Rockies (i.e. most of it,) it's not unusual for temperatures to vary by 20 C from one day to the next. $\endgroup$– reirabJun 25, 2015 at 5:39
2$\begingroup$ @reirab - No, the sample size is not satisafactory, but in modern times that's likely all you'll ever get; the FAA isn't going to ban all air traffic for a month to run a more controlled longer-term study. Anything that would keep the entire commercial U.S. fleet grounded for longer than a few days is likely going to skew the results in its own way (for instance, a massive eruption or an asteroid impact blanketing the skies in dust or ash) $\endgroup$– KeithSJun 25, 2015 at 16:22
2$\begingroup$ @VolkerSiegel: The study did not only measure temperature of those three days (nation-wide) with those of the days before (nation-wide). That would indeed be pretty useless. It also measured the relative differences in areas where there's usually a lot of air traffic (just not in those three days), and those where there isn't (all year long). But saying "I don't even need to read it to know it's nonsense" is, of course, your choice to make. $\endgroup$– DevSolarJun 26, 2015 at 9:49
Penn State researchers, led by Andrew M. Carleton, professor of geography, found that jet contrails can affect ground temperatures. (Source)
Bernhardt and Carleton looked at temperature observations made at weather station sites in two areas of the U.S., one in the South in January and the other in the Midwest in April. They paired daily temperature data at each contrail site with a non-contrail site that broadly matched in land use-land cover, soil moisture and air mass conditions. The contrail data, derived from satellite imagery, were of persisting contrail outbreaks. The researchers reported their results in a recent issue of the International Journal of Climatology.
They found that contrails depress the difference between daytime and nighttime temperatures, typically decreasing the maximum temperature and raising the minimum temperature. In this respect, the contrail clouds mimic the effect of ordinary clouds.
The researchers report that the "diurnal temperature range was statistically significantly reduced at outbreak stations versus non-outbreak stations." In the South, this amounted to about a 6 degree Fahrenheit reduction in daily temperature range, while in the Midwest, there was about a 5 degree Fahrenheit reduction. Temperatures the days before and after the outbreaks did not show this effect, indicating that the lower temperatures were due to the contrail outbreaks.
"Weather forecasting of daytime highs and lows do not include contrails," said Carleton. "If they were included in areas of contrail outbreaks, they would improve the temperature forecasts."
The National Science Foundation supported this work.
9$\begingroup$ "the contrail clouds mimic the effect of ordinary clouds" – They are clouds, aren't they? $\endgroup$ Jun 24, 2015 at 20:34
4$\begingroup$ yup, but they have a funny shape. $\endgroup$– hildredJun 25, 2015 at 4:04
$\begingroup$ @JörgWMittag: Haha, nice comment. $\endgroup$ Jun 25, 2015 at 7:29
$\begingroup$ @JörgWMittag They are clouds but not "ordinary" clouds. $\endgroup$ Jun 25, 2015 at 10:45
$\begingroup$ @DavidRicherby: (was looking over my older comments when I saw your reply, sorry for the necropost...) My impression was he didn't mean that seriously, rather it was a joke about chemtrails vs. contrails. Looking at it now though I'm not sure if I was right or wrong. $\endgroup$ Jan 11, 2017 at 6:40
Yes, contrails affect the weather. The vapour particles are nucleii for condensation of more water. In WW2 the huge bomber fleets leaving Britain caused rain. The effect of clouds on global warming is still not understood. They reflect the Sun's rays, but they also insulate the ground.
$\begingroup$ I was thinking of the same thing. Here's an article on the topic, with reference to WW2: scientificamerican.com/article/… $\endgroup$– sdenhamJun 25, 2015 at 22:57
They can very slightly affect surface temperatures, just as a similar amount of normal cloud cover would. However, this effect is slight and is not weather modification in the sense that conspiracy theorists claim regarding supposed 'chemtrails.' And, certainly, there is nothing clandestine about contrails. No one attempts to hide them (or, if they are, they're doing a very bad job of it, since it's public knowledge and they're quite easy to see.)
So, to answer your questions, yes, they can have very slight affects on the weather (specifically, surface temperature, usually near major airports or air traffic routes,) but, no they have nothing whatsoever to do with any sort of government conspiracy.
Not in a real sense. yes they do put water vapor in the air. so does drying your clothes in the dryer. or taking a shower. or driving your car. while it makes a visible cloud the amount of water is much less than cars traveling the same distance due to the fuel efficiency of flight vs. driving.
1$\begingroup$ There is one critical point missed in this reasoning: The contrails iced clouds are higher than the water vapor from the dryer. When high the condensation has an effect on the net exchange between Earth and space, known as radiative forcing. $\endgroup$– minsJun 25, 2015 at 12:54
$\begingroup$ the atmosphere is between the earth and space. the water vapor is in the atmosphere . what exactly am I missing here? Radiative Forcing, sounds more like a football penalty than a scientific term. it would be more like 'holding' or a 'face mask' penalty that 'forcing'. who comes up with this dribble? $\endgroup$ Jun 25, 2015 at 13:50
4$\begingroup$ Just click the links provided, they will tell you more than I could. $\endgroup$– minsJun 25, 2015 at 14:02