Where in the Bible does it say that Noah warned his contemporaries? Nowhere in the flood account does it say that Noah warned people of the flood.
I've often asked the same question. Surely if "preaching" was such an all important factor in who lived and who died at the Flood, that it would have been mentioned in Genesis.
Josephus (Jewish Antiquities 1:73) thus says that "Noah, displeased with the deeds of his [contemporaries] and finding their intentions to be odious, sought to persuade them to adopt a better way of thinking and to change their ways". According to rabbinical literature: "The righteous Noah used to warn them and say to them, 'Repent, for if you do not, God will bring a flood upon you.' " (b. Sanhedrin 108a).
OK, so maybe Noah did preach to them. But as I've mentioned before, I hardly think that Noah had to count how many hours he and his family spent in preaching to everyone and submit a timesheet to Jehovah every month. Plus, by all accounts, the people who lived at the time of the Flood were apparently extremely wicked. Has Jehovah ever destroyed the righteous with the unrighteous? In our day there are alot of people out there who are righteous people. Just because they're not Witnesses doesn't mean they're 'worthy of destruction'.