Oceanography

The water in the oceans, the clouds in the sky, and the ice of the polar seas are all parts of the dynamic solar energy-transfer system that makes the earth run. Our available fresh water comes from this global rain and ice-making machine.

The controls of climate and rainfall depend on just how the solar energy received is distributed to the atmosphere, the oceans, and the continents. The balance is delicate indeed, but tenacious. The earth is just emerging from a great Ice Age, and while there have been other ones in the past, things have never gotten so far out of control as to freeze much of the oceans into ice, or to boil them into the atmosphere as steam.

The earth loses as much energy back to outer space as it receives from the sun (plus a little bit more that escapes through the surface from its internal fires), and has maintained this balance closely for billions of years. Equality of gain and loss has held the average temperature of the surface environment, despite local variations, quite constant. Rocks containing fossils of organisms like those of today that were deposited in the oceans hundreds of millions of years ago show that sea water was about as warm (or cold) then as it is now.

The secret of the ocean thermostat is the ability of water to soak up heat without much temperature change. It takes a lot of heat to raise water to the boiling point and almost ten times as much again to convert it into steam. Even though there may have been great variations in solar energy received at the earth’s surface through time, the oceans have kept the temperature constant. When one part of the ocean is heated circulation results, so that it is not possible to boil water at the equator while keeping it frozen at the poles. The faster it is heated, the faster it circulates. The ocean basins are linked together and thus behave as one immense pot-heat part, heat all.

Because it takes so much heat to cause evaporation and so much must be removed to cause freezing, water maintains its liquid state in most natural circumstances. If the energy from the sun were to diminish for a long time, the earth would lose heat to space faster than it would gain heat. Glaciers and ice caps would grow but heat would be generated by the change from water to ice, and, rather than falling below freezing, temperatures would remain at the freezing point until all the water was frozen.

It takes about five times as much heat to cause a temperature change in water equal to the same change in rock. The scorching sidewalk beside the cool puddle is a model of the continents and oceans. It takes little heat to warm rock, and because the rigid concrete transmits its heat but slowly downward, its surface temperature rises rapidly in the sun. Not only does the water of the puddle require more heat per pound for temperature change than does the rock, it also circulates so that the whole puddle must be heated, evaporating eventually into water vapor. For every ounce of water evaporated fifty ounces of rock can be heated ten degrees. The same relation applies to the continents and oceans. In central Asia, summer temperatures may reach 90° F, and in winter may drop to 70° F below zero, while the whole ocean range is only from 32° F to 85° F, and more than 90 percent of all the water is a few degrees above freezing.

If we were going to make another planet for human habitation, with a free choice of materials, we would unhesitatingly demand that the planet have a water ocean to provide maximum safeguards against being scorched or frozen. It takes one unit of heat to warm an ounce of water one degree, it takes almost six hundred units to evaporate it, and eighty units must be removed to freeze it.