As a licensed pilot and former aircraft designer I have remained doubtful about this story. But, I admit that I have not dedicated enough of my own time (I don't rely on others, on "experts") to form an opinion I'd stand behind. At first glance, and with my understanding of contrails, it seems far-fetched. Then, a little voice in my head asks, "Would the government be so bold to actually try to do this kind of thing - to either affect weather change or simply dump crap on the public?" ....(pause).....no comment....

This reminds me of a VERY vivid dream I had this weekend. I was a young kid in the bay area when they started started spraying pesticide for fruit flies back in the 70s. Many people were upset, and some families left town when it was scheduled. Now, it's a common thing where I live..."west nile virus, you know..." Anyway, in my dream I was standing in my garage with the door up when I heard a plane flying really low. I walked out and this spray-rigged piper was cruising right down my line of houses, spraying this red mist - maybe 40 feet above the roofs. I jumped back and was horrified to watch it waft into my garage. Funny I just remembered that. Strange...

This is not the best site nor the best proof...

...But..:

Suspicious Observers and Adapt 2030 have been wrestling with this issue. Seems there is something to this.
The truth is coming out slow but true, little by precious little but there are still some that run off the rails with it.
It is harmful and will not accomplish anything good, but you bet your bottom dollar they'll take credit for the cooling that the Grand Solar Minimum will bring.

It says "WATCH QUICKLY BEFORE They DELETE This!" I think it's a parody, but I can't tell for sure.

[Extended Sarcasm]I just so happen to be part of the "they" who don't wantcha to know this. It's only for pilots, the developers who work on the avionics software, the mechanical and chemical engineers who design the nozzles, the people at YouTube who quickly delete these videos, the chemist and bio engineering teams that develop the aerosols, and of course the shadowy cabal that architected the conspiracy.

I suggested the control read "aerosol deployment", but they went with the variable name, CHEM_TRAIL_GEN_ON, shown at 2:25. The industrial design team wasn't in on it, but I told Boeing we could come up with something better than that. They went with CHEM_TRAIL_GEN_ON.

My role was PID loop controlling the aerosol deployment rate. The don't use a very accurate flow sensor. They just said "we'll solve it in software-- a few lines of code." But it turns out flow is a complicated function of temperature, pressure, and aerosol density, and aerosol vehicle viscosity. We came up with a formula, but pilots are reporting their tanks sometimes being empty half way through the flight, esp during summer months. So now we have nozzles with flow sensors, and I'm validating the firmware.

The hardest thing about the project is you need Top Secret clearance to get the spec. The guy at Boeing who has it can tell you if you're compliant with spec or not, but he can't tell you what the limits are.

There's this online form we fill out to request YouTube take these down, so you'd better watch it fast!
[/Extended Sarcasm]
What I wrote definitely was a parody.