Water has the highest specific heat of any commonly known substance. It takes more energy to raise the temperature of a kilo of water one degree than it takes for a kilo of almost any other substance.
Poseidous’s oceans act as giant thermal stabilizers for nearby land, preventing the temperature of the land from rising or dropping too fast. Water, like all substances, becomes less dense when heated and more dense when cooled. Rising and falling currents of water create a natural circulation that carries massive amounts of heat from a planet’s warmer regions to its colder regions. Land cannot flow about like this, so differences in temperature are much greater on land than on water. For these reasons the Earth’s coldest and hottest regions occur away from the oceans. Poseidous, being all ocean, lacks the temperature extremes of Earth, and the great continents that break up the circulation in Earth’s seas cause no irregularities in Poseidous’s weather.
Temperatures don’t vary much with the seasons either, for Poseidous has a smaller obliquity than any other Human colony. Hence our sun’s rays strike every point on the planet with the same angle throughout the year. “Winter,” “summer,” “spring,” and ” fall” have no meaning for us at all! The map of Poseidous shows the temperatures at each latitude. Anyone can literally pick the air temperature he likes best, then move to an island at that latitude and rest assured that, 95 percent of the time, the temperature won’t vary more than seven degrees either way.
The complete lack of seasons reduces the concept of a “year” to an astronomical measurement. I’ve suggested to the New Britain Council that we simply make our year coincident with’ Earth’s years to save fooling around with conversions all the time. In principle, the Council agreed with me, but getting every island on Poseidous to agree on anything is practically impossible. The Troon council suggested that the calendar be eliminated altogether so that people wouldn’t feel pressured by the passing of time! So we continue with a year that equals approximately 225 Earth days.
The map (figure 3.5) also shows that the flow of winds and currents on Poseidous is as regular as the temperature. Most islands have a rainy side where it rains almost daily and a dry side with less rain. Weather forecasters would have had no job at all, were it not for occasional storms that originate in the tropics. The development of an accurate climate model — the first for any human-habitable planet — solved the problem of predicting these storms.