Fiat Lux

What will kill us all? I don't know. It could be any number of things. There's a range of likely possibilities, and quite a few unlikely ones. The most likely and inevitable is evolution into a successor species. Unlike certain optimists, I'm not convinced that transhumanism is really likely in the short term, and the long term is going to make First World civilization quite a bit more difficult to maintain than people realize, with all kinds of nasty consequences for the Third World (which is usually entirely ignored in First World futurology).

The second-most likely cause of human extinction (and in any case, killing six billion large apes entirely is a monstrously difficult proposition to pull off. If the Toba event had been worse....Neanderthals would likely be ruling the planet as poorly/well as we are) is something like the Yellowstone Caldera blowing up. In an instant, half of North America, including much of the cropland is gone. Hilarity ensues.

Next-likely is population pressure in the Third World spiraling into a Malthusian trap. Somewhat less-likely than others at present.

Further down the list is the epidemic that actually will be the killer epidemic, down this low because any such mutation is not yet viable.

A bit further yet is global warming.

Further yet....K/T boundary size asteroid impact.

Last, but the most potentially serious....gamma ray burst. That happens, bye-bye everything in something as epic as the P-T boundary (which makes the K-T boundary look like a sissy extinction).

Have a nice day.