Could Aviation be part of the climate change solution?
 

Dunno,
I’m too busy making sure the chemtrails are deploying properly

No.
Water vapour is itself a potent greenhouse gas.

https://www.ncdc.noaa.gov/monitoring...-gases.php#h2o

To amplify from (google "increasing cloud cover in upper athmosphere effect on global warming" and look for the "Clouds and Global Warming - NASA Earth Observatory" entry, sorry cannot post links).

Using hydrogen instead of hydrocarbons would certainly eliminate the CO2 production but burning the fuel mostly used today, JET A-1, already produces about 1.4 tonnes of water vapour per tonne of fuel burned. Atmospheric O2 contributes the additional mass. The process also creates over 3 tonnes of CO2. Variations in existing atmospheric water vapour content determine whether contrails form and indeed whether they persist. Interestingly if the right conditions exist for contrails to persist, vast amounts of additional atmospheric water vapour will condense and freeze on the ice crystals that make up contrails. Some measurements have determined that 1 tonne of burnt jet fuel can lead to 200 tonnes of contrail forming.
I'm still researching this next statement but...my understanding of contrail formation is that the formation process is dependent on the presence of particles of soot in the exhaust plume that act as condensation nuclei. No hydrocarbons, no soot, no contrail.

Nope - they ( engines ) may help or hinder certain contrails , but contrails form from other areas of the airplane- dependent on local conditions. Wingtips re a prime area along with some protrubances which change ' local ' air pressure ( slipstream) . They can be ' stopped' by certain chemicals introduced in the slipstream or also by changing altitude and speed.

The data is very limited and largely circumstantial, however there is some evidence that - in the immediate aftermath of 9/11 - the grounding of virtually all commercial air traffic over the continental US resulted in slightly lower temperatures. Some researchers suspect the reduction in water vapor being injected into the upper atmosphere by all those grounded aircraft was responsible.
That the average ground temperatures dropped slightly is pretty much certain, cause and effect is rather more questionable (particularly with a single data point).

Besides, "practical" and H2 powered aircraft don't belong in the same sentence given current technology. There is simply no practical way to contain the volume of hydrogen necessary for long range flight - the density of even liquid H2 is far less than Jet A - and keeping a large volume of cryogenic fuel on a commercial aircraft wouldn't leave much room for passengers and cargo (you're not going to be putting it in the wing).

Some decades ago I read an article that seemed technically respectable (can't remember where, possibly Scientific American) which said that liquid hydrogen fueled aircraft would start to become economical around 1.4 million pounds. There was a tradeoff between fuel weight savings and fuel tank weight and bulk/drag (cylinder on top of fuselage). Lower fuel consumption per unit of payload might compensate for the greater greenhouse effect of water vapour and clouds (I'm not up to the data and math). However if the A380 is too big then immediate prospects for hydrogen fueled aircraft don't look good. In any case it would only be feasible for very high-traffic routes.

Grebe:
The type of condensation you describe is not generally called a contrail in my experience. When it formed in the reduced pressure areas around the lifting surfaces of a manouevring fighter we used to call it "ecto"-plasm but that was just a colloquillalism.
In any case my research leads me to believe that the ice crystal contrails to which the OP refers require a condensation nucleus to form.

Sort of splitting hairs- suggest you do a bit of research on contrail issues and stealth bombers eg B2- some claims/articles are phony, and some are ' probably' correct, and whether from wings and major pressure- temp changes at low alt re fighter or at high alt, the physical requirements are essentially the same- rapidly expanding air causes a temp drop- and the local humidity does the rest. IF one can make the necessary measurements in the right areas, then one knows at what altitudes and speeds contrails can be expected or practically nil.
granted, most " contrails " are from engines ( jet or prop ) and the easiest way to avoid is to change altitude and speed. Airliners dont care, but military does. And then if one wants to get real picky, other than the ' straight line ' - how does one determine the real diff between clouds a˜d contrails say with a physical measurement of a cloud and ditto for a contrail ? The net effect is the same.

And then there is your breath in cold weather or walk in freezer or on a cold mountaintop ..

At the risk of this becoming a thread-distracting pi55ing match, more research has confirmed that "exhaust" contrails are the predominant (I would like to say "only" but I honestly haven't read every peer-reviewed scholarly article on the subject) type of ice crystal based contrail and as such are the only persistent form of contrail. I have learned that the other type (for me "ecto") is an "aerodynamic" contrail and requires that the atmosphere be above freezing and reasonably close to saturation. As no energy is removed from the air parcel on aircraft passage the temperature will rise again above the saturation point and the localised condensation will evaporate hence be non-persistent.
I can say with relative certainty that I never saw an "aerodynamic" contrail form above the freezing level but I sure as hell formed a few "exhaust" ones when I didn't pay proper attention to the met man's morning brief.
But hey, contrails can be useful.
A 4 ship of Eaglejets in wide combat4 coming beak to beak at 50,000ft M1.5 and conning, accompanied by Eagle lead's gravelly voice on the back radio saying "Gentlemen, the Claw!!!" focusses your survival instincts sharpish!!!

