Regardless if you believe in chemtrails or not. The trails still not harmless. At least trails heat the earth. It eliminate rain clouds which can cool the earth and replacing it with cirrus that can heat the earth
http://www.pa.op.dlr.de/~pa1c/NatureGeosci4_RH_215_2011.pdf
"The researchers note that contrail cirrus also reduce natural cirrus coverage"
http://www.pa.op.dlr.de/pazi/Flyer_PAZI-2_Midterm_Status.pdf
"Contrail-cirrus clusters build up regionally and may prevent natural clouds from forming"
http://www.nature.com/nclimate/journal/v1/n1/pdf/nclimate1068.pdf?WT.ec_id=NCLIMATE-201104
"We also find that contrail cirrus cause a significant decrease in natural cloudiness"
This is something I already observe my self and still waiting for a chance to record them my self.
