Moving the Waters - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 93

but baldly stated it is 1 million billion watts. That might not get us
much further in understanding, but another way of putting it is that
it is roughly 50 times contemporary humanity's total energy output.
And we humans, one must remember, are no slouches at the produc-
tion of energy. 65
Part of the Sun's energy—some 30 per cent—is simply reflected
back into space. The rest is absorbed. Some of that gargantuan energy
input goes into driving the world's weather systems. The air, warmed
by the ocean, rises and carries yet more energy with it in the form of
water vapour evaporated from the ocean. As the air rises, it cools. The
water vapour condenses as cloud droplets and then rain, releasing that
transported energy and driving those weather systems yet faster.
Most of the Sun's heat, though, goes into the land and—
especially—the oceans. The oceans, indeed, absorb about four times
as much solar energy as do the continents, even though they only
take up about three times as much of the Earth's area (the difference
is because the oceans are darker than the continents, and so are better
at absorbing heat).
The heat translates into oceanic motion in different ways. The most
obvious effect, to us as observers, is secondary, through interaction
with moving masses of air in the atmosphere. The Earth's atmos-
phere, heated directly by sunlight and warmed also from below by the
Sun-warmed land or sea surface, expands and rises in the tropics, to
cool in the upper atmosphere and then descend at mid-latitudes, in
Hadley cells. Another couple of pairs of such cells of rising and falling
air masses form around the mid-latitudes and polar regions. These
moving atmospheric masses help redistribute heat from the hot
equatorial regions to the polar regions, where the Sun's rays, striking
at such a low angle, do little to heat the frigid surface.
The masses of air, as they move north or south, are twisted side-
ways by yet another force, one imparted from the Earth's spin.