As anyone who lives in northern latitudes can attest, it is significantly colder on clear days/nights, than cloudy.

Unfortunately, I spent quite a bit of time in Norfolk, VA, which has a lot of air traffic over it. It was easy to see how all of the "chemtrails" :oh: come together on many, many days and by early afternoon, it was all hazed over...I was not enthused about this observation.


https://cimg6.ibsrv.net/gimg/pprune....ae853e0e44.jpg


Stuff like this is common

Problem is too many people in the greenhouse

(and yes, Africa & India, I'm looking at you)

Mac

Yes.

So sod off all you third world people; there isn't enough room in the greenhouse for you to burn coal, drive cars, and fly places, we got here first?

Water vapour as a greenhouse gas
 

Yes, water vapour is the most powerful greenhouse gas in one sense. John Tyndall discovered the basics in the 1850s. The Wikipedia article "greenhouse gas" says that water supplies 36-72% of the warming effect, varying with location. CO2 is number 2. However. the average water molecule stays in the atmosphere for 9 days, while the residence time for CO2 molecules is thought to vary from 30 to 95 years. Evaporation of water varies with temperature. Therefor we call CO2 the "driver." Water vapour content of the atmosphere follows the CO2 content.

Regarding "we wouldn't be here without them"; yes, Joseph Fourier brought to notice in 1824 the fact that the Earth is considerably warmer than the physics of his time could explain, and proposed as one possible explanation that some property of the atmosphere caused it to retain heat. "The dose makes the poison." Recently the Earth's temperature has been like Goldilocks' third bowl of porridge, just right. We don't want it hotter, especially as the Sun's radiation has slowly increased over its lifetime, and the disposition of the continents right now is helpful for cooling.

Not sure about contrails but;

https://cimg5.ibsrv.net/gimg/pprune....a03e7effe0.jpg

See NASA page; https://earthobservatory.nasa.gov/im...-in-the-clouds

Source; https://earthobservatory.nasa.gov/fe...sols/page1.php

Interesting stuff td. Perhaps worthy of more research by scientists.

Aircraft and engine manufacturers have come a long way in reducing emissions but the capability to keep doing this without some radical new technology that is both practical and economically viable, means any future reductions are likely to incrementally much smaller than has currently been the case. But despite all that has been done to reduce engine emissions the contribution to greenhouse gases from aviation continues to climb as a result of increasing demand for air travel. Calls by the environmentalists to effectively ban air travel or heavily tax it are just not the answer. You cant un-invent the wheel (or in the case the wing!). Asking business and liesure sectors to limit their travel is more sensible and more doable. However voluntary buy-in is hard and limited. So, if scientists could actually prove a connection between the 9/11 grounding event and reduced temperatures, and could quantify what that would actually mean to temperatures across the big emitters of China, the USA and Europe, then aviation could in fact be part of the climate change solution. How? By mandating flightless days!

Imagine no fly days across the world on for example Wednesday and Sundays. In big hairy audacious numbers that's about a 30 percent reduction in greenhouse gasses caused by aviation activity. This doesn't require new technology, alternative fuels, onerous carbon taxes, elimination of incentives to fly such as air points programmes or complete bans on flying. It would of course have an impact on world economies and certainly airline economies. But that would be in the form of a one off adjustment, albeit a bit painful in places. Yes, all the Wednesday and Sunday travelers would book on the other days and initially create chaos but adjustments would eventually be made. That thrice weekly meeting that required air travel would eventual settle down to Monday and Friday meetings with a video conference on Wednesdays. The world and it's economies would slow but not stop because they would simply adapt to the longer leads times. That Fedex carton is going to be six days away, not four!

Asking business and holiday makers to reduce their travel is not new. But realistically, relying on voluntary personal choices and social pressure just doesn't seem to do it. So this cannot be voluntary and it cannot be done unilaterally since that would give immediate economic advantage to non-participants. It must be a UN agreed solution and then implemented by ICAO and its treaties. It's either everyone, or no one.

So, huge political hurdles and many practical issues to overcome if this was to work but, we are either serious about human activity causing undesirable climate change .. or we're not.

