The year is 2050, massive petawatt scale ocean based data centres are warming the ocean in their immediate vicinity, opening up new breeding grounds for a new killer algae. The algae once unable to grow in regular ocean tempatures thrives in this new ecosystem, and once it matures is able to leave the warmer waters and destroys other marine life it comes into contact with.
This destruction of life in the ocean reverberates around the world as food supply dwindles and hundreds of millions of people begin to starve.
It doesn't seem like AI is actually the problem here, as any new tech system could have given that kind of visibility to the DoorDash drivers and resulted in this problem, but either way, it's an interesting fail, where a maybe good idea, falls apart because of human behaviour.