Man and Global Temps

[RobBob]

Have to say that I never have believed the global warming gloom-and-doomers, since man has a history of over-rating his impact on the universe. I think that most climatologists would agree that catastrophic asteroid strikes, periodic changes in Earth's rotational orientation, tidal forces (both directly and their secondary trigger effect on volcanism), and volcanism itself have been key determinants in the wide fluctuation of Earth's temperatures over the long term.

 

However, to the extent that man does affect temperature, I wonder if anyone has really put the key factors into accurate perspective. Two factors, I believe, must contribute more to the human equation than they are being given credit for today:

 

1) Human infrastructure. Just the bricks, mortar, concrete and asphalt itself. Constantly absorbing and radiating heat. If you have an outside temp gage in your vehicle, watch how it fluctuates between cities and rural areas. Even small towns seem to have 1-3 degree F bumps in temp compared to backcountry areas.

 

2) Aircraft contrails. I rely on flying for business and recreation, and would be loath to reduce the amount of flying that I do. However, the more you observe the skies with this phenomenon in mind, the more you can actually see contrails take on the look of cirrus clouds. It stands to reason, in this layman's eye, that the combination of burned hydrocarbons and water vapor discharged into high atmosphere would have a much greater effect on climate than equal amounts discharged from the ground.

 

And this obviously relates to climbing in a roundabout way.

 

 

[freeclimb9]

FYI, aircraft contrails form from condensation caused by the sudden change in pressure that the plane causes. Not from introduced exhaust, or water vapor.

 

[RobBob]

Damn Freeclimb, don't screw up my troll ten minutes after I cobble it together, pointing out my muddled organization and writing. Obviously water vapor is not a product of combustion. Question: Is this a purely pressure-caused condensation, or is it not also a temperature-induced one? Vapor trails often appear to be shed at the engines...or are they actually at the wingtips?

[shuksan]

Why, then, do you get a contrail forming behind each engine in a multiengine plane? If general pressure changes were the cause, you would get a diffuse contrail forming from all parts of the plane? From what I've read the jet engines give out lots of H2O vapor and particulates that make nice condensation nucleii. Once this mixes w/ cold and drier atmosphere, you get a contrail.

[allthumbs]

 

The white streaks you see coming off airplanes are called contrails, which is short for condensation trail. Contrails are actually clouds made by the airplanes. There are two types of contrails.

Most contrails people see are caused by a jet's exhaust. The exhaust has some water vapor in it, which mixes with the air when it leaves the jet's engine. Sometimes this mixture has too much water vapor for the air to hold and it condenses into a cloud. This is the most common kind of contrail and it lasts the longest.

The other kinds of contrails are formed by an airplane's wing. Air moves over the wings really fast and cools because of the low pressure. The cool air can't hold as much water so some of it has to condense. This kind of contrail isn't as long-lived as the other kind. The picture above is an example of this kind of contrail.

Contrails last longer when there is a greater amount of water in the air. During the summer, the air generally has more water vapor in it than during the winter. You might notice that it's usually more humid in the summer. Because it's more humid in the summer, contrails take longer to evaporate. That's why they last longer than in the winter.

 

Great applause herd from the cc.com faithful

 

Thank you, thank you very much... trask

 

[RobBob]

I just did a quick search, got past the wacky UFO "chem-trail" posts, and found this

 

"Contrails develop when hot, humid fumes from a jet engine meet the cool air of the upper troposphere. Water vapor in the exhaust and atmosphere freezes to create tiny cloud particles, much like the mist that forms when a person exhales on a cold winter day. As turbulence in the upper atmosphere tears contrails apart, they can spread into wispy sheets essentially identical to natural cirrus clouds.

 

Engines can also stimulate cloud growth indirectly, by way of tiny aerosol particles within the exhaust. These aerosols-droplets of sulfuric acid and specks of soot-serve as seeds. They provide surfaces upon which water molecules can condense or freeze to create cloud particles, explains Eric J. Jensen, a participant in SUCCESS and a researcher at NASA's Ames Research Center in Mountain View, Calif. "

 

which was extracted from this: web page

 

 

[Dru]

They used the airplane shutdown after 9/11 to measure effects of contrails on solar radiation in the US SW. They found that contrails on an average day of regularly scheduled flights reduce direct insolation to the ground under the most used flightpaths by 3-7%.

[iain]

There was an article on this in New Scientist recently. Apparently it is a significant problem and there is a push to bring crusing altitudes down to reduce this problem. However, it costs a great deal more to cruise below the typical 30K feet of a commercial plane, due to increased wind drag and I would assume inability to hitch a ride on the jetstream.

[COL._Von_Spanker]

It seems like global warming has been going on since the end of the ice age if you look at the big picture, but I'm a designer not a scientist so what the hell do I know.

[Dru]

Just think if global warming goes ahead how many more whiners there are gonna be

 

"Feb 16 STILL NO ICE waaaah. I know it is +15C and sunny and dry at Squamish but Im whining about there being no ice"

[thelawgoddess]

i've witnessed the seattle part of the global warming phenom since i moved here ... some 12 years ago.

[Dru]

global warming not all bad - scientific proof the wine tastes better!

 

hi j_b