There are some pretty esteemed scientists (don't jump, science works) who verify that what you call "chemtrails" are nothing more than contrails.  This has been accomplished by observing them from both satellites and ground stations at the same time.  Below is just an abstract of an article that you can read to understand that.  No where, but no where is there even a thought that contrails are anything but tiny ice crystals emitted by commercial jet liners as well as military aircraft.  It all depends on the conditions and the altitude.  If you read the entire article you will find that these contrails have increased with the increase in commercial air travel and if it continues on the same scale, the contrails will be a serious contributor to global warming by 2050.  They create cirrus clouds which create a light overcast.

I have flown in formation in a jet fighter, watching in amazement as the jet no more than ten feet in front of me created contrails.  It is an awesome thing to watch, but creating them in the numbers we do today is harmful to our atmosphere.  Chemtrails are an urban myth.

Harry Truman once said that "...at one time the earth tipped and all the nuts rolled to California."  And that's why I left that area though I must confess I still love good old San Francisco.  

Just don't take chemtrails too seriously.

from: http://www-pm.larc.nasa.gov/sass/pub/journals/atlas_JAMC2006.pdf

DAVID ATLAS

ZHIEN WANG*

DAVID P. DUDA

(Manuscript received 27 December 2004, in final form 30 June 2005)

ABSTRACT

This work is two pronged, discussing 1) the morphology of contrails and their transition to cirrus uncinus,

and 2) their microphysical and radiative properties. It is based upon the fortuitous occurrence of an unusual

set of essentially parallel contrails and the unanticipated availability of nearly simultaneous observations by

photography, satellite, automated ground-based lidar, and a newly available database of aircraft flight

tracks. The contrails, oriented from the northeast to southwest, are carried to the southeast with a component

of the wind so that they are spread from the northwest to southeast. Convective turrets form along

each contrail to form the cirrus uncinus with fallstreaks of ice crystals that are oriented essentially normal

to the contrail length. Each contrail is observed sequentially by the lidar and tracked backward to the time

and position of the originating aircraft track with the appropriate component of the wind. The correlation

coefficient between predicted and actual time of arrival at the lidar is 0.99, so that one may identify both

visually and satellite-observed contrails exactly. Contrails generated earlier in the westernmost flight corridor

occasionally arrive simultaneously with those formed later closer to the lidar to produce broader cirrus

fallstreaks and overlapping contrails on the satellite image. The minimum age of a contrail is
2 h and

corresponds to the longest time of travel to the lidar. The lag between the initial formation of the contrail

and its first detectability by Moderate-Resolution Imaging Spectroradiometer (MODIS) is 33 min, thus

accounting for the distance between the aircraft track and the first detectable contrail by satellite. The lidar

also provides particle fall speeds and estimated sizes, optical extinction coefficients, optical thickness ( 

0.35), and ice water path (IWP  8.1 g m2). These values correspond to the lower range of those found

for midlatitude cirrus by Heymsfield et al. The ice water per meter of length along the cloud lines is 103–104

times that released by typical jet aircraft. The synthesis of these findings with those of prior investigators

provides confidence in the present results. Various authors find that contrail-generated cirrus such as

reported here contribute to net regional warming.