La Porte is a town in northern Indiana. For many years the people of the city were baffled by the storminess of it? weather. There were far more rain, snow, wind, fog, hail, and thunderstorms at La Porte than at any other town nearby- in Indiana, Michigan, and Illinois.

One year the weather bureau measured 31 percent more rain and snow, 38 percent more thunderstorms, and 246 percent more hail at La Porte than at any other weather station in the region.

Why was La Porte's weather so different? Since 1925 it had been noticed that bad weather came and went at La Porte in time with the output of steel in Gary and East Chicago, about thirty miles to the west.

But why? It seemed more than coincidence. Then it was discovered that stormy days at La Porte came at the same time as bad smog in Chicago, a few more miles farther west from the steel mills.

Then the mystery was answered. Polluted air, filled with nuclei for raindrops to form on, stimulated the growth of cumulus clouds at Chicago. On the prevailing westerly winds the cumulus clouds with their heavy load of pollutants drifted eastward, picking up more moisture as they passed over Lake Michigan.

By the time the clouds reached La Porte, having gathered yet more pollutants from the emissions billowing up from the steel mills, they had grown into full-fledged thunderstorms ready to be seeded by the pollution nuclei which drifted east with them.

Since the wind blows from the west most of the time, and since Chicago and the Gary steel mills are there all the time, La Porte gets a lot of stormy weather.

La Porte's experience shows in a striking way how man may change the weather without meaning to, simply as he goes about the business of making a living. There is no doubt that he is doing so. It has long been known that the climate of cities often differs from that of the surrounding country- side because of the pollution overhead.

Some industries more than others throw out pollutants which may affect the weather. Pulp and paper mills produce clouds downwind when there are none elsewhere. In Los Angeles during the rainy season cumulus clouds forming out of the plumes rising from the stacks of the power stations on the beach are a common sight.

A single factory can change the weather over an enormous area. A notorious example is a factory in Pennsylvania which sometimes hangs low clouds and fog over the entire valley where it is located, affecting the weather for twenty miles in all directions from its chimneys.

Vincent Schaefer, the man who discovered the principle of cloud-seeding, says every automobile with the engine running spews out ten billion particles a second from its exhaust pipe, all good for making raindrops. Lead particles, coming from the use of leaded gasoline, combine with iodine naturally present in the air and are as effective as silver iodide for forming raindrops, Schaefer says.

Automobiles put 400,000 tons of lead into the atmosphere over the United States every year, according to the National Academy of Sciences. That is nearly twice the amount of airborne lead which comes from nature's own sources. The skies of sunny California alone get 25,000 tons of lead a year from automobile exhaust pipes.

There is so much lead being poured into the air from auto mobiles, Schaefer believes, that there may be overseeding of the clouds, causing drought rather than rainfall. There may be so many nuclei competing for the moisture that there isn't enough to go around, keeping the raindrops from reaching full size so they can fall. Instead, they evaporate.

The effect of inadvertent cloud seeding, Schaefer suspects, are widespread and serious. "In a subtle manner, it seems to be changing the nature of clouds over increasingly large areas of the globe," he says, warning that there could be drastic changes in the weather pattern of the whole world.

Vincent Schaefer is not alone in these worries. "There has been a marked increase of concern that man may be causing changes in local weather and might also be influencing the climate on a planetary scale," says the National Academy of Sciences in its latest review of progress in modifying the weather.

For the past thirty years or so the earth, after getting warmer for a long time, has been growing cooler. It is now 0.3 degrees Centigrade cooler than it was in 1940. This may not seem enough to make much difference, but already the frost and ice of the north have started moving southward toward the Equator. There has also come a sharp increase in rain where there used to be little or none.

Are we on the way to a new ice age? Does man have some thing to do with it?

There is no doubt that man has the ability to change both the weather and the climate. The only question is whether he is actually doing so and, if he is, how much. If he is in fact altering the climate on a global scale, scientists warn, we had better find out in a hurry how he is doing it-before the climate starts to slide. Once deterioration begins, it will be too late.

