Dioxin is very strong chemical which could exist in nature for decades. If it were used as a doomsday weapon I think it could be made airborn on height of 10-20 kilometers from where it could slowly rain all over the world. Or it could be put in the oceans, contaminating all marine life and people who eat fishes. Dioxin is known to slowly accumulate in living tishues. Italy still strugle from the catastrophe where 1 kilogramm of dioxin was relized in nature in 1976. http://en.wikipedia.org/wiki/Seveso_disaster
But the main problem in my opinion is that the aproach of the author of the post is misleading. Risks are not mutualy independent, which could be suggested when we see a list of main 5 risks. For example by the methods of syntetic biology someone could create a plant which could produce dioxin or other toxins and which could colonise the surface of the Earth killing all other species.
Or nuclear war could result in counter attack by biological weapons. So interraction of risks could be more important when pure risks themselves. But x-risks researchers are attached to the magic of creating list of risks. I could call it list-bias.
Italy still strugle from the catastrophe where 1 kilogramm of dioxin was relized in nature in 1976. http://en.wikipedia.org/wiki/Seveso_disaster
And also 6 tonnes of other crap; further, I'm not terribly impressed when I read about 0 increase in all-cause mortality decades after the disaster, countered only by a later paper that smells like datamining ('neoplasms'? really? where's my all-cause mortality? That's what we care about!)
The FHI's mini advent calendar: counting down through the big five existential risks. The third one is a also a novel risk: nanotechnology.
Nanotechnology
Current understanding: low
Most worrying aspect: the good stuff and the bad stuff are the same thing
The potential of nanotechnology is its ability to completely transform and revolutionise manufacturing and materials. The peril of nanotechnology is its ability to completely transform and revolutionise manufacturing and materials. And it’s hard to separate the two. Nanotech manufacturing promises to be extremely disruptive to existing trade arrangements and to the balance of economic power: small organisations could produce as many goods as much as whole countries today, collapsing standard trade relationships and causing sudden unemployment and poverty in places not expecting this.
And in this suddenly unstable world, nanotechnology will also permit the mass production of many new tools of war – from microscopic spy drones to large scale weapons with exotic properties. It will also weaken trust in disarmament agreements, as a completely disarmed country would have the potential to assemble an entire arsenal – say of cruise missiles – in the span of a day or less.