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In the three days that followed the 9/11 attacks, when all commercial flights above the continental US were suddenly suspended, a veil was lifted on the profound, though until that point unconfirmed, effects that aviation-associated artificial clouds are having on our planetary environment.
In the August 2002 edition of Nature, which is ranked the world's most cited interdisciplinary journal, a report was published titled "Contrails reduce daily temperature range," where scientists discuss how "a brief interval when the skies were clear of jets unmasked an effect on climate." [Read Entire Article]
Three Days Without Contrails
The post-9/11 grounding of all commercial aircraft resulted in the sudden disappearance of condensation trails (contrails) from jet aircraft across the entire United States. According to the Nature study, the potential of contrails "...from jet aircraft to affect regional-scale surface temperatures has been debated for years...," but it was not until the three-day grounding period that doubts concerning the existence of the phenomenon could be put to rest.
The Phenomenon: A 1.8 Degree Celsius Increase In Temperature in North America
The study found "...an anomalous increase in the average diurnal temperature range (that is, the difference between the daytime maximum and night-time minimum temperatures) for the period 11-14 September 2001."
They go on to explain: "Because persisting contrails can reduce the transfer of both incoming solar and outgoing infrared radiation and so reduce the daily temperature range, we attribute at least a portion of this anomaly to the absence of contrails over this period."
They arrived at their measurements by analyzing maximum and minimum temperature data from approximately 4,000 weather stations through the conterminous United States (excluding Hawaii and Alaska) for the period 1971-2000, and compared them to the three-day post-9/11 grounding period.
They found an increase in the diurnal temperature range (DTR) of approximately 1.1 degree Celsius over normal 1971-2000 values, and an increase of 1.8 degrees during the grounding period in contrast to the adjacent three-day periods analyzed when DTR values were near or below the mean.
This is a highly significant finding as "The increase in DTR is larger than any during the 11-14 September period for the previous 30 years...," and since "...the 11-14 September increasing DTR was more than twice the national average for regions of the United States where contrail coverage has previously been reported to be most abundant (such as the Midwest, northeast and northwest regions)."
The study authors concluded
"Our findings indicate that the diurnal temperature range averaged across the United States was increased during the aircraft-grounded period, despite large variations in the amount of cloud associated with mobile weather systems. We argue that the absence of contrails was responsible for the difference between a period of above-normal but unremarkable DTR and the anomalous conditions that were recorded."
First, it is important to point out that the observed post-9/11 elevation in temperature is not one-dimensional. While clouds, including aviation-associated contrails may lower temperature by reflecting solar radiation off the planet in what is known as the "albedo" effect, they may also raise temperature by blanketing trapped heat preventing its nighttime radiative dissipation.
In fact, NASA's Earth Observatory states that "NASA scientists have found that cirrus clouds, formed by contrails from aircraft engine exhaust, are capable of increasing average surface temperatures enough to account for a warming trend in the United States that occurred between 1975 and 1994." The point, however, is that aviation-associated weather does profoundly affect temperature.
It is not necessary to believe in clandestine geoengineering programs, or malevolently dispensed chemical trails, in order to see the effect that modern day aviation is having – visibly -- on our skies. Billions of pounds of jet fuel are burned each year, adding a vast amount (albeit mostly invisible) of chemical pollution to our environment.
While the mainstream still considers the persistent condensation trails formed by jets to be a harmless and ephemeral, a growing sector of the public is increasingly concerned about the "chemtrails" they are seeing blanketing the sky – a term, in fact, which generates millions of searches and web page results through Google, but is equated with "conspiracy theory" via automatic redirection on sites like Wikipedia or Dictionary.com.