Contrails: How tweaking flight plans can help the climate.
B2N2
Agreed. I don't know about the merits/demerits of the proposals but, speaking as an occasional long-haul sardine, some occasional gentle-to-moderate aero's would at least relieve the tedium.
Agreed. I don't know about the merits/demerits of the proposals but, speaking as an occasional long-haul sardine, some occasional gentle-to-moderate aero's would at least relieve the tedium.
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Passengers DO look for comfort and a smooth flights as a good percentage usually feels somehow uncomfortable when flying, especially in rough weather conditions. Try and ask any of Your non aviation acquaintances if they’d rather fly from A to B 2 hours in a noisy and bumpy ATR ride or 2 hours in a smooth and quiet jet at high altitude above most of the convective weather, at least in winter time.
May I stick my head above the parapet as I am both a PhD qualified researcher in an allied area, and holder of a CPL; I've also been to many of the main conferences on this topic over the last few years - so have a better grasp of these issues than most (including possibly a better grasp than that of the author of that, actually quite good BBC article).
This issue is very real, and the author gets the perspective about right. At the moment aviation, globally, is responsible for around 2-3% of total CO2 emissions (and CO2 is responsible for around 70% of what most people call global warming). However the science that's emerged over the last 5 years indicates very strongly that aviation's true contribution to radiative forcing (the technical term for the mechanism that drives global warming, and thus climate change) is around treble what we thought - nearer 7%, with much of the gap being caused by contrails cirrus - that is persistent contrails.
Contrail cirrus' mechanism is pretty straightforward - it's the same mechanism that makes cloudless days warmer, and cloudless nights colder - and vice-versa. Depending upon time of day either it's either reflecting radiation back into space, or reflecting it back into the earth (okay, it's always doing both, but the critical value is the net radiation transmission. The clever people who model this stuff (particularly a Prof Keith Shine at the University of Reading along with his colleague Dr Lucy Irvine, who for some reason never got mentioned in that article) have concluded that through the daily cycle, this all adds up to net warming, and thus is a big problem.
Now some other significant aspects. Contrails, which are caused by sooty particles in exhaust causing supercooled water vapour to precipitate upon those particles into ice crystals. It's not, as is widely misunderstood, caused by water in the exhaust. Persistent contrails occur in around 3% of air transport flying hours only, and they can only occur in air that is supersaturated with respect to ice.
So to eliminate contrails, we need to understand where (in 3D + time) the ice-supersaturated air is, and steer traffic over, under, or around it. That should be around 3% of flights, but it requires a particular form of weather forecast we don't presently have, and an integration of air traffic management and meteorology which we just don't have at the moment. These are solvable problems, but not quickly, cheaply or easily. The Germans have done some initial trials (almost entirely in German airspace) over the last couple of years, and hit many snags - they need to iron those out, but then we really need to do it on a much bigger scale over, e.g. the North Atlantic and Pacific.
The maths justifying this is really easy from a climate viewpoint. Re-route around 3% of flights, adding about 10% to each of their fuel burn - that puts aviation's CO2 emissions up around a third of a percent. For that you better than halve the real climate impact, through eliminating contrail cirrus and the warming effect that creates. My maths here is very crude, but you get the idea.
So if we can do it, we should. But it will require a massive upgrade of global met/ATM integration, much better testing of the standard equations for contrail creation and persistence than we presently have (my meteorology colleagues love to glibly quote those equations as gospel, and they are good, but the reality is they need somewhat more fine tuning than they've already had), some form of legislative or financial structure to ensure that aircraft genuinely do avoid ice-supersaturated regions as well as possible, and monitoring capability, probably space based, to confirm that persistent contrails aren't being formed.
I'd also personally like to see a reasonable proportion of airliners carrying some form of instrumentation that measures ice-supersaturation (and that's not at all trivial to do), most likely transmitting the measurements back to ATC and other aircraft in real time through spare ADSB-out capacity. That would be really useful in enabling this to work well, not to mention improving understanding of global meteorology, to absolutely everybody's benefit.
Very happy to discuss more if anybody's interested.
This issue is very real, and the author gets the perspective about right. At the moment aviation, globally, is responsible for around 2-3% of total CO2 emissions (and CO2 is responsible for around 70% of what most people call global warming). However the science that's emerged over the last 5 years indicates very strongly that aviation's true contribution to radiative forcing (the technical term for the mechanism that drives global warming, and thus climate change) is around treble what we thought - nearer 7%, with much of the gap being caused by contrails cirrus - that is persistent contrails.
Contrail cirrus' mechanism is pretty straightforward - it's the same mechanism that makes cloudless days warmer, and cloudless nights colder - and vice-versa. Depending upon time of day either it's either reflecting radiation back into space, or reflecting it back into the earth (okay, it's always doing both, but the critical value is the net radiation transmission. The clever people who model this stuff (particularly a Prof Keith Shine at the University of Reading along with his colleague Dr Lucy Irvine, who for some reason never got mentioned in that article) have concluded that through the daily cycle, this all adds up to net warming, and thus is a big problem.
Now some other significant aspects. Contrails, which are caused by sooty particles in exhaust causing supercooled water vapour to precipitate upon those particles into ice crystals. It's not, as is widely misunderstood, caused by water in the exhaust. Persistent contrails occur in around 3% of air transport flying hours only, and they can only occur in air that is supersaturated with respect to ice.
