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Originally posted by Aqualung2012
1) Living near an international airport makes be able to observe many types of airplane all year round, in varying altitudes, weather conditions and temperatures. Thusly,
2) I constantly witness normal contrails (e.g. "short-lived," unform streaks which always dissapate in a matter of minutes if not seconds after the plane had passed.) This is under evey array of conditions.
3) I understand that contrails are mere water vapor... which dissapear sortly after being dispersed.
My opinion is not that of an expert, but of an experienced observer.
I suppose what makes it seem strange to me is simply the inconsistancy of it. I will watch one plane go by, billowing this aerosol, and a moment later, at roughly the same altitude and speed, i witnedd one with a perfectly normal contrail...
Or even more so, one day the sky will be covered in these streaks, and the next, almost identical day, there are none or very few.
My question to you is why does it NOT seem strange to you?
Originally posted by Imagewerx
reply to post by Iwinder
Come on,where's your sense of humour? I was just having a laugh.
But I am saying it's human.
Causes of Change Prior to the Industrial Era (pre-1780)
Changes in the Earth's orbit: Changes in the shape of the Earth's orbit (or eccentricity) as well as the Earth's tilt and precession affect the amount of sunlight received on the Earth's surface. These orbital processes -- which function in cycles of 100,000 (eccentricity), 41,000 (tilt), and 19,000 to 23,000 (precession) years -- are thought to be the most significant drivers of ice ages according to the theory of Mulitin Milankovitch, a Serbian mathematician (1879-1958). The National Aeronautics and Space Administration's (NASA) Earth Observatory offers additional information about orbital variations and the Milankovitch Theory.
Changes in the sun's intensity: Changes occurring within (or inside) the sun can affect the intensity of the sunlight that reaches the Earth's surface. The intensity of the sunlight can cause either warming (for stronger solar intensity) or cooling (for weaker solar intensity). According to NASA research, reduced solar activity from the 1400s to the 1700s was likely a key factor in the “Little Ice Age” which resulted in a slight cooling of North America, Europe and probably other areas around the globe. (See additional discussion under The Last 2,000 Years.)
Volcanic eruptions: Volcanoes can affect the climate because they can emit aerosols and carbon dioxide into the atmosphere.
Aerosol emissions: Volcanic aerosols tend to block sunlight and contribute to short term cooling. Aerosols do not produce long-term change because they leave the atmosphere not long after they are emitted. According to the United States Geological Survey (USGS), the eruption of the Tambora Volcano in Indonesia in 1815 lowered global temperatures by as much as 5ºF and historical accounts in New England describe 1816 as “the year without a summer.”
Carbon dioxide emissions: Volcanoes also emit carbon dioxide (CO2), a greenhouse gas, which has a warming effect. For about two-thirds of the last 400 million years, geologic evidence suggests CO2 levels and temperatures were considerably higher than present. One theory is that volcanic eruptions from rapid sea floor spreading elevated CO2 concentrations, enhancing the greenhouse effect and raising temperatures. However, the evidence for this theory is not conclusive and there are alternative explanations for historic CO2 levels (NRC, 2005). While volcanoes may have raised pre-historic CO2 levels and temperatures, according to the USGS Volcano Hazards Program, human activities now emit 150 times as much CO2 as volcanoes (whose emissions are relatively modest compared to some earlier times).
These climate change “drivers” often trigger additional changes or “feedbacks” within the climate system that can amplify or dampen the climate's initial response to them (whether the response is warming or cooling). For example:
Changes in greenhouse gas concentrations: The heating or cooling of the Earth's surface can cause changes in greenhouse gas concentrations. For example, when global temperatures become warmer, carbon dioxide is released from the oceans. When changes in the Earth's orbit trigger a warm (or interglacial) period, increasing concentrations of carbon dioxide may amplify the warming by enhancing the greenhouse effect. When temperatures become cooler, CO2 enters the ocean and contributes to additional cooling. During at least the last 650,000 years, CO2 levels have tended to track the glacial cycles (IPCC, 2007). That is, during warm interglacial periods, CO2 levels have been high and during cool glacial periods, CO2 levels have been low (see Figure 1).)
One observation I have made is that almost 100% of the time when a cold front is approaching, they pummel the sky with these things. They begin operations about 24 hours before it's arrival.
In conclusion, two main meteorological situations are found which have many persistent contrails:
(a) slow ascent of upper air far ahead of a surface warm front often near jet streams, and
(b) in more convective and turbulent regions with strong winds ahead of a surface cold front.