Some creationary scientists have also proposed a different structure to the atmosphere prior to the Flood of Noah's time. They note that day two mentions waters above and below the firmament. The waters below are obviously the oceans, lakes, rivers, and underground bodies of water. For waters above, some speculate on the existence of a vapor canopy of water high in the earth's atmosphere, which would be a source of water for Noah's flood. They look at the mention of no rain in Genesis 2:5, and they note the covenant of the rainbow in Genesis 9: 12-17 and think that there were no rainbows and no rain before the Flood.

Another theory suggests that in context, the lack of rain applies only before the creation of plants on day three of the Creation week. One idea continues that the absence of rain may also only apply to a limited area (observable) of the earth around the Garden of Eden, but substantiating such concepts is difficult at best. The adoption of the rainbow as a sign of a new covenant may not negate the existence of prior rainbows, just as the adoption of bread and wine by Jesus as elements of special remembrance does not negate their prior existence for ordinary purposes. Furthermore, the Genesis 1 description of day two specifically says that the upper part of the waters is above the firmament, which suggests to some creationary scientists that it could be beyond the starry second heavens, not between the atmosphere and space.

Water vapor is the gaseous form of water and is transparent in the visible wavelengths of light. In the near infrared, it absorbs some incoming solar energy. In the far infrared, it acts as the most powerful greenhouse gas, perhaps twenty times as powerful as carbon dioxide. Without water vapor in our atmosphere, the global average of surface air temperature around the earth would average a frigid -18 C, 0 F, rather than 15 C, 59 F. Compare that nearly 60 degree Fahrenheit greenhouse warming by water vapor to the few degrees promoted for potential warming by carbon dioxide in the future. We can thank God for giving us a planet significantly warmed by the greenhouse effects of water vapor.

Recent research involving detailed numerical simulations by Dr. Vardiman of The Institute for Creation Research and his partners has indicated that a significant water vapor canopy around the earth is not workable because of that greenhouse effect. At present, if all the water vapor in a vertical column of typical air is condensed into a puddle, there would be no more than inches of water-depth resulting. If there were so much water vapor placed in the stratosphere or above, equal to and in addition to the total mass of the present atmosphere (doubling the surface pressure), then the condensation would amount to only about thirty feet of water precipitated. While locally damaging, such an amount would not be sufficient for Noah's flood. Furthermore, such an extreme amount of water vapor would cause a runaway greenhouse effect (like on Venus) that would raise surface temperatures to that of scalding steam. The simulations by the team showed that to have reasonable temperatures for life on earth, the amount of water vapor in the canopy would be an insignificant contributor to Noah's flood. They point to the source of the rain of Noah's flood to be much more likely from the "fountains of the deep," as well as being caused by volcanic activity leading to rapid evaporation of sea water heated by igneous flows.

So, this research model indicates that the day-two atmosphere could have been comparable to that of today, even with some precipitation and perhaps more carbon dioxide for abundant plant growth. Other creationists point to Scripture that indicates the plants were only watered from the mist of the ground.