So to eliminate contrails, we need to understand where (in 3D + time) the ice-supersaturated air is, and steer traffic over, under, or around it. That should be around 3% of flights, but it requires a particular form of weather forecast we don't presently have, and an integration of air traffic management and meteorology which we just don't have at the moment. These are solvable problems, but not quickly, cheaply or easily. The Germans have done some initial trials (almost entirely in German airspace) over the last couple of years, and hit many snags - they need to iron those out, but then we really need to do it on a much bigger scale over, e.g. the North Atlantic and Pacific.
The maths justifying this is really easy from a climate viewpoint. Re-route around 3% of flights, adding about 10% to each of their fuel burn - that puts aviation's CO2 emissions up around a third of a percent. For that you better than halve the real climate impact, through eliminating contrail cirrus and the warming effect that creates. My maths here is very crude, but you get the idea.
So if we can do it, we should. But it will require a massive upgrade of global met/ATM integration, much better testing of the standard equations for contrail creation and persistence than we presently have (my meteorology colleagues love to glibly quote those equations as gospel, and they are good, but the reality is they need somewhat more fine tuning than they've already had), some form of legislative or financial structure to ensure that aircraft genuinely do avoid ice-supersaturated regions as well as possible, and monitoring capability, probably space based, to confirm that persistent contrails aren't being formed.
I'd also personally like to see a reasonable proportion of airliners carrying some form of instrumentation that measures ice-supersaturation (and that's not at all trivial to do), most likely transmitting the measurements back to ATC and other aircraft in real time through spare ADSB-out capacity. That would be really useful in enabling this to work well, not to mention improving understanding of global meteorology, to absolutely everybody's benefit.
Very happy to discuss more if anybody's interested.
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Depending upon time of day either it's either reflecting radiation back into space, or reflecting it back into the earth
Although not used for detecting contrail conditions, there may be elements in this research which could prove to be useful.
https://ral.ucar.edu/solutions/produ...nt-areas-alpha
sonicbum
You missed the point.
Pax won’t fly with you again if you’ve lost their luggage, they will fly with you again if it was a bumpy ride.
People don’t understand the logistics of luggage handling, they do somewhat understand you’re up in the air.
You missed the point.
Pax won’t fly with you again if you’ve lost their luggage, they will fly with you again if it was a bumpy ride.
People don’t understand the logistics of luggage handling, they do somewhat understand you’re up in the air.
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You’re mixing up different matters. Customers won’t come back or hardly will following a big disruption or a major issue ie. losing their luggage but that’s a common baseline for the industry.
Passengers are also looking for a cheap yet comfortable flight where they won’t spend a few hours in moderate turbulence because you need to reduce contrails.
Passengers are also looking for a cheap yet comfortable flight where they won’t spend a few hours in moderate turbulence because you need to reduce contrails.
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Genghis the Engineer
Ok , I only have a humble BSc so I dont profess to be an expert but my reading of Global Warming theory is that the atmosphere is largely transparent to incoming radiation but enthusiastically absorbs longer wave radiation re-radiated from surfaces heated by incoming radiation.
Most of the return radiation is already absorbed by the existing mix of gases , most importantly H2O vapour. But there is not an infinite amount left to absorb. The idea that cirrus at over 30,000 ft can capture any residual radiation on the way out seems fanciful.
Like to see a reference to the original paper. Reading has a reputation of seeing Global Warming in everything.
Ok , I only have a humble BSc so I dont profess to be an expert but my reading of Global Warming theory is that the atmosphere is largely transparent to incoming radiation but enthusiastically absorbs longer wave radiation re-radiated from surfaces heated by incoming radiation.
Most of the return radiation is already absorbed by the existing mix of gases , most importantly H2O vapour. But there is not an infinite amount left to absorb. The idea that cirrus at over 30,000 ft can capture any residual radiation on the way out seems fanciful.
Like to see a reference to the original paper. Reading has a reputation of seeing Global Warming in everything.
Thanks for that paper Dave, I had missed its publication - that is a SERIOUSLY high powered author list and a really useful resource.
Last edited by Genghis the Engineer; 26th Oct 2021 at 20:47.
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Not a rebuttal, however the contrail effect is estimated at 57.4 out of a total 100.9 mW m−2.
But their estimated uncertainty range is actually somewhere between 17 and 98.
Furthermore, they have made a few of statements indicating how “uncertain” they are about their “uncertainty range”. Basically, there is very little data to support their model. For example, in Appendix E:
But their estimated uncertainty range is actually somewhere between 17 and 98.
Furthermore, they have made a few of statements indicating how “uncertain” they are about their “uncertainty range”. Basically, there is very little data to support their model. For example, in Appendix E:
The statistical uncertainty of global contrail cirrus RF cannot be estimated from the small number of available studies. Uncertainties affecting our contrail cirrus estimates are, on the one hand, due to (A) uncertainties in the radiative response to the presence of contrail cirrus and, on the other hand, (B) uncertainties in the upper tropospheric water budget and the contrail cirrus scheme. In most cases, we can only infer very rough estimates for the uncertainties related to specific processes.