Cooling of the earth is caused primarily by dust in the atmosphere. The chief source of this dust has been nature herself. Sometimes she goes to extremes about it. New England in 1816 had no summer because of dust in the air. On June 5, after spring had made the usual start, cold winds and heavy rains suddenly swept across Connecticut. At Benning ton, Vermont, it snowed nearly all day.

The storm left six inches of snow over most of New Eng land, with drifts two feet deep-in what was summer time. July and August mornings began with temperatures in the forties and by late August temperatures were down in the thirties There were no crops that year.

The reason for this summerless year in colonial New Eng land was a layer of volcanic dust high in the atmosphere, put there when Mount Tambora on the island of Sumbawa in the Dutch East Indies blew up. The explosion added 100 cubic miles of dust to what the volcano had been throwing out for several years.

When Krakatoa blew up in 1883, with a blast heard 3,000 miles away by the naked ear, it sent up a cloud of dust which spread over most of the northern and southern hemispheres as it streamed around the earth on stratospheric winds above the equatorial belt. In many parts of the world, it was ten years before the climate returned to normal.

Volcanoes go on sending up dust as always. But to the contributions of dust from these and other natural sources are now being added the pollutants caused by man. One of these which especially worries scientists is the pollutant that comes from jet engines of high-flying airplanes.

Jet streams have already increased the cloud cover over the United States and Europe by ten percent, some experts claim, causing local changes in the weather. Dr. Walter Orr Roberts, director of the National Center for Atmospheric Research search, says contrails from jet aircraft are responsible for as much as half the cloud cover over the United States on thirty to forty days a year.

The advent of supersonic transport planes flying in the stratosphere threatens yet new problems. Some scientists have warned that 500 SSTs, operating at 65,000 feet for a few years, pouring out dust and trailing vapor in a stream of ice crystals, could change the weather worldwide by raising the water content of the stratosphere by half to one hundred percent.

Present jet airliners cruise at about half this altitude, in the troposphere. At these levels the air cleanses itself. Pollutants left behind by airplanes or carried up from the ground, are washed out in about a week.

But in the lower stratosphere, where the SSTs will travel, nature provides no such cleanup mechanism. Pollution there hangs on for roughly two years, and it builds up nearly a hundred times as fast. Moreover, because there is only about one-fifth as much air in the stratosphere as farther down, the pollution is more concentrated.

There is another thing about the stratosphere which bears heavily on the question of what may happen if it gets too dirty. The stratosphere is a kind of chemical factory with a great deal of activity taking place within it.

Prominent among the chemicals found in the stratosphere are ozone and oxides of nitrogen, the last a major constit uent of the pollution that pours from automobile exhaust pipes and factory smokestacks. Oxides of nitrogen, the product of very hot fire, are a photochemical pollutant, reacting with other pollutants in the presence of sunlight to form many more kinds of pollutants.

Scientists are concerned about what will happen when extra oxides of nitrogen and water vapor from SSTs combine with the chemicals naturally present in the stratosphere. In particular, they are afraid that in the reaction there may be a reduction of the ozone. Some scientists argue that there would be a very large reduction of the ozone.

Ozone is the shield which prevents ultraviolet rays from reaching the earth. Any increase in ultraviolet radiation could cause a rise in skin cancer, scientists say. What other adverse health effects there might be, and what the radiation would do to plant life, nobody knows.

All things considered, what the SSTs let loose in the strato sphere, where it takes longer for pollutants to disperse, could be as important as the far greater volume of pollution which industry and automobiles pump into the troposphere from below.

"Man clearly has no positive knowledge of the magnitude or the manner by which he is presently changing the climate of the earth," the National Academy of Sciences says. "There is no real question that inadvertent modification of the atmo sphere is taking place. . . .

"If society is to deal with long-term problems of inadvertent weather and climate changes caused by man and his activities, then urgent attention and action are required at the earliest possible moment."

In other words, unless we find out what we may be doing to damage the climate, it may not make much difference what we do to improve the weather.