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Posted on 12/31/2008 11:41:11 PM PST by neverdem
Grounding planes after the 11 September attacks may not have caused unusual temperature effects.
When all commercial air traffic in the United States was grounded after the terrorist attacks of 11 September 2001, scientists got an unexpected opportunity to test ideas about the climate effects of the condensation trails left behind by jets.
A study in 20021 suggested that these contrails could have a significant effect on daily temperature patterns (see 'Air-traffic moratorium opened window on contrails and climate'). But a new analysis now claims that altered US temperature patterns during the three flight-free days can be explained by natural variations in cloud cover, rather than the absence of planes.
Aircraft contrails can spread into cirrus-like clouds high in the atmosphere. Similar to natural clouds, they are thought to have an overall warming effect on the planet. But they can also moderate daily temperature extremes by trapping heat that escapes from the ground and reflecting sunlight. This raises the lowest overnight temperatures and, to a lesser degree, reduces the highs during daylight hours, scientists have suggested.
With air traffic projected to grow by 2–5% per year in the near future – amounting to at least a tripling in traffic by 2050 – the effects of contrails are expected to become an increasingly important factor in climate change. But atmospheric scientists are still unsure about the scale of the contrails' impact.
Two studies1,2 noted that when planes stopped flying on 11–14 September 2001, the average daily temperature range in the United States rose markedly, exceeding the three-day periods before and after by an average of 1.8 °C. The unusual size of the shift, says David Travis of the University of Wisconsin–Whitewater, who led both of the earlier studies, implied that an absence of contrails gave the temperature range a significant boost. But that idea, he says, was "more like a hypothesis" than a firm conclusion.
Research led by Gang Hong, an atmospheric scientist at Texas A&M University in College Station, now suggests that this hypothesis is wrong3. Examining patterns of cloud cover and temperature in early September at US weather stations from 1971 to 2001, Hong and his colleagues found that thicker, low clouds are the dominant influence on temperature extremes, whereas high clouds such as contrails have a minor effect at most. They add that the 2001 temperature swings seem to be within the range of natural variability over those decades.
Hong's work doesn't prove that the contrails have no effect on temperature, just that they are unlikely to have a major role, says Ulrich Schumann, director of the Institute of Atmospheric Physics at the German Aerospace Center in Oberpfaffenhofen, near Munich.
But that contrail effect, Schumann cautions, has been exaggerated in public discussions because the events of 2001 were so shocking. "Some not very good scientific arguments were misused," he says.
The research by Hong and his colleagues, published in Geophysical Research Letters, follows other studies arguing that the September 2001 temperature variations can be explained by the clear, dry weather on the crucial days4, and that climate-modelling results do not support the contrail effects claimed by Travis's group5.
Travis, however, stands by his findings. Absent contrails were never assumed to be the sole cause of the large temperature ranges, he emphasizes. "We've always said it's a combination of the lack of airplanes and the natural weather conditions," he says.
Because Hong's analysis studied high-level clouds in general – and not contrails in particular – Travis says that specific conclusions cannot be drawn about the role of contrails from the survey. "Their calculation of cloud influences was without any consideration of contrails," he says. "They were just looking at natural clouds, and not actually at the presence or absence of contrails."
He adds that Hong's study shows that an increase in the average daily temperature range of 1.8 °C is extremely rare. And although previous events on that scale can be explained by local meteorological effects, says Travis, the jump seen in 2001 cannot be accounted for in this way.
Travis maintains that contrails are an important factor in climate change. "Eventually these impacts will be felt," he says.
Who cares? After the 2nd arrival of Apophis it won't matter anyway.
LOL Must be pretty slow acting.
Contrails aren't even smoke they're water vapor FWIW.
I don’t know how I missed it. I’ve seen tons of shows on Sasquatch, UFOs, alien abductions ... I’ve even heard about chupacabras. Chemtrails must have gotten lost in the cosmic debris.
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Better check their bodies for cigarette burns...
I don’t know about chem trails, but there was a PBS special report on the phenomena after the three days absence of air travel with 9/11. The evidence the fascinated me was that evaporative pans used by agricultural scientists to track the water needs of farmers showed an unusually high level of evaporation during those 3 days. I had always thought that evaporation was caused by heat, but according to this program it was the increase of photons, because of the clear atmosphere, hitting the water that caused the extra evaporation. If I remember correctly it was also reported that the dirty air from Europe was implicated in the terrible Sahel drought in Africa. Since Europe has been cleaning up its skies there has not been such severe drought in Africa. There is more particulate pollution coming from China that actually reaches our continent. This may change with the worldwide economic slowdown.
Let us consider some of the implications. What influence might any of this have on hurricane strength since the conditions that develop them originate in Africa? What might be the influence on American agriculture, or droughts, or forest fires? So many questions, so complicated answers.
So many speculations. There is only one constant in weather and climate and that is change. Man is a part of the whole but at our most determined we’re still an insignificant factor.
Paging Art Bell was my first thought when I saw the title.
“Contrails aren’t even smoke they’re water vapor FWIW.”
Of course I know contrails are condensed water vapor.
Thats why they are called CONtrails.
I used “smoke” as a joke.
It is amazing how many kooks really believe the skies are being crisscrossed by thousands of planes spewing chemicals on us.
Not to mention the DANGER to the livestock!!!!
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