Karen Johnson, age 16, of Tulsa, Oklahoma, for her question:

Are the winds really useful?

If there were no breezes, city folk would stifle in stagnant air. If there were no global winds, fresh air from the forests could not be distributed around the world. Those same winds also carry our waste carbon dioxide to the outdoor greenery, where the plants can change it into tomorrow's supply of fresh oxygen. In a windless world, most likely the plants would perish    and so would the people and animals who depend on the plants to stay alive.

A howling hurricane makes us wonder whether such wild winds are really necessary. They cause disastrous destruction on land and sea and certainly seem to serve no useful purpose. But they do. Winds, including gentle breezes and mighty gales, are needed to keep the atmosphere and even the seas in a healthy condition.

The global atmosphere strives to keep its weight, its temperature and its mixture of gases evenly distributed. The only way to do this is by moving assorted masses of air    and this moving air is the wind. They also stir up waves on the sea and help to mingle the warm and cool waters between the equator and the poles. Without the winds, life on land and in the sea would soon stifle.

Fortunately, things on this planet are arranged to keep the winds in constant motion. They are governed by the nature of gases, by the sun and by our orbiting globe as it rotates around its tilted axis. Like all gaseous substances, the air spreads out to occupy all the space available. When warmed, it expands and becomes lighter. The earth's gravity strives to equalize the global weight of the atmosphere. As a general rule, heavier cooler air flows and blows toward masses of light, warm air. As a rule, the winds blow from high pressure pockets toward low pressure pockets.

These basic factors set up six belts of prevailing winds that circle the globe between the poles and the equator. The sun creates warm and cool patches that often disrupt the global wind systems with local storms and breezes. But everything that happens to the atmosFhere tends to start breezes blowing in one direction or another. As things are, there is no way to stop the winds from blowing, which is very lucky for us and all other living things.

There are a few places where no breezes blow for days or even weeks. The men of old sailing ships dreaded these deadly calm regions. Often they starved for food and water, unable to move while the sun blazed down through the stifling air.

In summer, the heat rises from our scorched city streets. Imagine what the hot, choking air would be like if no breezes ever came along to replace it. Sometimes desert winds are wild and cruel. But imagine if no cool breezes ever blew there, if no winds ever brought in fresh oxygen from faraway forests. Not only are the world winds useful, they are downright necessary to our survival.