It's not only that. Consider that the fish export of Norway is huge, compared to almost everything else (although oil is still in its own division). More importantly, export of fish from the area discussed has been going on for more than a millenium and can likely continue for another, or more. Unless a disaster happens, and one would be a huge oilspill in the middle of that area, which could destroy the fisheries for generations. Compare that to just a few decades of oil, and the latter doesn't look so important (economically) anymore. This part is what concern those who are against oil drilling there, even those who are not particularly concerned about CO2.