The anti-vaccine movement (which claims that vaccines cause autism) has long been on the fringes of science. The most well known scientific paper that claimed to demonstrate a link, one by Andrew Wakefield, was eventually retracted after it was not able to be replicated, and the original research was found to be deeply flawed. However the anti-vaxxers never seemed to be quite as fringe as the "chemtrail" movement, with their bizarre theories about how we are being sprayed by toxic chemicals.
That is, until quite recently.
There was always some overlap of course. Conspiracy theories form a rough hierarchy of implausibility. People who believe in a highly implausible theory like chemtrails will almost always believe every single theory that is a bit more plausible. So chemtrailers are almost always anti-vaxxers, but anti-vaxxers are less frequently chemtrailers.
But either the chemtrail movement is becoming more mainstream, or the anti-vaccine movement is becoming far less mainstream. Given increasingly apocalyptic and nonsensical rhetoric that the chemtrail movement has produced over the last year, then I strongly suspect the change here has been with the anti-vaccine movement.
On Oct 14, 2016 (just last week), there was an anti-vaccine protest at the CDC headquarters in Atlanta. Conditions were right for contrail formation, and many of those present took the trails criss-crossing the sky as being "chemtrails", and some even suggested they might have been sprayed deliberately.
Many people noted that they felt ill, others noted trails they had seen elsewhere. Some suggested the spraying was deliberate to target the protest, some shared links to chemtrail web sites like geoengineeringwatch.org, some suggested obtaining rocket launchers to shoot down the planes,. Nobody suggested they were just contrails.
They were in fact just contrails. Not only that, they were contrails that were mostly over ten miles away. If someone was targeting the protestors they were also targeting everyone who worked in the CDC building, and everyone in Atlanta, and several million other people in the Atlanta metro area. In fact if we look at the satellite images for October 14, the contrail conditions covered the entire states of Georgia, Alabama, Louisiana, and much of Florida.
And here's everything within 120 miles of the CDC protest in Atlanta:
The map of upper air (30,000 feet) humidity for that day shows why. The green areas are where humidity is high enough for contrails to form (60% and above)
The CDC is sitting in an ideal location for contrails that day. Not so humid the sky is covered with clouds, but humid enough for contrail formation and persistence.
But is this group of chemtrail-believing anti-vaxxers just a fringe subset of the movement? No, it actually seems like the adoption of chemtrails by the anti-vaxxers has gone all the way to the top.
One of the protestors at the CDC was Del Bigtree, who along with Andrew Wakefield created the widely debunked documentary film Vaxxed. Here he is pointing at a "chemtrail".
Andrew Wakefield himself, a hero in the anti-vaccine movement, appears to have embraced all manner of conspiracy theories. In early 2016 he headlined a "conspiracy-sea" cruise that included everything from crop-circles to mind-control. And while that does not necessarily mean he endorses those beliefs, he does seem to endorse the chemtrail belief. In August this year both Wakefield and Bigtree headlined a joint Vaxxed/Geoengineering (chemtrails) conference organized by Dane Wigington - the most prominent promoter of the chemtrail theory.
Wakefield said to Wigington: "you are doing an immense service to mankind".
Bigtree also discusses chemtrails with Dane. Curiously he laments the fact the people who are concerned about things like chemtrails, people he though were "evolved", do not always embrace the anti-vaccine movement. So perhaps the crossover is not quite as distinct as I thought.
Still that crossover is there, and now Wigington and Wakefield have joined forces it makes it okay for the anti-vaxxers to admit their belief in chemtrails. I'm not sure why the crossover happened, and I'm not sure if there will be any effect. I can't imagine it will help the credibility of the anti-vaccine movement, so perhaps that speaks to some desperation on their part. It will probably help the chemtrailers a little, by aligning them with a very slightly more mainstream movement. However it might backfire, as a lot of people new to chemtrails might see the anti-vaccine link, and be aware that it's pseudoscience because of the more mainstream coverage.