One vision of a "polar city' in an overheated world. (Illustration by Deng Cheng-hong)Danny Bloom, a freelance writer, translator and editor living in Taiwan, is on a one-man campaign to get people to seriously consider a worst-case prediction of the British chemist and inventor James Lovelock: life in "polar cities' arrayed around the shores of an ice-free Arctic Ocean in a greenhouse-warmed world. Dr. Lovelock, who in 1972 conceived of Earth's crust, climate and veneer of life as a unified self-sustaining entity, Gaia, foresees humanity in full pole-bound retreat within a century as areas around the tropics roast