Even a cursory Google search makes plain that the Genesis account of the Flood is one of the favorite targets of those who do not believe the Bible. “If the Flood covered the mountains,” they sneer, “it would put sea level at 29,055 feet, where everything on the ark would have frozen to death and not had enough oxygen to breathe.”
First, the presumption that the floodwaters rose to 29,055 feet (twenty feet higher than the elevation of Mount Everest) is misguided at best. Given the science of plate tectonics, it is abundantly clear that Everest is significantly higher today than it would have been at the time of the great Flood.
Furthermore, the biblical text is not designed to communicate whether the Flood was global with respect to the earth or universal with respect to humanity. That debate is ultimately settled by a proper “reading” of the book of nature* (Psalm 19:1–4).
Finally, since civilization was largely confined to the Fertile Crescent*, we need not automatically presume that the floodwaters covered the globe. When Scripture tells us that “the whole world sought audience with Solomon to hear the wisdom God had put in his heart” (1 Kings 10:24), only the most ardent fundamentalist supposes this to include aborigines from Australia and indigenous peoples of the Americas. Of one thing we can be certain: The text of Scripture, both Old and New, communicates the reality of a great Flood in which “only a few people, eight in all, were saved” (1 Peter 3:20).
For further study, see Hank Hanegraaff, Has God Spoken? Proof of the Bible’s Divine Inspiration (Nashville: Thomas Nelson, 2011).