Ai driven virus attacking infrastructure such as power and water would kill millions in a hot climate or cold climate. Very few people live in the "just right" zones. Then we have weoponized drones that could be controlled by the new AI and you suddenly have skynet. We already have the drones like the x-47 the newest c varient can carry 10k of munitions. Now imagine an automated factory controlled by AI mass producing them, and installing their AI in them, then them flying to a loading area where robots arm and fuel them all without a single human hand. Then think about how many of the world has cell phones, targeted malware to overcharge/overload the lithium batteries.