Other than offering a cloudless night which is always a little cooler, I'm not sure how the 9/11 event would achieve measurable cooling in 1 day across the US when aviation is only contributing about 4 percent of carbon emissions globally. But whether this is true or not, and in answer to the question that the title of this thread raises, mandated flightless days would almost instantly create and achieve significant contributions to the reduction of aviation induced greenhouse gases.There is nothing else radical enough to do it.

But if the question is, what cost to our economies would such a radical action be, then the answer may be in a corollary question. What is the cost to the planet if we don't take such action?

I am a better reader than a contributor but I have to say something!
Its happening; have been for millions of years and a few thousand liters of Jet A1 is not going to change evolution.
Just another cash cow to milk!

See this: https://www.britannica.com/science/g...ere-and-oceans

A turning propeller blade in only there intermittently but a wall stays in place permanently therefore ......

The thing with water (the hydrologic cycle) is that it is continually being replaced at a huge rate. The hydrologic cycle is very powerful so for example in extremes a Cat 3 type hurricane in a day dissipates as much energy as 200 times the daily world electricity generation capacity . Another way of seeing it is that a hurricane releases more than a megaton yield nuclear weapon every 10 seconds imagine the amount of energy from a frontal system across the entire US. All this is convective energy is based on latent heat release by water molecules and becomes radiant energy and leaves to space. The atmosphere contains very little energy compared to the oceans with the top 6 meters or so of the oceans having a heat content that is more than the entire atmosphere. It is the continual evaporation that maintains the humidity of the atmosphere and cools the surface of the oceans as does transpiration from plants. There is a hypothesis that as the atmospheric and ocean temperatures rise this causes more convective clouds and the clouds are not only evidence of evaporative/convective cooling but also raise the albedo reflecting solar radiation back to space. (Sometimes called the Iris Hypothesis)
It does appear that there is more correlation between atmospheric temperatures and the solar activity - we will find that out in the next decade or so as even NASA is expecting some cooling from the quiet sun

There are two things to be concerned about with graphs watch what is being done with the Y axis normally this exhibits a degree (cough) of precision in temperature measurement that would not be achieved by the accuracy of a met observer in howling sleet reading a temperature from a thermometer in a Stevenson Screen. The comparisons with 'global temperatures' from the past when in the Southern hemisphere a hundred years ago there were very very few observations - are extremely shaky as the much of the temperatures are based on guesswork but then expressed with a precision of hundredths of a degree (ever seen error bars on those graphs? No nor have I),

The other issue is correlation and causation all that can really be said is that if there is NO correlation between one value and another then there probably isn't causation. But two values closely correlating over a period definitely does not mean there is causation - see https://www.tylervigen.com/spurious-correlations

We are currently at the cold end of the Holocene - there is nothing special about the temperatures or their variance. So I wouldn't sell your coats. Definitely I wouldn't limit aviation as it is the most efficient transport in terms of miles per gallon per paying passenger. Work it out you'll find in those terms an A320 (and most other aircraft) has better consumption than a Prius and doesn't need road infrastructure between departure and destination.

Globally aviation contributes about 6% of the total man-made carbon emissions. Or so we are told.
You could stop every aircraft in the world flying tomorrow and it would not make a blind bit of difference.

Why there is this obsession with reducing air travel I just do not understand.

Fine, if man made global climate change is a thing, then target those that contribute the most to it, not the family going on a jolly to Spain for a week or two.

In fairness, the aviation contribution to high altitude carbon and H2O emissions is a lot more than 6%. There just are not that many fires at Everest altitudes.
That said, the current models have a hard time coping with clouds and the daytime/nighttime impacts, so it is unlikely that they can model high versus low altitude emissions.
We are doing an experiment on the only environment we have. Hopefully the results will be benign.

interesting re carbon emissions by jets. years ago, most jets left a trail of black ( carbon ) smoke. but for a variety of ' non scientific ' reasons re carbon emissions, the carbon smoke disappeared. One reason was efficiency, one reason was military - smoke trail make a good pointer as to where you are. one reason was the ' appearance ' of evil carbon.

OK- but to eliminate the carbon smoke trail, absent some real expensive methods- and generally impractical for airplanes - the easiest way was relatively simple - raise the combustion temperature. ( simplified explanation ). OK but when you do that, you create more Nitrous oxide ( disassociation of the 72 percent N2 in the air ). Nitrous oxide and related combustion products mixed with moisture- becomes ..."acid " rain . And in the extreme ( industrial ) process, can be made into Nitric Acid.


carbon is essential for life, nitrous ..... is NOT

Well, actually it would. By your own statement it would reduce human made carbon emissions globally by 6%...overnight!!

