Do jet contrails impact weather at the ground?
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.
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.
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.
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.
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.