In other discussions on the topic of unstoppable pollution, it has been described as a bug. A comparison between an emperor game and a prince game has me questioning that. It has been established by a number of players that at emperor level, the pollution starts when you discover future tech 64. In an old prince-level game that I've just dug out of my archives, the first hint of pollution trouble appeared when I discovered future tech 216. It seems very unlikely to me that a software bug would be indexed to difficulty level. I think the pollution was deliberately introduced as Sid's way of telling you that you have taken the game as far as it can go.