Shipping contributes some 2.5 % to global carbon emissions. Compared to air travel, that's a drop in the ocean really (see what I did there?). Even so, calls are being made to reduce cruise ship travel. So its not just air travel. .

Things are getting more complicated:


I have been guilty of both being a frequent flyer and using airmiles so I am not in a position to criticise however, the potential impact on prices and passengers makes for an interesting discussion.

Behind a paywall but: Axing Air Miles

IG

This encapsulates is so much of my objection to the current state climate science. The rules of evaluating and presenting data in a manner that accounts for precision do not apply.

This NASA GISS graph is what is normally shown in all the 'climate emergency' media reports note that the display is in 10ths of a degree centigrade for a 'global mean estimates on land and ocean data'. In 1880 there would be less than 100 observer thermometers in the entire Southern Hemisphere most of those in Australia. Some sea temperatures would be being taken by a disinterested boat crew using a canvas bucket dunked into the sea and a handheld thermometer. Even in the Northern Hemisphere before the 1940's it is unlikely that there was any precision in meteorological observations. It is only relatively recently that rules were applied internationally for rounding up or down to the nearest degree. Yet this inaccurate data is averaged (The 'average' is built from a daily 'average' which is actually the mean of the highest and lowest temperature. So if the lower temperatures have not been as low - this will be claimed as warming.) Comparing observations at hourly intervals by a bored meteorological observer to the recent automated observation systems that record transients of a few seconds is a statistical nonsense due to change in sampling rates. (The Heathrow automated observation system just North of the Northern runway at the express exit where it sits in jetwash much of the time. ) The error bars on the Y axis below would probably be +/- a degree - or outside the graph. Note that this is an 'anomaly' metric so is based on how much warmer than the standard temperature of the Earth the temperature is - and that is a whole different argument.
https://cimg8.ibsrv.net/gimg/pprune....13d9dfb1ca.jpg
You will see why those who want to report a crisis prefer to stretch the Y axis and show unreal precision reporting a very inaccurate input especially values reported before 1940. As said much of the southern hemisphere is 'estimated'. [or to be blunt " In [url=https://realclimatescience.com/2015/12/southern-hemisphere-temperature-fraud/]Climategate E-Mails, Phil Jones admitted that much of his southern hemisphere temperatures were made up, because there is no actual data. "]

So should we panic? Well below are the global average land/ocean temperature series shown by a line of red-alcohol thermometers.

https://cimg2.ibsrv.net/gimg/pprune....c67860c9ea.jpg

There's a lot more such as disregard of atmospheric enthalpy, but you are probably bored already.

Lots of interesting posts here.

My understanding of the 911 business is – current consensus – that contrails and often-ensuing stratus (same with ship exhaust) do more to prevent heat radiating outwards than they shade the Earth's surface.

Yes, let's face it: overpopulation is the Big Daddy of our problems every which way. We're choking the whole works. But lay off Africa, hitherto relatively lightly populated. India yes, scary, and when combined with China will, in a few years, amount to Three Billion people, far higher than total world population the day I was born – and I'm 64. Those two Industrial Giants ain't stoppin' for nuthin'.

So, after staying just one jump ahead of our own extinction for hundreds of thousands of years, we now have runaway overpopulation which spells ... our extinction. Along with that of millions of other species.

Hehe, but note that right now we have less hungry people than we had back then, when you were young. That's one thing.
Second - population is not an issue anymore.
Current Big Thing is climate change.
There will be something else in decade or two from now, do not worry.

And about aviation and CO2 - now think of banning flights and impact on economy of all those places which are destinations of all these flights? Me myself? I prefer if my place would get warmer by 2-3 Celsius rather than economy collapse.
Sorry!

&

Whatever your take on climate change (personally I think it's inevitable, and if we spike the atmosphere with CO2 now, we'll get it over and done with quicker...)

As the efficiency of aircraft increases, so does the aviation industry's CO2 emissions. This seems counter-intuitive at first, but the reasoning is:

1. Aircraft become more efficient
2, Price of air travel comes down (as it's dominated by the fuel cost)
3. Demand then goes up - in excess of the efficiency saving.

The only way to break this cycle is to impose a carbon tax, perhaps on each ticket.

Since C02 is a very very wimpy temperature driver there is no real climate emergency, only one that is manufactured. So Aviation, together with the entire fossil fuel economy has little to nothing to do with climate change so who cares?

Wow, the well known Trumpmenistan Mantra.
And 97% of worldwide climate scientists are wrong........:ugh: