During the Korean War, USAF F-86 Sabre pilots learned a trick while enroute to MiG Alley where they would tangle with North Korean MiG 15s. The Soviet-built fighters had a superior climb rate and service ceiling, so the Sabre pilots wanted to get as high as they could before engaging. But high-altitude contrails would give away their position, so while still well away from the combat area, they would climb to the altitude where the contrails would start to form, then either climb (preferred) or drop down slightly until the contrails disappeared. A similarly simple strategy for airliners is now part of a plan to cut back on greenhouse gases in the battle against global warming.
When hot jet exhaust gases and water vapor mix with cold air, especially at high altitude, they generate condensation trails, or “contrails,” the equivalent of man-made cirrus clouds. Studies cited in a paper published on ScienceDirect.com have shown that some 33 percent of the Earth’s longwave radiation, rather than reflecting back into space, bounces back to the surface of the planet when it encounters a contrail-generated cloud. Contrails are estimated to be responsible for about 2 percent of overall man-made “radiative forcing,” and the article cited research that calculated and inventoried coverage by contrails in the U.S. National Airspace System.
It found that an average of just 15 percent of daily flights generate contrails, and the coverage can be pinpointed by time of year (63 percent occurs from June to September) and geographic location of what are called Ice Super Saturated (ISS) regions, mostly concentrated on the Pacific Coast and the southeastern U.S.
According to the paper’s abstract, “The analysis found that elevating the cruise flight level of contrail-generating flights by 2000 or 4000 feet reduced the number of average daily flights with contrails by an average of 14.8 percent, the net radiative forcing by an average of 92 percent, with an average net small decrease in fuel-burn of 1 percent [due greater fuel efficiency at higher altitudes].”
Part of the proposed strategy would involve tapping into “Big” weather data to predict when and at what altitudes contrails are likely to be generated and using the air traffic management system to proactively assign flight paths and cruising altitudes to avoid that airspace.
Eurocontrol has a similar plan under consideration for European airspace.
I’m not a climatologist, or even a meteorologist, but I’d like explained to me the net effects of clouds, while I’m clear on the fact that they reflect LWIR back to the surface, It seem to me that clouds have a net increase in local albedo, which would correspond with reflection of shorter wavelengths, preventing them in some measure from contributing to warming.
Most airliners already use the most efficient altitude for cruise. With the supposed increase in air traffic, I just don’t see how there would be enough room for all the proposed altitude adjustments. This would negate any benefit RVSM has brought along. Now with a lot of privately operated jets, a lot of them are capable of flight above FL410, this might work.
This seems a strange premise, that cloud increases the amount of light reaching the earth’s surface from the sun. Perhaps it’s more to do with heat loss during the night?
I can understand how clouds (contrails or otherwise) can reflect heat from the surface that would otherwise radiate out into space at night. But during the day doesn’t it mostly work the other way? Clouds (contrails or otherwise) tend to reflect OUT heat from the sun that would otherwise warm the surface.
As I recall, it’s usually hotter on a clear day and cooler on a cloudy day. Yes, I’m pretty sure that’s right.
As mentioned above, airliners typically cruise at the highest available altitude for their weight, or the best altitude for winds. So for the most part, changing altitude will increase fuel burn which increases greenhouse gasses. Did the study account for that at all?
Hi Dave – took took the words right out of my mouth – what else can be said? over
The premise was that 2% of the reflected radiation was caused by contrails and the summation was that 92% of that 2% could be eliminated. So the net effect would be that overall reflected radiation caused by cloud cover and contrails can be reduced to 98.04% of total levels? The article also points out that an average of 15% of all flights generate contrails and this solution will reduce that number by 14.8% (or to 2.2% of the contrail generating flights per day).
Since climatologists cite an increase in global warming beginning long before the age of high-altitude flight (hence contrails), doesn’t their own science suggest this is a solution in search of a problem?
“The article also points out that an average of 15% of all flights generate contrails and this solution will reduce that number by 14.8% (or to 2.2% of the contrail generating flights per day).”
Should have read: …(or to 2.2% of the total flights per day).
@Andrew @Christopher @David
Suggest you re-read the article. If you still don’t understand the phenomenon, suggest that you read the link to the source article. Something to do with long wavelength radiation vs short wavelength radiation and how they are blocked or radiated back to the earth. Cleared it up for me.
I hope they have not wasted too much money on this and that we stop looking for ways to spend dollars in hopes to save pennies. During WWII the skies were darkened by contrails at times, we and everyone else turned our factories up to overdrive on fossil fuels, and bombs of all kinds rained down all over creation and the Earth cooled. Mankind is arrogant to think that it has any effect on what the Earth will do.
Lovely thoughtful response. Well put.
Errors!
Contrails do not affect ‘greenhouse gasses’ – they do not add or subtract any from the atmosphere compared to unseen exhaust components. They are simply condensation onto soot into ice crystals of water vapour in the exhaust, when air is below freezing. Note too that newer engines emit much less soot.
The push is for the climate catastrophist fallacy that humans are causing runaway warming of earth’s average climate, which is not and cannot happen.
Read accurate temperature data such as from weather balloons and satellite sensors, and government tide gages collated at PSMSL.org.
Study the basic physics of ‘greenhouse gasses’, recognizing the ‘saturation effect’ which limits the temperature rise from CO2 to a small amount most of which has already been realized. (Absorption/emission becomes saturated due to overlap of spectra of carbon dioxide and dihydrogen monoxide – the most common greenhouse gas.) Even the IPCC agrees but theorizes a positive feedback loop that is not occurring.
Note as well that the temperature increase is much more in polar regions – but is not melting much ice in relative terms, and is mostly at night. Both increases are good for life as warmth is better than cold, for humans and our food source (plants – which also grow better with more CO2, whether directly or via converters called animals).
Stop harming the creative productive aviation industry.
RIGHT ON KEITH ! !
From the paper cited in the article:
“These anthropogenic (human made) condensation trails, or “contrails,” create a green-house effect by absorbing or directing back to Earth approximately 33% of emitted outgoing longwave radiation. Although this effect is estimated to be <2% of the Earth's total anthropogenic radiative forcing, the effect on global warming is immediate, unlike CO2 emissions which have a two decade delay in affecting global warming."
I’m pretty much with You, Keith Sketchley.
+3 Keith. You saved me some typing with your excellent post.
@Keith Sketchley: the comment that “Contrails do not affect ‘greenhouse gasses’” is a straw man. Neither the article nor the abstract of the paper to which it links say that contrails affect, or are, greenhouse gasses. The abstract says that contrails ‘create a green-house effect by absorbing or directing back to Earth approximately 33% of emitted outgoing longwave radiation.’ (“Effect”, meet “affect”. “Affect”, meet “effect”.)
So, as you say, “Errors!” But this one is yours.