Longer Airline Flights Proposed to Combat Global Warming

Longer Airline Flights Proposed to Combat Global Warming
By Michael Schirber
LiveScience Staff Writer
posted: 26 January, 2005
7:00 a.m. ET

Tendrils of condensation that mark the paths of high-flying jets sometimes form a loose lacework of man-made clouds in the upper atmosphere. The extra blanket of atmospheric insulation from these spreading contrails, as they are called, could accelerate global warming, studies have shown.

Now a group of researchers says something should be done. Their proposal would lengthen the typical airline flight.

High-altitude cirrus clouds, both natural and jet-induced, are unlike thicker low-altitude clouds, which block sunlight from reaching the surface. The thinner cirrus, which float in the sky at 20,000 feet or higher, act like a see-through blanket -- letting sunlight pass in, while trapping reflected heat.

A rise in contrail formation -- and therefore blanketing -- is expected in the future, because air travel is growing at 3 percent to 5 percent a year, and cargo transportation by air is increasing by 7 percent a year.

In a recent investigation of air traffic trends, researchers at the Imperial College London came up with guidelines for minimizing the climate impact from contrails. They propose setting ceilings on the altitude that jets can fly: 31,000 feet in the summer and 24,000 feet in the winter.

On long flights, most jets cruise at about 35,000 feet. This conserves fuel, since there is less drag through the thinner, high-altitude air. But the environmental benefit of better fuel efficiency may be offset by the warming aspect of contrail formation.

"We'd like this research to inform government policies, not just in the UK but throughout the [European Union] and the rest of the world so that decision makers can take all the environmental issues into account and do the right thing," said Robert Noland, leader on the investigation.

Contrail effects are not now included in governmental assessments of the impact from air travel.

Condensation trails -- contrails -- form when hot, humid air coming out of a jet engine mixes with the colder surrounding air of the atmosphere. Water in the air condenses around particles in the exhaust.

Depending on how much moisture is in the air, contrails can be long-lived, spreading out to look more like the wispy cirrus clouds made by Nature.

Because the atmosphere becomes generally colder at higher altitudes, it is easier for contrails to form behind higher-flying aircraft. Therefore, imposing a maximum altitude for commercial flights could reduce contrail formation.

The impact from jet exhaust became evident in the days after the Sept. 11, 2001, terrorist attacks, when most air traffic in the United States was halted.

During the stoppage, astronaut Frank Culbertson, on the International Space Station, told flight controllers, "Normally when we go over the U.S., the sky is like a spider web of contrails. And now the sky is just about completely empty."

During this period, a study found that the difference between high and low temperatures rose one degree Celsius (1.8 degrees Fahrenheit) when the skies were clear of contrails.

A more recent report from NASA documented a 1 percent per decade increase in cirrus cloud cover over the United States, presumably due to increased air travel. The researchers claimed that this extra cloudiness could account for a warming trend of half a degree Fahrenheit per decade in the years between 1975 and 1994.

Requiring planes to cruise at lower altitudes would cause longer flights and require more fuel. But in weighing the two possibilities, Noland and his collaborators conclude that a rise in the number of contrails would be worse for the environment.

"There is little more that aircraft designers can do to increase engine fuel efficiency at high altitude," Noland said, "but designing new aircraft that can be as fuel efficient flying at 20,000 feet, as today's aircraft are at 35,000 feet, would help eliminate contrails."

Besides altitude, the researchers discovered that weather conditions affect the likelihood of contrails. In fact, there are days when the atmospheric conditions make it almost impossible to avoid forming the spindly clouds. The ultimate strategy might entail day-to-day decisions to avoid air masses that are susceptible to contrail formation. Moreover, simple software could be developed to warn a pilot when his or her plane is leaving a "jetprint" in the sky.

I live under a fairly major east/west flyway, and ever since I read about that study done in the days after 9/11 about contrail formation and the environment, I've been observing more closely. There are days that contrails last for 30 minutes or more, and there are days that contrails barely leave the aircraft before they dissipate. Then there are days that aircraft don't leave contrails at all.

Bogus subject, like most global warming topics, if you ask me.

Not really a bogus subject, but it affects us very little.

As the article said, the days after 9-11 were warmer, documented. I doubt it was that significant, tho. You could make the argument to keep cities from expanding (heat island) or a farmer from plowing his field.

Contrail formation is a function of temperature, pressure, and the amount of moisture in the jet fuel. As the temp gets colder, and the pressure is less (high altitude) the air can hold less moisture. A jet flys high enough, the water in the fuel condenses into a visible cloud because the relative humidity approaches 100%.

Programs exist today that can predict contrail formation. Do a google search using the term "skewt logp".

A simpler approach is to reduce the amount of moisture in jet fuel, IMHO.

In Fairbanks Alaska, when the temperature reaches 50 below, the automobiles create contrails, however, they call it ice fog, since it is on the ground.

A simpler approach is to reduce the amount of moisture in jet fuel, IMHO.

OK, I admit to only freshman level college chemistry, but I thought that the two byproducts of the perfect combustion of a hydrocarbon fuel was carbon dioxide and water. Something like:

H_xC_x + O₂ = CO₂ + H₂O

I thought it was imperfect combustion that also created CO and NO_x and other pollutants. So how does one reduce the amount of moisture in the fuel when the water is a product of efficient combustion?

I'm sitting inside looking at 14" of snow in my yard. It's going down to the single digits tonight on the good old fahrenheit scale and below zero tomorrow.

Would somebody please figure out how to speed up this global warming thing? It sounds really nice about now and, besides, I hear they're trying to figure out how to grow bananas in Georgia

Oh good! Now the airlines are getting in on the global warming act to save themselves so money on fuel.

I knew this global warming was useful. I just never realized it extended beyond lining the pockets of those promoting it.

I think science supports my idea of reducing global warming by introducing a shading effect from black particulates. In the 70's particulates of this kind were projected to cause world wide global cooling.

How do we do this? easy, burn tires. If every good environmentalist in this country burned just one LT235-15 each week could beat this thing.

I see "Burn-a thons" where we all gather in the park and light up a radial. The little kids could burn wheel barrow tires, the 5th graders could burn donut spares, etc.

"Bogus subject, like most global warming topics, if you ask me."

And you're absolutely correct.

Being the rabid long-time observer that I am of this "global warming" scam, I was going to write a long-winded, scientific but witty rebuttal to the posted article, but I declined since I didn't want to put anyone to sleep. Suffice it say, there are articles on NASA's own website based on the original article in Science that more or less claim that contrails don't make any significant difference. It seems that they can block sunlight as well as they can reflect heat, so the net gain is zero. NASA even goes as far as saying that cirrus clouds have a heat trapping effect where contrails have an opposite effect. Personally and scientifically speaking, I don't believe that contrails figure into the equation at all.

Worse yet is that the NASA article, this posted article and one by CNN conflict with each other on various levels. It's more evidence that no one knows what they're talking about... as if we didn't already realize that.

Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.