I was idly browsing the web when I happened upon the Truth Movement Australia website. It turns out that this is a website dedicated to finding out the "truth" about things like 9/11, the Bali bombings, reptilians and the New World Order.
I ended up having a look at one thread in particular, which claimed to have interesting proof about chemtrails being used by the U.S. Government.
For those of you who haven't heard of it before, the chemtrail conspiracy goes something like this; the government (or governments, or new world order, or whoever you fancy as your particular institution with a secret plan to dominate the world) uses aircraft to dump large quantities of poisonous gases into the air above population centers, in order to make people ill (or sterile, or whatever particular condition is in vogue).
There are some issues with this hypothesis which I will attempt to demonstrate.
Firstly, let's assume that the Government was trying to do something nefarious to us without us knowing about it. It would be much much simpler to dump chemicals straight into the water supply than it would be to put them into aerosol form and spray them from an airplane.
You aren't limited to spraying only when flights are scheduled. You don't have to bribe every single engineer designing, repairing or maintaining the aircraft to install or ignore the aerosol compartment. You don't have to bribe the pilots. You don't have to bribe the CEOs and staff of every single aircraft company. You also don't have to bribe all the other engineers, pilots and executives in the world who aren't in on your ploy so they don't point out that your planes aren't carrying as much fuel as they should be, given their size and lift coefficients. You have to make sure that planes that aren't carrying the extra payload of chemicals aren't out-performing your planes, meaning they can fly cheaper and charge much less for the same trip. The number of people you have to bribe to keep quiet goes on forever.
The other reason chemicals directly put into the water supply is easier is because the chemicals are much more likely to be absorbed by the population in larger doses. By the time chemicals float down to ground level (if they aren't caught up by atmospheric wind currents), they have dispersed and diluted to the point where they would almost be negligible.
Yet another reason it doesn't make sense for Governments to spray chemicals in the air is that they breathe the same air too. Unless I start to see Government officials running around with gas masks on, I'm not worried.
Or maybe, just maybe, contrails could just be the condensation of water vapour suspended in atmosphere when it comes into contact with the much warmer plane being affected by wind currents.