Contrails over Europe
 

Hi, I found a tweet indicating a trial under way @ Maastricht. Wonder how that develops - less contrails ? Might be good for the environment.

Umm, I always thought contrails were almost entirely water. If that is so, I would have thought the only impact they would have on the environment would be to very, very slightly increase the reflectivity of the upper atmosphere, which would be benign in an epoch of warming. What have I missed?

Yes, water vapour is, in itself, a greenhouse gas and whilst the condensate slightly attenuates irradiation of the earth from the shorter wavelength solar radiation it also reflects back downwards the longer wavelength earth radiation somewhat more efficiently.

Here you go for starters, I'm sure shorter reads are available:

https://agupubs.onlinelibrary.wiley....9/2018GL080899


Buried in the text:

AFAIK the effect of contrails - which can persist for some time in the right conditions - is to increase the high cloud cover somewhat, increasing reflectivity as mentioned above. It doesn't make any difference to the actual greenhouse effect because cruising aircraft emit water vapour into the upper atmosphere whether or not the conditions are right for contrails.

Thank you to the posters who have explained that to me. I see that the Wikipedia article cites a predominance of studies that suggest the greenhouse effects outweigh the increase of reflection.

The trial is mentioned in the German FIR NOTAMS

In the aftermath of 9/11 all flights over the US were banned for 2 days (or longer?). I remember that meteorologists reported that during this time the temperature amplitude in the US was slightly higher, meaning that at night more excess energy was able to radiate out into space instead of bouncing back from those water molecules. Now, was it the reduction in water molecules or the reduction in contrails that caused this?

Reducing contrails over the Netherlands was always a demand from the political green party in the country, They even had a plan years ago that wanted to restrict altitudes below the condensation layer, forcing on some days everybody below 30.000ft . That was years ago in their program , maybe as new elections are coming up in NL the idea resurfaces. Public is generally for as contrails can block the sun on certain days and everyone can see it.

So to prevent contrails, which have a slight (possible) effect on cllimate change, we burn more fuel when diverting from our most efficient route?

Unless of course if this means more directs, I am all for it, but that then poses the question why directs are possible now and not before?

Fine margins already for optimising fuel and therefore emissions.

Trading off visible contrails for additional emissions makes little sense imo

This gives an idea of the margins involved

On many occasions (pre-Covid) I have seen, driving eastwards in the early morning along the M4, that the contrails 0ver SE England had spread until they were covering, very, very thinly, at least 50% of what would otherwise have been a cloudless sky.

Hi, found a movie about the trial on the Eurocontrol Youtube channel . Fun to watch.

If water droplets in the atmosphere are so harmful, maybe we should consider measures to reduce cloud cover. Perhaps the greens think clouds are OK because they are not created by aircraft.

I seriously doubt that a two day window for data gathering on weather changes has any significance.

Contrails are not 'water droplets'. At -50C or so they very, very, very rapidly become ice particles.

Water droplet clouds, lower and medium levels, are the cause of overwhelmingly the most of the 'greenhouse effect' (CO2, methane, etc. are tiny by comparison).

Ice particle clouds, cirrus, reflect more solar radiation away from the earth than any tiny, tiny (from that high altitude) 'greenhouse effect' that they can have.

Therefore, because contrails are effectively cirrus clouds (and you can often see how they linger to form clear cirrus clouds), they have an overall cooling effect on the earth.

The temperature rise over North America (tiny, but still there) was due to the grounding of all airliners and the lack of contrails.

This last year there was an increase in melting of ice in Greenland because of increased sunshine. Guess what?! There were very, very few airliners on those northerly trans-Atlantic routes that cross Greenland last summer, meaning a loss of all of those cirrus clouds (contrails) and hence more sunshine and more ice melting.

Conclusion? If you are worried about global temperature rises and ice melt, we need more airliners flying!!

NoelEvans

But they trap heat radiating from the earth's surface at night, and their net effect on radiative forcing is positive
Estimates vary on the extent of it, just google for contrails and radiative forcing

Now wait a minute, doesn't the Virus and vaccination expert Bill Gates propose launching billions and billions and billions of tiny mirrors into space to reflect the sunlight back into space to reduce global warming? Seems to me that would have the same effect as contrails, but now contrails are a bad thing???
Is it any wonder people are sceptical about this global warming malarky, the story keeps changing.

The story never really changed.

Clouds and contrails do block the sun, reducing the temperature. However they also act as a blanket, trapping heat from escaping into space and therefore increasing the temperature.The net effect is still an increase in temperature. This in turn causes an increase in evaporation of surface water, further increasing cloudcover.

meleagertoo

Yes, but no. The greenhouse effect is a very long established explanation for why the earth is warmer than it would otherwise be. First proposed by Fourier (who has a few big discoveries to his name) in 1824, confirmed in the middle of the 19th century. Water vapour is the major gas responsible. Wikipedia on Greenhouse Effect

What all responsible people are worried about is that the large scale emission of other greenhouse gases since global industrialisation is increasing the degree of greenhouse warming, and that there are probably going to be positive feedback effects, so that the climate will change at an unprecedentedly rapid rate. This will not cause the earth to be uninhabitable by human beings, but will disrupt patterns of settlement and agriculture on a large enough scale to cause great disruption, huge movements of human beings, probably wars, and certainly great economic costs. Given the difficulty industrialised societies have with current movements of refugees from war and poverty, most people think it would be a good idea to minimise the degree of change, quite apart from any ethical considerations.

I am 76 and have no kids, so for myself, I don't give a monkey's. The contrail effect is probably small, but the way to determine whether it is worth doing anything about is by careful measurement of the effects, and the consequences of mitigation. There is obviously a need to balance efforts to limit change, and efforts to adjust to it. Since aviation is dependent on hydrocarbons, the first response must be adjustment requires such small gains as are possible, and arguing for the reduction of the use of fossil fuels wherever they are not essential; the second stage, limiting change, probably involves working on synthetic fuels which might be climate neutral.

This is no more a hoax than Covid-19. The way to consider it is by calm consideration of the best available knowledge (which may be incorrect, but which can be corrected) and by an acknowledgement of reality, not by echoing talking points put out by the owners of coal mines, or sounding like that contrarian with a loud voice who makes you find another pub.