—C. J. Cutliffe Hyne, The Lost Continent (1899)

Nearly all scientists are currently in agreement that climate change, even as quickly as it is occurring, will not produce flooding of major cities within the next 20 years. However, for the purposes of this story line, the increase in solar temperature, combined with the release of trapped methane (clathrates) in subpolar regions and ocean warming (hence thermal expansion) will produce dramatic melting of all ice fields on the planet and an equally catastrophic rise in sea level, progressing at an exponential rate at great speed.

In the first year after Zero Hour, melting of glaciers, snow caps, and polar ice will occur at a swifter pace than before, though only those living near glaciers and the like (or living downstream from the runoff) will notice the change. The defrosting of tundra and the release of methane from permafrost (for our purposes) will speed up the process. The release of such methane is believed to have occurred at least once before in Earth's history, during the Eocene period soon after the dinosaurs died out. This long-ago methane release (probably a result of vulcanism) also led to worldwide flooding, though at a much slower pace than is projected here.

Sea-level rise in DAYLIGHT will progress more or less at the following rate. Note that a rise of 15 cm in the first year is about 6 inches; coastal people might notice this (in very low-lying areas like New Orleans, Florida, or eastern Texas), or they might not. Maximum thermal expansion of ocean water is assumed to occur about 15 years after Zero Hour, raising the level even further. For the sake of argument, 100 meters is taken to be the maximum level the oceans will rise given all relevant factors.

The rise in sea level will additionally have a dramatic effect on global climate, which is addressed elsewhere.